Cruise Report of the US-GOSHIP 2025 Reoccupation of I09N
********************************************************


GO-SHIP I09N 2025 Hydrographic Program
======================================


Scientific Objectives & Background
----------------------------------

The I09N 2025 cruise aboard the UNOLS vessel R/V *Thomas G. Thompson*
was undertaken as part of the US GO-SHIP (Global Ocean Ship-based
Hydrographic Investigations Program), a major contributor to
international GO-SHIP. The program aims to collect highly accurate,
surface-to-bottom, coast-to-coast, physical, and biogeochemical
observations at quasi-decadal timescales. These measurements are
essential to understanding long-term changes in heat, freshwater,
carbon, oxygen, and other tracers in the global ocean—the main
reservoir in the Earth System.

The I09N is a meridional transect in the Eastern Indian Ocean that
spans from the Broken Ridge at about 28°S to the Bay of Bengal in the
North Fig. %s. When I09N and I08S transects are combined, the line
extends from the Antarctic continental shelf to the Bay of Bengal,
resulting in a coast-to-coast section.

   [image]GO-SHIP I09N 2025 occupation. Black circles are used for
   CTD/LADCP/rosette stations (0 to 98), and blue circle-dot symbols
   for test station locations (900 and 901). Shaded colors are bottom
   depths from GEBCO 2024. The dark green dot shows the departure
   port, and the red dot the arrival port. The dashed line marks the
   Equator.

The 2025 cruise is the fourth occupation of the I09N. The I09N was
first occupied in 1995 (130 stations; R/V *Knorr*) during WOCE (World
Ocean Circulation Experiment), then in 2007 (111 stations; R/V *Roger
Revelle*) as part of the CLIVAR (Climate Variability and
Predictability) and in 2016 (113 stations; R/V *Roger Revelle*) as
part of GO-SHIP. Except for 1995, when the cruise was during boreal
winter (January-March), all other occupations (including the present
ones) took place in boreal spring (March-May).

Compared with the last two occupations, the I09N 2025 ended further
north (20°N) thanks to the clearance granted by the Bangladesh
government to collect observations within Bangladesh’s exclusive
economic zone (EEZ) Fig. %s.

   [image]I09N occupations in the North Indian Ocean over the years.
   Red dots show stations for the present occupation, and yellow dots
   show stations for the 2016 occupation. Black circles are stations
   occupied in 2007, and blue circles are those occupied in 1995. The
   black polygon shows the area where we did not occupy in 2025 due to
   border interpretation (see text).

While the southern portion of the I09N has remained unchanged over the
years, extending nominally along the 95° E meridian, parallel to the
Ninety East Ridge, the North Indian Ocean portion has been
significantly modified. In 1995, the transect comprised two parts
north of the Equator: a quasi-meridional section confined to the east
of 90° E from the Equator to Myanmar and a slanted section with lower
spatial resolution across the Bay of Bengal Fig. %s. The quasi-
meridional section crossed Indonesia, India, and Myanmar EEZs, while
the slanted section was mostly over international waters. For 2007,
the two sections were merged into one, with all stations located over
international waters. Due to a dispute over EEZ delimitations, the
transect in 2007 ended at 17.5° N, far from the continental shelf.
Instead of occupying the northern end of the transect, a bow-tie
section was performed in the central Bay of Bengal between 6-10° N
Fig. %s. A similar trajectory was taken ten years later, but with the
bow tie extending even further. As in 2007, the 2016 occupation ended
far from the shelf due to clearance issues.

For the 2025 occupation, the I09N northern ending was extended from
17.5° N to 20° N along the 89.86° E meridian, with the last station
located at the continental slope at depths of about 1100 m Fig. %s.
The location of the northernmost station was chosen based on the total
number of at-sea days designed for the 2025 cruise. Compared to the
2007 and 2016 occupations, nine new stations were added at the
northern end, although, during the cruise, we had to skip the last two
stations of 2007 and 2016 as described later. For 2025, the bow-tie
feature in the central Bay of Bengal was also removed Fig. %s, making
the I09N more like other GO-SHIP meridional sections.

Furthermore, the I09N 2025 included the Bio GO-SHIP, which aims to
gather global oceanic observations to understand the planktonic
ecosystem. In 2025, the Bio component consisted of two parts:
analyzing surface waters from the underway system and obtaining
vertical profiles of bio-parameters from the surface to 1000 m at
specific hydrographic stations (from independent casts when time
allowed).

Ultimately, the I09N 2025 cruise, which took place between March 21
and April 27, 2025, occupied 98 CTD/LADCP/rosette stations. These
stations were nominally spaced about 30 nm (50 km) apart in the open
ocean, although some were spaced up to 42 nm, and they were closer at
boundary currents and prominent topographic features.

At each station, a suite of surface-to-bottom vertical profiles was
collected using electronic sensors (CTD-O, LADCP, fluorometer, and
transmissometer) and 36 10-L Niskin bottles for sampling water at
discrete vertical levels.

Data collected during the 2025 I09N were (some samplings will be
processed in labs onshore):

* Pressure, temperature, salinity, and dissolved oxygen from
  electronic sensors and bottles

* Fluorescence and light transmissivity

* Current velocities from lowered and shipboard ADCPs (Acoustic
  Doppler Current Profilers)

* Major inorganic nutrients (silicate, phosphate, nitrate, nitrite)

* Transient tracers: Chlorofluorocarbons (CFC-11 and -12), Sulphur
  Hexafluoride (SF_6), and Nitrous Oxide (N_2O)

* Carbon components: total dissolved inorganic carbon (DIC), total
  alkalinity, pH, and partial pressure of CO_2, dissolved organic
  carbon (DOC), total dissolved nitrogen (TDN), \delta^14C, and
  \delta^13C

* Oxidized iodine (iodate) and reduced iodine (iodide)

* Bathymetry (multibeam), shipboard meteorological and surface
  temperature and salinity observations

* \delta^18O (ratio of stable isotopes oxygen-18 and oxygen-16) and
  \delta^15N isotopes

* Bio GO-SHIP (bottles and underway): HPLC pigments, Flow cytometer
  (FCM), DNA, RNA, chemical oxygen demand (PCOD), particulate organic
  matter (nitrogen-PON, phosphorus-POP, carbon-POC), particulate
  inorganic carbon (PIC)

In addition to the above measurements, during the 2025 I09N, we
deployed 12 Argo (Core) floats, 7 GO-BGC floats, 6 EM-APEX SQUID
(Sampling QUantitative Internal-wave Distribution) floats, and 20
surface drifters (SVP) from the Global Drifter Program.

Along the way, the I09N crossed four distinct regimes Fig. %s:

1. Subtropical gyre regime characterized by the presence of the
   eastward South Indian Countercurrent and the Eastern Gyral Current
   in the upper layer. In this area, the salty Subtropical Underwater
   (STW; 0-400 m), the Subantarctic Mode Water (SAMW; 500-800 m), the
   cold and highly oxygenated Antarctic Intermediate Water (AAIW;
   centered around 1000 m), and at the abyss, the Antarctic Bottom
   Water/Lower Circumpolar Deep Water stand out.

2. Fresh Indonesian Throughflow (ITF) plume regime, which is carried
   westward by the South Equatorial Current (SEC). The fresh plume is
   expressed at the surface and subsurface through the Indonesian
   Throughflow Water (ITW; 0-500 m) and Intermediate Indonesian
   Throughflow Water (IIW; ~1000-1200 m)

3. The Equatorial regime with its vertically stacked jets. In 2025,
   the spring Wyrtki Jet at the surface (core around 120 m) was well
   developed

4. The low-oxygenated and fresh waters of the Bay of Bengal and its
   monsoon-dominated circulation.

   [image]Temperature-Salinity diagram from calibrated CTD
   observations collected during the I09N 2025 cruise. Colors show the
   latitude at which the data have been collected. Blue is used for
   the Subtropical South Indian Ocean, green for the tropical and
   equatorial area, and red for the Bay of Bengal. Primary water
   masses are highlighted.


Programs and Principal Investigators
------------------------------------

+------------------------------+------------------+-------------------------+-----------------------------------+
| Program                      | Affiliation      | Principal Investigator  | Email                             |
|==============================|==================|=========================|===================================|
| CTDO Data, Salinity,         | *UCSD* *SIO*     | Susan Becker            | sbecker@ucsd.edu                  |
| Nutrients, Dissolved O_2     |                  |                         |                                   |
+------------------------------+------------------+-------------------------+-----------------------------------+
| CFCs, SF_6                   | *UM* Rosenstiel  | Jim Happell             | jhappell@miami.edu                |
+------------------------------+------------------+-------------------------+-----------------------------------+
| DIC                          | *NOAA* *PMEL*    | Richard Feely, Rik      | Richard.A.Feely@noaa.gov,         |
|                              |                  | Wanninkhof              | rik.wanninkhof@noaa.gov           |
+------------------------------+------------------+-------------------------+-----------------------------------+
| Total Alkalinity, pH         | UCSD             | Andrew Dickson          | adickson@ucsd.edu                 |
+------------------------------+------------------+-------------------------+-----------------------------------+
| Lowered ADCP                 | *LDEO*           | Andreas Thurnherr       | ant@ldeo.columbia.edu             |
+------------------------------+------------------+-------------------------+-----------------------------------+
| Shipboard ADCP               | *UH*             | Julia Hummon            | hummon@hawaii.edu                 |
+------------------------------+------------------+-------------------------+-----------------------------------+
| Underway pCO_2               | NOAA PMEL        | Simone Alin             | simone.r.alin@noaa.gov            |
+------------------------------+------------------+-------------------------+-----------------------------------+
| Transmissometer              | UCSD             | Susan Becker            | sbecker@ucsd.edu                  |
+------------------------------+------------------+-------------------------+-----------------------------------+
| DOC/TDN                      | UCSD             | Craig Carlson           | craig_carlson@ucsb.edu            |
+------------------------------+------------------+-------------------------+-----------------------------------+
| \delta^14C                   | *WHOI*           | Roberta Hansman         | rhansman@whoi.edu                 |
+------------------------------+------------------+-------------------------+-----------------------------------+
| BGC & Core Argo              | UCSD             | Lynne Talley            | ltalley@ucsd.edu                  |
+------------------------------+------------------+-------------------------+-----------------------------------+
| SQUID/EM-APEX                | *UW*             | James Girton            | girton@uw.edu                     |
+------------------------------+------------------+-------------------------+-----------------------------------+
| Drifters                     | NOAA *AOML*      | Shaun Dolk              | shaun.dolk@noaa.gov               |
+------------------------------+------------------+-------------------------+-----------------------------------+
| BIO GO-SHIP                  | *UCI*/Bigelow    | Adam Martiny, Nicole    | amartiny@uci.edu,                 |
|                              |                  | Poutlon                 | npoulton@bigelow.org              |
+------------------------------+------------------+-------------------------+-----------------------------------+
| \delta^13C                   | *UDEL*           | Wei-Jun Cai             | wcai@udel.edu                     |
+------------------------------+------------------+-------------------------+-----------------------------------+
| NO_3 isotopes                | *ULB*            | Francois Fripat         | francois.fripiat@ulb.be           |
+------------------------------+------------------+-------------------------+-----------------------------------+
| Iodine                       | *USC*            | James Moffet            | jmoffett@usc.edu                  |
+------------------------------+------------------+-------------------------+-----------------------------------+


Science Team and Responsibilities
---------------------------------

+------------------------------+-------------------------+------------------+-----------------------------------+
| Role                         | Name                    | Affiliation      | Participant email                 |
|==============================|=========================|==================|===================================|
| Chief Scientist              | Viviane Menezes         | WHOI             | vmenezes@whoi.edu                 |
+------------------------------+-------------------------+------------------+-----------------------------------+
| Co-Chief Scientist           | Leah Chomiak            | UM-*CIMAS*       | leah.chomiak@earth.miami.edu      |
+------------------------------+-------------------------+------------------+-----------------------------------+
| CTDO Processing              | Allen Smith             | SIO              | als026@ucsd.edu                   |
+------------------------------+-------------------------+------------------+-----------------------------------+
| Nutrients                    | Megan Roadman           | SIO              | mroadman@ucsd.edu                 |
+------------------------------+-------------------------+------------------+-----------------------------------+
| Nutrients                    | Vincent Johnson         | SIO              | vijohnson@ucsd.edu                |
+------------------------------+-------------------------+------------------+-----------------------------------+
| Dissolved Oxygen, Database   | Andrew Barna            | SIO              | abarna@ucsd.edu                   |
| Management                   |                         |                  |                                   |
+------------------------------+-------------------------+------------------+-----------------------------------+
| Dissolved Oxygen, Database   | Elisa Aitoro            | SIO              | eaitoro@ucsd.edu                  |
| Management                   |                         |                  |                                   |
+------------------------------+-------------------------+------------------+-----------------------------------+
| Salts, CTD and Rosette       | John Calderwood         | SIO              | jcalderwood@ucsd.edu              |
| Maintenance                  |                         |                  |                                   |
+------------------------------+-------------------------+------------------+-----------------------------------+
| Salts, CTD and Rosette       | Jessica Mclaughlin      | SIO              | j1mclaughlin@ucsd.edu             |
| Maintenance                  |                         |                  |                                   |
+------------------------------+-------------------------+------------------+-----------------------------------+
| CTD Watchstander             | Alessandra Quigley      | Columbia         | atq2102@columbia.edu              |
+------------------------------+-------------------------+------------------+-----------------------------------+
| CTD Watchstander             | Genevieve Clow          | UC Boulder       | genevieve.clow@colorado.edu       |
+------------------------------+-------------------------+------------------+-----------------------------------+
| CTD Watchstander             | Roxanne Mina            | SIO              | roxannemina9@gmail.com            |
+------------------------------+-------------------------+------------------+-----------------------------------+
| LADCP                        | Ilmar Leimann           | Bremen           | ileimann@uni-bremen.de            |
+------------------------------+-------------------------+------------------+-----------------------------------+
| CFCs, SF_6                   | Jim Happell             | UM Rosenstiel    | jhappell@miami.edu                |
+------------------------------+-------------------------+------------------+-----------------------------------+
| CFCs, SF_6                   | Alexis Wysocki          | UM Rosenstiel    | awysocki544@gmail.com             |
+------------------------------+-------------------------+------------------+-----------------------------------+
| CFCs, SF_6                   | Mary Kate Dinneen       | USC              | mdinneen@usc.edu                  |
+------------------------------+-------------------------+------------------+-----------------------------------+
| Total Alkalinity             | Daniela Nestory         | SIO              | dnestory@ucsd.edu                 |
+------------------------------+-------------------------+------------------+-----------------------------------+
| Total Alkalinity             | Marshal Thrasher        | SIO              | marshalpthrasher@gmail.com        |
+------------------------------+-------------------------+------------------+-----------------------------------+
| pH                           | Cora Mckean             | SIO              | cora.mckean511@gmail.com          |
+------------------------------+-------------------------+------------------+-----------------------------------+
| pH                           | Anna Terrenzi           | SIO              | aterrenzi@ucsd.edu                |
+------------------------------+-------------------------+------------------+-----------------------------------+
| DIC,Underway pCO_2           | Abby Tinari             | UW-CICOES        | atinari@uw.edu                    |
+------------------------------+-------------------------+------------------+-----------------------------------+
| DIC                          | Chuck Featherstone      | NOAA AOML        | charles.featherstone@noaa.gov     |
+------------------------------+-------------------------+------------------+-----------------------------------+
| DOC,TDN, \delta^14C          | Kendra Hyles            | *UCSB*           | kendrafh@icloud.com               |
+------------------------------+-------------------------+------------------+-----------------------------------+
| \delta^13C                   | Songying (Tina) Tang    | UDEL             | tinatang@udel.edu                 |
+------------------------------+-------------------------+------------------+-----------------------------------+
| BIO GO-SHIP                  | Courtney (Star)         | UCI              | sdressle@uci.edu                  |
|                              | Dressler                |                  |                                   |
+------------------------------+-------------------------+------------------+-----------------------------------+
| BIO GO-SHIP                  | Eli Mally               | UCI              | cmally@uci.edu                    |
+------------------------------+-------------------------+------------------+-----------------------------------+
| BIO GO-SHIP                  | Laura Lubelczyk         | Bigelow          | llubelczyk@bigelow.org            |
+------------------------------+-------------------------+------------------+-----------------------------------+
| Core/BGC Argo, SQUID/EM-APEX | Guillaume Liniger       | *MBARI*          | liniger@mbari.org                 |
+------------------------------+-------------------------+------------------+-----------------------------------+
| Naval Observer               | Lt. Cmdr. Md. Sazzad    | Bangladesh Navy  | sazzad12b@gmail.com               |
|                              | Hossen                  |                  |                                   |
+------------------------------+-------------------------+------------------+-----------------------------------+
| Marine Technician            | Liz Ricci               | UW               | ericci@uw.edu                     |
+------------------------------+-------------------------+------------------+-----------------------------------+
| Marine Technician            | Brandon Russell         | *OSU*            | brandon.russell@oregonstate.edu   |
+------------------------------+-------------------------+------------------+-----------------------------------+


Cruise Narrative
================

The 2025 cruise sailed from Henderson, Australia, to Phuket, Thailand,
from March 21, 0800 (UTC+8) to April 27, 0800 (UTC+7), 2025, covering
38 days at sea and 5078.8 nautical miles. Instead of Fremantle port,
which had been used in all previous I09N occupation, this time the AMC
Australian Marine Complex served as our departure point. AMC is
located in Henderson, Western Australia, a suburb of Perth in the City
of Cockburn, approximately 30 minutes from Fremantle.

Like the last two occupations, the arrival port was Phuket Deep Sea
Port in the Andaman Sea, about 23 miles (37 km) from Phuket town.


Mobilization & Delayed Departure
--------------------------------

The AMC is a marine industrial complex that is also used by the Royal
Australian Navy. Due to its higher security protocols, the
mobilization required more coordination effort than typical GO-SHIP
cruises. Given that the AMC is in a relatively remote area with
tightly controlled access (even walking on the dock outside the vessel
is prohibited), the science party stayed in Fremantle during
mobilization. We used a shuttle kindly provided by Scripps to go to
the AMC daily (arriving at 0800 and returning at 1700). With all
science party members adhering to the required protocols and the
efficiency of the R/V *Thompson* crew, our mobilization was flawless,
except for the delay in the arrival of the DIC container.

The late arrival of the DIC container was due to a hold requested by
the Australian government. This hold was placed in Singapore because
of a small volume of acetone inside. With this minor incident, we
(including the Agent) learned that acetone is a controlled substance
in Australia. The acetone was removed from the container, allowing it
to be released and continue its journey to Australia. After
discussions at the GO-SHIP Executive Committee, we decided to wait a
few days for the container, as DIC is a critical Level 1 GO-SHIP
measurement. Consequently, the I09N departure from AMC was postponed
by five days, from March 17, 2025, to March 21, 2025.

Due to the DIC van’s late arrival, we experienced an extended
mobilization period in Henderson from March 13 to 20 (instead of March
13-16), which was more than sufficient to set up all labs well before
departure. The R/V *Thompson* port captain coordinated with the Gulf
Agency Company (GAC) to provide us with a shore crane on the first and
last days of mobilization to load the ODF and float containers (on the
first day) and the DIC (on the last day). A dedicated container for
the floats was the solution found by R/V *Thompson* due to the large
number of lithium batteries on this trip (25 floats).

As a backup plan, the DIC PIs also worked diligently to assemble and
air freight thousands of bottles to Australia. These backup bottles
were stored at the Bio Lab and traveled with us until Phuket.
Fortunately, we did not need to use them, as the DIC team put in a lot
of effort on the last day of mobilization to set up the lab, which
functioned well during the cruise.

Due to logistical issues with a few groups (including the DIC), the
berthing arrangement was only finalized at the last minute, and we
thank the R/V *Thompson* for understanding the situation.
Additionally, one of the CTD watchstanders was not cleared to sail due
to a medical incident. To help the CTD team, the LADCP student kindly
agreed to serve as a watchstander when not involved in LADCP tasks.

Notice that on March 12 (the day before our mobilization), Jim Happell
tested the R/V *Thompson*’s main lab for background \delta^14C and
tritium as part of the UNOLS (University-National Oceanographic
Laboratory System) SWAB program.


Changes Due to Late Departure
-----------------------------

Although the I09N 2025 was initially set to have a similar duration
(41 days) as previous occupations (39 days in 2016; 41 days in 2007
and 1995), our original program was slightly different from past ones:
37 days for occupying the full extent of I09N, 2 days to re-occupy the
northern end of I08S (34°S-28°S), and 1.54 days for activities related
to Bio GO-SHIP (“bio casts”).

A bio-cast is an independent daily cast down to a depth of 1000 m, in
which 22-26 of the 36 10-L Niskin bottles are fired to sample
exclusively biological parameters. For the I09N 2025, the bio team
predetermined the bottles as follows: two bottles at 1000 m, one at
500 m, two at 200 m, one at 150 m, two at 100 m, one at 75 m, one at
40 m, and the remainder at 5 m. In the event of a concurrent BGC float
deployment, two additional depths were incorporated into the bio cast
at the chlorophyll maximum and 50 m below it.

We planned to conduct a bio-cast once a day at the stations closer to
noon. Unfortunately, the late departure and issues at sea (described
later) prevented us from adhering to the original plan. This led to
several modifications related to Bio GO-SHIP operations that were
implemented during the cruise to save time. In the end, from the 18
independent bio-casts that we initially scheduled, we performed 14 of
them, mainly within the Bay of Bengal. The combined bio/core casts
totalized 11.

From ‘at-sea’ days allocated for the I09N 2025 cruise, approximately 8
days were spent transiting to and from ports (4.32 days from AMC to
the 1st station, including a stop for a test cast, and 3.14 days from
the last station to Phuket, assuming a vessel speed of 12 knots). Due
to the late departure, the total length of the cruise was reduced by 5
days (12.2%), but transit times did not change significantly (7.35
days). Fortunately, the R/V *Thompson* had kindly extended our period
at sea by one day. Instead of arriving on April 26 as initially
scheduled, our arrival was moved to April 27. Consequently, the I09N
2025 lasted for 38 days in the end.

With the reduction of the cruise length from 41 to 38 days, the
reoccupation of the I08S stations (south of Broken Ridge) was excluded
from the plan. Prior to the DIC issue, we intended to conduct eleven
stations belonging to the I08S to fill a gap in the data left by the
2024 occupation of that line. This gap resulted from a storm that
prevented the I08S team from collecting data in that area. The
decision not to proceed with the I08S stations also considered the
weather forecast for the period of March 21-28, 2025, which indicated
stormy seas around 34° S, potentially causing further delays for our
cruise. Consequently, the I09N 2025 commenced at Broken Ridge at
28.313° S and 95° E, just as in the last two occupations.

Additionally, we increased the distance between stations in the
equatorial region (3° S-3° N) from 20 nm (1995, 2007, and 2016
occupations) to 30 nm. Given these changes, upon departing from
Fremantle, we planned to occupy 106 stations between the Broken Ridge
and the Bay of Bengal continental slope, instead of 122 stations.
However, issues at sea, as described next, reduced the number of
stations to 98, which is 20% less than our original plan (122
stations) and 13.3% less than in 2016 (113 stations). The reduction
was achieved at sea by increasing the spacing between stations to
about 40 nm between 4.3° S and 1° S.


At Sea Time
-----------

We departed Henderson on March 21 at 11:00 AWST (UTC+8) heading
towards the Broken Ridge to occupy the first I09N 2025 station. While
in transit to the first station, which took about four days, we
stopped halfway (on March 23) for a test station in international
waters (29.87° S-104.05° E and 3527 m deep). Time was carefully picked
so both watches could participate and be trained. We had several
objectives for the test station: first, to train our CTD watch-
standers and incoming lab technicians; second, to verify if the
instruments and the winch were functioning properly; and third, to
coordinate the workflow between bio and core GO-SHIP casts.

The plan for the test station was as follows: perform a shallow bio-
cast down to 1000 m while firing 22 bottles at pre-determined depths
set by the Bio GO-SHIP team on board, sample these bottles, re-cock
the rosette, deploy the rosette again for a deep cast (down to 10 m
above the bottom), fire the 36 bottles, sample all bottles and analyze
afterward.

At the test station, we began the procedure as usual, and nothing
indicated the sequence of problems we would encounter: the winch
software froze, the bottles could not be fired and the cable became
tangled. Ultimately, we lost communication with the CTD package. The
cast was aborted, and the package was retrieved to the surface. No
water was collected, and the deep cast was not attempted.

Resolving the multiple issues we encountered at the test station,
including the DASH-5 winch problem, required time. Given our late
departure, we continued sailing toward the first station. At the same
time, R/V *Thompson* Marine Techs debugged the winch, and the ODF team
addressed the CTD package issues. The problems were fixed by replacing
the carousel (SBE32) and cables.

A second test station (29° S-98.98° E; 2197 m) was conducted on March
24 at 11:00. We only performed the bio-cast (from the surface to a
depth of 1000 m) to save time. The main objective was to verify the
readiness of the winch and the CTD package, train the CTD watch
standers, and provide water for the Bio team to begin their work. All
36 bottles were fired, and the transmissometer was covered with black
tape for calibration (a procedure that the Bio team conducted weekly
throughout the cruise). Everything worked well this time. During the
second test station, the CTD watch standers learned from Scripps ODF
(Ocean Data Facility) technicians how to prepare the rosette, fill in
the logs, and fire the bottles. As it was a shallow cast, they did not
have the opportunity to conduct a bottom approach, which they needed
to learn in effective stations.

We arrived at the first station late on March 25 (23:40, AWST). The
station was located on the northern flank of the Broken Plateau
(28.31°S-95°E), at a depth of 3093 m. Everything functioned well
despite the spiky altimeter readings during our bottom approach.
Problems with the altimeter were common throughout the I09N 2025
cruise, leading us to change units and cables several times, as
described later. This was the first experience for our CTD watch
standers with bottom approximation. The first bottle was fired 10 m
above the bottom, as is standard in GO-SHIP. It was a slow cast as
everyone was learning, and mistakes were being corrected.

On Station 2, the aft winch display stopped working. We had no
information about the speed or wire payout. The altimeter also had
issues, so we fired the first bottle 20 m above the bottom. Later in
the cruise, we found that the multibeam readings tended to be deeper
than the LADCP bottom estimates Fig. %s. After we identified the bias,
Marine Tech Brandon Russell and LADCP student Ilmar Leimann worked
diligently to regularly feed the multibeam with sound speed profiles
derived from our collected CTD data, resulting in multibeam readings
that became much closer to LADCP estimates.

   [image]Probability distribution of the differences between the
   multibeam readings and LADCP bottom estimations for the whole
   cruise.

Due to the winch failure, we postponed operations at Station 3 to
replace the winch and conduct a mechanical re-termination. From
Station 3 until the end of the cruise, we utilized the forward winch
instead of the aft winch. Both winches were DASH-5. We also changed
the ship’s local time from UTC+8 to UTC+7, which persisted until the
end of the cruise.

Stations 4 and 5 progressed without major incidents, aside from the
noisy altimeter that troubled us throughout the cruise. We replaced
the altimeter and cables for station 4, but this did not resolve the
problem as we had hoped. The only other issue was a leak in the
underway system used by the Bio team, which the R/V *Thompson* crew
worked swiftly to address.

We began Station 6 with a bio-cast and encountered no issues, except
for the slow sampling of 22 bottles for bio measurements for the first
time. However, during the deep cast that followed the bio-cast, the
altimeter completely failed during the bottom approximation, which
became a recurring issue.

The problems, however, drastically worsened at Stations 7 and 8,
causing further cruise delays and significant adjustments in the
station plan and bio-casts. On Station 7 (March 27), we again were
unable to fire bottles from the CTD console. The deck box was rebooted
several times, but this did not solve the problem. Some bottles were
closed and collected water, while others remained open. Due to these
issues, it is unknown at what depths many of the bottles were closed.
After that, the fish (CTD unit, SBE 9+) was replaced.

At Station 8 (24.14° S-95° E), everything went wrong. Nothing worked;
there were multiple modulo errors and a conductivity sensor had
failed. After aborting the cast, we held position at Station 8 from
March 26 at 10:00 to March 29 at 05:30.

A confluence of problems occurred at Station 8, leading to a 3-day
hold. First, the ODF team discovered an issue with the wire. To solve
the problem, they cut 20 m of wire and performed full mechanical and
electrical terminations. Second, the ship’s z-drive failed and
required repairs. Finally, the winch heave compensation system did not
function satisfactorily and needed repairs.

Last but not least, at Station 8, the sea became slightly rough due to
Tropical Cyclone (TC) Courtney approaching us Fig. %s. TC Courtney was
a severe tropical hurricane that formed in the Indian Ocean on March
26, around 16.6° S and 111° E, and moved westward, passing over the
95° E meridian. According to weather forecasts, TC Courtney may have
reached Category 4 and was the world’s strongest storm of the month,
which resulted in a weather hold. Only after TC Courtney moved west of
our line at 95° S did the sea state begin to improve. This allowed the
R/V *Thompson* crew to repair the z-drive, although we continued to
encounter minor issues with it (and the bow thruster) throughout the
Equatorial zone, both components critical to the ship’s dynamic
positioning system to keep the ship in position on station.

   [image]TC Courtney. Forecast for March 28, 2025, from Windy.com
   based on the ECMWF model. Highlighted is our position on Station 8
   on that day.TC Courtney even reached Cat 4 in the following days
   during our 3-day hold.

After all repairs and with an improved sea state, we performed a
shallow cast (1000 m) on March 29 at 04:00 for testing. We fired 22
bottles on the fly (to save time) and 14 bottles at the surface for
the Bio team. Except for Bio, no water samples were drawn from the
rosette. We labeled this cast 008/03 (the previous two had been
aborted). With the success of the shallow cast, we proceeded to
execute a deep cast. Unfortunately, the altimeter stopped functioning
at about 40 m above the bottom, and as a precaution, we fired the
first bottle at that depth. Aside from the altimeter malfunction, it
was a successful cast (008/04).

Due to the three days lost at Station 8 and the decrease in vessel
speed caused by TC Courtney’s influence, we had to modify our station
plan, reducing the total number of stations from 106 to 89. In the
updated plan, stations north of 4.3° S were set to be 41.8 nm (4.3°
S-0.3° N), 25-33 nm (0.3° N-3.9° N), 37.3 nm (3.9° N-9.8° N), 42-45 nm
(9.8° N-17° N), 30-42 nm (17° N-19.3° N), and less than 22 nm north of
that. The stations south of 4.3° S were maintained as previous
occupations (nominally at 30 nm) due to the richness of water mass
distribution in the Southern Hemisphere and their frontal zones. This
choice was also influenced by the fact that the I09N trajectory south
of the Equator has not changed since the first occupation in 1995,
allowing for direct evaluation of property changes over the last 30
years. While there was a significant reduction in the number of
stations, we still aimed to accomplish all critical mission
objectives.

After all the problems leading up to Station 8, there were no major
technical problems afterward. Issues that persisted while sailing in
the Southern Hemisphere were related to the z-drive and bow thruster,
causing further delays at some stations. Another persistent problem
was the intermittency of the altimeter, which sometimes functioned and
sometimes failed completely Fig. %s. Following our discovery that we
may have had a few near-miss bottom touches (Fig. %s, black circles),
we changed the protocol for the bottom approach. This finding was
based on the LADCP data processed in real-time by Ilmar Leimann. For
stations after Station 41, when the altimeter was not functioning, our
maximum depth was 30 m above the multibeam reading, particularly if
the local bottom was rough.

   [image]Altimeter status during the I09N 2025 cruise. Blue is used
   for stations when the altimeter worked, and red when there was no
   altimeter signal. Black circles highlight the near-miss stations,
   i.e., when the CTD package was 5 m or less from the ocean bottom,
   according to the LADCP data.

Station 12 marked the last station with independent bio-casts,
although we resumed them by the cruise’s end (Station 64) when the
ship’s overall performance improved. At that point in the cruise, the
bio-casts took about two hours, accounting for the rosette
preparation, deployment, firing of 22-26 bottles, sampling, and the
issues the ship faced with positioning due to problems in the z-drive
and bow thruster. Our time forecast calculations indicated that we
would not arrive in Phuket on time if we performed all the remaining
bio-casts.

Between Stations 12 and 64, instead of conducting independent bio-
casts, we created an integrated bio/core cast (described in the next
section) that occurred at the closest station to noon. During this
period, we only conducted independent bio-casts at stations where BGC
floats were deployed due to water demand. We could not meet the water
demand of all groups with just 36 bottles.

Starting in the equatorial zone (around 2°-3° S), far from the
influence of TC Courtney, the ship’s performance improved drastically.
The z-drive and bow thruster issues subsided (thanks to the tireless
efforts of R/V *Thompson* engineers), and the ship began to sustain
speeds of 12-13 knots between stations, giving us some time back. We
initially added two stations to our plan near the Equator: one at
0.63° S and another at 0°. These stations had been previously occupied
in 1995, 2007, and 2016. Adding these new stations reduced the spacing
between them near the Equator from 41.8 nm to 18-23 nm. We chose to
add these stations because forecasts from CMEMS Operational Mercator
indicated that the near-surface eastward Wyrtki Jet along the Equator
was well developed, and the I09N track would cross its core in the
eastern basin Fig. %s. According to the GLORYS-12 reanalysis, the
Wyrtki Jet was absent in 2016 but present in 2007. Wyrtki Jets occur
during boreal spring (April-May) and fall (October-November) within
+/- 2° of the Equator and are essential features in heat and mass
transport between the western and eastern Indian Ocean. The
observations we collected will allow us to evaluate the multi-decadal
differences.

   [image]Zonal velocities at 110 m from the CMEMS Operational
   Mercator forecast for April 11, 2025, when the I09N 2025 cruise
   crossed the equatorial zone. Circles show all I09N trajectories
   (1995, 2007, 2016, 2025).

With the ship’s performance sustained over time, we reduced the
spacing between stations north of 3.9° N to 26-34 nm until 17° N and
6-19 nm north of it. These changes resulted in the potential for 100
stations to be occupied by the I09N, which, in the end, could not be
as later explained.

Although the altimeter readings remained spiky until the end of the
cruise, their functioning became less erratic north of the Equator
Fig. %s. The improvement occurred after the ODF implemented a series
of changes, but the culprit for the previous faults could not be
pinpointed. The better performance and more accurate multibeam
readings enabled the CTD watchstanders to safely maneuver the package
to 10 m above the bottom.

The pleasant weather and calm sea after we crossed TC Courtney’s zone
of influence made CTD deployments straightforward, and no other
significant technical problems occurred. Only minor issues were noted,
as documented later in this report: a few unfired bottles and missed
target depths, a few mistakes in filling out sample logs and sampling
from Niskin bottles, LADCP cable and instrument reconfigurations,
among others. These issues, typical of any cruise, were sporadic and
resolved promptly.

An unusual occurrence happened at Station 75 (10.3° N-87° E) when a
fishing boat came very close to the CTD package in the water. As a
precaution, the bridge required the package to resurface without all
bottles being fired. The crew acted swiftly to prevent any problems.

Unfortunately, we had to skip the last two northern stations occupied
in 2007 and 2016 due to the nuanced difference between the Exclusive
Economic Zone and the Extended Continental Shelf boundaries, the
latter of which is in dispute. We learned about this issue just when
arriving at the first of these stations, and after discussing it with
the captain, we concluded that not occupying them was the best course
of action. Consequently, there was a gap of about 72 nm between 17° N
and 18.2° N, with only 98 stations occupied in total during the I09N
2025 cruise.

Near the end of the line, stations became progressively closer
together, with spacing varying from 6 to 19 nm. In GO-SHIP cruises,
the time required for lab analysis and equipment charging (e.g.,
LADCP) is critical. Thus, we increased the time between stations. To
accomplish this, we slowed the pace between stations, even waiting at
stations when necessary. This arrangement allowed the labs to take and
analyze as many samples as possible, resulting in a more complete
dataset of carbon parameters, particularly by performing all planned
full carbon stations. Full carbon stations mean that carbon parameter
samples are taken from all 36 Niskin bottles. At partial stations,
samples are collected from 24 Niskin bottles, with depths chosen to
capture good vertical resolution. Due to the combined bio-core casts
between Stations 12 and 64, the sequence of full and partial stations
during the I09N 2025 occupation did not follow the usual GO-SHIP
pattern (full-partial-full-partial-…); in combined bio-core casts, all
stations were ‘full carbon’ as we were using only 24 bottles for the
core GO-SHIP measurements.

Additionally, we did not collect any data from the underway system for
most Bio GO-SHIP measurements north of 17.5° N, as those measurements
were not requested as part of the Bangladesh EEZ clearance process.
Instead, these data were collected only from the Niskin bottle, as
granted by the Bangladesh government. In this case, the only
measurement not collected was PIC, as it was not part of the set of
variables included in the MSR (Marine Science Research) request.

During the cruise, floats and surface drifters were deployed by the
end of stations at a ship speed of a few knots. BGC floats were
deployed only during daylight, preferably at stations closer to noon.
For each of the seven BGC floats deployed, an independent bio cast was
conducted, sometimes before the deep cast and sometimes after,
depending on the time we arrived at the stations. All floats and
surface drifters were deployed south of the Bangladesh EEZ following
the plan determined by the respective PIs.


Choice of Discrete Depths and Staggering Scheme
-----------------------------------------------

For the 2025 occupation of the I09N, the standard WOCE/CLIVAR/GO-SHIP
staggering scheme for 36 bottles was adopted for all regular stations.
In this scheme, the vertical distribution of discrete depths rotates
every three stations (I-II-III) and depends on the local bottom depth
(shallow, mid, and deep). The first Niskin bottle is fired 10 m above
the bottom, and the last at the surface, nominally at 5 m Fig. %s.
Most of our stations had bottom depths above 6000 m, except for
stations 20 to 22, which have bottom depths that exceed that. The
first bottle was fired at 6000 m for those stations because the
instruments are rated to this depth. In this latter case, we used the
staggering scheme I for deep stations. For all other stations, we used
the staggering scheme for medium depths.

   [image]Dissolved oxygen at discrete Niskin bottles collected during
   the 2025 of the I09N line. Highlighted is Station 7, where the
   depths of several bottles closed are unknown, and the two stations
   we did not occupy (72 nm gap).

For stations with integrated bio/core casts, we used the GO-SHIP
24-bottle staggering scheme instead (surface to 10 m above the
bottom). We combined the selected 24 depths of the latter scheme with
12 depths determined by the Bio GO-SHIP team (1000 m, 200 m, 100 m,
and nine bottles deployed at the surface). Given the large volume of
water needed by the Bio team, we adjusted our closest depths to match
5, 100, 200, and 1000 m of bio, ensuring they had an adequate water
supply when required. This merged scheme was the compromise we reached
that allowed us to maintain our pace to the north while still
partially achieving the objectives of GO-SHIP and Bio GO-SHIP.

Additionally, we reduced the number of fired bottles at stations with
bottom depths shallower than 3900 m while keeping a vertical
resolution like previous stations. This new pattern started at station
62 (4.36° N-90.98° E) and lasted until the end of the cruise. For
that, we used the 36-bottle staggering medium depth scheme as a basis.
The number of fired bottles varied from 22 to 34.


CTD and Rosette Setup
=====================

   [image]*Image credit Allen Smith*

For I09N a SIO/STS 36-place yellow rosette and bottles were used. A
steel bridle was added to the top of the rosette to adapt to the winch
head. The bottles were made with new PVC, with new non-baked o-rings.
Springs within the Bullister-style Niskin bottles were electropolished
stainless steel. Bottle lanyards were made from 300-pound
monofilament. No sample contamination from the o-rings and springs was
detected. The package used on I09N weighs roughly 1500 lbs in air
without water, 2350 lbs in air with water and approximately 950 lbs in
water. In addition to the standard CTDO package, two LADCP were
mounted on the rosette.


Underwater Sampling Package
---------------------------

   [image]36-place rosette with bottles and instrument package.

Rosette/CTD/LADCP casts were performed with a package consisting of a
36-bottle rosette frame (SIO/STS), a 36-place carousel (SBE32), and 36
10-L Bullister bottles (SIO/STS) with an absolute volume of 10.4 L.
Underwater electronic components consisted of a Sea-Bird Electronics
SBE9plus CTD with dual pumps (SBE5T), dual temperature (SBE3plus),
dual conductivity (SBE4C), dissolved oxygen (SBE43), transmissometer
(Wetlabs), fluorometer (Wetlabs FLRTD), altimeter (Valeport VA500) and
an optical oxygen sensor (RINKO). An SBE35RT reference temperature
sensor was connected to the SBE32 carousel and recorded a temperature
for each bottle closure. The sea cable armor was used for ground
(return). Power to the SBE9plus CTD (and CTD sensors), SBE32 carousel,
and auxiliary sensors was provided through the sea cable from the
SBE11plus deck unit in the computer lab. The sensor serial numbers,
calibration dates, and A/D channel are listed in Table %s below.


Rosette Sensors
^^^^^^^^^^^^^^^

+-----------------------------------+-----------------------------------+-----------------------------------+
| Sensor & Serial Number            | Cal. Date                         | A/D Channel                       |
|===================================|===================================|===================================|
| 9plus SN 0381 (removed)           | 9/29/2023                         |                                   |
+-----------------------------------+-----------------------------------+-----------------------------------+
| 9plus SN 0569                     | 4/23/2024                         |                                   |
+-----------------------------------+-----------------------------------+-----------------------------------+
| 3plus SN 2039 (primary)           | 12/10/2024                        |                                   |
+-----------------------------------+-----------------------------------+-----------------------------------+
| 3plus SN 4588 (secondary)         | 12/10/2024                        |                                   |
+-----------------------------------+-----------------------------------+-----------------------------------+
| 4C SN 1744 (primary - removed)    | 10/24/2024                        |                                   |
+-----------------------------------+-----------------------------------+-----------------------------------+
| 4C SN 2319 (primary)              | 1/22/2025                         |                                   |
+-----------------------------------+-----------------------------------+-----------------------------------+
| 4C SN 1879 (secondary)            | 12/11/2024                        |                                   |
+-----------------------------------+-----------------------------------+-----------------------------------+
| 5T SN 1799 (secondary - removed)  | 10/9/2023                         |                                   |
+-----------------------------------+-----------------------------------+-----------------------------------+
| 5T SN 3342 (secondary)            | 11/1/2022                         |                                   |
+-----------------------------------+-----------------------------------+-----------------------------------+
| 5T SN 8689 (primary)              | 10/9/2023                         |                                   |
+-----------------------------------+-----------------------------------+-----------------------------------+
| 35RT SN 0035                      | 12/19/2024                        |                                   |
+-----------------------------------+-----------------------------------+-----------------------------------+
| 43 SN 4355 (initial sensor -      | 11/6/2024                         | Aux4 V6                           |
| removed)                          |                                   |                                   |
+-----------------------------------+-----------------------------------+-----------------------------------+
| 43 SN 1136 (suspected cracked     | 11/6/2024                         | Aux4 V6                           |
| cell - removed)                   |                                   |                                   |
+-----------------------------------+-----------------------------------+-----------------------------------+
| 43 SN 1071 (on rosette for the    | 12/17/2024                        | Aux4 V6                           |
| remainder)                        |                                   |                                   |
+-----------------------------------+-----------------------------------+-----------------------------------+
| Transmissometer SN 1873           | 8/2/2023                          | Aux1 (low order) V0               |
+-----------------------------------+-----------------------------------+-----------------------------------+
| Alt. VA500 SN 88639               | 3/11/2023                         | Aux3 V4                           |
+-----------------------------------+-----------------------------------+-----------------------------------+
| Alt. VA500 SN 78548               | 8/20/2021                         | Aux3 V4                           |
+-----------------------------------+-----------------------------------+-----------------------------------+
| RINKO SN 0479                     | 9/27/2023                         | Aux2 V2 & V3                      |
+-----------------------------------+-----------------------------------+-----------------------------------+
| FLRTD SN 9157                     | 10/22/2024                        | Aux1 (high order) V1              |
+-----------------------------------+-----------------------------------+-----------------------------------+

All electronics were mounted below the carousel. The SBE9plus was
mounted into its cage mount and attached to the bottom of the rosette
frame across grid bars in the center of the rosette. The SBE4C
conductivity, SBE3plus temperature, and SBE43 dissolved oxygen sensors
and their respective pumps and tubing were assembled as recommended by
SBE on the CTD cage. The SBE35 sensor was mounted to the SBE9 between
the primary and secondary SBE3 sensors.

   [image]CTD instrument package showing sensor locations. Altimeter
   is seen mounted to the rosette frame.

   [image]CTD instrument package showing sensor locations. LADCP
   battery is visible  behind.

The transmissometer was mounted horizontally, and the fluorometer,
altimeter, and RINKO were mounted vertically along the bottom of the
rosette frame. Both the upward-looking and the downward-looking ADCP’s
were mounted vertically on one side of the frame between the bottles
and the CTD. The ADCP battery pack was located on the opposite side of
the center grid bars, mounted on the bottom of the frame. In front of
the battery pack, the transmissometer was mounted along a Unistrut on
the bottom frame.

   [image]Downward-looking LADCP and battery pack.

   [image]Transmissometer, Rinko oxygen optode and fluorometer mounted
   to the rosette frame with LADCP battery pack.

Additionally, an RBRduet3 TD/deep temperature and pressure logger (S/N
234746) was mounted beside the SBE35. Data were collected from this
instrument for testing purposes only, and are not presented here.

The top, inside, and bottom end cap lanyards were replaced before the
rosette was shipped to Australia. Lanyard measurements on the niskin’s
accounted for the addition of the lifting ring mounted to the frame
above the water sampler. This ring ensures that all the bottles are
cocked at the appropriate angle and will close when fired. All bottle
o-rings were replaced during the transit to the first station.

The rosette system was suspended from a UNOLS-standard three-conductor
0.322” electro-mechanical (EM) sea cable. The sea cable underwent 4
full mechanical terminations and 1 electrical termination, all within
the first 15 stations. These reterminations occurred due to
communication errors with the SBE9plus and SBE32, and errors in the
ship’s winch readouts. During the ship’s troubleshooting of the aft
winch, the termination with the .322 wire was moved to the forward
winch. The following stations gave sufficient wire data until the
winch speed readings cut out. The winch errors could not be resolved
and required another retermination on the forward spool.

During cast 00802, there were several modulo errors, resulting in an
electrical retermination, as it had been found that the armor and
ground pigtail connection was not fully connected. However, the
subsequent test cast gave the same pylon communication issues as
before, as well as over 30 modulo errors. This led to another
retermination with the Figi fittings, which passed the ships’ pull
test, but upon testing the conductors, all 3 were found to be shorted,
as the inner barrel of the fitting cut through the conductors and the
inner armor cut through the PVC jacket. Between all the lost time as
well as the finite amount of Figi fitting supplies, the final
retermination used 3 Crosby clips for the tertiary termination point
and guy grips on the other two points. Any delays after the last
retermination were due to weather or ship issues with the z-drive (bow
thruster).

Kinks in the EM cable result from the shock loading on sheaves at
shallow depths during launch and recovery. Shock loading did not occur
on this cruise, as the winch would use the heave compensation setting
during less-than-ideal sea states, and the wire remained free of kinks
and in good working condition.

The CTD watchstanders prepared the rosette 15-30 minutes before each
cast. The bottles were cocked, and all spigots, vents, and lanyards
were checked for proper orientation. LADCP technician would check for
LADCP battery charge, prepare instruments for data acquisition, and
disconnect cables. The Marine Technician would check the sea state ~15
minutes before station arrival and decide if conditions were
acceptable for bringing out the rosette. The rosette was moved from
the sampling bay to the starboard side of the deck using the
Thompson’s (accordion) deployment platform. Once on deck, sea cable
slack was pulled up by the winch operator and taglines were manned by
the AB’s.

The CTD was powered up, and the data acquisition system started from
the computer lab when directed by the marine technician from the deck.
The winch operator was directed by the deck to raise the package. The
hydro boom and rosette were extended outboard, and the package was
kept level quickly lowered into the water. At the surface, the
technician told the winch operator to “zero” the wire out and lower
the rosette to 10 meters, where it was held until the console
operators determined that all sensors had turned on and data looked
good. The winch operator was then directed to bring the package back
to the surface and to begin the descent. Each rosette cast was lowered
to within 10 meters of the bottom, using the altimeter, winch wireout,
and multibeam depth to determine the distance.

For each upcast, the winch operator was directed to stop the winch at
some number (between 10 and 36) of standard sampling depths. These
standard depths were staggered at every station based on different
schemes derived by the Chief Scientists. To ensure the package shed
wake had dissipated, the CTD console operator waited 30 seconds prior
to tripping sample bottles. Before moving to the next consecutive trip
depth, an additional 15-second pause was observed. The marine
technician directed the package to the surface for the last bottle
trip. Recovering the package at the end of the deployment was
essentially the reverse of launching. Once the rosette was on deck,
the console operator terminated the data acquisition, turned off the
deck unit, and assisted with rosette sampling. The rosette was secured
on the cart and moved into the aft hanger for sampling. The bottles
and rosette were examined before samples were taken, and anything
unusual was noted on the sample log. Routine CTD maintenance included
flushing the conductivity and oxygen sensors with freshwater between
casts to maintain sensor stability and rinsing the rest of the sensors
(including the carousel) with freshwater.

Rosette maintenance was performed regularly. Caps, spigots, and
o-rings were inspected for leaks. Occasional reorientation of the
bottles was required to ensure proper firing and sampling. Lanyards
were replaced as needed. A few vents needed to be replaced after
damage from tagline hooks during recovery.

Several stations revealed erroneous sensor data requiring multiple
spare sensor swaps. A test cast during transit to the first station
had no communication with the SBE32 carousel, so bottles were fired on
the fly during the upcast. Once on deck, only 3 bottles had
successfully fired, none of which were manually fired at the console.
After an attempted cable swap failed to resolve the issue, and a deck
test of the Thompsons’ spare 24-place SBE32 proved successful, the
pylon was switched with the spare 36-place SN-0187.

Station 00701 experienced multiple bottle-fire failures, and during
troubleshooting, the SBE9+ was swapped from SN 0381 to SN 0569.

Attempted cast 00801 revealed that the primary conductivity sensor SN
1744 had failed. This sensor was swapped to SBE4C SN 2319 after the
cast was aborted.

Throughout the cruise, the VA500 altimeter(s) data did not
consistently pick up the seafloor. Data looked good during 00101, but
all subsequent casts only saw intermittent readings at best between
90-20 m from the bottom until cast 00602, which saw no altimeter
readings at all despite reaching appx 10 m from the bottom (confirmed
by LADCP data post cast). Both cable and sensor were swapped (from SN
78548 to SN 88639) with no better results. After 01501, the ship’s
altimeter was installed onto the rosette (SN 67356) and performed
about the same as ODF’s sensors. The ships’ spare VA500, ODF’s spare
VA500, and the installed VA500 all had settings verified and performed
well in the Valeport terminal during bucket tests. All sensors had no
signs of any corrosion or hot pins so bad readings were assumed to be
caused by the aux port on the SBE9+. To prove this, a generic wye
cable was used on the SBE43 aux port to see if the altimeter would
perform a cleaner bottom approach.

Station 05401 was the first cast after removing the generic wye cable
from the altimeter/SBE43. During this cast, the SBE43 data looked
noisy, resulting in both a cable swap and an aux port swap. Failure to
make a cleaner profile caused the sensor to be swapped to SN 1136. The
resulting profile looked suspiciously like a cracked cell. SBE43 SN
1071 was installed and looked good from station 05801 until the end of
operations.

The altimeter and fluorometer were swapped in position on the rosette
to attempt to eliminate the excess of noise (on the altimeter). This
was futile, but almost all the noise was eliminated during a cast
where the LADCP was never powered on. Altimeter depths vs the
multibeam depths look realistic when doing the bottom approach but
during some casts, if the payout speed dropped too significantly, the
reading from the altimeter would also drop out.


CTDO and Hydrographic Analysis
==============================

PIs
   * Todd Martz (SIO)

   * Susan Becker (SIO)

Technicians
   * Allen Smith (SIO)


CTDO and Bottle Data Acquisition
--------------------------------

The CTD data acquisition system consisted of an SBE 11plus V2 deck
unit and a networked Windows 10 PC workstation. Sea-Bird SeaSave V7
version 7.26.7 software was used for data acquisition and to close
bottles on the rosette.

CTD deployments were initiated by the console watch operators (CWO)
once the ship was positioned on each station. The CWO maintained a
detailed console log for each attempted cast to record cast metadata,
each bottle fired and any notable issues encountered.

CTD data acquisition was begun with the rosette on deck. Deck crew
deployed the rosette and immediately lowered it to 10 meters. The CTD
sensor pumps were configured to start immediately after the primary
conductivity cell detects salt water. The CWO checked the CTD data for
proper sensor operation, waited for sensors to stabilize, and
instructed the winch operator to bring the package back to the
surface. Deck crew determined the surface depth based on their
judgement of weather and sea state. The winch operator was then
instructed to lower the rosette to the initial target wire-out at no
more than 60 m/min after 100 m depending on depth, sea-cable tension,
and the sea state. During periods of higher sea states, automatic
heave compensation was enabled on the winch, resulting in variable
payout rates at a maximum of 50 m/min.

The CWO monitored the progress of the deployment and quality of the
CTD data through real-time displays. The altimeter, CTD pressure,
wire-out and multi-beam depth sounder were all monitored to determine
the distance of the package from the bottom. The winch was directed to
slow decent rate to 30 m/min at 100 m from the bottom, and 20 m/min
when 30 m from the bottom. The bottom depth of the cast was usually
within 10 meters of the bottom as determined from the altimeter data.
For each full upcast, the winch operator was directed to stop the
winch at up to 36 predetermined depths. The CWO allowed 30 seconds at
each stop before closing the sample bottle. An additional 15 seconds
were allowed after bottle closure for the SBE35RT reference
temperature sensor to record 13 samples and compute an average. The
rosette was then raised to the next target depth. For the last bottle,
the winch operator was instructed to return the rosette to the
surface, and then used their judgement to bring the rosette as close
to the surface as was possible in the prevailing wind and sea
conditions. After the last surface bottle was closed, the CWO directed
the deck crew to recover the rosette.

Once the rosette was out of the water and on deck, the CWO terminated
the data acquisition. Each bottle and the rosette were examined before
sampling began. A sample log was kept during sampling, recording all
analytical samples drawn from each bottle. The CTD sensors were rinsed
after every cast using syringes of fresh water connected to Tygon
tubing. Between casts, the tubing was left in place to keep the
temperature and conductivity sensors immersed in fresh water.

Each bottle on the rosette had a unique serial number, independent of
the bottle position on the rosette. If a Niskin bottle was replaced,
the new bottle was tracked in the cruise database.

Several software issues arose affecting data acquisition. At station
7, communication with the water sampler became unreliable and
acquisition was stopped and restarted twice during the upcast in
effort to restore communication, resulting in multiple data files for
the cast. At station 20, acquisition was unintentionally stopped
during the upcast. Operators restarted acquisition and completed the
cast, which also resulted in multiple data files. For both casts, raw
data files were manually cut-and-pasted together in a single file for
processing with CTDCAL, described below.

At two stations, 9 and 12, Sea Save failed to record the 36th bottle,
even though in both cases the bottle did indeed close. For the purpose
of data processing, we assume these bottles closed at the surface as
intended, but since there is no record of the closure in the raw CTD
data to confirm, we treat these bottle data as suspect.


CTDO Data Processing
--------------------

Shipboard CTD data processing was performed after deployment. Sea-Bird
SeaSoft V2 Data Processing software was used to generate bottle
summary files and bin-averaged converted files in 1 Hz, 1 dbar and 2
dbar bins for immediate use aboard the ship following the cast. An
additional converted raw file was generated with parameters specified
by the LADCP group for their use.

Raw CTD data were manually fit and quality controlled using SIO/ODF
CTD processing software ctdcal v. 0.1.4 running on an Apple MacOS
system. CTD data at bottle stops were extracted to create a 2 db
downcast pressure series. The pressure series data were submitted for
CTD data distribution after corrections outlined in the following
sections were applied.

A total of 100 CTD stations were occupied including two test-cast
stations. A total of 115 casts were processed.

CTD data were examined at the completion of each cast for clean
corrected sensor response and any calibration shifts. As bottle
salinity and oxygen results became available, they were used to refine
conductivity and oxygen sensor calibrations.

Temperature, salinity and dissolved oxygen comparisons were made
between upcasts and downcasts as well as between groups of adjacent
deployments. Vertical sections of measured and derived properties from
sensor data were checked for consistency.

For Bio-GO-SHIP casts where bottle sampling for salts and oxygen was
not performed, fit coefficients were obtained from the nearest
proximal cast, which in most cases was the same station.

Issues that directly impacted CTD analysis are described in this
section. Issues that affected bottle closures are detailed in the CTD
and Rosette Setup section of this report. Temperature, conductivity
and oxygen sensor issues are detailed in the subsections below.


Pressure Analysis
-----------------

CTD pressure was provided by an SBE 9plus profiling CTD unit. Serial
number 09-0381 was used through station 7. Serial number 09-0569 was
used for the remainder of the cruise. No performance issues were noted
with either instrument.

Laboratory calibrations of CTD pressure sensors were performed prior
to the cruise. Dates of laboratory calibration are recorded in Table
%s. Calibration documents are provided in the APPENDIX.

The lab calibration coefficients provided on the calibration report
were used to convert raw sensor frequency to pressure. Initial SIO
pressure lab calibration coefficients were entered into SeaSave
configurations and applied to cast data during acquisition.

Additionally, on-deck pressures were recorded at the start and end of
each cast to characterize offsets for each sensor. Starting offsets
remained consistent, and the mean starting offset was subtracted from
all casts for each sensor. Offsets at the end of casts were more
variable.

On-deck pressure offsets observed throughout the cruise are shown in
Fig. %s. Maximum, minimum and average offsets observed for each sensor
are presented in Table %s.

   [image]SBE9+ on-deck pressure offsets by cast.


SBE9plus Pressure Offsets
^^^^^^^^^^^^^^^^^^^^^^^^^

+--------------------+--------+------------+------------+
| Pressure Offsets   |        | Start      | End (dbar) |
|                    |        | (dbar)     |            |
|====================|========|============|============|
| CTD SN: 09-0381    | Min    | -0.5721    | -1.1416    |
|                    +--------+------------+------------+
|                    | Max    | 1.0240     | -0.0427    |
|                    +--------+------------+------------+
|                    | Mean   | -0.3505    | -0.8201    |
+--------------------+--------+------------+------------+
| CTD SN: 09-0381    | Min    | 0.8724     | -0.0263    |
|                    +--------+------------+------------+
|                    | Max    | 1.8142     | 1.1318     |
|                    +--------+------------+------------+
|                    | Mean   | 1.1073     | 0.7393     |
+--------------------+--------+------------+------------+


Temperature Analysis
--------------------

CTD temperature was provided by primary and secondary SBE 3plus
temperature sensor units. Serial number 03-2039 was used on the
primary CTD channel, and serial number 03-4588 was used on the
secondary channel. Both were used for the duration of the cruise with
no performance issues noted. Reference temperatures were provided by
an SBE35RT Digital Reversing Thermometer. Serial number 35-0035 was
used for the duration of the cruise with no performance issues noted.

Laboratory calibrations of temperature sensors were performed prior to
the cruise at the SIO Calibration Facility. Dates of laboratory
calibration are recorded in Table %s. Calibration documents are
provided in the APPENDIX.

The pre-cruise laboratory calibration coefficients were used to
convert SBE3plus frequency to ITS-90 temperature. Additional shipboard
calibrations were performed to correct systematic sensor bias. Two
independent metrics of calibration accuracy were used to determine
sensor bias. At each bottle closure, the primary and secondary
temperature were compared with each other and with a SBE35RT reference
temperature sensor.

The SBE35RT Digital Reversing Thermometer is an internally-recording
temperature sensor that operates independently of the CTD. The SBE35RT
was located equidistant between the two SBE3plus temperature sensors.
The SBE35RT is triggered by the SBE32 carousel in response to a bottle
closure. According to the manufacturer’s specifications, the typical
stability is 0.001 °C/year. The SBE35RT was set to internally average
13 samples, which is approximately a 15 second period.

The SBE3plus sensor typically exhibits a consistent well-modeled
response, which is second-order with respect to pressure and second-
order with respect to temperature:

   T_{cor} = T + cp_2 P^2 + cp_1 P + ct_2 T^2 + ct_1 T + c_0

Fit coefficients are shown in the following tables.


Primary temperature (T1) coefficients.
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

+------------------+------------------+------------------+------------------+------------------+------------------+
| Station          | cp_2             | cp_1             | ct_2             | ct_1             | c_0              |
|==================|==================|==================|==================|==================|==================|
| All              | 0.0              | -4.4934e-7       | 0.0              | 0.0              | 2.0278e-3        |
+------------------+------------------+------------------+------------------+------------------+------------------+


Secondary temperature (T2) coefficients.
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

+------------------+------------------+------------------+------------------+------------------+------------------+
| Station          | cp_2             | cp_1             | ct_2             | ct_1             | c_0              |
|==================|==================|==================|==================|==================|==================|
| All              | 0.0              | -4.3224e-7       | 0.0              | 0.0              | 1.6706e-3        |
+------------------+------------------+------------------+------------------+------------------+------------------+

Corrected temperature differences are shown in the following figures.

   [image]SBE35RT-T1 versus station.

   [image]Deep SBE35RT-T1 by station (Pressure \geq 2000dbar).

   [image]SBE35RT-T2 versus station.

   [image]Deep SBE35RT-T2 by station (Pressure \geq 2000dbar).

   [image]T1-T2 versus station.

   [image]Deep T1-T2 versus station (Pressure \geq 2000dbar).

   [image]SBE35RT-T1 versus pressure.

   [image]SBE35RT-T2 versus pressure.

   [image]T1-T2 versus pressure.

The 95% confidence limits for the mean low-gradient (values -0.002 °C
\leq T1-T2 \leq 0.002 °C) differences are ±0.00561 °C for SBE35RT-T1,
±0.00559 °C for SBE35RT-T2 and ±0.00163 °C for T1-T2. The 95%
confidence limits for the deep temperature residuals (where pressure
\geq 2000 dbar) are ±0.00113 °C for SBE35RT-T1, ±0.00132 °C for
SBE35RT-T2 and ±0.00118 °C for T1-T2.

Issues affecting SBE35RT reference temperature data were:

* On several occasions, internal recorder memory was exceeded,
  resulting in incomplete or no samples recorded for some casts. Casts
  with incomplete reference samples were 03201, 03901, 05201 and
  06701. Casts with no reference samples were 03301, 05301, 06801,
  06901, 06902, 07001 and 07101.


Conductivity Analysis
---------------------

CTD conductivity was provided by primary and secondary SBE 4C
conductivity sensor units. Serial numbers 04-1744 and 04-2319 were
used on the primary CTD channel, and serial number 04-1879 was used on
the secondary channel. Issues with the primary conductivity sensors
are detailed later in this section.

Laboratory calibrations of conductivity sensors were performed prior
to the cruise at the Sea-Bird calibration facility. Dates of
laboratory calibration are recorded in Table %s. Calibration documents
are provided in the APPENDIX.

The pre-cruise laboratory calibration coefficients were used to
convert SBE 4C frequency to mS/cm. Additional shipboard calibrations
were performed to correct sensor bias. Corrections for both pressure
and temperature sensors were finalized before analyzing conductivity
differences. Two independent metrics of calibration accuracy were
examined. At each bottle closure, the primary and secondary
conductivity were compared with each other. Each sensor was also
compared to conductivity calculated from bottle sample salinity using
CTD pressure and temperature.

The differences between primary and secondary temperature sensors were
used as filtering criteria to reduce the contamination of conductivity
comparisons by package wake. The coherence of this relationship is
shown in the following figures.

   [image]Coherence of conductivity differences as a function of
   temperature differences.

   [image]Corrected C_Bottle - C1 versus station.

   [image]Deep Corrected C_Bottle - C1 versus station (Pressure >=
   2000dbar).

   [image]Corrected C_Bottle - C2 versus station.

   [image]Deep Corrected C_Bottle - C2 versus station (Pressure >=
   2000dbar).

   [image]Corrected C1-C2 versus station.

   [image]Deep Corrected C1-C2 versus station (Pressure >= 2000dbar).

   [image]Corrected C_Bottle - C1 versus pressure.

   [image]Corrected C_Bottle - C2 versus pressure.

   [image]Corrected C1-C2 versus pressure.

The SBE 4C sensor typically exhibits a predictable modeled response.
Offsets for each sensor were determined using C_Bottle - C_CTD
differences in a deeper pressure range (500 or more dbars).

After conductivity offsets were applied to all casts, response to
pressure, temperature and conductivity were examined for each
conductivity sensor. The response model is second-order with respect
to pressure, second-order with respect to temperature, and second-
order with respect to conductivity:

   C_{cor} = C + cp_2 P^2 + cp_1 P + ct_2 T^2 + ct_1 T + cc_2 C^2 +
   cc_1 C + \text{Offset}

Fit coefficients are shown in the following tables.


Primary conductivity (C1) coefficients.
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

+--------------+--------------+--------------+--------------+--------------+--------------+--------------+--------------+
| Station      | cp_2         | cp_1         | ct_2         | ct_1         | cc_2         | cc_1         | c_0          |
|==============|==============|==============|==============|==============|==============|==============|==============|
| 1-7          | 0.e+0        | -6.2152e-7   | 0.e+0        | 0.e+0        | 0.e+0        | 1.3869e-4    | -1.9726e-3   |
+--------------+--------------+--------------+--------------+--------------+--------------+--------------+--------------+
| 8-98         | 0.e+0        | -7.5055e-7   | 0.e+0        | 0.e+0        | 0.e+0        | -1.4376e-5   | 3.7609e-3    |
+--------------+--------------+--------------+--------------+--------------+--------------+--------------+--------------+


Secondary conductivity (C2) coefficients.
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

+--------------+--------------+--------------+--------------+--------------+--------------+--------------+--------------+
| Station      | cp_2         | cp_1         | ct_2         | ct_1         | cc_2         | cc_1         | c_0          |
|==============|==============|==============|==============|==============|==============|==============|==============|
| 1-7          | 0.e+0        | -6.8127e-7   | 0.e+0        | 0.e+0        | 0.e+0        | 2.7767e-4    | -5.4275e-3   |
+--------------+--------------+--------------+--------------+--------------+--------------+--------------+--------------+
| 8-98         | 0.e+0        | -9.1548e-7   | 0.e+0        | 0.e+0        | 0.e+0        | -1.6001e-4   | 9.0660e-3    |
+--------------+--------------+--------------+--------------+--------------+--------------+--------------+--------------+

Salinity residuals after applying shipboard P/T/C corrections are
summarized in the following figures. Only CTD and bottle salinity data
with acceptable quality codes are included in the differences.

   [image]Salinity residuals versus station.

   [image]Deep Salinity residuals versus station (Pressure >=
   2000dbar).

   [image]Salinity residuals versus pressure.

The 95% confidence limits for the mean low-gradient (values -0.002 °C
\leq T1-T2 \leq 0.002 °C) differences are ±0.06026 mPSU for salinity-
C1SAL. The 95% confidence limits for the deep salinity residuals
(where pressure \geq 2000 dbar) are ±0.00289 mPSU for salinity-C1SAL.

Issues affecting SBE 4C salinity data were:

* The primary conductivity sensor 04-1744 failed during the pre-cast
  soak for 00801. The cast was immediately aborted and the sensor was
  replaced by sensor 04-2319. No other data were affected.


CTD Dissolved Oxygen (SBE43)
----------------------------

A Sea-Bird SBE 43 oxygen sensor installed on the CTD primary T-C
channel provided one of two sources of dissolved oxygen data. Serial
numbers 43-4355, 43-1136 and 43-1071 were used during the cruise.
Performance issues are noted below.

Laboratory calibrations of the dissolved oxygen sensors were performed
prior to the cruise at the SBE calibration facility. Dates of
laboratory calibration are recorded in Table %s. Calibration documents
are provided in the APPENDIX.

The pre-cruise laboratory calibration coefficients were used to
convert SBE 43 frequency to µmol/kg oxygen values for acquisition
only. Additional shipboard fitting was performed to correct for the
sensor’s non-linear response and for calibration drift over the course
of the cruise. Corrections for pressure, temperature, and conductivity
sensors were finalized before analyzing dissolved oxygen data.
Corrections for hysteresis are applied following Sea-Bird Application
Note 64-3. The SBE 43 sensor data were compared to dissolved oxygen
bottle samples by matching the downcast CTD data to the upcast bottle
stop locations along isopycnal surfaces. CTD dissolved oxygen was then
calculated using Clark Cell MPOD oxygen sensor response model for
Beckman/SensorMedics and SBE 43 dissolved oxygen sensors. The residual
differences of bottle values versus CTD dissolved oxygen values are
minimized by optimizing the PMEL DO sensor response model coefficients
using the BFGS non-linear least-squares fitting procedure.

The general form of the PMEL DO sensor response model equation for
Clark cells follows Millard [Mill82] and Owens [Owen85]. Dissolved
oxygen concentration is then calculated:

   O_2 = S_{oc} \cdot (V + V_{\textrm{off}} + \tau_{20} \cdot e^{(D_1
   \cdot p + D_2 \cdot (T - 20))} \cdot dV/dt) \cdot O_{sat} \cdot
   e^{T_{cor} \cdot T} \cdot e^{[(E \cdot p) / (273.15 + T)]}

Where:

* V is oxygen voltage (V)

* D_1 and D_2 are (fixed) SBE calibration coefficients

* T is corrected CTD temperature (°C)

* p is corrected CTD pressure (dbar)

* dV/dt is the time-derivative of voltage (V/s)

* O_sat is oxygen saturation

* S_oc, V_off, \tau_20, T_cor, and E are fit coefficients

All stations were fit together to get an initial coefficient estimate.
Stations were then fit individually to refine the coefficients as the
membrane does not deform the same way with each cast. If the
individual cast’s coefficients yielded worse residuals, they were
reverted to the original group fit coefficients.


SBE43 group fit coefficients. Coefficients were further refined station-by-station.
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

+------------------+------------------+------------------+------------------+------------------+------------------+
| Station          | S_oc             | V_off            | \tau_20          | T_cor            | E                |
|==================|==================|==================|==================|==================|==================|
| All              | 4.8434e-1        | -5.1537e-1       | 1.9201e+0        | -7.2898e-4       | 3.7639e-2        |
+------------------+------------------+------------------+------------------+------------------+------------------+

CTD dissolved O_2 residuals are shown in figures Fig. %s through Fig.
%s.

   [image]CTD (SBE43) O_2 residuals versus station

   [image]CTD (SBE43) deep O_2 residuals versus station (Pressure >=
   2000dbar)

   [image]CTD (SBE43) O_2 residuals versus pressure.

The 95% confidence limits of 1.16 (µmol/kg) for all acceptable (flag
2) dissolved oxygen bottle data values and 1.09 (µmol/kg) for deep
dissolved oxygen values are only presented as general indicators of
the goodness of fit. CLIVAR GO-SHIP standards for CTD dissolved oxygen
data are < 1% accuracy against on-board Winkler titration
measurements.

Issues affecting SBE 43 oxygen data were:

* Sensor 43-4355 became increasingly noisy with depth around cast
  05401. It was replaced with sensor 43-1136 prior to cast 05601,
  which exhibited similar symptoms. Sensor 43-1071 was installed prior
  to cast 05801 and was used for the remainder of the cruise.


CTD Dissolved Oxygen (RINKO)
----------------------------

A JFE Advantech Co., LTD RINKO III (ARO-CAV) provided the second of
two sources of dissolved oxygen data. Serial number 0479 was used for
the duration of the cruise with no performance issues noted.

RINKO data are reported as primary CTD oxygen for all stations.

RINKO raw voltage data were acquired, converted to oxygen saturation,
and then multiplied by the oxygen solubility to give values in
µmol/kg. The resulting data were then fitted using the equations
developed by [Uchida08]:

   [O_2] = (V_0 / V_c - 1) / K_{sv}

   K_{sv} = c_0 + c_1 T + c_2 T^2, \hspace{6pt} V_0 = 1 + d_0 T,
   \hspace{6pt} V_c = d_1 + d_2 V_r

where:

* T is temperature (°C)

* V_r is raw voltage (V)

* V_0 is voltage at zero O_2 (V)

* c_0, c_1, c_2, d_0, d_1, d_2 are calibration coefficients

Oxygen is further corrected for pressure effects:

   [O_2]_c = [O_2] (1 + c_p P / 1000) ^ {1/3}

where:

* P is pressure (dbar)

* c_p is pressure compensation coefficient

Lastly, salinity corrections are applied [GarciaGordon1992]:

   [O_2]_{sc} = [O_2]_c \exp[{S (B_0 + B_1 T_S + B_2 T_S^2 + B_3
   T_S^3) + C_0 S^2}]

where:

* T_S is scaled temperature (T_S = ln[(298.15 – T)/(273.15 + T)])

* B_0, B_1, B_2, B_3, C_0 are solubility coefficients

All stations were fit together to get an initial coefficient estimate.
Station were then fit in groups of similar profiles to get a further
refined estimate. Individual casts were then fit to remove the
noticeable time drift in coefficients. If the fit of the individual
cast had worse residuals than the group, they were reverted to the
original group fit coefficients.


Rinko group fit coefficients. Coefficients were further refined station-by-station.
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

+--------------+--------------+--------------+--------------+--------------+--------------+--------------+--------------+
| Station      | c_0          | c_1          | c_2          | d_0          | d_1          | d_2          | c_p          |
|==============|==============|==============|==============|==============|==============|==============|==============|
| 1-7          | 1.1163e+0    | 4.9784e-3    | -7.8398e-6   | -6.6075e-3   | -9.3903e-2   | 3.1071e-1    | 6.7441e-2    |
+--------------+--------------+--------------+--------------+--------------+--------------+--------------+--------------+
| 8-59         | 1.1043e+0    | 5.2558e-3    | 3.0062e-4    | -2.3692e-3   | -8.4537e-2   | 3.1824e-1    | 9.6997e-2    |
+--------------+--------------+--------------+--------------+--------------+--------------+--------------+--------------+
| 60-98        | 1.1815e+0    | 1.4274e-2    | 5.8961e-4    | 3.1956e-3    | -1.2031e-1   | 3.3551e-1    | 1.1923e-1    |
+--------------+--------------+--------------+--------------+--------------+--------------+--------------+--------------+

CTD (Rinko) dissolved O_2 residuals are shown in figures Fig. %s
through Fig. %s.

   [image]CTD (Rinko) O_2 residuals versus station.

   [image]CTD (Rinko) deep O_2 residuals versus station (Pressure >=
   2000dbar).

   [image]CTD (Rinko) O_2 residuals versus pressure.

The 95% confidence limits of 0.72 (µmol/kg) for all acceptable (flag
2) dissolved oxygen bottle data values and 0.40 (µmol/kg) for deep
dissolved oxygen values are only presented as general indicators of
the goodness of fit. CLIVAR GO-SHIP standards for CTD dissolved oxygen
data are < 1% accuracy against on-board Winkler titration
measurements.

No performance issues were noted with the RINKO III sensor.

[Mill82] Millard, R. C., Jr. (1982). “CTD calibration and data
         processing techniques at WHOI using the practical salinity
         scale,” Proc. Int. STD Conference and Workshop, p. 19, Mar.
         Tech. Soc., La Jolla, Ca.

[Owen85] Owens, W. B. and Millard, R. C., Jr. (1985). “A new algorithm
         for CTD oxygen calibration,” Journ. of Am. Meteorological
         Soc., 15, p. 621.

[Uchida08] Uchida, H., Kawano, T., Kaneko, I., Fukasawa, M. (2008).
           “In Situ Calibration of Optode-Based Oxygen Sensors,” J.
           Atmos. Oceanic Technol., 2271-2281.

[GarciaGordon1992] García, H. E., and L. I. Gordon, (1992). Oxygen
                   solubility in sea- water: Better fitting equations.
                   Limnol. Oceanogr., 37, 1307– 1312.


Salinity
========

PIs
   * Todd Martz (SIO)

   * Susan Becker (SIO)

Technicians
   * John Calderwood (SIO)

   * Jessica McLaughlin (SIO)


Equipment and Techniques
------------------------

Two Guildline Autosals were on board and operational, SIO-owned 8400B
S/N 74309 and 8400B S/N 74307. S/N 74309 was used for all salinity
measurements during this cruise. The salinity analysis was run in the
ship’s Climate Controlled Chamber, a refrigerator, port and amidships
between the Computer Lab and Bioanalytical Lab. The chamber
temperature varied between about 21.5 and 24.5 degrees Celsius around
3 times each hour, with an average (based on measuring temperatures of
items in the chamber) of about 23.5°C. IAPSO Standard Seawater Batch
P167 was used for all calibrations: K15 = 0.99988, Practical salinity
= 34.995, expiration 2026-02-21.

A LabView program developed by Carl Mattson was used for monitoring
temperatures, logging data, and prompting the operator. Salinity
analyses were performed after samples had equilibrated to a laboratory
temperature of 24 °C, 8 hours or more after collection. Samples were
placed under fans to speed their acclimatization to the set room
temperature. The salinometer was standardized for each group of
samples analyzed (up to 2 casts, or up to 72 samples) using two
bottles of standard seawater: one at the beginning and one at the end
of each set of measurements. For each calibration standard and sample
reading, the salinometer cell was initially flushed at least 2 times
before a set of conductivity ratio readings was recorded.
Standardization conductivity offsets did not exceed 0.00005 mS/cm for
all casts. Between runs, the water from the last standard was left in
the cell.


Sampling and Data Processing
----------------------------

The salinity samples were collected in 200 ml Kimax high-alumina
borosilicate bottles that had been rinsed at least three times with
sample water prior to filling. The bottles were sealed with plastic
insert thimbles and Nalgene screw caps. This assembly provides very
low container dissolution and sample evaporation. Prior to sample
collection, inserts were inspected for proper fit, and loose inserts
were replaced to ensure an airtight seal. Laboratory temperature was
also monitored electronically throughout the cruise. PSS-78 salinity
[UNESCO1981] was calculated for each sample from the measured
conductivity ratios. The offset between the initial standard seawater
value and its reference value was applied to each sample. Then the
difference (if any) between the initial and final vials of standard
seawater was applied to each sample as a function of elapsed run time.
The corrected salinity data were then incorporated into the cruise
database. During I09N, approximately 108 bottles of standard seawater
were used for analysis.


Narrative
---------

3,159 samples were analyzed, and seven sample bottles were broken over
the course of the cruise. No major problems were encountered.

[UNESCO1981] UNESCO 1981. Background papers and supporting data on the
             Practical Salinity Scale, 1978. UNESCO Technical Papers
             in Marine Science, No. 37 144.


Oxygen Analysis
===============

PIs
   * Todd Martz (SIO)

   * Susan Becker (SIO)

Technicians
   * Elisa Aitoro (SIO)

   * Andrew Barna (SIO)


Equipment and Techniques
------------------------

Dissolved oxygen analyses were performed with an SIO/ODF-designed
automated oxygen titrator using photometric end-point detection based
on the absorption of 365nm wavelength ultra-violet light.

The titration of the samples and the data logging were controlled by
PC LabView software. Thiosulfate was dispensed by a Dosimat 665 buret
driver fitted with a 1.0 ml burette.

ODF used a whole-bottle modified-Winkler titration following the
technique of Carpenter [Carpenter1965] with modifications by
[Culberson1991] but with higher concentrations of potassium iodate
standard (~0.012 N), and thiosulfate solution (~55 g/L).

Pre-made liquid potassium iodate standards and reagent/distilled water
blanks were run every day (approximately every 3-4 stations), with
samples analysed within 24 hours of the last standard.


Sampling and Data Processing
----------------------------

A total of 3,173 oxygen measurements were made, all of which were
niskin samples.

Niskin samples were collected soon after the rosette was secured on
deck, either from fresh niskins or immediately following CFC sampling.

Nominal 125 mL volume-calibrated biological oxygen demand (BOD) flasks
were rinsed 3 times with minimal agitation using a silicone draw tube,
then filled and allowed to overflow for at least 3 flask volumes,
ensuring no bubbles remained. Pickling reagents MnCl_2 and NaI/NaOH (1
mL of each) were added via bottle-top dispensers to fix samples before
stoppering. Flasks were shaken twice (10-12 inversions) to assure
thorough dispersion of the precipitate - once immediately after
drawing and then again after 30-60 minutes.

Sample draw temperatures, measured with an electronic resistance
temperature detector (RTD) embedded in the draw tube, were used to
calculate umol/kg concentrations, and as a diagnostic check of bottle
integrity.

Niskin samples were analysed within 2-12 hours of collection, and the
data incorporated into the cruise database.

Thiosulfate normalities were calculated for each standardisation and
corrected to 20°C. The 20°C thiosulfate normalities and blanks were
plotted versus time and were reviewed for possible problems, and were
subsequently determined to be stable enough that no smoothing was
required.


Volumetric Calibration
----------------------

Oxygen flask volumes were determined gravimetrically with degassed
deionised water to determine flask volumes at ODF’s chemistry
laboratory. This is done once before using flasks for the first time
and periodically thereafter when a suspect volume is detected. The 10
mL Dosimat buret used to dispense standard iodate solution was
calibrated using the same method.


Standards
---------

Liquid potassium iodate standards were prepared in 6 L batches and
bottled in sterile glass bottles at ODF’s chemistry laboratory prior
to the expedition. The normality of the liquid standard was determined
by calculation from weight. The standard was supplied by Alfa Aesar
and has a reported purity of 99.4-100.4%. All other reagents were
“reagent grade” and were tested for levels of oxidising and reducing
impurities prior to use.


Narrative
---------

The oxygen analytical rig was setup in the main lab of the R/V
Thompson abeam of the aft air handler. Except for the single batch of
thiosulfate, four batches of each reagent were made during
mobilization in Fremantle. Additional batches were made as needed
throughout the cruise.

When the ODF Oxygen standard was swapped the second time (third
standard to be used), and unacceptable jump in thiosulfate normality
was observed. A fourth standard was opened and used instead. This
fourth standard resulted in a normality that was within our tolerances
for day to day normality variation.

A few high end points occurred and were corrected for.

The thiosulfate stability was considered in 3 batches and showed
stability throughout the entire cruise.

No trends were observed or corrected for.

No data updates are expected.

   [image: Section plot of dissolved oxygen concentrations along
   |CRS|][image]Section plot of dissolved oxygen concentrations along
   I09N.

[Carpenter1965] Carpenter, J. H., “The Chesapeake Bay Institute
                technique for the Winkler dissolved oxygen method,”
                Limnology and Oceanography, 10, pp. 141-143 (1965).

[Culberson1991] Culberson, C. H., Knapp, G., Stalcup, M., Williams, R.
                T., and Zemlyak, F., “A comparison of methods for the
                determination of dissolved oxygen in seawater,” Report
                WHPO 91-2, WOCE Hydrographic Programme Office (Aug
                1991).


Nutrients
=========

PIs
   * Todd Martz (SIO)

   * Susan Becker (SIO)

Technicians
   * Megan Roadman (SIO)

   * Vincent Johnson (SIO)


Summary of Analysis
-------------------

* 3173 samples from 98 CTD stations

* The cruise started with new pump tubes and they were changed three
  times, before stations 34, 53 and 76.

* 4 sets of Primary/Secondary mixed standards and 2 sets of primary
  Nitrite standards were made up over the course of the cruise.

* The cadmium column efficiency was checked periodically and ranged
  between 95%-100%. Columns were changed when the efficiency fell
  below 95%. Seven columns were used for this cruise.


Equipment and Techniques
------------------------

Nutrient analyses (phosphate, silicate, nitrate+nitrite, and nitrite)
were performed on a Seal Analytical continuous-flow AutoAnalyzer 3
(AA3). The methods used are described by Gordon et al [Gordon1992]
Hager et al. [Hager1972], and Atlas et al. [Atlas1971]. Details of
modification of analytical methods used in this cruise are also
compatible with the methods described in the nutrient section of the
updated GO-SHIP repeat hydrography manual (Becker et al., 2019,
[Becker2019]).


Nitrate/Nitrite Analysis
------------------------

A modification of the Armstrong et al. (1967) [Armstrong1967]
procedure was used for the analysis of nitrate and nitrite. For
nitrate analysis, a seawater sample was passed through a cadmium
column where the nitrate was reduced to nitrite. This nitrite was then
diazotized with sulfanilamide and coupled with
N-(1-naphthyl)-ethylenediamine to form a red dye. The sample was then
passed through a 10mm flowcell and absorbance measured at 520nm. The
procedure was the same for the nitrite analysis but without the
cadmium column.

**REAGENTS**

Sulfanilamide
   Dissolve 10g sulfamilamide in 1.2N HCl and bring to 1 liter volume.
   Add 2 drops of Brij, a surfactant. Store at room temperature in a
   dark poly bottle.

   Note: 35% Brij - 35g in DIW.

N-(1-Naphthyl)-ethylenediamine dihydrochloride (N-1-N)
   Dissolve 1g N-1-N in DIW, bring to 1 liter volume. Add 2 drops 40%
   surfynol 465/485 surfactant. Store at room temperature in a dark
   poly bottle. Discard if the solution turns dark reddish brown.

Imidazole Buffer
   Dissolve 13.6g imidazole in ~3.8 liters DIW. Stir for at least 30
   minutes to completely dissolve. Add 60 ml of CuSO_4 + NH_4Cl mix
   (see below). Let sit overnight before proceeding. Using a
   calibrated pH meter, adjust to pH of 7.83-7.85 with 10% (1.2N) HCl
   (about 10 ml of acid, depending on exact strength). Bring final
   solution to 4L with DIW. Store at room temperature.

NH_4Cl + CuSO_4 mix
   Dissolve 2g cupric sulfate in DIW, bring to 100 m1 volume (2%).
   Dissolve 250g ammonium chloride in DIW, bring to 1l liter volume.
   Add 5ml of 2% CuSO_4 solution to this NH_4Cl stock. This should
   last many months.


Phosphate Analysis
------------------

Ortho-Phosphate was analyzed using a modification of the Bernhardt and
Wilhelms (1967) [Bernhardt1967] method. Acidified ammonium molybdate
was added to a seawater sample to produce phosphomolybdic acid, which
was then reduced to phosphomolybdous acid (a blue compound) following
the addition of dihydrazine sulfate. The sample was passed through a
10 mm flowcell and absorbance measured at 820 nm.

**REAGENTS**

Ammonium Molybdate H_2SO_4 sol’n
   Pour 420 ml of DIW into a 2 liter Ehrlenmeyer flask or beaker,
   place this flask or beaker into an ice bath. SLOWLY add 330 ml of
   conc H_2SO_4. This solution gets VERY HOT!! Cool in the ice bath.
   Make up as much as necessary in the above proportions.

   Dissolve 27g ammonium molybdate in 250ml of DIW. Bring to 1 liter
   volume with the cooled sulfuric acid sol’n. Add 3 drops of 5% SDS
   surfactant. Store in a dark poly bottle.

Dihydrazine Sulfate
   Dissolve 6.4g dihydazine sulfate in DIW, bring to 1 liter volume
   and refrigerate.


Silicate Analysis
-----------------

Silicate was analyzed using the basic method of Armstrong et al.
(1967). Acidified ammonium molybdate was added to a seawater sample to
produce silicomolybdic acid which was then reduced to silicomolybdous
acid (a blue compound) following the addition of stannous chloride.
The sample was passed through a 10 mm flowcell and measured at 660nm.

**REAGENTS**

Tartaric Acid
   Dissolve 200g tartaric acid in DW and bring to 1 liter volume.
   Store at room temperature in a poly bottle.

Ammonium Molybdate
   Dissolve 10.8g Ammonium Molybdate Tetrahydrate in 1000ml dilute
   H_2SO_4. (Dilute H_2SO_4 = 2.8ml conc H_2SO_4  or 6.4ml of H_2SO_4
   diluted for PO_4 moly per liter DW) (dissolve powder, then add
   H_2SO_4) Add 3-5 drops 5% SDS surfactant per liter of solution.

Stannous Chloride
   stock: (as needed)

   Dissolve 40g of stannous chloride in 100 ml 5N HCl. Refrigerate in
   a poly bottle.

   NOTE: Minimize oxygen introduction by swirling rather than shaking
   the solution. Discard if a white solution (oxychloride) forms.

   working: (every 24 hours) Bring 5 ml of stannous chloride stock to
   200 ml final volume with 1.2N HCl. Make up daily - refrigerate when
   not in use in a dark poly bottle.


Sampling
--------

Nutrient samples were drawn into 30 ml polypropylene screw-capped
centrifuge tubes. The tubes and caps were cleaned with 10% HCl and
rinsed 3 times with sample before filling. Samples were analyzed
within 4 hours after sample collection, allowing sufficient time for
all samples to reach room temperature. The centrifuge tubes fit
directly onto the sampler.


Data Collection and Processing
------------------------------

Data collection and processing was done with the software provided
with the instrument from Seal Analytical (AACE). After each run, the
charts were reviewed for any problems during the run, any blank was
subtracted, and final concentrations (micro moles/liter) were
calculated, based on a linear curve fit. Once the run was reviewed and
concentrations calculated a text file was created. That text file was
reviewed for possible problems and then converted to another text file
with only sample identifiers and nutrient concentrations that was
merged with other bottle data.


Standards and Glassware Calibration
-----------------------------------

Primary standards for silicate (Na_2SiF_6), nitrate (KNO_3), nitrite
(NaNO_2), and phosphate (KH_2PO_4) were obtained from Johnson Matthey
Chemical Co. and/or Fisher Scientific. The supplier reports purities
of >98%, 99.999%, 97%, and 99.999 respectively.

All glass volumetric flasks and pipettes were gravimetrically
calibrated prior to the cruise. The primary standards were dried and
weighed out to 0.1 mg prior to the cruise. The exact weight was noted
for future reference. When primary standards were made, the flask
volume at 20 °C, the weight of the powder, and the temperature of the
solution were used to buoyancy-correct the weight, calculate the exact
concentration of the solution, and determine how much of the primary
was needed for the desired concentrations of secondary standard. The
new standards were compared to the old before use.

All the reagent solutions, primary and secondary standards were made
with fresh distilled deionized water (DIW).

Standardizations were performed at the beginning of each group of
analyses with working standards prepared every 12-16 hours from a
secondary. Working standards were made up in low nutrient seawater
(LNSW). Two batches of LNSW was used on the cruise. One was collected
on I08S and was treated in the lab. The water was re-circulated for ~8
hours through a 0.2 micron filter, passed a UV lamp and through a
second 0.2 micron filter. The actual concentration of nutrients in
this water was empirically determined during the standardization
calculations. The LNSW was brought in multiple 5L bottles. The second
batch was collected during the cruise, on station 45.

The concentrations in micro-moles per liter of the working standards
used were:

+-----+-------+-------+-------+-------+
| -   | N+N   | PO_4  | SIL   | NO_2  |
|     | (uM)  | (uM)  | (uM)  | (uM)  |
|=====|=======|=======|=======|=======|
| 0   | 0.0   | 0.0   | 0.0   | 0.0   |
+-----+-------+-------+-------+-------+
| 3   | 15.50 | 1.2   | 60    | 0.50  |
+-----+-------+-------+-------+-------+
| 5   | 31.00 | 2.4   | 120   | 1.00  |
+-----+-------+-------+-------+-------+
| 7   | 46.50 | 3.6   | 180   | 1.50  |
+-----+-------+-------+-------+-------+


Quality Control
---------------

All final data was reported in micro-moles/kg. NO_3, PO_4, and NO_2,
were reported to two decimals places and SIL to one. Accuracy is based
on the quality of the standards the levels are:

+-------+-----------------------------+
| NO_3  | 0.05 µM (micro moles/Liter) |
+-------+-----------------------------+
| PO_4  | 0.004 µM                    |
+-------+-----------------------------+
| SIL   | 2-4 µM                      |
+-------+-----------------------------+
| NO_2  | 0.05 µM                     |
+-------+-----------------------------+

As is standard ODF practice, a deep calibration “check” sample was run
with each set of samples to estimate precision within the cruise. The
data are tabulated below.

+---------------+----------------------+----------+
| Parameter     | Concentration (µM)   | stddev   |
|===============|======================|==========|
| NO_3          | 33.76                | 0.17     |
+---------------+----------------------+----------+
| PO_4          | 2.33                 | 0.01     |
+---------------+----------------------+----------+
| SIL           | 114.3                | 0.56     |
+---------------+----------------------+----------+

Reference materials for nutrients in seawater (RMNS) were used as a
check sample run with every station. The RMNS preparation,
verification, and suggested protocol for use of the material are
described by [Aoyama2006] [Aoyama2007], [Aoyama2008], Sato [Sato2010]
and Becker et al. [Becker2019]. RMNS batch CM was used on this cruise,
with each bottle being used for 2 runs before being discarded and a
new one opened. The RMNS was analyze both before and after the
samples. Data are tabulated below.

+-----------+---------------+---------+---------------+
| Parameter | Concentration | stddev  | assigned conc |
|===========|===============|=========|===============|
| -         | (µmol/kg)     | -       | (µmol/kg)     |
+-----------+---------------+---------+---------------+
| NO_3      | 33.16         | 0.15    | 33.2          |
+-----------+---------------+---------+---------------+
| PO_4      | 2.38          | 0.03    | 2.38          |
+-----------+---------------+---------+---------------+
| SIL       | 100.9         | 0.4     | 100.5         |
+-----------+---------------+---------+---------------+
| NO_2      | 0.029         | 0.009   | 0.02          |
+-----------+---------------+---------+---------------+


Analytical Problems
-------------------

Occasional baseline drift and jumps for the nitrite and phosphate
channels and were closely monitored throughout cruise. The values of
the reference material and were used to monitor data quality.
Adjustments based on the values obtained for the reference material
were made as necessary, using the RMNS values from the end of each
run.

[Armstrong1967] Armstrong, F.A.J., Stearns, C.A., and Strickland,
                J.D.H., “The measurement of upwelling and subsequent
                biological processes by means of the Technicon
                Autoanalyzer and associated equipment,” Deep-Sea
                Research, 14, pp.381-389 (1967).

[Atlas1971] Atlas, E.L., Hager, S.W., Gordon, L.I., and Park, P.K., “A
            Practical Manual for Use of the Technicon AutoAnalyzer in
            Seawater Nutrient Analyses Revised,” Technical Report 215,
            Reference 71-22, p.49, Oregon State University,
            Department of Oceanography (1971).

[Aoyama2006] Aoyama, M., 2006: 2003 Intercomparison Exercise for
             Reference Material for Nutrients in Seawater in a
             Seawater Matrix, Technical Reports of the Meteorological
             Research Institute No.50, 91pp, Tsukuba, Japan.

[Aoyama2007] Aoyama, M., Susan B., Minhan, D., Hideshi, D., Louis, I.
             G., Kasai, H., Roger, K., Nurit, K., Doug, M., Murata,
             A., Nagai, N., Ogawa, H., Ota, H., Saito, H., Saito, K.,
             Shimizu, T., Takano, H., Tsuda, A., Yokouchi, K., and
             Agnes, Y. 2007. Recent Comparability of Oceanographic
             Nutrients Data: Results of a 2003 Intercomparison
             Exercise Using Reference Materials. Analytical Sciences,
             23: 1151-1154.

[Aoyama2008] Aoyama M., J. Barwell-Clarke, S. Becker, M. Blum, Braga
             E. S., S. C. Coverly,E. Czobik, I. Dahllof, M. H. Dai, G.
             O. Donnell, C. Engelke, G. C. Gong, Gi-Hoon Hong, D. J.
             Hydes, M. M. Jin, H. Kasai, R. Kerouel, Y. Kiyomono, M.
             Knockaert, N. Kress, K. A. Krogslund, M. Kumagai, S.
             Leterme, Yarong Li, S. Masuda, T. Miyao, T. Moutin, A.
             Murata, N. Nagai, G.Nausch, M. K. Ngirchechol, A. Nybakk,
             H. Ogawa, J. van Ooijen, H. Ota, J. M. Pan, C. Payne, O.
             Pierre-Duplessix, M. Pujo-Pay, T. Raabe, K. Saito, K.
             Sato, C. Schmidt, M. Schuett, T. M. Shammon, J. Sun, T.
             Tanhua, L. White, E.M.S. Woodward, P. Worsfold, P. Yeats,
             T. Yoshimura, A.Youenou, J. Z. Zhang, 2008: 2006
             Intercomparison Exercise for Reference Material for
             Nutrients in Seawater in a Seawater Matrix, Technical
             Reports of the Meteorological Research Institute No. 58,
             104pp.

[Becker2019] Becker, S., Aoyama M., Woodward M., Baaker, K., Covery,
             S., Mahaffey, C., Tanhua, T., “GO-SHIP Repeat Hydrography
             Nutrient Manual, 2019: The Precise and accurate
             determination of dissololved inorganic nutrients in
             seawater;Continuos Flow Analysis methods.  Ocean Best
             Practices, August 2019.

[Bernhardt1967] Bernhardt, H., and  Wilhelms, A., “The continuous
                determination of low level iron, soluble phosphate and
                total phosphate with the AutoAnalyzer,” Technicon
                Symposia, I,pp.385-389 (1967).

[Gordon1992] Gordon, L.I., Jennings, J.C., Ross, A.A., Krest, J.M., “A
             suggested Protocol for Continuous Flow Automated Analysis
             of Seawater Nutrients in the WOCE Hydrographic Program
             and the Joint Global Ocean Fluxes Study,” Grp. Tech Rpt
             92-1, OSU College of Oceanography Descr. Chem Oc. (1992).

[Hager1972] Hager, S.W.,  Atlas, E.L., Gordon L.I., Mantyla, A.W., and
            Park, P.K., “ A comparison at sea of manual and
            autoanalyzer analyses of phosphate, nitrate, and silicate
            ,” Limnology and Oceanography, 17,pp.931-937 (1972).

[Sato2010] Sato, K., Aoyama, M., Becker, S., 2010. RMNS as Calibration
           Standard Solution to Keep Comparability for Several Cruises
           in the World Ocean in 2000s. In: Aoyama, M., Dickson, A.G.,
           Hydes, D.J., Murata, A., Oh, J.R., Roose, P., Woodward,
           E.M.S., (Eds.), Comparability of nutrients in the world’s
           ocean. Tsukuba, JAPAN: MOTHER TANK, pp 43-56.


Dissolved Inorganic Carbon (DIC)
================================

PIs
   * Richard A. Feely (NOAA/PMEL)

   * Rik Wanninkhof (NOAA/AOML)

Technicians
   * Abigail Tinari (UW-CICOES)

   * Chuck Featherstone (NOAA-AOML)


Introduction
------------

The discrete dissolved inorganic carbon and underway fCO_2
measurements on the I09N cruise (March 21st – April 27th, 2025) were
conducted by Abigail Tinari of the Pacific Marine Environmental
Laboratory (UW/CICOES) and Chuck Featherstone of the Atlantic
Oceanographic and Meteorological Laboratory (NOAA/AOML). The PMEL
Carbon Group’s Dissolved Inorganic Carbon (DIC) mobile container-based
laboratory slated for deployment on this cruise was delayed in
Singapore during transit between Seattle, WA, USA and Perth, WA, AU.
To ensure DIC samples could be collected, carbon chemistry
laboratories at PMEL and SIO air shipped 2,100 backup sample bottles
directly to the vessel in port in Fremantle, WA, AU. The back up plan,
if the container-based laboratory did not arrive, was to collect
samples and bring them back to PMEL to analyze after the cruise. The
van was expected to arrive in Fremantle, WA, AU three days after the
initial cruise departure. A decision was made by GO-SHIP leadership to
delay the cruise and wait for the DIC van to arrive in Fremantle. The
van arrived on March 20th and the ship departed the following day.


Sample collection
-----------------

Samples for DIC measurements were drawn according to procedures
outlined in the PICES Publication, Guide to Best Practices for Ocean
CO_2 Measurements [Dickson07], from Niskin bottles into 310 ml
borosilicate glass bottles using silicone tubing. The flasks were
rinsed three times and filled from the bottom with care not to entrain
any bubbles, overflowing by one half- to one full-volume. The sample
tube was pinched off and withdrawn, creating a ~6 ml headspace,
followed by the addition of 0.12 ml of saturated HgCl_2 solution as a
preservative. The sample bottles were then sealed with glass stoppers
lightly coated with Apiezon-L grease and were stored at room
temperature for a maximum of 12-24 hours until analysis. DIC samples
were collected from a variety of depths with approximately 10% of
these samples collected as duplicates.


Equipment
---------

The dissolved inorganic carbon analyses was conducted by coulometry
with two analytical systems (PMEL1 and PMEL2) used simultaneously on
the cruise. Each system consisted of a coulometer (5015O, UIC Inc)
coupled with a Dissolved Inorganic Carbon Extractor (DICE). The DICE
system was developed by Esa Peltola and Denis Pierrot of NOAA/AOML and
Dana Greeley of NOAA/PMEL to modernize a carbon extractor called SOMMA
(Johnson et al. [Johnson85], [Johnson87], [Johnson93], and
[Johnson99]; Johnson [Johnson92]). The two DICE systems were set up
within the seagoing container modified for the use as a shipboard
laboratory on the aft main working deck of the R/V Thomas G. Thompson.


DIC Analysis
------------

In coulometric analysis of DIC, all carbonate species are converted to
CO_2 (gas) by addition of excess hydrogen ion (acid) to the seawater
sample, and the evolved CO_2 gas is carried into the titration cell of
the coulometer with CO_2 free pure air or compressed nitrogen, where
it reacts quantitatively with a proprietary reagent based on
ethanolamine to generate hydrogen ions. In this process, the solution
changes from blue to colorless, triggering a current through the cell
and causing coulometrical generation of \text{OH}^- ions at the anode.
The \text{OH}^- ions react with the \text{H}^+, and the solution turns
blue again. A beam of light is transmitted through the solution, and a
photometric detector at the opposite side of the cell measures the
change in light transmission. Once the percent transmission reaches
its original value, the coulometric titration is stopped, and the
amount of CO_2 that entered the cell is determined by integrating the
total change during the titration.


DIC Calculation
---------------

The amount of CO_2 injected was calculated according to the CO_2
handbook [DOE94]. The concentration of CO_2 ([CO_2]) in the samples
was determined according to:

   [CO_2]=\text{Cal. Factor}*\text{(Counts}-\text{Blank} * \text{Run
   Time})*\frac{\text{K µmol/count}}{\text{pipette
   volume}*\text{density of sample}}

where Cal. Factor is the calibration factor, Counts is the instrument
reading at the end of the analysis, Blank is the counts/minute
determined from blank runs performed at least once for each cell
solution, Run Time is the length of coulometric titration (in
minutes), and K is the conversion factor from counts to micromoles.

All DIC values were recalculated to a molar weight (µmol/kg) using
density derived from the CTD’s salinity sensor. The DIC values were
corrected for dilution due to the addition of 0.12 ml of saturated
HgCl_2 used for sample preservation. The correction factor used for
this dilution is 1.000397. A correction was also applied for the
offset from the CRM. This additive correction was applied for each
cell using the CRM value obtained at the beginning of the cell. The
coulometer cell solution was replaced after 25 – 28 mg of carbon was
titrated, typically after 9 – 12 hours of continuous use.


Calibration, Accuracy and Precision
-----------------------------------

The stability of each coulometer cell solution was confirmed three
different ways: Gas loops were run at the beginning of each cell, CRMs
supplied by Dr. A. Dickson of SIO, were analyzed at the beginning of
the cell before sample analysis, and duplicate samples from the same
Niskin, were measured near the beginning, middle and end of each cell.

Each coulometer was calibrated by injecting aliquots of pure CO_2
(99.999%), as a standard, by means of an 8-port valve (Wilke et al.,
[Wilke93]) outfitted with two calibrated sample loops of different
sizes (~1ml and ~2ml). The instruments were each separately calibrated
at the beginning of each cell with a minimum of two sets of these gas
loop injections.

The accuracy of the DICE measurement is evaluated with the use of
CRMs, consisting of filtered and UV irradiated seawater, supplied by
Dr. A. Dickson of Scripps Institution of Oceanography (SIO). The CRM
accuracy is determined manometrically on land in San Diego and the DIC
data reported have been corrected to the certified value (DIC =
2029.30 µmol/kg) for the batch used (219). The summary table below
lists information for the CRMs.

The precision of the two DICE systems can be demonstrated via the
replicate samples. Approximately 10% of the Niskins sampled had
analytical replicates taken as a check of our precision. These
replicate samples were interspersed throughout the station analysis
for quality assurance and integrity of the coulometer cell solutions.
The average absolute difference from the mean of these replicates was
1.2 µmol/kg; no systematic differences between the replicates were
observed.


Summary
-------

The overall performance of the analytical equipment during I09N 2025
was good. A few minor equipment issues were encountered, but nothing
that compromised the quality of the data. While in transit to the
port, the door to the van had shifted and would not close. The
*Thompson*’s engineers repaired the problem at the beginning of the
cruise. Throughout the cruise there was higher than usual background
noise (i.e. blanks) when the cells initially started. After running a
few samples the increments (counts between minutes of the titration)
would lower and the noise seemed to settle out. This occurred more
often on the day shift (noon to midnight local time) than on the night
shift (midnight to noon). When removing the ship’s air line there was
water that came out. This may have caused the air to become
compromised and may be why the background noise was so high.

Including the duplicates, 3102 samples were analyzed for dissolved
inorganic carbon during this I09N cruise. Assuming that ~15% of total
niskins tripped during this cruise were used for biological analysis,
DIC was analyzed for approximately 84.4% of niskins made available to
us. The DIC data reported to the database directly from the ship are
considered preliminary until a more thorough quality assurance can be
completed shore side.

+--------+-----------------------------+----------------+-----------+
| SYSTEM | Average Gas Loop Cal Factor | Pipette Volume | Duplicate |
|========|=============================|================|===========|
| PMEL1  | 1.00741                     | 27.603         | 1.05      |
+--------+-----------------------------+----------------+-----------+
| PMEL2  | 1.00448                     | 26.403         | 1.34      |
+--------+-----------------------------+----------------+-----------+

+------------------+----------+----+----------+----------+----+----------+
| CRM Info         | PMEL1    |    |          | PMEL2    |    |          |
|==================|==========|====|==========|==========|====|==========|
| Batch-Cert       | Average  | N  | Std. Dev | Average  | N  | Std. Dev |
+------------------+----------+----+----------+----------+----+----------+
| 219–2029.30      | 2029.71  | 60 | 2.82     | 2026.97  | 70 | 2.5      |
+------------------+----------+----+----------+----------+----+----------+

[DOE94] DOE (U.S. Department of Energy). (1994). Handbook of Methods
        for the Analysis of the Various Parameters of the Carbon
        Dioxide System in Seawater. Version 2.0. ORNL/CDIAC-74. Ed. A.
        G. Dickson and C. Goyet. Carbon Dioxide Information Analysis
        Center, Oak Ridge National Laboratory, Oak Ridge, Tenn.

[Dickson07] Dickson, A.G., Sabine, C.L. and Christian, J.R. (Eds.),
            (2007): Guide to Best Practices for Ocean CO2
            Measurements. PICES Special Publication 3, 191pp.

[Dickson10] Dickson, A.G., (2010): Standards for Ocean Measurements.
            Oceanography, v.23, 2010, 34.

[Feely09] Feely, R.A., C.L. Sabine, D. Greeley, R.H. Byrne, J.C. Orr,
          and F. Millero (2009): Changes in the carbonate system of
          the global oceans. Global Change Newsletter, 73, 25, April
          2009.

[Johnson85] Johnson, K.M., A.E. King, and J. McN. Sieburth (1985):
            “Coulometric DIC analyses for marine studies: An
            introduction.” Mar. Chem., 16, 61-82.

[Johnson87] Johnson, K.M., P.J. Williams, L. Brandstrom, and J. McN.
            Sieburth (1987): “Coulometric total carbon analysis for
            marine studies: Automation and calibration.” Mar. Chem.,
            21, 117-133.

[Johnson92] Johnson, K.M. (1992): Operator’s manual: “Single operator
            multiparameter metabolic analyzer (SOMMA) for total carbon
            dioxide (CT) with coulometric detection.” Brookhaven
            National Laboratory, Brookhaven, N.Y., 70 pp.

[Johnson93] Johnson, K.M., K.D. Wills, D.B. Butler, W.K. Johnson, and
            C.S. Wong (1993): “Coulometric total carbon dioxide
            analysis for marine studies: Maximizing the performance of
            an automated continuous gas extraction system and
            coulometric detector.” Mar. Chem., 44, 167-189.

[Johnson99] Johnson, K.M., Körtzinger, A.; Mintrop, L.; Duinker, J.C.;
            and Wallace, D.W.R. (1999). Coulometric total carbon
            dioxide analysis for marine studies: Measurement and
            internal consistency of underway surface T|CO2|
            concentrations. Marine Chemistry 67:123–44.

[Lewis98] Lewis, E. and D. W. R. Wallace (1998) Program developed for
          CO_2 system calculations. Oak Ridge, Oak Ridge National
          Laboratory. http://cdiac.ornl.gov/oceans/co2rprt.html

[Sabine08] Sabine, C.L., R.A. Feely, and R. Wanninkhof (2008): The
           global ocean carbon cycle. In State of the Climate in 2007,
           3. Global Oceans. Bull. Am. Meteorol. Soc., 89(7), S52–S56,
           doi: 10.1175/1520-0477-89.7 S10.

[Wilke93] Wilke, R.J., D.W.R. Wallace, and K.M. Johnson (1993):
          “Water-based gravimetric method for the determination of gas
          loop volume.” Anal. Chem. 65, 2403-2406


Total Alkalinity
================

PIs
   * Andrew G. Dickson (SIO)

Technicians
   * Daniela Nestory (SIO)

   * Marshal Thrasher (SIO)


Total Alkalinity
----------------

The total alkalinity of sea water is defined as the number of moles of
hydrogen ion equivalent to the excess of proton acceptors (bases
formed from weak acids with a dissociation constant K < 10E-4.5 at 25
°C and zero ionic strength) over proton donors (acids with K >
10E-4.5) in 1 kilogram of sample.


Total Alkalinity Measurement System
-----------------------------------

*Sample Delivery System:*

Samples are dispensed using a Sample Delivery System (SDS) which has
been calibrated for volume in the lab prior to the cruise. Its volume
is confirmed immediately before use at sea to ensure a consistent
volume will be delivered for each sample. The SDS consists of a
volumetric pipette, various relay valves, an air pump, and is
controlled by a program in LabVIEW 2012.

Before attaching a sample bottle to the SDS, the volumetric pipette is
cleared of any residual solution. The pipette is then rinsed and
filled with the sample. The sample overflows and time is allowed for
the sample temperature to equilibrate.

The sample bottle temperature is measured using a DirecTemp thermistor
probe inserted into the sample bottle and the volumetric pipette
temperature is measured using a DirecTemp surface probe placed
directly on the pipette. These temperature measurements, along with
the bottle salinity, are used to convert the sample volume to mass for
analysis.

Samples are delivered into a 250 mL water-jacketed open cell for
titration analysis. While one sample is undergoing titration, a second
sample is prepared with the SDS and equilibrated to 20 °C for
analysis.

*Open-Cell Titration:*

The total alkalinity is measured through an open-cell titration with a
dilute hydrochloric acid titrant of known concentration. A Metrohm 876
Dosimat Plus is used for all standardized hydrochloric acid additions.

An initial aliquot of approximately 2.3-2.4 mL of standardized
hydrochloric acid (~0.1M HCl in ~0.6M NaCl solution) is first
delivered and the sample is stirred for 5 minutes while air is bubbled
into at a rate of 200 scc/m to remove any liberated carbon dioxide
gas.

After equilibration, ~19 aliquots of 0.035 ml are added. Between the
pH range of 3.5 to 3.0, the progress of the titration is monitored
using a pH glass electrode/reference electrode cell, and the total
alkalinity is computed from the titrant volume and e.m.f. measurements
using a non-linear least-squares approach (Dickson, 2007).

A Thermo Scientific Isotemp water bath is connected to the water-
jacketed open cell to maintain a cell temperature of approximately 20
°C. An Agilent 34970A Data Acquisition/Switch Unit with a 34901A
multiplexer is used to read the voltage measurements from the
electrode and monitor the temperatures from the sample, acid, and
room.

The calculations for this procedure are performed automatically using
LabVIEW 2012.


Sample Collection
-----------------

Alkalinity samples are drawn using silicone tubing connected to the
niskin bottle and collected into 250 mL Pyrex bottles. The sample
bottles and Teflon-sleeved glass stoppers were rinsed at least twice
before the final filling. A headspace of approximately 3 mL was
removed and 0.12 mL of 50% saturated mercuric chloride solution was
added to each sample for preservation. The samples were equilibrated
prior to analysis at approximately 20 °C using a Thermo Scientific
Isotemp water bath.

Samples for total alkalinity were taken at all stations where a core
cast was completed.

Alkalinity samples were collected from each niskin where DIC and pH
were collected, to completely characterize the CO_2 system. The
typical sample scheme was as follows: Alternated between a full
collection (36 niskins) and a half collection (24 bottles).

To evaluate the reproducibility of the alkalinity system, 2 duplicate
samples (two separate alkalinity bottles) were collected on each cast.


Problems and Troubleshooting
----------------------------

We experienced electrical issues between stations 7 and 8 where either
dirty power from the ship lines or an external EMF force was
preventing the electrode from accurately recording voltages. Stations
10 and 11 were collected and stored in 500 mL borosilicate bottles and
sealed with grease and rubber bands while we attempted to troubleshoot
the issue. After ~24 hours, the problem seemed to have resolved
itself, as voltage readings and CRMs returned to normal.

Further, the certified hydrochloric acid concentration of Batch A29
(obtained from Dickson CO2 Standards Lab) was not analyzed before use
so we used average CRM values to estimate the value. Between stations
1 and 6 we used an HCl concentration of 1.00020 µmol kg^–1; however,
this proved to be too high and was subsequently changed to 0.0999333
µmol kg ^–1 for the remaining stations.


Quality Control
---------------

Certified Reference Material (CRMs) and duplicate samples (two bottles
collected from one niskin) were used to quality check the functioning
of the total alkalinity system throughout the cruise.

Dickson laboratory Certified Reference Material (CRM) Batches 219 and
220 were used to determine the accuracy of the total alkalinity
analyses.

The total alkalinity certified values for these batches are:

* Batch 219: 2183.64 ± 0.80 µmol/kg (36; 18)

* Batch 220: 2148.32 ± 0.78 µmol/kg (12; 6)

*Preliminary value

The cited uncertainties represent the standard deviation. Figures in
parentheses are the number of analyses made (total number of analyses;
number of separate bottles analyzed).

A CRM sample was analyzed at a minimum frequency of once per every 20
runs, but more often once per every 15 runs. Because total alkalinity
is not affected by gas-exchange, brand new CRM bottles were reserved
for pH and DIC analysis. These pre-opened bottles were subsequently
used for alkalinity analysis. The reported values include materials
ran alongside stations 6–98 due to changes in the hydrochloric acid
concentration (detailed above).

242 reference material samples were analyzed during I09N.

The average measured total alkalinity value for each batch is:

* Batch 219: 2182.40 ± 1.30 µmol/kg (134; 74)

* Batch 220: 2147.00 ± 1.50 µmol/kg (72; 46)

Duplicate samples were also used to check the reproducibility of the
system. The pooled standard deviation of duplicate samples is given
below.

Duplicate precision: ± 1.07 µmol kg-1 (n = 187 pairs)

2785 total alkalinity values were submitted for I09N.

These data are to be considered preliminary.


Discrete pH Analyses (Total Scale)
==================================

PI
   * Dr. Andrew Dickson (SIO)

Technicians
   * Daniela Nestory (SIO)

   * Cora McKean (SIO)

   * Anna Terrenzi (SIO)


Analysis
--------

pHT was measured spectrophotometrically on the total hydrogen scale
using an Agilent 8453 spectrophotometer and in accordance with the
methods outlined by Carter et al, 2013. [Carter2013]. A Kloehn V6
syringe pump was used to autonomously fill, mix, and dispense sample
through the custom 10cm flow-through jacketed cell. A Thermo Fisher
Isotemp recirculating water bath was used to maintain the cell
temperature at 25.0 °C during analyses, and a YSI 4600 precision
thermometer and probe were used to monitor and record the temperature
of each sample during the spectrophotometric measurements. Purified
meta-cresol purple (mCP) was the indicator used to measure the
absorbance of light measured at two different wavelengths (434 nm, 578
nm) corresponding to the maximum absorbance peaks for the acidic and
basic forms of the indicator dye. A baseline absorbance was also
measured and subtracted from these wavelengths. The baseline
absorbance was determined by averaging the absorbances from 725-735
nm. The ratio of the absorbances was then used to calculate pH on the
total scale using the equations outlined in Liu et al., 2011
[Liu2011]. The salinity data used was obtained from the salinity
analysis conducted on board.


Reagents
--------

The mCP indicator dye was made up to a concentration of approximately
2.0 mM and a total ionic strength of 0.7 M. A total of two dye batches
were used during I09N. The pHT of these batches was adjusted with 0.1
mol kg–1 solutions of HCl and NaOH (in 0.6 mol kg–1 NaCl background)
to approximately 7.80, measured with a pH meter calibrated with NBS
buffers. The indicator was obtained from Dr. Robert Byrne at the
University of Southern Florida and was purified using the flash
chromatography technique described by Patsavas et al., 2013.
[Patsavas2013].


Data Processing
---------------

An indicator dye is itself an acid-base system that can change the pH
of the seawater to which it is added. Therefore it is important to
estimate and correct for this perturbation to the seawater’s pH for
each batch of dye used during the cruise. To determine this
correction, multiple bottles from each station were measured twice,
once with a single addition of indicator dye and once with a double
addition of indicator dye. The measured absorbance ratio (R) and an
isosbestic absorbance A_{iso} were determined for each measurement,
where:

R=(A_{578}-A_{base})/(A_{434}-A_{base})

and

R=A_{488}-A_{base}

The change in R for a given change in A_{iso}, \Delta R/(\Delta
A)_{iso}, was then plotted against the measured R-value for the normal
amount of dye and fitted with a linear regression. From this fit the
slope and y-intercept (b and a respectively) are determined by:

\Delta R/\Delta A_{iso} = bR + a

From this the corrected ratio R’ corresponding to the measured
absorbance ratio if no indicator dye were present can be determined
by:

R'= R-A_{iso} (bR + a)


Sample Collection
-----------------

Samples were collected in 250 mL Pyrex glass bottles and sealed using
butyl rubber stoppers held in place by aluminum-crimped caps. Each
bottle was rinsed two times and allowed to overflow by one half
additional bottle volume. Prior to sealing, each sample was given a 1%
headspace and 0.11 mL of 50% saturated mercuric chloride solution was
added to each sample for preservation. Samples were collected only
from niskin bottles that were also being sampled for both total
alkalinity and dissolved inorganic carbon to completely characterize
the carbon system. Additionally, duplicate samples were collected from
all stations for quality control purposes.

The typical sample scheme was as follows: Alternation between a full
collection (36 niskins) and a half collection (24 bottles).


Problems and Troubleshooting
----------------------------

We did not experience any major issues with the pH system during this
cruise.


Standardization/Results
-----------------------

The precision of the data was assessed from measurements of duplicate
analyses and certified reference material (CRM) Batch 207 (provided by
Dr. Andrew Dickson, UCSD).

To evaluate the reproducibility of the pH system, two duplicate
samples (two samples from one niskin bottle) were collected on each
cast.

CRMs were measured at the beginning and ending of each day.

The precision statistics for I09N are:

Duplicate precision     ± 0.0008 (n = 193 pairs) CRM Batch 220
7.7921 ± 0.0011 (n = 63)

2790 pH values were submitted for I09N.

Additional corrections will need to be performed and these data should
be considered preliminary until a more thorough analysis of the data
can take place on shore.

[Carter2013] Carter, B.R., Radich, J.A., Doyle, H.L., and Dickson,
             A.G., “An Automated Spectrometric System for Discrete and
             Underway Seawater pH Measurements,” Limnology and
             Oceanography: Methods, 2013.

[Liu2011] Liu, X., Patsavas, M.C., Byrne R.H., “Purification and
          Characterization of meta Cresol Purple for
          Spectrophotometric Seawater pH Measurements,” Environmental
          Science and Technology, 2011.

[Patsavas2013] Patsavas, M.C., Byrne, R.H.,  and Liu X. “Purification
               of meta-cresol purple and cresol red by flash
               chromatography: Procedures for ensuring accurate
               spectrophotometric seawater pH measurements,” Marine
               Chemistry, 2013.


CFC-11, CFC-12, SF_6, and N_2O
==============================

PIs
   * Jim Happell (University of Miami)

   * Rana Fine (University of Miami)

Technicians
   * Jim Happell (lead analyst, University of Miami)

   * Alexis Wysocki (2nd analyst, University of Miami)

   * Mary Kate Dinneen (Tracer Student, USC)


Sample Collection
-----------------

All water samples were collected from the 10.4 liter Niskin bottles on
the ODF rosette. A water sample was collected from the Niskin bottle
petcock using silcone tubing to fill a 300 ml BOD bottle. The tubing
was flushed of air bubbles. The BOD bottle was placed into a plastic
overflow container. Water was allowed to fill BOD bottle from the
bottom into the overflow container. The stopper was held in the
overflow container to be rinsed. Once water started to flow out of the
overflow container the overflow container/BOD bottle was moved down so
the tubing came out and the bottle was stoppered under water while
still in the overflow container. Air samples, pumped into the system
using an Air Cadet pump from a polyethylene air intake hose mounted
high on the foremast were also run. Air measurements are used as a
check on accuracy.


Equipment and Technique
-----------------------

CFC-11, CFC-12, SF_6, and N_2O were measured on 97 out of 98 stations
for a total of 2619 discrete sample depths. Analyses were performed on
a custom-built purge and trap gas chromatograph (GC) equipped with an
electron capture detector (ECD). This system had recently been
rebuilt, with a new gas chromatograph, new values actuators, and new
instrument control and data acquisition software. Modifications were
also made to measure N_2O, along with the other three parameters. The
samples were stored at room temperature and analyzed within 12 hours
of collection. Every 18 to 24 samples were followed by a blank and a
standard. A subset of samples were held after measurement and was sent
through the process again in order to “restrip” it to determine the
efficiency of the purging process.


Calibration
-----------

A gas phase standards, 426505, was used for calibration. The
concentrations of the compounds in this standard are reported on the
SIO 2005 absolute calibration scale. Calibration curves were run over
the course of the cruise. Estimated accuracy is +/- 2%. Precision for
CFC-12, CFC-11, SF_6 and N_2O was less than 2% based on 47 replicate
measurements. Estimated limit of detection is 1 fmol/kg for CFC-11, 3
fmol/kg for CFC-12 and 0.05 fmol/kg for SF_6.


Lowered Acoustic Doppler Current Profiler (LADCP)
=================================================

PI:
   * Andreas Thurnherr (LDEO)

Cruise Participant:
   * Ilmar Leimann (University of Bremen)

Lowered Acoustic Doppler Current Profiler (LADCP) data were collected
on all stations (001/01–098/01). For all profiles a dual head system
was used consisting of a downlooker and an uplooker. All profiles were
sent daily to A. Thurnherr for shore-based processing and QC.
Preliminary processing for horizontal velocity was also performed
onboard using the LDEO_XI_0 (Beta) software
(https://www.ldeo.columbia.edu/~ant/LADCP/).

Four different 300 kHz TRDI Workhorse Monitor ADCPs were used during
this cruise: WH units #22656 and #24497, and WH2 units #27076 and
#27077. The corresponding configurations used during the cruise are
shown in  Table %s. In all configurations, the downlooker (DL) was
used as the primary (master) instrument.


Configurations of ADCPs during I09N
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

+----------------------------------------------------+----------------------------------------------------+
| Station/Cast                                       | WH/WH2 S/N                                         |
|====================================================|====================================================|
| 00101 - 02101                                      | #27076 - DL, #24497 - UL                           |
+----------------------------------------------------+----------------------------------------------------+
| 02201 - 04301                                      | #27076 - DL, #22656 - UL                           |
+----------------------------------------------------+----------------------------------------------------+
| 04302 - 04401                                      | #27076 - DL, #27077 - UL                           |
+----------------------------------------------------+----------------------------------------------------+
| 04501 - 06901                                      | #22656 - DL, #27077 - UL                           |
+----------------------------------------------------+----------------------------------------------------+
| 06902 - 07001                                      | #22656 - DL, #27076 - UL                           |
+----------------------------------------------------+----------------------------------------------------+
| 07101 - 09801                                      | #22656 - DL, #27077 - UL                           |
+----------------------------------------------------+----------------------------------------------------+

The 2025 occupation of I09N is the first US GO-SHIP cruise where TRDI
Workhorse 2 (WH2) ADCPs were used. Lab-testing prior to the cruise
revealed communications problems when two WH2 instruments are
connected using a star cable—on wakeup, the break sent to the second
instrument would freeze the first. Additionally, both WH2 units
exhibited long and inconsistent delays, sometimes exceeding one
minute, after erasing data from the internal memory cards. As a
result, most LADCP profiles on this cruise were collected using a
WH/WH2 combination. While diagnosing instrument issues, two profiles
(04302 and 04401) were taken using a dual WH2 setup. A new script
(LADCPstart_sequential) was introduced into the acquire software to
enable sequential programming of the two WH2s without needing to
connect both at the same time. Another issue identified with the WH2s
is that their data files differ somewhat in format from older TRDI
ADCPs. Onboard processing software for both horizontal and vertical
velocity was updated during the cruise to handle these differences.

The data from station 07201 is missing due to human error. After
station 02101, the UL was changed because the data quality of the
previous UL was poor. One of the old WH ADCPs was found to return
valid but low-quality data, which was the reason for the change after
station 02101 (#24497). At station 04301, the UL generated multiple
raw files, so it was replaced. However, the same issue reoccurred at
station 04401, leading to a change in the DL instead. For testing
purposes, the UL was changed again for stations 06902 to 07001. When
the problem with the UL reoccurred, the previous configuration of DL
and UL was reinstated. Additionally, one of the new WH2 ADCPs was
discovered to have a problem that causes data anomalies about half an
hour into a profile (#27076).

The standard US GO-SHIP ADCP setup was used for all profiles; this
setup uses 8 m pulse and bin lengths, as well as a zero blanking
distance, which requires the data from the first bin to be discarded.

After station 06101, the battery (SeaBattery Power Module) was
changed. Although the previous battery (S/N 01223) was performing
well, oil was observed on the deck and in the water after recovering
the CTD on several stations, suggesting a possible slow leak. It was
therefore replaced with another battery (S/N 01009).

Additionally, the Independent Measurement Package (IMP) was used until
it became flooded during station 05101 (see Table %s). The IMP is a
small, standalone device that enhances the accuracy of velocity
measurements from Lowered Acoustic Doppler Current Profilers (LADCPs)
by providing precise external readings of heading, pitch, and roll.
Field tests have shown that incorporating IMP data can reduce
discrepancies between LADCP and shipboard ADCP (SADCP) measurements by
10–20%, resulting in more reliable ocean current observations
(Thurnherr et al., 2017 [Thurnherr2017]).


IMP profile groups with the same relative instrument orientation and according recording mode
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

+----------------------------------------------------+----------------------------------------------------+
| Station/Cast                                       | Recording mode                                     |
|====================================================|====================================================|
| 00101 - 01401                                      | sync pulses                                        |
+----------------------------------------------------+----------------------------------------------------+
| 01501 - 03401                                      | sync pulses                                        |
+----------------------------------------------------+----------------------------------------------------+
| 03501 - 04001                                      | sync pulses                                        |
+----------------------------------------------------+----------------------------------------------------+
| 04801 - 05001                                      | independent/autonomously                           |
+----------------------------------------------------+----------------------------------------------------+

Fig. %s and Fig. %s, show the preliminary results of the zonal and
meridional velocity components from the LADCP. These are presented for
both the upper ocean (down to 1000 m) and the full water column along
the I09N section.

The figures clearly show strong horizontal velocities in the zonal
Equatorial Undercurrent region near the Equator. Additionally, in the
upper 150 meters, a distinct pattern in zonal velocities is visible
from 10° S to 4° S, corresponding to the locations of the Eastern
Gyral Current, the South Equatorial Current, and the South Equatorial
Countercurrent (Phillips et al., 2021 [Phillips2021]). Along the
Equator, a narrow, jet-like current flows eastward at high speed at a
depth of around 150 meters. This is known as the Wyrtki Jet (Wyrtki,
1973 [Wyrtki1973]), which develops during both transition periods
between the monsoons.

Post-cruise processing and additional QC will be conducted at LDEO. At
that point it will be determined which profiles are of sufficient
quality for inclusion in the final CLIVAR ADCP archives.

   [image]Preliminary zonal (upper panel) and meridional (lower panel)
   velocities from the LADCP. The blanked-out regions indicate areas
   with insufficient acoustic backscatter. Vertical dashed lines mark
   station locations, and the filled black area represents topography.

   [image]Preliminary zonal (upper panel) and meridional (lower panel)
   velocities in the upper 1000 m from the LADCP. Black solid lines
   indicate potential density contours, and vertical dashed lines mark
   station locations.

[Wyrtki1973] Wyrtki, K. (1973), An equatorial jet in the Indian Ocean,
             Science, 181, 262–264.

[Phillips2021] Phillips, H. E., Tandon, A., Furue, R., Hood, R.,
               Ummenhofer, C. C., Benthuysen, J. A., Menezes, V., Hu,
               S., Webber, B., Sanchez-Franks, A., Cherian, D.,
               Shroyer, E., Feng, M., Wijesekera, H., Chatterjee, A.,
               Yu, L., Hermes, J., Murtugudde, R., Tozuka, T., Su, D.,
               Singh, A., Centurioni, L., Prakash, S., and Wiggert,
               J.: Progress in understanding of Indian Ocean
               circulation, variability, air–sea exchange, and impacts
               on biogeochemistry, Ocean Sci., 17, 1677–1751,
               https://doi.org/10.5194/os-17-1677-2021, 2021.

[Thurnherr2017] Thurnherr, A. M., Goszczko, I., and Bahr, F. (2017).
                Improving LADCP velocity with external heading, pitch,
                and roll. J. Atmos. Oceanic Technol. 34, 1713–1721.
                doi: 10.1175/JTECH-D-16-0258.1


Underway Data Acquisition
=========================

Additional underway measurements were collected as available from the
systems aboard the R/V Thomas G. Thompson throughout the cruise,
notably including:

**Meteorological and Marine Surface Variables**

* Meteorological sensor suite (air temperature, wind speed and
  direction, humidity, barometric pressure)

* Scientific Wave Radar: Rutter WAMOS II-300

* Underway surface seawater diaphragm pump

* Seabird Thermosalinograph (surface temperature, salinity)

* Underway surface pCO_2

**Shipboard Acoustic Doppler Current Profiler (SADCP; PI: Jules
Hummon, UH)**

* RDI Ocean Surveyor 75kHz

* RDI Workhorse 300kHz

* UHDAS digital data acquisition system

**Seafloor Mapping**

* Shipboard Multibeam Sonar: Kongsberg EM-302

**Gravimeter**

* DCS Gravimeter


Carbon Isotopes (\delta^14C and \delta^13C)
===========================================

PIs
   * Roberta Hansman (WHOI)

   * Alan Gagnon (WHOI)

   * Rolf Sonnerup (UW)

Technician
   * Kendra Hyles (UCSB)


Sampling Details
----------------

A total of 672 samples were collected from 28 stations.
\delta^14C/\delta^13C samples were collected every 2 degrees change in
latitude, from 28°S to 20°N. Samples were collected in 100 mL airtight
glass bottles. Using silicone tubing, the flasks were rinsed 3 times
with the water from the sample bottle. While keeping the tubing near
the bottom of the flask, the flask is filled and flushed by allowing
it to overflow one and a half times its full volume. 22 unique depths
were selected from the 36 niskin rosette utilized, and two duplicate
samples were collected at every station at the upper and lower halves
of the eater column, respectively. Once the samples were taken, a
small amount of water (~5 mL) was removed to create a headspace and
100 µL of 50% saturated mercuric chloride solution was added in the
sampling bay. This is the same supply of mercuric chloride solution
used for the other DIC samples collected. After all samples are
collected from a cast the glass stoppers are dried and greased using
Apiezon M high vacuum seal grease, and rubber banded shut to keep the
glass stoppers in place during shipping. The filled bottles are stored
in NOSAMS crates inside the ship’s main laboratory prior to being
loaded into a container and shipped back to the United States for
analysis.


Dissolved Organic Matter (DOM)
==============================

PI
   * Craig Carlson (UCSB)

Technician
   * Kendra Hyles (UCSB)


Project Goals
-------------

The goal of the DOM project is to provide high resolution, long term
monitoring of Dissolved Organic Carbon (DOC) and Total Dissolved
Nitrogen (TDN) distributions throughout the water column, in order to
help better understand biogeochemical cycling in global oceans. For
2025 the Carlson Lab at UCSB will evaluate dissolved organic carbon
(DOC) and total dissolved nitrogen (TDN) concentrations along the US
GO-SHIP IO9N transect.


Sampling Plan
-------------

Over the course of the I09N cruise, DOC/TDN was sampled at every other
station in conjunction with DIC, Alkalinity, and pH. For these, DOM
was sampled from up to 36 unique Niskins ranging the full depth of the
water column, with two duplicates randomly selected for a total of 38
samples collected per cast. At 4 stations, every depth was sampled in
replicate. In addition, at intermediate stations where DOM was not
collected for the full depth profile, a single surface sample was
collected (in replicate) to increase surface resolution across this
section. DOM was sampled at 49 stations for full depth profiles, and
an additional 49 surface sample-only stations were also collected for
a total of 1,860 individual samples.


Sampling Details
----------------

DOC samples were passed through an inline filter holding a combusted
GF/F filter attached directly to the Niskin for samples shallower than
500 meters. This was done to eliminate particles larger than 0.7 µm
from the sample. Samples from deeper depths were not filtered.
Previous work has demonstrated that there is no resolvable difference
between filtered and unfiltered samples in waters below the upper 500
m at the µmol kg^-1 resolution.

To avoid contamination, nitrile gloves were used when handling all
sampling equipment and clean lab surfaces were used for processing
samples. After each station, all equipment used for sampling was
rinsed with 10% hydrochloric acid and MilliQ water in preparation for
the following station. All samples were rinsed 3 times with ~5 mL of
seawater and collected into 40 mL glass EPA vials.

Sample vials were prepared in advance for this cruise by combusting at
450 °C for 4 hours to remove any organic matter. Vial caps were
cleaned by soaking in 10% hydrochloric acid, followed by a soak in
Nanopure water overnight, followed by a 3 times rinse with Nanopure
water and left out to dry. Samples were fixed with 50 µL of 4M
hydrochloric acid and stored upright in well sealed pelican coolers
just below room temperature (~12-15 °C) on board. Samples were never
frozen. Samples will be shipped back to UCSB for analysis via high
temperature combustion on Shimadzu TOC-V or TOC-L analyzers.


Standard Operating Procedure for DOM analyses (Carlson Lab, UCSB)
-----------------------------------------------------------------

DOC samples will be analyzed via high temperature combustion using a
Shimadzu TOC-V or Shimadzu TOC-L in a shore based laboratory at the
University of California, Santa Barbara. The operating conditions of
the Shimadzu TOC-V have been slightly modified from the manufacturer’s
model system. These methods have been added to the GO SHIP Practices
collection and are fully detailed in Halewood et. al, 2022
[Halewood2022], and previously [Carlson2010] [Hansell2005]
[Hansell1998] [Walsh1989]. Final results are reported in units of µmol
kg^-1. Where possible direct measures of sample salinity and
analytical temperature are used to calculate average seawater density.
In practice we have found that applying an average seawater density of
1.027 kg m^-3 to open ocean water column DOM samples, compared to
direct measure of sample density results in a difference of less than
0.01 µmol kg^-1 (i.e., less than analytical resolution). However, when
salinity and an average analytical lab temperature are available or in
regions where salinity varies strongly, a more accurate density
correction is determined and applied for each sample. Each parameter
includes a field for quality control flags.

[Halewood2022] Halewood E, Opalk K, Custals L, Carey M, Hansell D.A.
               and Carlson, C.A. (2022) Determination of dissolved
               organic carbon and total dissolved nitrogen in seawater
               using High Temperature Combustion Analysis. Front. Mar.
               Sci. 9:1061646. doi: 10.3389/fmars.2022.1061646.

[Carlson2010] Carlson, C. A., D. A. Hansell, N. B. Nelson, D. A.
              Siegel, W. M. Smethie, S. Khatiwala, M. M. Meyers and E.
              Halewood 2010. Dissolved organic carbon export and
              subsequent remineralization in the mesopelagic and
              bathypelagic realms of the North Atlantic basin. Deep
              Sea Research II, 57: 1433-1445.

[Hansell1998] Hansell, D.A. and C.A. Carlson 1998. Deep ocean
              gradients in the concentration of dissolved organic
              carbon. Nature, 395: 263-266.

[Hansell2005] Hansell, D.A. 2005 Dissolved Organic Carbon Reference
              Material Program. EOS, 35:318-319.

[Walsh1989] Walsh, T.W., 1989. Total dissolved nitrogen in seawater: a
            new high temperature combustion method and a comparison
            with photo-oxidation. Mar. Chem., 26:295-311.


Underway Surface CO_2
=====================

Principal Investigator
   * Simone Alin (NOAA/PMEL)

Technician
   * Abigail Tinari (UW-CICOES)

The mole fraction of carbon dioxide (xCO_2) in the surface ocean was
measured throughout the cruise track with a General Oceanics 8050 CO_2
Measuring System. Uncontaminated seawater was continuously passed
(~2.5-3.5 L/min) through a chamber where the seawater concentration of
dissolved CO_2 was equilibrated with an overlying headspace gas. The
CO_2 mole fraction of this headspace gas (xCO_2) was measured every
two minutes via a non-dispersive infrared analyzer (LiCor 7000) for 60
consecutive measurements. At the end of these 60 discrete
measurements, a set of five standard gases was analyzed; four of these
standards have known CO_2 mole fractions certified by the NOAA Earth
System Research Laboratories (ESRL) ranging from ~300 to ~900 ppm CO_2
(see Table 18.1). The fifth standard is a tank of 99.9995% ultra-high
purity nitrogen gas, used as a baseline 0% CO_2. Following the
measurements of standard gases, six consecutive measurements of
atmospheric CO_2 mole fractions were made of air supplied through
tubing fastened to the ships forward jack staff. Approximately twice a
day, the infrared analyzer was zeroed and spanned using the nitrogen
gas and the highest concentration CO_2 standard (704.20 ppm). This
occurred until April 17th, 2025 when it was deemed necessary to zero
and span the infrared analyzer after every set of discrete
measurements and standards. This was due to the infrared analyzer’s
significant drift over the course of 12 hours. In addition to
measurements of seawater  xCO_2 , atmospheric  xCO_2 , and standard
gases, other variables were monitored to evaluate system performance
(e.g. gas and water flow rates, pump speeds, equilibrator pressure and
temperature, etc.). For more detail on the general design and
operation of this underway CO_2 system, see Pierrot et al., 2009
[Pierrot09].

Before departing from Fremantle, the underway CO_2 system received
routine maintenance. Some of the maintenance items were: replaced the
water pump, installed a UPS. Model and serial numbers for the CO_2
instrument components and ancillary instruments have been recorded in
a separate Excel file and will reported as part of the metadata that
will accompany the final/processed pCO_2 data submission. The underway
CO_2 system on this cruise was installed in the aft, port side
Hydrolab. Uncontaminated seawater from the bow of the vessel is pumped
to the system via the ship’s uncontaminated seawater system. On this
cruise, the pump used was a baffle/diaphragm pump at the request of
the onboard biologists, who were concerned about damage to the
organisms by the centrifugal pump normally used for this purpose. This
pump was delivering sufficient water volume to the underway CO_2
system on this cruise. The vessel provides meteorological data,
salinity (TSG45), intake temperature (SBE38), and GPS information from
vessel owned and maintained instruments, which are recorded in the
data file alongside every sample measurement.

There were a number of separate interruptions in data collection
throughout the cruise during periods where adjustments were made to
gas flows and when troubleshooting was necessary to ensure the best
quality data. Whenever possible, these interruptions were done when
the vessel was on station. As mentioned above, the infrared analyzer
had significant drift throughout the cruise so a new sampling plan, of
zeroing and spanning the instrument after every set of standards, was
enacted to attempt to reduce the drift. A few hours’ worth of
transiting data was affected due to a burst hose within the ship’s
underway system. Measurements of gas standards were mostly within 1%
of their certified value throughout the duration of the cruise.

+----------+---------------------+----------------------------------+
| Standard | Concentration (ppm) | Tank Serial Numbers              |
|==========|=====================|==================================|
| 1        | 304.26              | LL12289                          |
+----------+---------------------+----------------------------------+
| 2        | 493.30              | LL122858                         |
+----------+---------------------+----------------------------------+
| 3        | 639.36              | LL122359                         |
+----------+---------------------+----------------------------------+
| 4        | 704.20              | LL132516                         |
+----------+---------------------+----------------------------------+
| 5        | 0                   | Praxair 5.0 Ultra High Purity N2 |
+----------+---------------------+----------------------------------+

While the raw data are not reported here or included in the Scripps
Ocean Data Facility (SIO-ODF) database for this cruise, they has been
collected and will be returned to PMEL and analyzed using MATLAB®
routines developed by Dr. Denis Pierrot of the Atlantic Oceanographic
and Meteorological Lab (AOML) in Miami, FL. The data will be submitted
along with other cruise data and also submitted to the Surface Ocean
CO_2 Atlas (SOCAT).

[Pierrot09] Pierrot, D., Neill, C., Sullivan, K., Castle, R.,
            Wanninkhof, R.W., Lüger, H., Johannessen, T., Olsen, A.,
            Feely, R.A., Cosca, C.E.; 2009. Recommendations for
            autonomous underway pCO_2 measuring systems and data
            reduction routines. Deep-Sea Research II 56 (2009):
            512–522.


NO_3^- and DON Isotopes (\delta^15N & \delta^18O)
=================================================

PI
   * François Fripat (Université Libre de Bruxelles, Brussels)

At-Sea Sampling
   * Alessandra Quigley (Columbia)

   * Genevieve Clow (University of Colorado-Boulder)

   * Roxanne Mina (University of South Florida)

   * Ilmar Leimann (University of Bremen & MARUM, Germany)


Sampling
--------

Samples for nitrogen (N) and oxygen (O) isotope analysis in nitrate
(NO_3^-), combined nitrate and nitrite (NO_3^- + NO_2^-), and
dissolved organic nitrogen (DON) were collected at 33 stations evenly
distributed along the transect. Between stations 1 and 37, samples
were collected from all sampled niskins every 4 stations. Between
stations 37 and 94, samples were collected from all sampled niskins
every 3 stations. Between stations 94-98, samples were collected from
all sampled niskins on each station. In total, 1026 samples were
obtained. High-resolution measurements of NO_3^- \delta^15N and
\delta^18O provide a powerful means to trace the sources and sinks of
bioavailable (i.e., fixed) nitrogen at the scale of the Indian Ocean,
and to investigate the coupling between biogeochemical cycling and
ocean circulation. Meanwhile, \delta^15N in DON may offer novel
insights into this still poorly characterized pool of bioavailable
nitrogen—particularly regarding potential in situ production and
consumption processes.


Analysis
--------

Unfiltered samples for N and O isotopic composition of NO_3^- and DON
were collected in 60 mL plastic bottles and stored frozen (-20 °C)
until analysis. NO_3^- + NO_2^- \delta^15N and \delta^18O will be
measured at the Université Libre de Bruxelles using the denitrifier
method (Sigman et al., 2001 [Sigman2001]; Casciotti et al., 2002
[Casciotti2002]). Briefly, 3-20 nmol of NO_3^- + NO_2^- is
quantitatively converted to N_2O gas by denitrifying bacteria that
lack an active N_2O reductase. The N_2O is then analysed by gas
chromatography-isotope ratio mass spectrometer (MAT253, Thermo) with
on-line cryo-trapping (Weigand et al., 2016 [Weigand2016]).
Measurements are referenced to air N_2 for \delta^15N and VSMOW for
\delta^18O using the nitrate reference materials IAEA-NO3 and USGS-34.
For NO_3^- \delta^15N and \delta^18O analysis, NO_2^- is removed with
the sulfamic acid method prior to the isotopic analysis (Granger and
Sigman, 2009 [Granger2009]). The reproducibility is generally better
than 0.1‰ for \delta^15N and \delta^18O, respectively. DON \delta^15N
will be measured on the same samples as for NO_3^- using the combined
persulfate-denitrifier method (Knapp et al., 2005 [Knapp2005]).
Briefly, DON is oxidized to nitrate using a persulfate oxidizing
reagent. The nitrate is then quantitively converted to N_2O using the
‘denitrifier’ method as described above, allowing to measure both the
concentration and \delta^15N.

[Casciotti2002] Casciotti, K.L., D.M. Sigman, M. Galanter Hastings,
                J.K. Böhlke, and A. Hilkert. 2002. Measurement of the
                oxygen isotopic composition of nitrate in seawater and
                freshwater using the denitrifier method. Anal. Chem.
                74: 4905-4912.

[Granger2009] Granger, J., and D.M. Sigman. 2009. Removal of nitrite
              with sulfamic acid for nitrate N and O isotope analysis
              with the denitrifier method. Rapid Commun. Mass
              Spectrom. 23: 3753-3762, doi:10.1002/rcm.4307.

[Knapp2005] Knapp, A.N., D.M. Sigman, and F. Lipschultz. 2005. N
            isotopic composition of dissolved organic nitrogen and
            nitrate at the Bermuda Atlantic time-series study site.
            Global Biogeochemical Cycles 19(1),
            doi:10.1029/2004GB002320.

[Sigman2001] Sigman, D.M., K.L. Casciotti, M. Andreani, C. Barford, M.
             Galanter, and J.K. Böhlke. 2001. A bacterial method for
             the nitrogen isotopic analysis of nitrate in seawater and
             freshwater. Anal. Chem. 73: 4145-4153.

[Weigand2016] Weigand, M.A., J. Foriel, B. Barnett, S. Oleynik, and
              D.M. Sigman. 2016. Updates to instrumentation and
              protocols for isotopic analysis of nitrate by the
              denitrifier method. Rapid Commun. Mass Spectrom. 30:
              1365-1383.


\delta^13C - Dissolved Inorganic Carbon (DIC)
=============================================

PI
   * Wei-jun Cai (University of Delaware)

Technician
   * Songying Tang (University of Delaware)


Sampling
--------

Samples for \delta^13C-DIC measurements were drawn according to
procedures outlined in the PICES Special Publication, Guide to Best
Practices for Ocean CO_2 Measurements (Dickson et al., 2007
[Dickson2007]), from the rosette sample bottles into cleaned 250 mL
and 125 mL borosilicate glass bottles. Bottles were rinsed three times
and filled from the bottom, with one bottle volume of overflow. After
collection, approximately 2 mL of headspace was removed, and saturated
mercuric chloride solution was added to each sample for preservation
(0.1 mL for 250 mL bottles and 0.05 mL for 125 mL bottles). Sample
bottles were then sealed with glass stoppers lightly covered with
Apiezon-L grease and stoppers were fixed with rubber bands and clips.
\delta^13C-DIC samples were collected at every station in conjunction
with DIC, Alkalinity, and pH measurements, with some deep depths
skipped at DIC partial casts to ensure enough bottles remained for
future stations. Two to three replicate samples were typically taken
from the surface, at the oxygen minimal depth, and from bottom rosette
sample bottles. All samples are being securely stored on the ship and
will be shipped back to the United States for analysis. A special
thanks to Daniela Nestory for providing the saturated mercuric
chloride solution. Another special thanks to Genevieve Clow who took
the night shift samples.


Analysis
--------

The analysis will be conducted in the laboratory of University of
Delaware.

[Dickson2007] Dickson, A. G., Sabine, C. L., & Christian, J. R.
              (2007). Guide to best practices for ocean CO2
              measurements. North Pacific Marine Science Organization.


Iodine
======

PIs
   * James Moffett (USC)

   * Adam Martiny (UCI)

At Sea
   * Mary Dinneen (USC)

   * Star Dressler (UCI)

   * Eli Mally (UCI)


Significance of Iodine in the Bay of Bengal OMZ
-----------------------------------------------

Iodine is a redox-reactive element that exhibits a disequilibrium
between iodate and iodide in seawater, particularly within oxygen
minimum zones (OMZs). Iodide has been observed to accumulate along the
upper boundaries of OMZs (Farrenkopf and Luther, 2002
[Farrenkopf2002]), likely due to its redox sensitivity under low-
oxygen conditions. This accumulation also shows a strong correlation
with nitrate, at times more distinctly related than oxygen levels
(Reyes-Umana et al., 2022 [ReyesUmana2022]). Furthermore, iodide plays
a specialized role in the metabolic pathways of certain bacteria found
in OMZs, particularly those associated with the *idrA* gene (Reyes-
Umana et al., 2022 [ReyesUmana2022]). Recent studies in the Bay of
Bengal reveal distinct iodide features associated with the region’s
low-oxygen environment (Shaikh et al., 2024 [Shaikh2024]),
highlighting the potential for similar iodide-based microbial
metabolism in this setting as well as geochemical reduction of iodate
to iodide associated with high nitrate and low oxygen. Our analyses
aim to investigate the biogeochemical relationships between low
oxygen, elevated nutrients, and iodate reductase pathways in the Bay
of Bengal’s prominent OMZ.


Iodine Sampling Method
----------------------

100 mL filtrate taken in two 50 mL falcon tubes were collected daily
using a Sterivex filter and peristaltic pump filtering setup from Bio
GO-SHIP casts, as well as from mid-day underway seawater, via the Bio
GO-SHIP DNA filtering system. Samples were initially frozen at –20 °C
and later transferred to –80 °C for long-term storage. After reaching
10° N, additional 125 mL samples were collected directly from the CTD
rosette from depths of interest—selected based on features of the Bay
of Bengal (BoB) oxygen minimum zone (OMZ) profile—and processed using
the same filtering system, then similarly frozen.

A total of 134 iodide samples were collected and will be transported
back to the University of Southern California, where they will be
analyzed for iodide content by Mary Dinneen in the Moffett Lab.

[Farrenkopf2002] Farrenkopf, A.M. and G.W. Luther III. 2002. Iodine
                 chemistry reflects productivity and denitrification
                 in the Arabian Sea: evidence for flux of dissolved
                 species from sediments of western India into the OMZ.
                 Deep-Sea Research II. 49: 2303-2318.

[ReyesUmana2022] Reyes-Umana, V., Z. Henning, K. Lee, T.P. Barnum,
                 J.D. Coates. 2022. Genetic and phylogenetic analysis
                 of dissimilatory iodate-reducing bacteria identifies
                 potential niches across the world’s oceans. ISME
                 Journal. 16(1): 38-49.

[Shaikh2024] Shaikh, A., S. Kurian, D.M. Shenoy, A.K. Pratihary, S.S.
             Shetye. 2024. Biogeochemical cycling of iodine in the Bay
             of Bengal: A comparison with the Arabian Sea. Mar Pollut
             Bull. 209(Pt B):117329.


Bio-GO-SHIP
===========

PIs
   * Harriet Alexander (WHOI)

   * Jason Graff (OSU)

   * Adam Martiny (UC Irvine)

   * Catherine Mitchell (Bigelow Laboratory for Ocean Sciences)

   * Nicole Poulton (Bigelow Laboratory for Ocean Sciences)

   * Luke Thompson (AOML)

Technicians
   * Star Dressler (UC Irvine)

   * Laura Lubelczyk (Bigelow Laboratory for Ocean Sciences)

   * Eli Mally (UC Irvine)

Bio-GO-SHIP sampled I09N with underway and CTD water at distinct time
points throughout each day. This included continuous inline, discrete
transit inline, PACE OCI satellite overpass discrete transit inline,
CTD “bio-cast”, and CTD bio-cast with Global Ocean Biogeochemistry
Array (BGC) float deployments. During I09N, Bio-GO-SHIP completed 100
transit inline stations (including 33 PACE overpass transit inline
stations), 31 CTD bio-cast stations, and 7 BGC float deployment bio-
cast stations. Once the ship entered the Bangladesh EEZ, transit
inline stations were taken from the CTD, making 7 stations counted as
both “transit” and “CTD” stations.


Continuous Inline
-----------------

A diaphragm pump underway system provided continuous flow from surface
waters for optical instrumentation (BB3, ACS), Imaging Flow CytoBot
(IFCB), flow cytometer (FCM), and particulate inorganic carbon via
acid labile backscattering (PIC using ECO-VSF) as well as temperature,
salinity, and fluorescence. All underway water was run through a
vortex debubbler before being sampled. Continuous instrumentation was
run until the final station at 19° 57.36’ N 89° 51.6’ E.


Inline Optics
~~~~~~~~~~~~~

The BB3 backscatter casket and Wet Labs ACS-111 received continuous
inline water throughout I09N, passing through a filter for 10 minutes
of every hour. Inlinino software, connected to communication channels,
monitored flow rate, filtration timing, latitude/longitude
coordinates, UTC time, and data from the sensors. The BB3 and ACS were
cleaned with DI water and isopropyl alcohol wipes about once per week.


Imaging FlowCytobot
~~~~~~~~~~~~~~~~~~~

The McLane IFCB received continuous inline water throughout I09N, with
a single 5 mL sample processed every 20 minutes. Underway water passed
through a 200 micron screen (cleaned 2 times per day) and a 150 micron
screen (cleaned once per week) before reaching the instrument. Every
25 samples the instrument was cleaned and every 25 samples calibration
beads were run. Files will be analyzed for particle size distribution
and functional phytoplankton groups at a later point in time.


Cytek Northern Lights Spectral Flow Cytometer
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The shipboard Cytek flow cytometer received continuous inline water
and operated on a SpectroFlo software template where a three minute
inline water sample (approximately 180 microliters) was processed
followed by a wait time of four minutes, collecting approximately 190
samples in each 24 hour period. Underway water passed through a 200
micron screen before reaching the instrument. Maintenance included
once-daily particle size calibration, twice-daily cleanings of the
instrument and the prefilter, and cleaning of the inline tubing and
sample port once per week. Files will be analyzed for pico- and
nanoplankton populations at a later point.


Acid-Labile Backscattering for Particulate Inorganic Carbon
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Continuous inline water passed through a series of instruments as
follows and data was recorded in LabView software:

1. SeaBird T-sal to measure salinity and temperature

2. WetLabs WetSTAR chlorophyll fluorometer

3. WetLabs VSF in a dark housing (Backscattering at 100, 125, and 150
   degrees at three wavelengths)

4. WetLabs Flow Meter to record flow rate through the system (avg 2L
   per minute)

On a cycle of roughly 20 minutes, 10% acetic acid was pumped through a
mixing coil at a sufficient rate to bring the pH below the
dissociation point for calcite (< 6.0). After 60 points were recorded
at this low pH, the acid pump shuts off, raw seawater is restored, and
60 more points were recorded at normal pH. The difference between
total and acidified backscattering represents “acid-labile
backscattering” which is an optical proxy for the concentration of
PIC, particulate organic carbon (Balch and Drapeau, 2004 [Balch2004]).
Once daily (while on station if possible), water was passed through a
0.2 um filter for 20-30 minutes, providing a filtered seawater blank.
Approximately once per week the pH probe was calibrated and the
fluorometer and VSF were cleaned.


Discrete Transit Inline Sampling
--------------------------------

Flow cytometry (FCM), particulate inorganic carbon (PIC),
environmental DNA (eDNA), RNA, particulate organic matter (POM), high
performance liquid chromatography (HPLC), and iodine samples were
discretely collected from the underway system at approximately 0600,
1200, and 2000 local time. If the PACE overpass or bio-cast timing
occurred within three hours in either direction of these time points,
then the inline sampling effort was modified to be included with the
PACE overpass or bio-cast sampling.

A single sample was taken for FCM, PIC, eDNA, HPLC, and iodine. POM
comprises three sample types with each type sampled as a triplicate,
including particulate organic phosphorus (POP), particulate organic
carbon and nitrogen (POCN), and particulate chemical oxygen demand
(PCOD). A single RNA sample was taken at the 1200 time point only. The
total number of samples listed below includes all discrete transit
inline samples for each sample type, including samples taken during
PACE overpass transit inline samples.

Discrete inline sampling was discontinued once the ship entered the
Bangladesh EEZ at 17° 19.424’ N 89° 51.582’ E, after which the transit
station samples were gathered from the CTD until the final station.


Flow Cytometry
~~~~~~~~~~~~~~

Discrete FCM samples were collected in 50-mL dark Falcon tubes and
preserved for later analysis. Nitrile gloves were worn for sample
collection and processing. Falcon tubes were rinsed quickly three
times with sample water prior to sample collection, and sample
processing took place as quickly as possible. However, for times when
the bio-cast was combined with a main cast, FCM was the last sample
taken from the rosette, typically around 1 hour after the CTD was
brought onboard. From the Falcon tubes, 1.8 mL of seawater was
pipetted into a 2 mL cryovial. In a fume hood, 18 µL of a preservation
mixture (half 25% Glutaraldehyde and half 2% Kolliphor) was added to
each cryovial. The cryovial was inverted several times and placed on a
vial stand in a refrigerator for approximately 10 minutes. The vials
were flash frozen in a cryo-cane in a liquid nitrogen dewar then later
moved to storage in the -80 °C freezer. On I09N, 140 total FCM samples
were processed from underway transit stations. These samples will be
analyzed for pico- and nano-plankton populations as well as for total
bacteria (stained with SYBR Green DNA stain) at the laboratory.


Particulate Inorganic Carbon
~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Discrete PIC samples were collected in a 1 L dark Nalgene bottle after
the bottle was rinsed three times. Nitrile gloves were worn for sample
collection and processing. A graduated cylinder was used to measure
out 200 mL and filter it onto a 25 mm 0.4 micron Nuclepore filter
using a filter manifold and vacuum pump. The filter cup and filter
were rinsed with a potassium tetraborate solution (3.06 g in 500 mL of
deionized water). Filters were folded in half with the sample facing
inward and stored in a 15 mL centrifuge tube. Caps were left loose and
samples were placed in a 60 °C drying oven for a minimum of 24 hours.
When samples were completely dry, caps were tightened and the tubes
stored at room temperature to be analyzed in the laboratory. On I09N,
157 total PIC samples were collected from underway transit stations.


eDNA and RNA
~~~~~~~~~~~~

Discrete eDNA and RNA samples were gathered in ~9.00 L spigoted
carboys. Filtering of sample water through 0.22 µm Sterivex filters
took place as quickly as possible following sampling. Nitrile gloves
were worn for sample collection and processing. Prior to gathering
sample water, each carboy was quickly rinsed three times with sample
water. For filtration, clean tubing ran from each carboy through a
peristaltic pump head to the Sterivex filter and emptied directly into
the sink. Five samples could be run simultaneously. Prior to attaching
the Sterivex, a small amount of sample water was flushed through the
line. Following filtration, each filter was cleared of remaining
liquid and processed with 1000 µl of DNA/RNA Shield. All samples were
labeled following protocol and stored at –80 °C for later analysis.
Following filtration, sample lines were cleaned with 2% bleach
solution and DI water. On I09N, 72 total samples were processed for
eDNA from underway transit stations, and 17 total samples were
processed for RNA from underway transit stations.


Particulate Organic Matter
~~~~~~~~~~~~~~~~~~~~~~~~~~

Discrete POM (including POP, POCN, and PCOD) samples were gathered in
triplicates of ~9.00 L spigoted carboys. Filtering of sample water
through pre-combusted 25 mm glass fiber filters (GF/Fs) took place as
quickly as possible following sampling. Nitrile gloves were worn for
sample collection and processing. Prior to gathering sample water,
each carboy was quickly rinsed three times with sample water. Tubing
connected to each spigot flowed through the filter housing with GF/Fs
and to an aspirator pump that emptied into a sink. Following
filtration, POP sample filters were rinsed with approximately 5 mL of
Na_2SO_4 solution to remove traces of dissolved phosphorus from the
filter. Each filter was removed with tweezers, folded sample-side
inwards into pre-combusted aluminum foil, labeled according to
protocol, and stored at –80 °C for later analysis. Sample lines and
filter housings were rinsed with DI water. On I09N, 237 POP samples,
201 POCN samples, and 203 PCOD samples were processed from underway
transit stations.


High Performance Liquid Chromatography
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Discrete HPLC samples were gathered in ~2.00 L sample bottles, with
approximately 10% of samples gathered as duplicates. Filtering of
sample water through pre-combusted 25 mm glass fiber filters (GF/Fs)
took place as quickly as possible following sampling. Nitrile gloves
were worn for sample collection and processing. Prior to gathering
sample water, each bottle was quickly rinsed three times with sample
water. GF/F filters were secured on a filtration manifold attached to
a vacuum pump. After filtration, filters were folded in half sample-
side inwards, placed in a cryovial, labeled following protocol, and
stored at –80° C for later analysis. On I09N, 141 total HPLC samples
were processed for underway transit sampling.


Iodine
~~~~~~

Iodine was discretely gathered by Bio-GO-SHIP technicians for James
Moffett of the University of Southern California. A total sample
volume of ~90 mL was gathered in two 50 mL falcon tubes after the
sample water passed through the 0.22-µm Sterivex filter of the
eDNA/RNA filtration rig. Falcon tubes were frozen upright in a tube
rack in a -20° C freezer before being stored in a ziplock bag and
transferred to the –80° C freezer. On I09N, 46 total iodine samples
were processed during the cruise.


PACE Overpass Discrete Inline Sampling
--------------------------------------

At the approximate overpass time of the PACE OCI satellite at the
ships given location throughout the cruise, a suite of discrete inline
samples were taken, including small volume particulate organic carbon
and nitrogen (small volume POCN), FCM, PIC, and HPLC. Small volume
POCN was sampled in a three volume regression (~2L, 1L, 0.5L) with a
1L wet blank taken each day and a dry blank taken approximately every
three days. FCM, PIC, and HPLC were sampled in triplicates. If the
skies were completely overcast, only a single HPLC sample was taken.
The same sampling protocols were followed as listed in section 2, and
the protocol for small volume POCN is described below.

These samples will serve as ground truthing/validation data for NASA’s
PACE OCI satellite. This daily sampling effort often aligned with the
1200 discrete inline sampling effort outlined in section 2, in which
case eDNA, RNA, POM, and iodine were also discretely sampled. During
the 33 number of PACE overpass inline sampling stations on I09N, 87
total small volume POCN samples (not including wet and dry blanks), 85
total HPLC samples, 93 total PIC samples, and 79 total FCM samples
were processed.

PACE overpass discrete sampling was gathered from the underway system
until the ship entered the Bangladesh EEZ at 17° 19.424’ N 89° 51.582’
E, after which the overpass samples were gathered from the CTD until
the final station.


Small Volume Particulate Organic Carbon and Nitrogen
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Discrete small volume POCN samples were gathered in ~2.00 L sample
bottles. Filtering of sample water through pre-combusted 25 mm glass
fiber filters (GF/Fs) took place as quickly as possible following
sampling. Nitrile gloves were worn for sample collection and
processing. Prior to gathering sample water, each bottle was quickly
rinsed three times with sample water. GF/F filters were secured on a
filtration manifold attached to a vacuum pump. After filtration,
filters were folded in half sample-side inwards, placed in pre-
combusted tin foil, labeled following protocol, and stored at –80° C
for later analysis.


CTD Sampling
------------

CTD bio-cast sampling occurred about once a day, with preference to a
station that was as close to local 1200 as possible. Original protocol
had the bio-cast occuring separately of the full GO-SHIP cast,
descending to a maximum depth of 1000 meters, and firing 26 Niskin
bottles for Bio-GO-SHIP sampling. Following the delays and technical
difficulties of I09N, separate 1000 meter bio-casts were discontinued
as a time-saving measure. A sampling scheme that merged the bio-cast
with the full cast was implemented, which provided Bio-GO-SHIP with 12
Niskin bottles. The remaining Bio-GO-SHIP samples were taken from the
remaining sample water left in Niskin bottles after GO-SHIP finished
sampling. With shallower depths, more Niskin bottles became available
for Bio-GO-SHIP. The majority of the bio-casts performed on I09N were
combined casts.

The original 1000 m separate bio-cast had the following sampling
scheme: eDNA at depths 1000 m, 200 m, 100 m, and 5 m; RNA at 5 m; POM
at 5 m; HPLC at 100 m, 40 m, and 5 m; FCM at 1000 m, 500 m, 200 m, 150
m, 100 m, 75 m, 40 m, and 5 m. Iodine was sampled at the same depths
as eDNA at the majority of bio-cast stations. Each sampling protocol
is the same listed in section 2, and water was sampled from the Niskin
bottles using a small piece of silicone tubing. When the bio-cast was
combined with the full cast, there were slight changes to this scheme.
eDNA, RNA, POM, and some FCM depths received their own Niskin bottles
at the preferred listed depth. One replicate of POP and PCOD were not
sampled on the shared casts. HPLC and some FCM depths were sampled
from remaining sample water from GO-SHIP bottles. If GO-SHIP depths
were not aligned with the preferred Bio-GO-SHIP scheme, the closest
available depth was chosen. HPLC at around 40 m and 100 m on the
shared casts did not always have a full 2 L of remaining sample water.

A beam transmissometer, attached to the Niskin rosette, was
additionally managed by Bio-GO-SHIP. The lenses of the transmissometer
were cleaned with isopropyl alcohol wipes and deionized water daily.
“Dark casts” were performed about once per week, where electrical tape
was placed over the lenses during deployment. These dark casts serve
as calibration of temperature and pressure during data analysis.

During I09N bio-casts, 109 total samples were gathered for eDNA, 26
samples for RNA, 91 samples for POP, 87 samples for POCN, 76 samples
for PCOD, 108 samples for HPLC,  and 236 samples for FCM.
Additionally, at the second GO-SHIP CTD test station (8.217° N 95.0°
E), 28 eDNA samples from surface waters were processed as reference
samples for DNA extraction protocol.


BGC Float Stations
~~~~~~~~~~~~~~~~~~

At CTD stations aligned with BGC float deployments, a separate 1000 m
bio-cast was implemented. The same sampling scheme for a separate bio-
cast, as listed above, was followed. Additional HPLC and small volume
POCN samples were taken for BGC float calibration/validation analysis.
Small volume POCN was gathered at depths 100 m, 40 m, and 5 m. HPLC
and small volume POCN was additionally gathered at depths of the
chlorophyll maximum and the chlorophyll maximum + 50 m depth. HPLC was
sampled in duplicates at the chlorophyll maximum + 50 m depth, and
small volume POCN was sampled in duplicates at the chlorophyll maximum
depth. The chlorophyll maximum was determined during the CTD down-cast
by the fluorometer attached to the Niskin rosette. The same sampling
protocols for all sample types are the same as listed in section 2 and
3, and water was sampled from the Niskin bottles using a small piece
of silicone tubing. For small volume POCN at float stations, sample
processing always included a dry blank and a wet blank from the
chlorophyll maximum duplicate.

During the 7 BGC float deployments on I09N, 42 total samples were
gathered for HPLC, and 42 total samples were gathered for small volume
POCN (not including wet and dry blanks).

[Balch2004] Balch, W. M., Drapeau, D. T., Bowler, B. C., Booth, E. S.,
            Goes, J. I., Ashe, A., & Frye, J. M. (2004). A multi-year
            record of hydrographic and bio-optical properties in the
            Gulf of Maine: I. Spatial and temporal variability.
            Progress in Oceanography, 63(1-2), 57-98.


Iron
====

PI
At Sea
   * Mary Dinneen (USC)


Background
----------

Iron is an essential micronutrient that functions as a metal cofactor
in numerous critical metalloenzymes involved in microbial growth and
metabolism. The Indian Ocean, influenced by substantial aeolian dust
deposition and riverine inputs, presents a unique environment to
investigate the distribution of iron and other trace metals, such as
manganese and cadmium. Understanding the biogeochemical cycling of
these metals in this region is key to forming a more integrated
picture of their roles in oceanic nutrient dynamics and microbial
ecology.


Sampling Method
---------------

   [image]Mary Dinneen and Jake Howat retrieving a surface water pole
   sample. *Image by Laura Lubelczyk*

Surface water samples were collected in 125 mL triplicates using a
pole sampling system (Fig. %s) deployed from the starboard side of the
ship at every 5 degrees of latitude along the I09 transect.

Nine stations total were sampled immediately upon arrival. All samples
were stored at 4 °C in two sealed bags. The 125 mL polyethylene
bottles were cleaned to trace metal clean standards by soaking in 10%
HCl for 3 weeks and thoroughly rinsing with Milli-Q water before being
double-bagged for storage at the Moffett Lab at the University of
Southern California. All bottles were handled with appropriate
personal protective equipment (PPE) and immediately bagged after
sampling to minimize the risk of contamination.

Samples will be transported back to the University of Southern
California, where they will be acidified and analyzed for iron and
other trace metals (e.g., cadmium and manganese) using a SeaFAST
system followed by ICP-MS. Analyses will be conducted by Mary Dinneen
in the Moffett Lab.


Surface Drifters
================

PI
   * Shaun Dolk (NOAA AOML)

Deployment
   * Leah Chomiak (U Miami-CIMAS)

A total of 20 surface drifters from NOAA’s Global Drifter Program
(https://www.aoml.noaa.gov/global-drifter-program/) were deployed at
targeted locations provided by the PI along the I09N transect.
Targeted locations were determined based on drifter priority as of
March 24, 2025 using Drifter Value Maps
(https://www.aoml.noaa.gov/phod/gdp/value_maps.php). This priority
scheme was set to maximize drifter lifetimes and account for active
drifters within the region (including their age and number of
operational sensors). Despite low value within the Bay of Bengal, the
region was considered low priority due to the immense amount of local
activity, which historically result in short drifter lifetimes.

All drifters were deployed off the port stern at a speed of 5 kts once
the ship began to get underway following a CTD cast. Targeted
deployments followed the nearest planned CTD station. All drifters
were staged on the aft deck shortly before launch, where all plastic
was removed according to instruction. Two people assisted with each
deployment, and deployment times, locations, and drifter
identification numbers were logged appropriately (see Table %s). Real-
time data and visualization are available through the Observing System
Monitoring Center (OSMC;
https://viz.pmel.noaa.gov/osmc/?color_by=platform_type). More tools
are available at https://www.aoml.noaa.gov/phod/gdp/real-
time_data.php.

   [image]Targeted deployment strategy along the I09N transect using
   the Drifter Deployment Value Map of the Indian Ocean. Figure by
   Shaun Dolk, NOAA AOML.


Drifter Deployments
^^^^^^^^^^^^^^^^^^^

+------------------+------------------+------------------+------------------+------------------+------------------+
| Drifter ID       | Station          | Latitude         | Longitude        | Date (UTC)       | Time (UTC)       |
|==================|==================|==================|==================|==================|==================|
| 300534064294230  | 13               | 21°18.997 S      | 94°59.986 E      | 3/30/25          | 17:31            |
+------------------+------------------+------------------+------------------+------------------+------------------+
| 300534064293290  | 17               | 19°05.001 S      | 95°00.000 E      | 4/1/25           | 00:54            |
+------------------+------------------+------------------+------------------+------------------+------------------+
| 300534064293640  | 17               | 19°05.001 S      | 95°00.000 E      | 4/1/25           | 00:54            |
+------------------+------------------+------------------+------------------+------------------+------------------+
| 300534064292630  | 21               | 16°49.703 S      | 94°59.987 E      | 4/2/25           | 07:46            |
+------------------+------------------+------------------+------------------+------------------+------------------+
| 300534064293280  | 21               | 16°49.911 S      | 94°59.987 E      | 4/2/25           | 07:45            |
+------------------+------------------+------------------+------------------+------------------+------------------+
| 300534064293350  | 24               | 15°10.200 S      | 95°00.000 E      | 4/3/35           | 05:43            |
+------------------+------------------+------------------+------------------+------------------+------------------+
| 300534064293670  | 24               | 15°10.200 S      | 95°00.000 E      | 4/3/25           | 05:44            |
+------------------+------------------+------------------+------------------+------------------+------------------+
| 300534064294240  | 27               | 13°33.965 S      | 94°59.999 E      | 4/4/25           | 03:43            |
+------------------+------------------+------------------+------------------+------------------+------------------+
| 300534064294270  | 27               | 13°33.965 S      | 94°59.999 E      | 4/4/25           | 03:44            |
+------------------+------------------+------------------+------------------+------------------+------------------+
| 300534064293240  | 30               | 11°56.885 S      | 94°59.977 E      | 4/5/25           | 02:40            |
+------------------+------------------+------------------+------------------+------------------+------------------+
| 300534064294230  | 30               | 11°56.885 S      | 94°59.977 E      | 4/5/25           | 02:39            |
+------------------+------------------+------------------+------------------+------------------+------------------+
| 300534064293940  | 37               | 8°13.110 S       | 95°00.000 E      | 4/7/25           | 04:49            |
+------------------+------------------+------------------+------------------+------------------+------------------+
| 300534064293960  | 37               | 8°13.110 S       | 95°00.000 E      | 4/7/25           | 04:49            |
+------------------+------------------+------------------+------------------+------------------+------------------+
| 300534064293230  | 41               | 6°3.622 S        | 94°59.865 E      | 4/8/25           | 10:50            |
+------------------+------------------+------------------+------------------+------------------+------------------+
| 300534064293660  | 41               | 6°3.720 S        | 94°59.867 E      | 4/8/25           | 10:48            |
+------------------+------------------+------------------+------------------+------------------+------------------+
| 300534064293950  | 45               | 3°39.215 S       | 94°34.464 E      | 4/9/25           | 18:52            |
+------------------+------------------+------------------+------------------+------------------+------------------+
| 300534064293360  | 45               | 3°39.215 S       | 94°34.464 E      | 4/9/25           | 18:53            |
+------------------+------------------+------------------+------------------+------------------+------------------+
| 300534064293650  | 47               | 2°19.370 S       | 94°8.704 E       | 4/10/25          | 09:30            |
+------------------+------------------+------------------+------------------+------------------+------------------+
| 300534064292940  | 57               | 2°4.586 N        | 94°3.794 E       | 4/13/25          | 05:32            |
+------------------+------------------+------------------+------------------+------------------+------------------+
| 300534064293930  | 83               | 14°4.439 N       | 89°18.354 E      | 4/20/25          | 04:19            |
+------------------+------------------+------------------+------------------+------------------+------------------+


Float Deployment
================

Deployment
   * Guillaume Liniger (MBARI)

A total of 25 floats were deployed during the I09N cruise: 6 EM-APEX
SQUID floats from the Applied Physics Laboratory at the University of
Washington (APL-UW), 12 SOLO II core Argo floats from Scripps
Institution of Oceanography, UCSD (SIO), and 7 S2-BGC Biogeochemical
(BGC) Argo floats also from SIO as part of the GO-BGC program. Details
are provided below for each float category.


SQUID Floats
------------

PI:
   * James Girton (APL-UW)

Six EM-APEX (ElectroMagnetic Autonomous Profiling EXplorers) were
deployed during this I09N 2025 cruise. These floats measure
temperature, salinity, horizontal velocity, and turbulence
(temperature microstructure) and are part of the Sampling Quantitative
Internal-wave Distribution project (SQUID), sponsored by NSF as a
component of the National Oceanographic Partnership Program’s Global
Internal Waves initiative and led by James Girton (APL-UW,
girton@uw.edu). The SQUID program aims to quantify the broad scale
characterization of internal waves climates through the use of
autonomous profiling floats. Prior to cruise departure, floats were
tested by engineer Jacob Dossett (APL-UW) to make sure all were
responding and ready to be deployed.

The EM-APEX float details and deployment locations are listed in Table
%s below.


Summary of EM-APEX float deployment
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

+------------------+------------------+------------------+------------------+------------------+------------------+
| Float ID         | Station number   | Lat (N)          | Lon (E)          | Date (UTC)       | Time (UTC)       |
|==================|==================|==================|==================|==================|==================|
| 10330            | 8                | -28.08           | 95.00            | 29/3/25          | 2:12             |
+------------------+------------------+------------------+------------------+------------------+------------------+
| 10339            | 20               | -17.4            | 95.00            | 1/4/25           | 23:55            |
+------------------+------------------+------------------+------------------+------------------+------------------+
| 10340            | 39               | -7.13            | 95.00            | 7/4/25           | 20:12            |
+------------------+------------------+------------------+------------------+------------------+------------------+
| 10691            | 48               | -1.67            | 93.94            | 10/4/25          | 17:20            |
+------------------+------------------+------------------+------------------+------------------+------------------+
| 10692            | 60               | 3.34             | 91.54            | 13/4/25          | 23:53            |
+------------------+------------------+------------------+------------------+------------------+------------------+
| 10693            | 74               | 9.83             | 86.78            | 17/4/25          | 19:30            |
+------------------+------------------+------------------+------------------+------------------+------------------+

All floats were stored horizontally in individual crates outside or in
a container on the aft deck with core and BGC-Argo floats. All SQUID
floats followed the same protocol for deployment:

1. About 30 to 45 min before deployment, the 5 caps on the electrodes
   were removed and replaced by shade caps with small air hole on top.

2. At deployment time, after the CTD/rosette cast was completed and
   secured on deck, floats were secured using the A-frame with the
   help of the marine crew. Once attached, the 3 caps on top of the
   floats were removed as well as the Tµ probe’s protective cover (by
   lifting and tilting the cover over and past the probes without
   contact).

3. Finally, floats were deployed from the monofilament loop on the
   side of the float using a quick release system at a speed of 1 to 2
   kts once the ship began to get underway following a CTD cast.

   [image]EM-APEX floats in their individual crates. *Image credit
   Guillaume Liniger*

   [image]EM-APEX float getting ready for deployment. Caps and
   protection are carefully removed. Deployment was handled by
   Guillaume Liniger with the help of the marine crew. *Image credit
   Allen Smith*

   [image]EM-APEX float being deployed from the A-frame and put in
   water using the quick release white line. Deployment was handled by
   Guillaume Liniger with the help of the marine crew. *Image credit
   Allen Smith*


Core Argo Floats
----------------

PIs:
   * Sarah Purkey (SIO)

   * John Gilson (SIO)

A total of 12 SOLO-II core Argo built by the Instrument Development
Group (IDG) at SIO in Sand Diego, CA, were deployed during this I09N
2025 cruise. Each float is equipped with temperature, salinity and
pressure sensors and can profile the water column down to 2000 m.

The floats follow the Argo profiling protocol of parking at 1000 and
profiling from 2000 m to the surface every 10 days.

All floats were stored vertically in individual degradable cardboard
box in a plastic bag and wrapped to protect the cardboard boxes. The
cardboard box was held together with two bands of soluble PVA tape on
the side and red plastic tape at the top and bottom end. Floats were
stored in a container on the aft part of the ship with the SQUID and
BGC-Argo floats.

Prior departure during mobilization, a performing self-test was
carried on each individual float by Melissa Miller (SIO), and
Guillaume Liniger. All 12 floats passed self-test and were ready for
deployment.

All core floats were deployed in their individual cardboard box after
the CTD/rosette cast was completed and back on deck, with the ship
speed going from 1 to 2 knots. They were deployed from of the aft part
of the boat with a lowering line. The box protects the delicate parts
of the floats from impact during deployment. The plastic wrap and the
red plastic packing tape at the top and bottom of the cardboard box
was removed just prior deployment. Once in the water, the PVA tape
dissolves, the box unfurls and the float is released. Floats were
deployed by Guillaume Liniger with the help of the marine crew.

Each float was assigned a serial number and specific location for
deployment that is summed up in Table %s below.


Summary of Core Argo float deployment
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

+------------------+------------------+------------------+------------------+------------------+------------------+
| Float ID         | Station number   | Lat (N)          | Lon (E)          | Date (UTC)       | Time (UTC)       |
|==================|==================|==================|==================|==================|==================|
| 3164             | 2                | -27.72           | 94.96            | 25/3/25          | 6:38             |
+------------------+------------------+------------------+------------------+------------------+------------------+
| 3223             | 5                | -25.91           | 94.99            | 26/3/25          | 6:21             |
+------------------+------------------+------------------+------------------+------------------+------------------+
| 3264             | 8                | -24.08           | 95.00            | 29/3/25          | 2:05             |
+------------------+------------------+------------------+------------------+------------------+------------------+
| 3303             | 12               | -21.88           | 95.00            | 30/3/25          | 10:05            |
+------------------+------------------+------------------+------------------+------------------+------------------+
| 3310             | 33               | -10.35           | 95.00            | 6/4/25           | 00:17            |
+------------------+------------------+------------------+------------------+------------------+------------------+
| 3322             | 37               | -8.22            | 95.01            | 7/4/26           | 4:47             |
+------------------+------------------+------------------+------------------+------------------+------------------+
| 3233             | 39               | -7.13            | 95.00            | 7/4/25           | 20:17            |
+------------------+------------------+------------------+------------------+------------------+------------------+
| 3324             | 41               | -6.07            | 95.00            | 8/4/25           | 10:49            |
+------------------+------------------+------------------+------------------+------------------+------------------+
| 3325             | 46               | -2.99            | 94.36            | 10/4/25          | 2:00             |
+------------------+------------------+------------------+------------------+------------------+------------------+
| 3326             | 48               | -1.67            | 93.94            | 10/4/25          | 17:15            |
+------------------+------------------+------------------+------------------+------------------+------------------+
| 3332             | 56               | 1.56             | 92.26            | 12/4/25          | 11:13            |
+------------------+------------------+------------------+------------------+------------------+------------------+
| 3344             | 60               | 3.34             | 91.54            | 13/4/25          | 23:57            |
+------------------+------------------+------------------+------------------+------------------+------------------+


BGC-Argo Floats
---------------

PIs:
   * Sarah Purkey (SIO)

   * John Gilson (SIO)

   * Lynne Talley (SIO)

   * Ken Johnson (MBARI)

Seven S2-BGC BGC-Argo floats were deployed on the cruise as part of
the GO-BGC (Global Ocean Biogeochemistry Array) programs (NSF
OPP-1936222 and OCE-1946578). All the BGC floats were manufactured by
MRV Systems and prepared by IDG for deployment (inspected and
ballasted). The GO-BGC program utilizes autonomous robotic floats to
measure temperature, salinity, pH, nitrate, chlorophyll, suspended
particles, light, and derived parameters such as dissolved organic
carbon (DIC), pCO2 and total alkalinity in the ocean from the surface
to 2000 m. These floats can operate continuously for years in all
weather conditions, providing near real-time observations of ocean
biogeochemistry and ecosystems throughout the world’s oceans.

Each float deployed carries sensors for temperature, salinity,
dissolved oxygen, pH, nitrate, oxygen, chlorophyll-a fluorescence
(chl-a), particulate backscatter (bbp) and downwelling irradiance.

The floats follow the Argo profiling protocol of parking at 1000 m,
and profiling from 2000 m to the surface every 10 days.

Eight floats were originally shipped to be deployed. As for the core
Argo, each float underwent a performing self-test prior departure.
Float 4033 did not respond and failed the test three times and was
therefore shipped back to SIO prior to departure.

   [image]Schematic of a SOLO BGC-Argo float deployed during the
   cruise. From https://www.go-bgc.org/floats

The deployment followed the same protocol as the core floats, except
that the SUNA (nitrate), ECO (chl-a and b_(bp)) and OCR (irradiance)
sensors were cleaned just before deployment.

1. The three sensors were first cleaned by rinsing lenses using
   deionized water and cleaned using pre-moistened pads by gently
   tap/dabbing the lens surface with the wipe.

2. Rinsing using deionized water

3. Tab/dab dry with lens paper

Note that for the SUNA sensor, it was cleaned using a Q-tip.

All S2-BGC floats were deployed according to the same protocol
discussed above for the SOLO-IIs. Plastic wrap and non-water soluble
tape were removed, and floats were lowered into the water in their
cardboard deployment boxes by rope (see Fig. %s and Fig. %s).

   [image]First profiles taken by float 4002.

GO-BGC is partnering with teachers and classrooms across the country
and around the world to inspire and educate students about global
ocean biogeochemistry and climate change through our “Adopt-A-Float”
initiative (https://www.go-bgc.org/outreach/adopt-a-float). Each float
was sponsored by a school (see Table %s) and were already decorated by
Melissa Miller before being shipped.

At each deployment, a BIO cast was performed to collect particulate
organic carbon (POC) and high-performance liquid chromatography (HPLC)
samples. The POC samples were collected at 5 m, 40 m, 100 m, Deep
chl-a maximum (DCM) and DCM+50 m, and filtered onboard by Guillaume
Liniger. In addition to these samples, the bio team (Star Dressler,
Eli Mally and Laura Lubelczyk) collected and filtered sampled for HPLC
at 5 m, 40 m, 100 m, DCM and DCM+50 m. All HPLC and POC samples were
frozen to be sent to for analysis at NASA for HPLC and SIO/UCSD for
POC, and will be used to calibrate the floats’ sensors. See more
details in the Bio-GO-SHIP section.

   [image]BGC-Argo float getting ready for deployment. Float was
   brought outside the container on deck and all tapes and stickers
   were removed. Deployment was handled by Guillaume Liniger with the
   help of the marine crew. *Image credit Allen Smith.*

   [image]BGC-Argo float getting ready for deployment. Float was
   deployed using two lines and rolled down slowly to the water in its
   cardboard box. Deployment was handled by Guillaume Liniger with the
   help of the marine crew. *Image credit Leah Chomiak.*


Summary of BGC-Argo float deployment
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

+--------------+--------------+--------------+--------------+--------------+--------------+--------------+--------------+
| Float ID     | WMO          | Station      | Lat (N)      | Lon (E)      | Date (UTC)   | Time (UTC)   | Adopt-a-flo  |
|              |              | number       |              |              |              |              | at name      |
|==============|==============|==============|==============|==============|==============|==============|==============|
| 4002         | 2903885      | 30           | -11.95       | 95.00        | 5/4/25       | 2:41         | Floater the  |
|              |              |              |              |              |              |              | explorer     |
+--------------+--------------+--------------+--------------+--------------+--------------+--------------+--------------+
| 4032         | 1902372      | 43           | -4.98        | 95.00        | 9/4/25       | 2:45         | Iron         |
|              |              |              |              |              |              |              | Seahorse II  |
+--------------+--------------+--------------+--------------+--------------+--------------+--------------+--------------+
| 4014         | 1902373      | 53           | 0.317        | 93.3         | 12/4/25      | 2:40         | Sakai Coho   |
|              |              |              |              |              |              |              | II           |
+--------------+--------------+--------------+--------------+--------------+--------------+--------------+--------------+
| 4009         | 2903829      | 64           | 5.27         | 90.29        | 15/4/25      | 1:38         | Cougar 7300  |
+--------------+--------------+--------------+--------------+--------------+--------------+--------------+--------------+
| 4023         | 2903831      | 72           | 8.92         | 87.49        | 17/4/25      | 6:55         | Humbertito   |
|              |              |              |              |              |              |              | the Squid    |
+--------------+--------------+--------------+--------------+--------------+--------------+--------------+--------------+
| 4015         | 1902367      | 83           | 14.07        | 89.31        | 20/4/25      | 4:36         | Grace        |
+--------------+--------------+--------------+--------------+--------------+--------------+--------------+--------------+
| 4025         | 2903915      | 88           | 16.50        | 89.85        | 21/4/25      | 8:13         | Coast Union  |
|              |              |              |              |              |              |              | High School  |
+--------------+--------------+--------------+--------------+--------------+--------------+--------------+--------------+
| 4033         |              |              |              |              |              |              | Ethan Allen  |
+--------------+--------------+--------------+--------------+--------------+--------------+--------------+--------------+

Float 4025 was last deployed at station 88 latitude 16.50N instead of
targeted latitude 17.88N due to time constraints (deployment during
the day).


Student Statements
==================

U.S. GO-SHIP thanks all of the students who participated on the cruise
for their important contribution to collection of this essential
global ocean data set, used as the benchmark for accuracy of all other
deep ocean observing systems. The training opportunity for students
and leadership is an important part of US GO-SHIP’s mission. We are
committed to do so in a fair, cooperative and professional
environment, ensuring an inclusive, safe and productive climate at
sea.

We thank the students for their honest reflections on their
experiences that are included in this section. We have reached out to
those who expressed concerns and are taking issues raised seriously,
by working to address and prevent these issues from occurring in the
future. We also thank them for their feedback in the anonymous post-
cruise survey, which we are using to continue to improve our program.
This will include ongoing education for all members of our community
to create a more inclusive environment.


Alessandra Quigley
------------------

*Columbia University*

Setting sail on I09N has been an incredible adventure. As a
biophysical modeller working on drivers and impacts of marine
extremes, it was exciting to actually go to sea and experience the
data collection process myself. On the *Thompson*, I was a CTD
watchstander; responsible for preparing the rosette, monitoring and
controlling its descent via the winch operator, and collecting water
samples at various depths. There proved to be a learning curve,
especially with (unexpectedly) no other watchstanders on my shift, and
at times the 12 hour shift was a test of stamina. But I was rewarded
richly with sightings of manta rays, spinner dolphins, flying fish,
and some of the best stars I’ve ever seen. Thank you to the crew, who
supplied me with ginger tea and a bucket I could carry around while I
was seasick; and to my coworkers, who let me take breaks when nature
called. I wanted to find out if I enjoy this type of work, and I found
out I don’t. But this has been an immense learning experience, and I
am incredibly grateful for the opportunity.


Genevieve Clow
--------------

*University of Colorado-Boulder*

I’m grateful for the opportunity to have joined the I09N GO-SHIP
cruise as a CTD watchstander. My responsibilities included preparing
the rosette for deployment, monitoring the sensor data on the
downcast, and firing bottles at specified depths on the upcast. In
addition to these duties, I sampled ^13C isotopes and assisted with
sampling salts and other isotopes.

This was both my first extended time at sea and my first fieldwork
experience. I enjoyed spending time on the ocean, which I love but
rarely get to visit. I’m currently a graduate student at the
University of Colorado Boulder, where I study marine biogeochemistry
using Earth system models and satellite observations. I wanted to gain
hands-on field experience before graduating, and I’m grateful that I
had the chance to do so. I’ve learned a ton and broadened my
perspective as an oceanographer. I now have a greater appreciation for
the effort that it takes for every single sample to be collected and
analyzed. Additionally, I witnessed the immense coordination,
teamwork, and perseverance required for a successful research cruise.
I’ve been continually impressed by the work ethic and endurance of
every member of the team. Working 12-hour shifts for 40 days straight
is challenging—especially while living in an unfamiliar environment,
far from home.

I would like to thank the ship’s crew for their tireless work in
supporting the science and making the ship a comfortable home for our
time at sea. I’m also incredibly grateful to the science team,
especially my night shift colleagues. Special thanks to our co-chief
scientist, Leah, who led the night shift and patiently showed me the
ropes. Thanks to Leah, Allen, and John for sharing their CTD wisdom. I
was also lucky to work alongside fellow CTD watchstander Roxanne Mina,
who was an outstanding co-worker and friend. Thank you all so much!


Ilmar Leimann
-------------

*University of Bremen & MARUM, Germany*

Participating in the 2025 GO-SHIP I09N Indian Ocean cruise aboard the
R/V Thomas G. Thompson was an incredible opportunity to engage
firsthand with oceanographic research beyond the desk and into the
open sea. My primary responsibility on the cruise was managing the
LADCP (Lowered Acoustic Doppler Current Profiler), a vital instrument
used to measure velocity profiles throughout the water column during
CTD casts. Before each deployment, I ensured the instrument was
correctly configured, powered, and securely mounted to the CTD
rosette. After recovery, I downloaded and processed the data, working
closely with the science team to assess data quality and troubleshoot
the occasional surprises. As I quickly learned, LADCPs are a bit like
cats—sometimes temperamental, and occasionally only cooperative after
a snack and some patience.

Beyond the science, the Indian Ocean offered us unforgettable
moments—fiery sunsets, mirror-calm mornings, and the kind of
brilliant, star-filled skies you only see in the middle of nowhere.

I’m incredibly grateful to the GO-SHIP team, the crew of the R/V
Thomas G. Thompson, and especially to Andreas Thurnherr for the LADCP
training both on land and at port, as well as for his continued
support throughout the cruise. I also want to thank my fellow
shipmates for their camaraderie, humor, and dedication. This
experience has reinforced my passion for oceanography—not just as a
theoretical pursuit, but as something dynamic, hands-on, and full of
discovery. It’s hard to explain to someone back home just how exciting
it is to watch real-time velocity data scroll across the screen while
the ship gently rocks beneath your feet—it’s something you simply have
to experience for yourself to know whether you’ll love it or not.


Mary Kate (MK) Dinneen
----------------------

*University of Southern California*

When I learned about the opportunity to study CFCs, N_2O, and SF_6
through shipboard analyses in the Bay of Bengal, I was thrilled for a
long stint at sea learning an entirely new analysis method. I
typically study metals, specifically Fe(II), which involves a
completely different method of analysis - although iron, like CFCs, is
gas sensitive, making the rush of sampling that much more exciting (no
sarcasm intended, it really is quite fun). I honed in skills that I
didn’t realize were weak, such as laboratory plumbing. Working with
gas lines and mass flow controllers for experiments in a lab on land
has often made me feel like a sort of plumber, but working with a gas
chromatograph system on a moving ship is the next level of plumbing,
and hopefully by the end of this cruise I will have earned my badge as
professional gas line plumber.

In addition to the skillbuilding opportunity of measuring CFCs, SF_6,
and N_2O at sea, I’ve also never been a part of such a routine and
thorough research transect. GO-SHIP runs a tight ship of 12-hour
shifts and around-the-clock 36-bottle (depth depending) casts. The
discipline required to maintain 12-hour shifts of sampling and
analyzing for over 30 days was an incredible opportunity for character
strengthening. Although I have to admit, I genuinely love the
communion and bustle of sampling, and the cold water from the deep
ocean is always a welcomed relief from the hot days at sea in the
Indian Ocean. Observing real data take shape is also such an
immediately gratifying experience that gives a boost of encouragement
and challenges the mind to ask questions of “how” and “why”.
Furthermore, the collaboration of various backgrounds on GO-SHIP
allowed me to gain various perspectives that I’m not typically exposed
to in my own trace metal discipline, allowing these “hows” and “whys”
to be both answered and expanded upon.

Since beginning my journey in the field of chemical oceanography I
have been enamored by unique chemical niches within our oceanic
systems. One such niche that I have built my PhD thesis around is low
oxygen regimes. The Bay of Bengal has been an exciting place to be
able to see these low oxygen features develop. I am also increasingly
fascinated by the interactions of physical and chemical signatures,
which this cruise fostered with the unique opportunity to see the
chemical signatures of water masses completely shift over distance.
Visually observing the Antarctic intermediate water mass dissipate
through dilution and age via firsthand experience of analyzing
remarkably shallow CFC features highlighted the innate cohesiveness of
chemical and physical oceanography. Although I have always had an
interest in the physical and chemical oceanographic disciplines, they
have often seemed distinct in objectives. This cruise has thus allowed
me to conceptualize how effortlessly they can be intertwined and how
we should resist ignoring one discipline for the sake of the other.

I’ve grown a tremendous appreciation for consensus data and research
through being a part of the I09N GO-SHIP transect, and I hope there
will be more opportunities to further explore and contribute to
consensus transects in the future.


Roxanne Mina
------------

*University of South Florida*

I told myself that I09N would be my last attempt to get on a GO-SHIP
cruise before focusing on school as an incoming graduate student. I
was initially accepted to join ARC01, then A16S, before postponements
and ship mechanical issues prevented both cruises from going forward.
I’m grateful to my past-self for going forward with my decision to
apply for the third time because I had a great experience being a CTD
Watchstander to support the I09N hydrographic cruise.

As a CTD Watchstander, my main role was to prepare the CTD-rosette
bottle system on deck, monitor the CTD and fire bottles at various
depths in the lab, and upon recovery, assist with water sampling. In
addition, I assisted with LADCP during the night shift, deployed a few
drifters, and helped sample a wide variety of parameters like salts,
isotopes, total alkalinity, dissolved organic carbon, and more. After
five weeks at sea, I’ve learned that observational oceanography is
more than just getting ready to sample the next station. With every
station, I was repeatedly reminded how much effort, coordination, and
teamwork it takes to monitor the global ocean.

Science at sea is not without its challenges. The computer lab is the
first to know when a problem occurs: unresponsive CTD, modulo errors,
cyclone-induced weather hold, faulty altimeter, and replacing just
about every part of the CTD-rosette bottle system. How do you react
when things don’t go according to plan? How do you choose to go
forward and solve each issue? Watching the experienced members solve
each issue gave me the optimism and belief that for every problem
there’s a solution. Outside of CTD issues, I also realized that when
the excitement of the cruise wears out and some days feel harder than
others, having a good science and ship makes a huge difference. The
people who are communicators, collaborators, and team players are the
ones who make the work more enjoyable and the difficult days a little
easier.

Now that the cruise is over and the job is done, I can see myself
going out onto another oceanographic cruise in the future. I’m
thankful for the many people that I met, especially our chief and co-
chief scientist Leah and Viviane for making me feel welcome and
supported throughout the ~40 days on board. Science at sea requires
people who are not only dedicated to every station we sample and every
sample we collect. Despite our initial challenges, I’m proud of the
work that was done and the future research that will be possible as a
result of this cruise. I plan to take the lessons I learned forward
into my future interests and career. I would love to go on another
oceanographic cruise with GO-SHIP or with another program. This was a
positive experience and I can see myself being in a career within
observational oceanography.
