Cruise Report for the 2021 Reoccupation of A20
**********************************************


GO-SHIP A20 2021 Hydrographic Program
=====================================


Cruise Scientific Objectives
----------------------------

Ryan Woosley

Complex oceanic responses to climate change can only be characterized
with regular repeat high-quality shipboard measurements of climate-
relevant ocean properties. GO-SHIP repeat transoceanic surveys
(www.goship.org) provide full water column hydrographic observations
with temporal and spatial resolutions adequate to resolve decadal
variability in oceanic storage of heat, freshwater, carbon, oxygen,
nutrients and transient tracers. Repeat hydrographic physical-
biogeochemical measurements nominally along 52° 20’N in the North
Atlantic Ocean enables scientists to better tackle important
unresolved aspects of the Atlantic Ocean’s response to decadal scale
variability and increases in both heat and carbon dioxide as a result
of anthropogenic activies. The U.S. GO-SHIP A20 2021 hydrographic
section revisited this line for the fourth time, with prior transects
occurring in 1997, 2003, and 2012. Temperature, salinity, and velocity
measurements from A20 2021 reveal how the heat content of deep and
bottom waters in the North Atlantic have changes over the last 24
years. A20 2021 measurements of oxygen, nutrients, transient tracers,
and dissolved inorganic carbon allow quantifying the anthropogenic
component in the total inventory changes of surface and deep waters.
Combined carbon and current measurements from the repeat A20 line are
used to determine rates of regional carbon accumulation and exchange
with adjacent circulations. The overarching achievement of GO-SHIP A20
2021 measurements was the reoccupation of 90 full-depth CTD stations
and the collection of water samples at different levels with 36 Niskin
bottles. Measured temperature, salinity, pressure, oxygen,
fluorometry, shear and micro-scale temperature,and the major
nutrients, oxygen, salinity, CFC and carbon components (total
dissolved inorganic carbon, total alkalinity, pH, and fugacity of CO2)
were discretely analyzed on board. Measurements of dissolved organic
carbon, nitrate isotopes, radiocarbon, and Sargassum seaweed samples
were collected and will be measured in laboratories on shore. Core
Argo and BGC-Argo floats along with SOFAR drifters were also deployed,
generally after a CTD cast while leaving station.

   [image]Cruise track and station locations. The lack of cruise track
   between the last station and the end port of St. Thomas, USVI is
   due to the ship science data logger being turned off after the last
   station since the ship would enter Surinamese waters shortly after
   departing.


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

+---------------------------+---------------------------+---------------------------+---------------------------+
| Program                   | Affiliation               | Principal Investigator    | Email                     |
|===========================|===========================|===========================|===========================|
| *CTDO* Data, Salinity,    | *UCSD*, *SIO*             | Susan Becker, Jim Swift   | sbecker@ucsd.edu,         |
| Nutrients, Dissolved O_2  |                           |                           | jswift@ucsd.edu           |
+---------------------------+---------------------------+---------------------------+---------------------------+
| Total CO_2 (DIC)          | *AOML*, *PMEL*, *NOAA*    | Richard Feely, Rik        | richard.a.feely@noaa.gov, |
|                           |                           | Wanninkhof                | Rik.Wanninkhof@noaa.gov   |
+---------------------------+---------------------------+---------------------------+---------------------------+
| Underway Temperature,     | *PMEL*, *NOAA*            | Simone Alin               | simone.r.alin@noaa.gov    |
| Salinity, and pCO_2       |                           |                           |                           |
+---------------------------+---------------------------+---------------------------+---------------------------+
| Total Alkalinity, pH      | *SIO*, *RSMAS*            | Andrew Dickson, Frank     | adickson@ucsd.edu,        |
|                           |                           | Millero                   | fmillero@rsmas.miami.edu  |
+---------------------------+---------------------------+---------------------------+---------------------------+
| Discrete pCO_2            | *PMEL*, *NOAA*            | Rik Wanninkhof            | Rik.Wanninkhof@noaa.gov   |
+---------------------------+---------------------------+---------------------------+---------------------------+
| *SADCP*                   | *UH*                      | Eric Firing               | efiring@soest.hawaii.edu  |
+---------------------------+---------------------------+---------------------------+---------------------------+
| *LADCP*                   | *LDEO*                    | Andreas Thurnherr         | ant@ldeo.columbia.edu     |
+---------------------------+---------------------------+---------------------------+---------------------------+
| *CFCs*, *SF6*, *N2O*      | *UW*                      | Mark Warner               | warner@u.washington.edu   |
+---------------------------+---------------------------+---------------------------+---------------------------+
| *DOC*, *TDN*              | *RSMAS*                   | Dennis Hansell            | dhansell@rsmas.miami.edu  |
+---------------------------+---------------------------+---------------------------+---------------------------+
| Microgels                 | *RSMAS*                   | Dennis Hansell            | dhansell@rsmas.miami.edu  |
+---------------------------+---------------------------+---------------------------+---------------------------+
| C13 & C14                 | *UW*, *WHOI*              | Rolf Sonnerup, Roberta    | rolf@uw.edu,              |
|                           |                           | Hansman                   | rhansman@whoi.edu         |
+---------------------------+---------------------------+---------------------------+---------------------------+
| Transmissometry           | *TAMU*                    | Wilf Gardner              | wgardner@ocean.tamu.edu   |
+---------------------------+---------------------------+---------------------------+---------------------------+
| Chipod                    | *OSU*                     | Jonathan Nash             | nash@coas.oregonstate.edu |
+---------------------------+---------------------------+---------------------------+---------------------------+
| Argo Floats               | *WHOI*                    | Susan Wijffels, Steven    | swijffels@whoi.edu,       |
|                           |                           | Jayne, Pelle Robbins      | sjayne@whoi.edu,          |
|                           |                           |                           | probbins@whoi.edu.        |
+---------------------------+---------------------------+---------------------------+---------------------------+
| BGC Floats                | *MBARI*, *UW*,            | Kenneth Johnson, Steven   | johnson@mbari.org,        |
|                           | *Princeton*, *SIO*,       | Riser, Jorge Sarmiento,   | riser@uw.edu,             |
|                           | *WHOI*                    | Lynne Talley, Susan       | jls@princeton.edu,        |
|                           |                           | Wijffels                  | ltalley@ucsd.edu,         |
|                           |                           |                           | swijffels@whoi.edu        |
+---------------------------+---------------------------+---------------------------+---------------------------+
| Nitrate isotopes          | *Princeton*               | Daniel Sigman             | sigman@princeton.edu      |
+---------------------------+---------------------------+---------------------------+---------------------------+
| Spotter drifters          | Sofar Ocean               | Cameron Dunning           | cameron@sofarocean.com    |
+---------------------------+---------------------------+---------------------------+---------------------------+
| Sargassum                 | *WHOI*                    | Dennis McGillicuddy       | dmcgillicuddy@whoi.edu    |
+---------------------------+---------------------------+---------------------------+---------------------------+


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

+---------------------------+---------------------------+---------------------------+---------------------------+
| Duty                      | Name                      | Affiliation               | Email Address             |
|===========================|===========================|===========================|===========================|
| Chief Scientist           | Ryan Woosley              | *MIT*                     | rwoosley@mit.edu          |
+---------------------------+---------------------------+---------------------------+---------------------------+
| Co-Chief Scientist, LADCP | Andreas Thurnherr         | *LDEO*                    | ant@ldeo.columbia.edu     |
+---------------------------+---------------------------+---------------------------+---------------------------+
| CTD Watchstander          | Elena Perez               | *WHOI*                    | eperez@whoi.edu           |
+---------------------------+---------------------------+---------------------------+---------------------------+
| CTD Watchstander          | Cassondra Defoor          | *UNR*                     | cdefoor@nevada.unr.edu    |
+---------------------------+---------------------------+---------------------------+---------------------------+
| CTD Watchstander          | Paige Hoel                | *UCLA*                    | paigehoel@atmos.ucla.edu  |
+---------------------------+---------------------------+---------------------------+---------------------------+
| CTD Watchstander          | Francesca Alatorre        | *UCSC*                    | falatorr@ucsc.edu         |
+---------------------------+---------------------------+---------------------------+---------------------------+
| Nutrients, *ODF*          | Susan Becker              | *UCSD* *ODF*              | sbecker@ucsd.edu          |
| supervisor                |                           |                           |                           |
+---------------------------+---------------------------+---------------------------+---------------------------+
| Nutrients                 | Alexandra Fine            | *NOAA*                    | alexandra.fine@noaa.gov   |
+---------------------------+---------------------------+---------------------------+---------------------------+
| CTDO Processing           | Michael Kovatch           | *UCSD* *ODF*              | mkovatch@ucsd.edu         |
+---------------------------+---------------------------+---------------------------+---------------------------+
| Salts, ET, CTD/Rosette    | John Calderwood           | *UCSD* *SEG*              | jcalderwood@ucsd.edu      |
| Maintenance               |                           |                           |                           |
+---------------------------+---------------------------+---------------------------+---------------------------+
| Salts, CTD/Rosette        | Patrick A’Hearn           | *TAMU*                    | pnahearn@gmail.com        |
| Maintenance               |                           |                           |                           |
+---------------------------+---------------------------+---------------------------+---------------------------+
| Dissolved O_2, Database   | Andrew Barna              | *UCSD* *ODF*              | abarna@ucsd.edu           |
| Management                |                           |                           |                           |
+---------------------------+---------------------------+---------------------------+---------------------------+
| Dissolved O_2             | Robert Freiberger         | *UCSD*                    | rfreiberger@ucsd.edu      |
+---------------------------+---------------------------+---------------------------+---------------------------+
| *DIC*, underway pCO2      | Andrew Collins            | *UW*                      | andrew.collins@noaa.gov   |
+---------------------------+---------------------------+---------------------------+---------------------------+
| *DIC*                     | Charles Featherstone      | *NOAA*                    | charles.featherstone@noa  |
|                           |                           |                           | a.gov                     |
+---------------------------+---------------------------+---------------------------+---------------------------+
| Discrete pCO_2            | Patrick Mears             | *U Miami*                 | patrick.mears@noaa.gov    |
+---------------------------+---------------------------+---------------------------+---------------------------+
| *CFCs*, SF6               | Mark Warner               | *UW*                      | warner@u.washington.edu   |
+---------------------------+---------------------------+---------------------------+---------------------------+
| *CFCs*, SF6               | Rolf Sonnerup             | *UW*                      | rolf@uw.edu               |
+---------------------------+---------------------------+---------------------------+---------------------------+
| *CFCs*, SF6 student       | Carla Mejías-Rivera       | *U Puerto Rico*           | clmejiasrivera@gmail.com  |
+---------------------------+---------------------------+---------------------------+---------------------------+
| pH, Total Alkalinity      | Manuel Belmonte           | *UCSD*                    | mbelmont@ucsd.edu         |
+---------------------------+---------------------------+---------------------------+---------------------------+
| pH, Total Alkalinity      | Daniela Nestory           | *UCSD*                    | dnestory@ucsd.edu         |
+---------------------------+---------------------------+---------------------------+---------------------------+
| pH, Total Alkalinity      | Carmen Rodriguez          | *U Miami*                 | crodriguez@rsmas.miami.e  |
|                           |                           |                           | du                        |
+---------------------------+---------------------------+---------------------------+---------------------------+
| pH, Total Alkalinity      | Albert Ortiz              | *U Miami*                 | albert.ortiz@rsmas.miami  |
|                           |                           |                           | .edu                      |
+---------------------------+---------------------------+---------------------------+---------------------------+
| *DOC*, *TDN*              | Abigail Tinari            | *U Miami*                 | abigail.tinari@rsmas.mia  |
|                           |                           |                           | mi.edu                    |
+---------------------------+---------------------------+---------------------------+---------------------------+
| Indep/Nurse               | Lauren Elium              | Other                     | n/a                       |
+---------------------------+---------------------------+---------------------------+---------------------------+
| Marine Technician         | Stephen Jalickee          | *UW*                      | jalickee@uw.edu           |
+---------------------------+---------------------------+---------------------------+---------------------------+
| Marine Technician         | Elizabeth Ricci           | *UW*                      | ericci@uw.edu             |
+---------------------------+---------------------------+---------------------------+---------------------------+


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

The 2021 A20 cruise is the fourth occupation of the line, nominally
52º 20’ N, formally occupied as part of WOCE in 1997 and reoccupied in
2003 and 2012. A CTD transect of the line was also conducted in 1983.
This occupation closely followed the 2012 GO-SHIP occupation except
for an eastward shift of ~0.5 – 4 nm of the South American continental
shelf stations (75 – 90) due to a slight change in the French Guiana
EEZ in 2018. The original WOCE occupation had continental shelf and
slope stations in the Suriname rather than French Guiana EEZ. A total
of 98 stations were planned and a total of 90 were actually occupied.
Unlike in 2012, the transect was conducted from north to south, as was
done in 1997 and 2003. The March – April timing was slightly different
than the April – May timing of the 2012 occupation, compared to July –
August in 1997 and October – September in 2003. The full suite of core
GO-SHIP chemical and physical parameters were measured (as described
in the following sections) and will be compared to prior occupations
for analysis of decadal scale changes covering 24 years.

The cruise departed Woods Hole, Massachusetts at 13:00 on March 16,
2021, after a four-day mobilization beginning on March 12. Due to the
ongoing COVID-19 pandemic all participants were required to self-
isolate for 14 days before boarding and receive two negative COVID
tests prior to boarding. Those based in Florida were able to do their
self-isolation there and board in Port Everglades, FL to avoid the
risks of air travel. Once on-board, participants were not allowed to
leave until arrival in St. Thomas, or back in Woods Hole for those
also participating in A22. Mask wearing and social distancing was
practiced as required by Coast Guard rules. Also, to reduce the risks
of ocean research during a pandemic the number of science crew was
kept to a minimum. Therefore, ancillary measurements which required an
additional berth were not allowed. The smaller than normal science
crew did present some challenges, as there were fewer extra helping
hands than usual.

The station plan followed the 2012 stations closely, especially near
the Grand Banks across the continental slope and shelf, as well as on
the South American continental rise where tight station spacing (10
–13 nm) was maintained in water depths of up to 4900 m. Such tight
spacing off of South America allowed for resolution of the Deep
Western Boundary Current (DWBC) and the Guiana recirculation. Station
resolution in the interior, deep, portion of the section was higher
than that achieved in 2012. South of the continental shelf and slope
of the Grand Banks (southeast of Newfoundland) 30 nm spacing was
maintained between ~39 – 41º N (stations 16 – 21) which included
crossing of the Gulf Stream, located near 40º N during our occupation.
The location of the Gulf Stream was further north than it was in 2012
(between 38 and 39º N). Altimetry and sea surface temperature data
indicate that the Gulf Stream had migrated slightly northward in the
month proceeding this occupation. A storm awaited us at the first
station causing a 24-hour delay to the beginning of science
operations. Between 38º 33.36’ N and 35º 13.32’ N (stations 22 – 26)
spacing was widened to 40 nm both to allow us to make up some of the
time lost to weather, and also to avoid a large storm moving across
the North Atlantic. The storm avoidance was successful and station
spacing was narrowed to 35 nm from 35º 13.32’ N to 10º 8.34’N
(stations 27 – 69), at which point the South American rise was reached
and station spacing tightened to follow the same spacing as in 2012.
After the storm encountered at the first station, winds calmed down
over the first few days of scientific operations and warm calm weather
graced the remainder of the cruise.


Physical Oceanography
---------------------

After a 1500-m-deep shakedown profile (station number 900) was
collected at 41º 00.4’ N  66º 14.4’ W, the vessel proceeded to the
first station of the section at 43º 06.3’ N 50º 43.9’ W. Sampling
commenced on March 21, proceeding SSW-ward down the continental slope
before turning southward at station 16. On stations 1-7 the upper 200m
of the water column was comprised of cold Labrador Sea coastal water
with temperatures below 3 degrees flowing predominantly eastward over
the shelf break (stations 2-6) and northward on station 7 (Figures 1
and 2). The velocity field over the slope was complex and both
horizontally and vertically sheared with evidence for eddy motion over
the upper slope. Between 2000 m and 4500 m the density measurements
show an approximately 200-m-thick boundary current carrying North
Atlantic Deep Water (NADW) westward along the slope beneath a
spatially variable current field. Between stations 9 and 19, the
velocities above 3000 m are consistent with the “strong Northern
Recirculation Gyre (NRG)” described in the cruise report of the
previous occupation of this section [McCartney2012]. Below 3000 m,
there were alternating currents with both east and westward flow
likely affected by the topography. Westward zonal flow in the southern
limb of the NRG (stations 18-19) extended across the full water
column, consistent with the inferred forcing by the Gulf Stream, which
dominated the currents on stations 20-22.

   [image]Zonal velocity in the northern part of the section from the
   LADCP measurements; contours show arbitrarily spaced sigma-2
   surfaces from the CTD data.

   [image]Meridional velocity in the northern part of the section from
   the LADCP measurements; contours show arbitrarily spaced sigma-2
   surfaces from the CTD data.

South of the Gulf Stream the cross-sectional (i.e. zonal) currents in
the upper 1000 m show alternating bands with west- and eastward flow
components extending all across the basin interior well into the
tropics (figure 3). At greater depths the currents along the base of
the flank of the Mid-Atlantic Ridge (MAR) that is corrugated by
Fracture Zone valleys are both weaker and without clear spatial
patterns, except for an apparent anticyclonic circulation around and
above the Corner Seamounts near 36º N. South of about 32º N there is
evidence (figure 4) for the topographic roughness of the MAR to
elevate the energy in the high-frequency internal-wave field, which is
closely related to turbulence and mixing.

   [image]Zonal velocity along the entire section from the LADCP
   measurements; contours show arbitrarily spaced sigma-2 surfaces
   from the CTD data. The data gap at depth between 24 and 32N is
   caused by insufficient acoustic backscatter contaminating the LADCP
   velocities.

   [image]Vertical kinetic energy from the LADCP-derived vertical
   velocity measurements scaled into units of dissipation of turbulent
   kinetic energy [Thurnherr2015]; contours and data gap as in Figure
   3.

South of ~15º N the Mid-Atlantic Ridge trends southeastward and the
remainder of the section crosses a smooth abyssal plain before
encountering the base of the South American continental slope of the
Demerara Plateau on station 76 (figure 5). The zonal currents over the
abyssal plain were meridionally banded and mostly spanned the full
ocean depth. Over the continental slope the currents were complex and
vertically sheared. The strong eastward flow below 2000 m over the
lower slope (stations 76-79) is part of the DWBC carrying NADW along
the American continent into the South Atlantic [Johns1993]. In the
2012 occupation of A20, eastward flow along this slope extended all
the way up to about 1000m [McCartney2012] but during our occupation an
anticyclonic eddy occupied the water column between 1000 and 2000 m
extending out to about 10º N. Between 200 and 1000 m all LADCP data
collected in 2003, 2012 as well as in our occupation show a meridional
dipole structure with westward flow banked against the slope and
eastward flow further offshore, also extending to 10º N. In the upper
200 m of the water column, the North Brazil Current is flowing
westward along the shelf break. In our data as well as in the 2003
occupation the North Brazil Current is bounded offshore by a strong
eastward current, which could be its retroflection or, alternatively,
a Brazil Current Ring. (In 2012 the North Brazil Current was similar
to our observations but there was no eastward flow further offshore.)

   [image]Zonal velocity in the southern part of the section from the
   LADCP measurements; contours show arbitrarily spaced sigma-2
   surfaces from the CTD data.

Similar to the observations in 2012 (McCartney et al., 2012) we
encountered the Amazon River Plume extending a considerable distance
off the shelf break. In our observations (figure 6) this freshwater
plume is limited to depths shallower than 10m, with the fresh water at
the offshore edge of the plume (~100 km from the shelf break; station
80) extending no further than 80 cm below the sea surface. (The 10-30
cm thick almost completely fresh layers very close to the surface in
profiles 82, 88 and 89 are likely caused by rainfall.)

   [image]CTD-derived salinity profiles close to the sea surface at
   the end of the upcasts, derived from specially processed 24-Hz
   data.


Chemical Oceanography
---------------------

The distribution of basic chemical and physical parameters were very
similar to those of prior occupations in the deep water. The early
March timing of this occupation explains the generally colder surface
waters compared to 2012. The difference was most noticeable in the
northern portion of the section over the Grand Banks, which were
generally ~5ºC colder in 2021 compared to 2012. The deeper winter
mixing was also obvious by the deeper penetration of high oxygen, and
fresher, lower total alkalinity waters over the continental shelf and
rise.

The slightly more northern location of the Gulf Steam in 2021 leads to
significantly different structure to the chemical and physical
properties between ~38 – 40ºN and must be accounted for when comparing
the different occupations. The oxygen minimum between ~30 – 40ºN
appears to be slightly deeper in 2021 as evidenced by a slight shift
in the density structure in the upper water column. The shift is also
clearly visible in the inorganic carbon parameters.

The upper 1000 m shows a general increase in dissolved inorganic
carbon (DIC) of ~20 µmol/kg since 2012 with a corresponding decrease
in pH. The increase in DIC is consistent with the increasing CO_2
content of the atmosphere due to anthropogenic activities. The near
constant salinity normalized total alkalinity (TA) further supports
the anthropogenic cause of increased DIC and decreased pH. There is
also an area of increased DIC (~10 µmol/kg) compared to 2003 at around
1500 m consistent with Labrador Sea Water as identified in the 2012
occupation [Woosley2016].

The outflow from the Amazon River can clearly be seen as a thin plume
of freshwater in the upper ~10 m at the southernmost portion of the
section. In 2012 the plume extended unusually far north (to about 11º
N). In this occupation the plume was clearly marked by a drop in
surface salinity to < 30 at ~ 7.8º N. Although the plume did not
extend as far north, it was slightly fresher this occupation compared
to 2012.

[Johns1993] Johns, W. E., D. M. Fratantoni, and R. J. Zantopp (1993),
            Deep western boundary current variability off northeastern
            Brazil, Deep-Sea Research, 40(2), doi:
            10.1016/0967-0637(93)90005-N.

[McCartney2012] McCartney,  M. (2012) US Global Ocean Carbon and
                Repeat Hydrography Program Section CLIVAR A20 RV
                Atlantis AT20

[Thurnherr2015] Thurnherr, A. M., E. Kunze, J. M. Toole, L. St.
                Laurent, K. J. Richards, and A. Ruiz-Angulo (2015).
                Vertical kinetic energy and turbulent dissipation in
                the ocean. Geophys. Res. Lett. 42, 7639–7647.

[Woosley2016] Woosley, R. J., F. J. Millero, and R. Wanninkhof (2016),
              Rapid anthropogenic changes in CO2 and pH in the
              Atlantic Ocean: 2003–2014, Global  Biogeochem. Cycles,
              30, doi:10.1002/2015GB005248.


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

For A20-2021 the new STS 36 place yellow rosette and bottles, built in
2017, were used. The rosette and bottles were built before P06 2017,
making this the fifth time this package has been deployed. The bottles
were made with new PVC, with new non-baked o-rings and electro-
polished steel springs. This represents a change from the past, where
on GO-SHIP cruises using ODF equipment before P06 2017 o-rings were
baked for 3 days at 100°C at 1-3 Torr in a sweeper gas of hydrogen.
Springs used to be painted and Tygon tubing added to the ends to
prevent paint wearing away from bottle firing. As on P06 2017 no
sample contamination has been noticed by the change in o-rings and
springs. The package used on A20-2021 weighs roughly 1500 lbs in air
without water, and 2350 lbs in air with water. The package used on
A20-2021 weighs roughly 950 lbs in water. In addition to the standard
CTDO package on GO-SHIP cruises three chipods, two LADCPs, and one
experimental CTD were mounted on the rosette. During the cruise we
encountered a handful of problems, most notably noisy altimeter data
and bottle firing issues. We describe all of the above in more detail
in the sections below.


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

CTDO/rosette/LADCP/chipod casts were performed with a package
consisting of a 36 bottle rosette frame, a 36-place carousel and 36
Bullister style Niskin bottles with an absolute volume of 10.6L.
Underwater electronic components primarily consisted of a SeaBird
Electronics housing unit with Paroscientific pressure sensor with dual
plumbed lines where each line has a pump, temperature sensor,
conductivity sensor, and exhaust line. A SeaBird Electronics membrane
oxygen sensor was mounted on the “primary” line. A reference
thermometer, Rinko oxygen optode, transmissometer, chlorophyll-a
fluorometer, and altimeter were also mounted on the rosette. Chipod
and LADCP instruments were deployed with the CTD/rosette package and
their use is outlined in sections of this document specific to their
titled analysis.

CTD and cage were horizontally mounted at the bottom of the rosette
frame, located below the carousel for all stations. The temperature,
conductivity, dissolved oxygen, respective pumps and exhaust tubing
was mounted to the CTD and cage housing as recommended by SBE. The
reference temperature sensor was mounted between the primary and
secondary temperature sensors at the same level as the intake tubes
for the exhaust lines. The transmissometer was mounted horizontally on
the lower LADCP brace with hose clamps around both of its ends,
avoiding shiny metal or black tape inside that would introduce noise
in the signal. The oxygen optode, fluorometer, and altimeter were
mounted vertically inside the bottom ring of the rosette frames, with
nothing obstructing their line of sight. The 150 KHz bi-directional
Broadband LADCP (RDI) unit was mounted vertically on the bottom side
of the frame. The 150 Khz LADCP was later replaced with a 300 Khz
LADCP during the cruise in the same position. The 300 KHz bi-
directional Broadband LADCP (RDI) unit was mounted vertically on the
top side of the frame. The LADCP battery pack was also mounted on the
bottom of the frame. The LADCP and LADCP battery pack were mounted
next to each other at the beginning of the cruise. If we imagine the
LADCP battery being north on the rosette, the LADCP was mounted east,
and the CTD mounted south.

+------------------+------------------+------------------+------------------+------------------+------------------+
| Equipment        | Model            | S/N              | Cal Date         | Stations         | Group            |
|==================|==================|==================|==================|==================|==================|
| Rosette          | 36-place         | Yellow           | –                | 901-90           | *STS*/*ODF*      |
+------------------+------------------+------------------+------------------+------------------+------------------+
| CTD              | SBE9+            | 0914             | –                | 901-90           | *STS*/*ODF*      |
+------------------+------------------+------------------+------------------+------------------+------------------+
| Pressure Sensor  | Digiquartz       | 110547           | Feb 5, 2021      | 901-90           | *STS*/*ODF*      |
+------------------+------------------+------------------+------------------+------------------+------------------+
| Primary          | SBE3+            | 32309            | Feb 2, 2021      | 901-90           | *STS*/*ODF*      |
| Temperature      |                  |                  |                  |                  |                  |
+------------------+------------------+------------------+------------------+------------------+------------------+
| Primary          | SBE4C            | 43399            | Nov 25, 2020     | 901-90           | *STS*/*ODF*      |
| Conductivity     |                  |                  |                  |                  |                  |
+------------------+------------------+------------------+------------------+------------------+------------------+
| Primary Pump     | SBE5             | 51871            | –                | 901-90           | *UCSD*           |
+------------------+------------------+------------------+------------------+------------------+------------------+
| Secondary        | SBE3+            | 32380            | Feb 2, 2021      | 901-90           | *STS*/*ODF*      |
| Temperature      |                  |                  |                  |                  |                  |
+------------------+------------------+------------------+------------------+------------------+------------------+
| Secondary        | SBE4C            | 41880            | Dec 4, 2020      | 901-90           | *STS*/*ODF*      |
| Conductivity     |                  |                  |                  |                  |                  |
+------------------+------------------+------------------+------------------+------------------+------------------+
| Secondary Pump   | SBE5             | 58690            | –                | 901-90           | *UCSD*           |
+------------------+------------------+------------------+------------------+------------------+------------------+
| Transmissometer  | Cstar            | 1803DR           | Aug 9, 2019      | 901-90           | *TAMU*           |
+------------------+------------------+------------------+------------------+------------------+------------------+
| Fluorometer      | WetLabs ECO-FL-  | 1156             | –                | 901-90           | *STS*/*ODF*      |
| Chlorophyll      | RTD              |                  |                  |                  |                  |
+------------------+------------------+------------------+------------------+------------------+------------------+
| Primary          | SBE43            | 431138           | Dec 5, 2020      | 901              | *ODF*            |
| Dissolved Oxygen |                  |                  |                  |                  |                  |
+------------------+------------------+------------------+------------------+------------------+------------------+
| Primary          | SBE43            | 430275           | Nov 14, 2020     | 1-14             | *ODF*            |
| Dissolved Oxygen |                  |                  |                  |                  |                  |
+------------------+------------------+------------------+------------------+------------------+------------------+
| Primary          | SBE43            | 430255           | Nov 13, 2020     | 15-90            | *ODF*            |
| Dissolved Oxygen |                  |                  |                  |                  |                  |
+------------------+------------------+------------------+------------------+------------------+------------------+
| Oxygen Optode    | JFE Advantech    | 0297             | April 7, 2017    | 901-35, 41-46    | *ODF*            |
|                  | RINKO-III        |                  |                  |                  |                  |
+------------------+------------------+------------------+------------------+------------------+------------------+
| Oxygen Optode    | JFE Advantech    | 0296             | April 7, 2017    | 36-90            | *ODF*            |
|                  | RINKO-III        |                  |                  |                  |                  |
+------------------+------------------+------------------+------------------+------------------+------------------+
| Reference        | SBE35            | 0105             | Feb 9, 2021      | 901-90           | *STS*/*ODF*      |
| Temperature      |                  |                  |                  |                  |                  |
+------------------+------------------+------------------+------------------+------------------+------------------+
| Carousel         | SBE32            | 1178             | –                | 901-14           | *STS*/*ODF*      |
+------------------+------------------+------------------+------------------+------------------+------------------+
| Carousel         | SBE32            | 0187             | –                | 15-90            | *STS*/*ODF*      |
+------------------+------------------+------------------+------------------+------------------+------------------+
| Altimeter        | Valeport 500     | 59116            | –                | 901-15           | *UCSD*           |
+------------------+------------------+------------------+------------------+------------------+------------------+
| Altimeter        | Valeport 500     | 53821            | –                | 16-36, 39-90     | *UCSD*           |
+------------------+------------------+------------------+------------------+------------------+------------------+
| Altimeter        | Valeport 500     | 67356            | –                | 37               | *UW*             |
+------------------+------------------+------------------+------------------+------------------+------------------+
| Altimeter        | Valeport 500     | 67355            | –                | 38               | *UW*             |
+------------------+------------------+------------------+------------------+------------------+------------------+
| DL *LADCP*       | Teledyne RDI     | 19394            | –                | 1-17, 35-40      | *LDEO*           |
|                  | WH150            |                  |                  |                  |                  |
+------------------+------------------+------------------+------------------+------------------+------------------+
| DL *LADCP*       | Teledyne RDI     | 24497            | –                | 18-31, 40-90     | *LDEO*           |
|                  | WH300            |                  |                  |                  |                  |
+------------------+------------------+------------------+------------------+------------------+------------------+
| DL *LADCP*       | Nortek           | –                | –                | 901, 32-34       | *LDEO*           |
|                  | Signature100     |                  |                  |                  |                  |
+------------------+------------------+------------------+------------------+------------------+------------------+
| UL *LADCP*       | Teledyne RDI     | 12734            | –                | 901-90           | *LDEO*           |
|                  | WH300            |                  |                  |                  |                  |
+------------------+------------------+------------------+------------------+------------------+------------------+
| D2 CTD           | D2 CTD           | 02-1564          | –                | 901-36           | *WHOI*           |
+------------------+------------------+------------------+------------------+------------------+------------------+
| D2 CTD           | D2 CTD           | 02-1563          | –                | 37-90            | *WHOI*           |
+------------------+------------------+------------------+------------------+------------------+------------------+
| Chipods          | Chipod           | 2018 Ti44-2      | –                | 901-90           | *OSU*            |
+------------------+------------------+------------------+------------------+------------------+------------------+
| Chipods          | Chipod           | 2024 Ti44-7      | –                | 901-90           | *OSU*            |
+------------------+------------------+------------------+------------------+------------------+------------------+
| Chipods          | Chipod           | 2032 Ti44-15     | –                | 901-90           | *OSU*            |
+------------------+------------------+------------------+------------------+------------------+------------------+

   [image]Package sensor looking into the rosette from the south.

   [image]Package sensor setup from east.

   [image]Package sensor setup from north.

   [image]From left to right: oxygen optode, fluorometer, LADCP
   battery pack, altimeter.

   [image]Package setup from southwest, with CTD in foreground and
   downlooking chipod to the right.

   [image]Packaget setup from west

   [image]Package  setup from west, top view.


Winch and Deployment
--------------------

The aft DESH-5 winch deployment system was used for all stations. The
rosette system was suspended from a UNOLS-standard three-conductor
0.322” electro-mechanical sea cable. The sea cable was terminated at
the beginning of A20-2021, electrical retermination after station 9,
and full retermination after station 23.

The deck watch prepared the rosette 10-30 minutes prior to each cast.
The bottles were cocked and all valves, vents, and lanyards were
checked for proper orientation. Any biofouling noted was cleaned off
the outside of the rosette before the next cast, and the inside of the
bottles were checked for biofouling and sprayed down. LADCP technician
would check for LADCP battery charge, prepare instrument for data
acquisition, and disconnect cables. Once stopped on station, the
Marine Technician would check the sea state prior to cast and decide
if conditions were acceptable for deployment. The rosette was moved
from the sampling bay out to the deck using the Thompson’s new winch-
driven cart. Once on deck, the ratchet straps connecting the rosette
to the cart were removed and sea cable slack was pulled up by the
winch operator. CTD watch standers would then turn on the deckbox and
begin data acquistion, and the cast would begin. Recovering the
package at the end of the deployment was the reverse of launching.
Once rolled back into the sampling bay, the ship crew secured the cart
to the deck using additional ratchet straps. The carousel was rinsed
and sensors were cleaned (as described below) after every cast, and
then samplers were allowed to begin collecting water.


Maintenance and Calibrations
----------------------------

During A20-2021 routine maintenance was done to the rosette to ensure
quality of the science done. Actions taken included rinsing all
electrical instruments on the rosette down with fresh water after each
cast and adjusting hose clamps and guide rings as needed such that
lanyards had appropriate tension. Care was taken not to rinse the
spigots and other parts of the bottle that might be touched by
samplers in order to not contaminate the samples. After each cast,
syringes of fresh water were connected to the plumbed lines to rinse
the sensors and allow them to soak between casts. While in freezing
conditions, water was drained after rinse to avoid freezing in the
plumbing. Overhead heaters recently installed on the Thompson were run
while in freezing or near-freezing conditions. The rosette was
routinely examined for valve and o-ring leaks, which were maintained
as needed. SBE35RT temperature data was routinely downloaded each day.

Every 20 stations, the transmissometer windows were cleaned and on
deck blocked and un-blocked voltage readings were recorded prior to
the cast. The transmissometer was also calibrated before the start and
after the end of science operations.


Logs
----

In port: Preparation of the CTD and rosette took all but the first day
allocated in port, which was used for unloading the container and
setting up the labs. Additional integrity checks on the rosette, such
as checking lanyard angles, o-ring and lanyard replacement, and spigot
movement waited until being underway to be checked as lower priority
tasks. We are using a new mounting system for the downward looking
LADCP which has the LADCP clamped facing inward instead of outward,
which will cause problems if we need to change that LADCP in rough
weather.

March 17, 2021

90101 – Test cast down to 1500 m in 2020 m water depth. SBE43 oxygen
had noticeable near-surface spiking during both up and downcast. The
sensor is suspected to have frozen and was replaced. Variable
transmissometer data were observed at depth but were simply due to
loose electrical tape flapping in front of the beam path.

March 21, 2021

No problems noted for stations 00101-00801.

March 22, 2021

00801 – No problems noted.

00901 – During upcast, bottle 31 did not receive firing confirmation.
Attempted to manually fire from deck box but still did not receive any
confirmation. Upcast continued as normal, stopping and “firing”
bottles at target depths, but rosette was recovered with bottles 31-36
still open. Modulo errors started occuring after firing bottle 30,
with 17 total errors at depth and 2 additional during recovery. The
issue was found to be the electrical termination, which was done using
butt connectors with low-temperature solder. The ground wire had a
solid connection but the communcation wire connection separated after
applying tension. Communcation wire was re-connected using regular
solder.

01001 – Oxygen spike at ~2400 m.

March 23, 2021

01101 – SBE43 had normal behavior during downcast but erratic readings
started in the upper 25 m during upcast.

01201 – SBE43 data were spiky during soak, even after pumps were
activated. Spikiness continued while brought up to the surface before
normalizing during the downcast. No more spikes occurred until 15 m
from surface during upcast.

01301 – Similar to previous cast, spikiness was noted during soak and
down to 70 m. Downcast data were fine but two large spikes occurred at
~1950 and ~160 m during upcast, with spikiness again occurring near-
surface. All connections between 9+ and 43 were inspected and looked
okay (no spikes occurred in altimeter, which shared a Y-cable with the
SBE43). Straight cable from Y to SBE43 was replaced after cast. Bottle
12 did not close, bottle 36 fired on the fly.

01401 – SBE43 still spiky at surface and down to 80 m but “fuzziness”
of signal at depth seems improved with new cable. Sensor 43-0275 was
replaced with 43-0255, with the suspected issue being frozen sensor
membrane. Bottle 12 did not close again. Carousel changed out,
solenoid 12 was swollen.

01501 – New SBE43 data were significantly improved. Altimeter reading
during bottom approach was “stuck” at 20 m for longer than reasonable,
replaced S/N 59116 with 53821 after cast.

March 24, 2021

01601 – SBE43 oxygen “fuzziness” at depth has returned. New altimeter
appears to be functioning properly.

01701 – Botle 36 fired on the fly.

01801 – Multibeam depth estimate and altimeter not in agreement, CTD
got within 3 m of bottom. Multibeam software was updated with new
soundspeed profile, continue to regulary update after subsequent
casts. Heave compensation used after 400 m.

01901 – Bottle 28 closed itself on deck before deployment.

March 25, 2021

02001 – Strong Gulf Stream currents (2 m/s at surface), large wire
angle and far drift expected.

02101 – No problems noted.

March 26, 2021

02201 – No problems noted.

02301 – During recovery, new AB was training on winch and mistakenly
pulled wire in too fast and the Evergrip mechanical termination was
pulled into the block and became stuck (two-blocked). Ship crew used a
chain-fall and were able to safely pull the stuck termination from
block. Log of tension data recorded a maximum of 11,000 lbs, above the
nominal 10,000 lb breaking strength of the sea cable. 50 m of cable
was removed and re-termination was done during transit to next
station.

02401 – No problems noted.

March 27, 2021

02501 – No problems noted.

02601 – SeaSave failed to connect to water sampler, likely started
software too soon after turning on deck box.

02701 – No problems noted.

02801 – No problems noted.

March 28, 2021

02901 – During deployment, tagline became tangled on rosette and CTD.
Line was cut as rosette was mostly in the water. Recovered with
tagline still badly tangled. Chipod S/N 2024 sensor tip poking out of
its pressure case, both o-rings were exposed, and the interior was
full of water. Entire sensor and housing were replaced prior to next
cast.

03001 – No problems noted.

03101 – No problems noted.

March 29, 2021

03201 – No problems noted.

03301 – Erratic altimeter readings near bottom.

03401 – Erratic altimeter readings near bottom.

March 30, 2021

03501 – Erratic altimeter readings near bottom.

03601 – Rinko S/N 0297 was replaced with 0296 due to intermittent
spiking during casts. Upon recovery, D2 S/N 1564 spit out oil,
replaced with 1563 using same logger. Altimeter still erratic,
replaced Valeport 500 S/N 53821 with TGT’s 67356.

03701 – Altimeter S/N 67356 failed (was already bad?), replaced with
TGT’s 67355 which deck tested okay.

03801 – Altimeter was very noisy during bottom approach and then
became completely unreliable, reading 99.9 m despite being near
bottom. Cast was ended higher than normal to be safe, ~20 m. Swapped
back to ODF altimeter S/N 53821. Bottle 2 closed at wrong depth,
unclear if early or late.

April 1, 2021

04101 – Attached second Rinko (S/N 0297) in spare voltage channel,
mounted behind the replacement (S/N 0296) to compare data signals.
0297 data are much more spiky than 0296, with voltages completely
deviating on the upcast. End cap on 0297 may not have been removed
prior to cast. Altimeter was spiky at bottom but reliable enough to
get to 10 m from bottom.

04201 – Downlooking LADCP switched from 150 kHz to 300 kHz. Multibeam
continuing to be unreliable, CTD was 40 m from bottom before
watchstanders noticed. Proceeded to ~10 m from bottom, altimeter
working much better. Suspected there was interference with 150 kHz
possibly (though this has not been observed before by LADCP PI).
Plumbing on secondary T/C line was loose after cast, replaced with
spare/backup tubing.

04301 – Console “glitched” while attempting to fire bottle 30. Firing
confirmation was not received and interface reset next bottle to be
fired back to bottle 1. Students fired 1-6, assuming it was 31-36, at
the appropriate depths, but upon recovery bottles 31-36 were
open/unfired. Both the .bl file and reference thermometer have data
recorded for 31-36. No recording for 30 despite bottle being closed
upon recovery. SeaSave bottle firing settings updated to allow
changing next bottle, instead of purely sequential.

April 2, 2021

04401 – No problems noted.

04501 – Bottle 2 likely closed at wrong depth, unclear if early or
late. O_2 analyst recorded temperatures for bottles 1-3 as 8.0, 15.5,
and 8.3 ºC.

04601 – No problems noted.

April 3, 2021

04701 – No problems noted.

04801 – Bottle 2 likely closed at wrong depth, unclear if early or
late. O_2 analyst recorded temperatures for bottles 1-3 as 8.3, 14.6,
and 9.0 ºC.

04901 – No problems noted.

05001 – No problems noted.

April 4, 2021

No problems noted for stations 05101–05301.

April 5, 2021

05401 – No problems noted.

05501 – Bottle 2 possibly closed at wrong depth, unclear if early or
late. O_2 analyst recorded temperatures for bottles 1-3 as 7.6, 8.0,
and 7.8 ºC. Replaced the entire latch mechanism on the water sampler.

05601 – Bottle 10 did not close. During upcast NMEA time froze for
several seconds, ended up being ship problem of interference with
Iridium antenna (not a CTD problem).

05701 – No problems noted.

April 6, 2021

No problems noted for stations 05801–06101.

April 7, 2021

No problems noted for stations 06201–06501.

April 8, 2021

06601 – No problems noted.

06701 – Fired bottles 1, 4, 3, 2, then normal (to avoid continually
losing near-bottom depth, i.e., bottle 2).

06801 – Fired bottles 1, 4, 3, 2, then normal (to avoid continually
losing near-bottom depth, i.e., bottle 2).

April 9, 2021

06901 – Bottle 10 didn’t close, one chipod missing cap upon recovery.

07001 – No problems noted.

07101 – No problems noted.

April 10, 2021

07201 – Bottle 25 mistrip, temperatures for 24-26 were 14.5, 20.0,
15.8 ºC.

07301 – Bottle 2 mistrip again, temperatures 7.3, 23.2, and 8.0 ºC.

07401 – Fired bottles 1, 4, 3, 2, then normal (to avoid continually
losing near-bottom depth, i.e., bottle 2).

07501 – Fired bottles 1, 4, 3, 2, then normal (to avoid continually
losing near-bottom depth, i.e., bottle 2).

07601 – Getting bad SBE35RT readings in high gradient regions (16 ºC
change over ~200 m). Waiting for 1 minute prior to firing when
possible.

April 11, 2021

07701 – Fired bottles 1, 4, 3, 2, then normal (to avoid continually
losing near-bottom depth, i.e., bottle 2).

07801 – Fired bottles 1, 4, 3, 2, then normal (to avoid continually
losing near-bottom depth, i.e., bottle 2).

07901 – Fired bottles 1, 4, 3, 2, then normal (to avoid continually
losing near-bottom depth, i.e., bottle 2).

08001 – Fired bottles 2 and 3 at same depth for the remaining casts to
test for misfires (casts no longer deep enough to have 36 unique
bottles).

08101 – No problems noted.

April 12, 2021

08201 – Primary T/C line had large spike on downcast, likely
biofouling in plumbing which eventually flushed out. Using secondary
line for this cast.

08301 – No problems noted.

08401 – No problems noted.

08501 – No problems noted.

08601 – Strong surface currents, drifting slightly.

08701 – Strong surface currents, drifting slightly.

08801 – Strong surface currents, drifting slightly.

08901 – Bottle 8 misfired/dry fired in air after recovery.

09001 – No problems noted.


Sensor Problems
---------------

*Oxygen sensor spikiness:* The SBE 43 oxygen sensor showed erratic
spikiness that disappeared after the cast was below ~50-100 m, but
returned in the same depth range on the upcast. The suspicion is that
some/all of the sensors froze, either during transit or while sitting
in port, partially damaging but not completely ruining the internal
membrane. Under sufficient pressure, the issue “fixed” itself for the
duration of the cast. After swapping to the second spare, the issue
was resolved. Rinko optode data were also used as primary for station
36 onward.

*Altimeter spikiness:* Four separate altimeters were used over the
course of the cruise, two belonging to ODF and two belonging to TGT.
The first ODF one flooded, the second was noisy. After trying the two
owned by TGT, which were more noisy than the ODF spare, we swapped
back. All altimeters were reporting spiky data, occasionally to the
point of being unusable during the bottom approach (e.g. Fig 8,
station 38). Additionally, multibeam depth estimates were inaccurate
which caused further difficulty.

The multibeam issue was resolved by updating the sound speed profiles
periodically to have a more reliable depth estimate. The altimeter
issue was resolved after multiple changes to the rosette, including
swapping downlooking ADCPs (from 150 KHz to 300 KHz) and adding
additional rubber to increase the distance between the sensor and the
unistrut mount. One suspicion was that the 150 KHz ADCP was
interfering with the signal. It is also possible that the altimeter
was not acoustically decoupled from the frame and was ringing with the
ADCP frequency output. The downlooking ADCP was swapped multiple times
(see ADCP section) during this time period so it is difficult to
isolate exactly which solution was most important.

   [image]Altimeter readings during bottom approach on stations 34 and
   38.

*Bottle mistrips:* Throughout the cruise, guide rings had to regularly
be raised up to ensure the bottle ends caps were could not close
themselves before being fired. Water sampler latches failed to release
multiple times, with bottles coming to the surface still latched open
despite being “fired.” Entire water sampler/carousel was replaced
after station 14 due to a swollen solenoid inhibiting bottle firing.


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

PIs
   * Susan Becker

   * James Swift

Technicians
   * Michael Kovatch


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

The CTD data acquisition system consisted of an SBE-11+ (V2) deck unit
and a networked generic PC workstation running Windows 10. SBE
SeaSave7 v.7.26.7.107 software was used for data acquisition and to
close bottles on the rosette.

CTD deployments were initiated by the console watch operators (CWO)
after the ship had stopped on station. The watch maintained a CTD cast
log for each attempted cast containing a description of each
deployment event and any problems encountered.

Once the deck watch had deployed the rosette, the winch operator would
lower it to 10 meters. The CTD sensor pumps were configured to start
10 seconds after the primary conductivity cell reports salt water in
the cell. The CWO checked the CTD data for proper sensor operation,
waited for sensors to stabilize, and instructed the winch operator to
bring the package to the surface in good weather or no more than 5
meters in high seas. The winch was then instructed to lower the
package to the initial target wire-out at no more than 30 m/min for
the first 100 m and no more than 6 0m/min after 100 m depending on
sea-cable tension and the sea state.

The CWO monitored the progress of the deployment and quality of the
CTD data through interactive graphics and operational displays. The
altimeter channel, CTD pressure, wire-out and center multi-beam depth
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 100 m
from the bottom. The bottom of the CTD cast was usually to within
10-20 meters of the bottom determined by altimeter data. For each
upcast, the winch operator was directed to stop the winch at up to 36
predetermined sampling pressures. These standard depths were staggered
every station using 3 sampling schemes. The CTD CWO waited 30 seconds
prior to tripping sample bottles, to ensure package had shed its wake.
An additional 15 seconds elapsed before moving to the next consecutive
trip depth, which allowed for the SBE35RT to record bottle trip
temperature averaged from 13 samples.

After the last bottle was closed, the CWO directed winch to recover
the rosette. Once the rosette was out of the water and on deck, the
CWO terminated the data acquisition, turned off the deck unit and
assisted with rosette sampling.

Additionally, the watch created a sample log for the deployment which
recorded the depths bottles were tripped and correspondence between
rosette bottles and analytical samples drawn.

Normally the CTD sensors were rinsed after each station using syringes
of fresh water connected to Tygon tubing. The tubing was left on the
CTD between casts, with the temperature and conductivity sensors
immersed in fresh.

Each bottle on the rosette had a unique serial number, independent of
the bottle position on the rosette. Sampling for specific programs
were outlined on sample log sheets prior to cast recovery or at the
time of collection. The bottles and rosette were examined before
samples were drawn. Any abnormalities were noted on the sample log,
stored in the cruise database and reported in the APPENDIX.


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

Shipboard CTD data processing was performed after deployment using
SIO/ODF CTD processing software “ctdcal” v. 0.1. CTD acquisition data
were copied onto a OS X system, and then processed. CTD data at bottle
trips were extracted, and a 2-decibar downcast pressure series
created. The pressure series data set was submitted for CTD data
distribution after corrections outlined in the following sections were
applied.

A total of 90 CTD stations were occupied including one test station. A
total of 91 CTDO/rosette/LADCP/chipod casts were completed.

CTD data were examined at the completion of each deployment 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 O_2 comparisons were made between
down and upcasts as well as between groups of adjacent deployments.
Vertical sections of measured and derived properties from sensor data
were checked for consistency.

A number of issues were encountered during A20-2021 that directly
impacted CTD analysis. Issues that directly impacted bottle closures,
such as slipping guide rings, were detailed in the Underwater Sampling
Package section of this report. Temperature, conductivity, and oxygen
analytical sensor issues are detailed in the following respective
sections.


Sensor Problems
---------------

Throughout the cruise, there were problems with multiple SBE43 oxygen
sensors. The suspicion is that the sensor membranes were frozen either
during transit or while in port. Erratic readings were observed in the
upper ~100 m which then disappeared as the cast went deeper. Station
14 is shown as an example.

   [image]Spiky oxygen in upper 80 m during downcast of station 14.


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

Laboratory calibrations of CTD pressure sensors were performed prior
to the cruise. Dates of laboratory calibration are recorded on the
underway sampling package table and calibration documents are provided
in the APPENDIX.

The lab calibration coefficients provided on the calibration report
were used to convert frequencies to pressure. Initial SIO pressure lab
calibration slope and offsets coefficients were applied to cast data.
A shipboard calibration offset was applied to the converted pressures
during each cast. These offsets were determined by the pre and post-
cast on-deck pressure offsets. The pressure offsets were applied per
cast.

CTD #0914:

+-----------------------------------+-----------------------------------+-----------------------------------+
|                                   | Start P (dbar)                    | End P (dbar)                      |
|===================================|===================================|===================================|
| Min                               | -0.09                             | -0.24                             |
+-----------------------------------+-----------------------------------+-----------------------------------+
| Max                               | 0.53                              | 0.35                              |
+-----------------------------------+-----------------------------------+-----------------------------------+
| Average                           | 0.15                              | 0.02                              |
+-----------------------------------+-----------------------------------+-----------------------------------+

On-deck pressure reading varied from -0.09 to 0.53 dbar before the
casts, and -0.24 to 0.35 dbar after the casts. The pressure offset
varied from -0.25 to 0.02, with a mean value of -0.13 dbar.


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

Laboratory calibrations of temperature sensors were performed prior to
the cruise at the SIO Calibration Facility. Dates of laboratory
calibration are recorded on the underway sampling package table and
calibration documents are provided in the APPENDIX.

The pre-cruise laboratory calibration coefficients were used to
convert SBE3plus frequencies 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
over 13 samples, approximately a 15 second period.

A functioning SBE3plus sensor typically exhibit a consistent
predictable well-modeled response. The response model 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         |
|=========|==============|==============|==============|==============|=============|
| 901-8   | 0.0          | -1.5802e-7   | 0.0          | 0.0          | -1.4125e-3  |
+---------+--------------+--------------+--------------+--------------+-------------+
| 9-19    | 0.0          | -2.0278e-7   | 0.0          | 0.0          | -1.0778e-3  |
+---------+--------------+--------------+--------------+--------------+-------------+
| 20-90   | 0.0          | -3.5676e-7   | 0.0          | 0.0          | 8.3290e-5   |
+---------+--------------+--------------+--------------+--------------+-------------+


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

+---------+--------------+--------------+--------------+--------------+-------------+
| Station | cp_2         | cp_1         | ct_2         | ct_1         | c_0         |
|=========|==============|==============|==============|==============|=============|
| 901-8   | 0.0          | -3.4637e-7   | 0.0          | 0.0          | -7.6459e-4  |
+---------+--------------+--------------+--------------+--------------+-------------+
| 9-19    | 0.0          | -1.4643e-7   | 0.0          | 0.0          | -7.5597e-4  |
+---------+--------------+--------------+--------------+--------------+-------------+
| 20-90   | -5.0915e-11  | 1.4995e-7    | 0.0          | 0.0          | -8.5699e-4  |
+---------+--------------+--------------+--------------+--------------+-------------+

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 ±0.00456°C for SBE35RT-T1,
±0.00452°C for SBE35RT-T2 and ±0.00153°C for T1-T2. The 95% confidence
limits for the deep temperature residuals (where pressure \geq
2000dbar) are ±0.00107°C for SBE35RT-T1, ±0.00119°C for SBE35RT-T2 and
±0.00098°C for T1-T2.

Minor complications impacted the temperature sensor data used for the
A20-2021 cruise.
   * Early stations had bottles fired on the fly, leading to some
     SBE35RT averaging periods outside of the intended depth.

   * Near-surface temperature gradients in the southern end of the
     survey were extremely sharp, occasionally causing SBE35RT
     readings to be questionable.

The resulting affected sections of data have been coded and documented
in the quality code APPENDIX.


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

Laboratory calibrations of conductivity sensors were performed prior
to the cruise at the Sea-Bird Calibration Facility. Dates of
laboratory calibration are recorded on the underway sampling package
table and calibration documents are provided in the APPENDIX.

The pre-cruise laboratory calibration coefficients were used to
convert SBE4C frequencies to mS/cm conductivity values. 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 check sample
salinities 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 figure.

   [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.

A functioning SBE4C sensor typically exhibit a predictable modeled
response. Offsets for each C 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         |
|=========|==============|==============|==============|==============|==============|==============|=============|
| 901-90  | 0.0          | -1.5095e-6   | 0.0          | 0.0          | 0.0          | 0.0          | 2.3449e-3   |
+---------+--------------+--------------+--------------+--------------+--------------+--------------+-------------+
| 9-19    | 1.6923e-10   | -1.3208e-6   | 0.0          | 0.0          | 0.0          | -8.4712e-4   | 2.8040e-2   |
+---------+--------------+--------------+--------------+--------------+--------------+--------------+-------------+
| 20-90   | 1.0156e-10   | -1.0508e-6   | 0.0          | 0.0          | 0.0          | -4.0501e-4   | 1.4077e-2   |
+---------+--------------+--------------+--------------+--------------+--------------+--------------+-------------+


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

+---------+--------------+--------------+--------------+--------------+--------------+--------------+-------------+
| Station | cp_2         | cp_1         | ct_2         | ct_1         | cc_2         | cc_1         | c_0         |
|=========|==============|==============|==============|==============|==============|==============|=============|
| 901-90  | 0.0          | -9.2611e-7   | 0.0          | 0.0          | 0.0          | 0.0          | 4.8941e-3   |
+---------+--------------+--------------+--------------+--------------+--------------+--------------+-------------+
| 9-19    | 0.0          | -6.3966e-7   | 0.0          | -7.0707e-4   | 0.0          | 0.0          | 5.249e-3    |
+---------+--------------+--------------+--------------+--------------+--------------+--------------+-------------+
| 20-90   | 1.7710e-10   | -1.6402e-6   | 0.0          | 0.0          | 0.0          | -6.1245e-4   | 2.4370e-2   |
+---------+--------------+--------------+--------------+--------------+--------------+--------------+-------------+

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.
Quality codes and comments are published in the APPENDIX of this
report.

   [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
mPSU \leq T1-T2 \leq 0.002 mPSU) differences are ±0.00559 mPSU for
salinity-C1SAL. The 95% confidence limits for the deep salinity
residuals (where pressure \geq 2000dbar) are ±0.00163 mPSU for
salinity-C1SAL.

Minimal issues affected conductivity and calculated CTD salinities
during this cruise.
   * Early stations had bottles fired on the fly.

The resulting affected sections of data have been coded and documented
in the quality code APPENDIX.


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

Laboratory calibrations of the dissolved oxygen sensors were performed
prior to the cruise at the SBE calibration facility. Dates of
laboratory calibration are recorded on the underway sampling package
table and calibration documents are provided in the APPENDIX.

The pre-cruise laboratory calibration coefficients were used to
convert SBE43 frequencies to µmol/kg oxygen values for acquisition
only. Additional shipboard fitting were performed to correct for the
sensors non-linear response. 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 SBE43 sensor data were compared to
dissolved O_2 check samples taken at bottle stops by matching the
downcast CTD data to the upcast trip locations along isopycnal
surfaces. CTD dissolved O_2 was then calculated using Clark Cell MPOD
O_2 sensor response model for Beckman/SensorMedics and SBE43 dissolved
O_2 sensors. The residual differences of bottle check value versus CTD
dissolved O_2 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 Brown and Morrison [Mill82] and Owens [Owen85].
Dissolved O_2 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 fit of
the individual cast had worse resdiuals than the group, 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            |
|=========|==============|===============|=========================|===============|==============|
| 901-90  | 4.6882e-1    | -4.9580e-1    | 1.20                    | -1.6209e-4    | 3.7331e-2    |
+---------+--------------+---------------+-------------------------+---------------+--------------+

CTD dissolved O_2 residuals are shown in the following figures O2
residuals versus station. through Deep O2 residuals versus station
(Pressure >= 2000dbar)..

   [image]O_2 residuals versus station.

   [image]Deep O_2 residuals versus station (Pressure >= 2000dbar).

   [image]O_2 residuals versus pressure.

The 95% confidence limits of 1.69 (µmol/kg) for all acceptable (flag
2) dissolved oxygen bottle data values and 1.61 (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 titrated dissolved O_2
lab measurements.

A number of complications arose with the acquisition and processing of
CTD dissolved oxygen data.
   * Multiple SBE43 sensors were suspected to have frozen during
     transit or while sitting in port, causing erratic issues in the
     upper 100 m.

All compromised data signals were recorded and coded in the data
files. The bottle trip levels affected by the signals were coded and
are included in the bottle data comments section of the APPENDIX.


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

A two-point calibration was performed prior and after deployment on
the rosette. These calibrations produced sets of calibration
coefficients (G and H) to adjust factory calibration of dissolved
oxygen raw voltage. The calibrations also provided an assessment of
foil degradation over the course of the 90 stations. As per
manufacturer (JFE Advantech Co., Ltd.) recommendation, 100% saturation
points were obtained via bubbling ambient air in a stirred beaker of
tap water about 30 minutes, removing air stone, then submersing the
powered Rinko. Zero point calibrations also followed general
manufacturer recommendations, using a sodium sulfite solution (25g in
500mL deionized water). Dissolved oxygen raw voltage (DOout),
atmospheric pressure, and solution temperature were recorded for
calculation of new oxygen sensor coefficients (G and H).

Rinko temperature (factory coefficients) was used for pre-cruise
calibration. Generally, the Rinko III sensor appears to have performed
as expected with no major problems or sharp drift throughout the
deployment. An SBE 43 dissolved oxygen sensor was deployed
simultaneously. Both oxygen sensor data sets were analyzed and quality
controlled with Winkler bottle oxygen data. SBE 43 data are reported
as primary oxygen (CTDOXY) for Stations 1-35, with Rinko III data used
for the remaining stations (36-90).

RINKO data was acquired, converted from volts to oxygen saturation,
and then multipled by the oxygen solubility to find 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 (ºC)

* 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.
Stations 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 resdiuals 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         |
|=========|==============|==============|==============|==============|==============|==============|=============|
| 901-18  | 1.8737       | 4.7519e-2    | 1.1875e-3    | 7.2293e-3    | -2.2105e-1   | 3.1239e-1    | 7.7734e-2   |
+---------+--------------+--------------+--------------+--------------+--------------+--------------+-------------+
| 19-37   | 1.8699       | 6.6118e-2    | 1.406e-3     | 1.4025e-2    | -2.2853e-1   | 3.1893e-1    | 8.586e-2    |
+---------+--------------+--------------+--------------+--------------+--------------+--------------+-------------+
| 38-70   | 1.8734       | -8.3703e-3   | 9.3629e-4    | -6.6252e-3   | -1.9367e-1   | 3.0974e-1    | 1.1084e-1   |
+---------+--------------+--------------+--------------+--------------+--------------+--------------+-------------+
| 71-90   | 7.8045e-1    | 3.7031e-2    | -2.5300e-4   | 5.8055e-3    | -3.9786e-2   | 3.2919e-1    | 5.0959e-2   |
+---------+--------------+--------------+--------------+--------------+--------------+--------------+-------------+

CTD dissolved O_2 residuals are shown in the following figures.

   [image]O_2 residuals versus station.

   [image]Deep O_2 residuals versus station (Pressure >= 2000dbar).

   [image]O_2 residuals versus pressure.

The 95% confidence limits of 1.35 (µmol/kg) for all acceptable (flag
2) dissolved oxygen bottle data values and 0.91 (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 titrated dissolved O_2
lab measurements.

A number of complications arose with the acquisition and processing of
CTD dissolved oxygen data.
   * Rinko S/N 297 was very noisy for the first ~35 casts and
     subsequently replaced with S/N 296 which had a much cleaner
     signal.

[Mill82] Millard, R. C., Jr., “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. (1982).

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

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

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


Salinity
========

PIs
   * Susan Becker

   * James Swift

Technicians
   * John Calderwood

   * Patrick A’Hearn


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

Two Guildline Autosals were on board and operational, SIO-owned 8400B
S/N 69-180, and UW-owned 8400B S/N 94-894. S/N 69-180 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. Both
instruments were serviced prior to the cruise by their respective
institutions and shipped to WHOI with other equipment in March. IAPSO
Standard Seawater Batch P-164 was used for all calibrations: K15
=0.99985, salinity 34.994, expiration 2023-03-23. 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 laboratory temperature of
23°C, usually 8 hours or more after collection. The salinometer was
standardized for each group of samples analyzed (normally 1 or 2
casts, up to 72 samples) using two bottles of standard seawater: one
at the beginning and one at the end of each set of measurements.
Between runs the water from the last standard was left in the cell.
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.


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
replaced to insure 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 linear function of elapsed
run time. The corrected salinity data was then incorporated into the
cruise database.


Narrative
---------

No major problems were encountered during this cruise. Minor problems:

   There was a temperature excursion of the climate control chamber on
   the last day of analysis which had to be corrected before the last
   samples could be run.

   Three bottles were broken during sampling; four had their rims
   chipped. In all, seven sample bottles were damaged and replaced.

2963 total salinity samples were taken from a test cast, 90 CTD casts,
and some underway seawater samples. 11 boxes (110 vials) of std
seawater were consumed.

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


Nutrients
=========

Technicians
   * Susan Becker (SIO)

   * Alexandra Fine (AOML/CIMAS)


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

* 2952 samples from 90 CTD stations

* The cruise started with new pump tubes and they were changed twice,
  before station 033 and station 064.

* 2 sets of Primary/Secondary standards were made up over the course
  of the cruise.

* The cadmium column efficiency was checked periodically and ranged
  between 90%-100%.


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,
[Becker 2019]_.


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 40% surfynol 465/485 surfactant. Store at room
   temperature in a dark poly bottle.

   Note: 40% Surfynol 465/485 is 20% 465 plus 20% 485 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 CuSO4 + NH4Cl mix (see
   below). Add 4 drops 40% Surfynol 465/485 surfactant. 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.

NH4Cl + CuSO4 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% CuSO4 solution to this NH4Cl 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
10mm flowcell and absorbance measured at 820nm.

**REAGENTS**

Ammonium Molybdate H2SO4 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 H2SO4. 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 15% DDS
   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 10mm 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
   H2SO4. (Dilute H2SO4 = 2.8ml conc H2SO4  or 6.4ml of H2SO4 diluted
   for PO4 moly per liter DW) (dissolve powder, then add H2SO4) Add
   3-5 drops 15% 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 2-3 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 (Na2SiF6), nitrate (KNO3), nitrite
(NaNO2), and phosphate (KH2PO4) 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 0.1mg prior to the cruise. The exact weight was noted
for future reference. When primary standards were made, the flask
volume at 20C, 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 were used on the cruise. The first batch
of LNSW 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 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 stations 01-055 to estimate precision within the cruise.  The
water for the check samples was collected on the test cast from 1500m
and was fixed with 1ml of saturated mercuric chloride to precent
biological growth and stabilize the nutrient concentration.  The deep
check samples were discontinued when trouble shooting the issues with
cadmium column efficiency since the mercuric chloride may have been
contributing to the loss of column efficiency. The data are tabulated
below for the first 55 stations.

+-----------+---------------------+--------+
| Parameter | Concentration (µM)  | stddev |
+-----------+---------------------+--------+
| NO_3      | 17.75               | 0.29   |
+-----------+---------------------+--------+
| PO_4      | 1.16                | 0.03   |
+-----------+---------------------+--------+
| SIL       | 12.8                | 0.3    |
+-----------+---------------------+--------+

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. [Becker 2019]. RMNS batch C0 was used on this
cruise, with each bottle being used for all runs in one day before
being discarded and a new one opened. Data are tabulated below.

+-----------+---------------+---------+---------------+
| Parameter | Concentration | stddev  | assigned conc |
|===========|===============|=========|===============|
| -         | (µmol/kg)     | -       | (µmol/kg)     |
+-----------+---------------+---------+---------------+
| NO_3      | 15.79         | 0.16    | 15.86         |
+-----------+---------------+---------+---------------+
| PO_4      | 1.18          | 0.01    | 1.177         |
+-----------+---------------+---------+---------------+
| Sil       | 34.8          | 0.16    | 34.7          |
+-----------+---------------+---------+---------------+
| NO_2      | 0.04          | 0.01    | 0.04          |
+-----------+---------------+---------+---------------+


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

There were issues with the cadmium column efficiency for a series of
stations/days. The exact issue was never clearly identified but it
appears to have been a combination of buffer that was not stable which
affected the efficiency and life span of the cadmium reduction
columns. The values of the reference material and the deep check
samples were used to calculate adjustment factors for the affected
stations. The adjusted data for the affected stations was compared to
adjacent stations and historical data during the QC checks.

[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.

[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).

[Kerouel1997] Kerouel, R., Aminot, A., “Fluorometric determination of
              ammonia in sea and estuarine waters by direct segmented
              flow analysis.” Marine Chemistry, vol 57, no. 3-4, pp.
              265-275, July 1997.

[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.


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

PIs
   * Susan Becker

   * James Swift

Technicians
   * Andrew Barna

   * Robert “Ben” Freiberger


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 2947 oxygen measurements were made, of which 2937 were
niskin samples and 10 were underway 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 MnCl2 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. Underway samples were
analysed within 96 hours of collection.

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
---------

Cruise setup began on March 12th 2021 in Woods Hole, MA, USA.

A 5x batch (4.3L) of MnCl and a 4x (3.5L) batch of NaI/NaOH was made
in port so more reagents would not need to be made while underway.
Only a 2L of thiosulfate was made and would need to be made at least
once more with the anticipated number of samples.

Due to low temperatures in Woods Hole, there was concern that the ODF
oxygen standards may have frozen in the shipping container before load
started. Good agreement with both the expected normality of a
carefully prepared thiosulfate batch and an OSIL oxygen standard
alleviated these concerns. The OSIL oxygen standard was run against
the usual ODF oxygen standard during the a standardization around
station 48. The OSIL standardization followed the same procedure as
normal with the exception of using an Eppendorf pipette to dispense
the standard.

The need for smoothing thiosulfate normality was considered separately
for each thiosulfate batch (2 in total). Smoothing was performed on
both batches, the first batch having no trend (averaged), the second
batch showing a trend related to temperature control difficulty the
ship had as the sea and air temperature warmed. The smoothed final
values had differences no more than ±0.3 µmol/kg from the non smoothed
values.

No further data updates are expected.

   [image]Bottle oxygen data gridded on isopycnals.

[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
                deter mination of dissolved oxygen in seawater,” Repor
                t WHPO 91-2, WOCE Hydrographic Programme Office (Aug
                1991).


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

PI
   * Andrew G. Dickson – SIO

   * Frank Millero - RSMAS

Technicians
   * Manuel Belmonte

   * Carmen Rodriguez


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

The total alkalinity of a sea water sample 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 \leq
10–4.5 at 25°C and zero ionic strength) over proton donors (acids with
K > 10–4.5) in 1 kilogram of sample.


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

Samples are dispensed using a Sample Delivery System (SDS) consisting
of a volumetric pipette, various relay valves, and two air pumps
controlled by LabVIEW 2012. Before filling the jacketed cell with a
new sample for analysis, the volumetric pipette is cleared of any
residual from the previous sample with the aforementioned air pumps.
The pipette is then rinsed with new sample and filled, allowing for
overflow and time 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 are used to
convert the sample volume to mass for analysis.

Samples are analyzed using an open cell titration procedure using two
250 mL jacketed cells. One sample is undergoing titration while the
second is being prepared and equilibrating to 20°C for analysis. After
an initial aliquot of approximately 2.3-2.4 mL of standardized
hydrochloric acid (~0.1M HCl in ~0.6M NaCl solution), the sample is
stirred for 5 minutes while air is bubbled into it at a rate of 200
scc/m to remove any liberated carbon dioxide gas. A Metrohm 876
Dosimat Plus is used for all standardized hydrochloric acid additions.
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 ([Dickson2007]). 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
-----------------

Samples for total alkalinity measurements were taken at all A20
Stations (1-90). Three Niskin bottles at each station were sampled
twice for duplicate measurements except for stations where 24 or less
Niskin bottles were sampled. Stations at which 24 or less Niskin
bottles were sample one or two Niskin bottles were sampled twice for
duplicate measurements. Using silicone tubing, the total alkalinity
samples were drawn from Niskin bottles into 250 mL Pyrex bottles,
making sure to rinse the bottles and Teflon sleeved glass stoppers at
least twice before the final filling. A headspace of approximately 3
mL was removed and 0.05 mL of saturated mercuric chloride solution was
added to each sample for preservation. After sampling was completed,
each sample’s temperature was equilibrated to approximately 20°C using
a Thermo Scientific Isotemp water bath.


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

On one occassion, during analysis of station 25, the Agilent 34901A
Data Acquisition/Switch Unit shut off and did not power back on. The
unit had to be replaced with a spare and sample analysis was not
interrupted. Throughout the cruise, glitches from the Sample Delivery
System were experienced at random. At one point, the laptop
controlling the SDS powered off and would not return back on. This too
was replaced with a spare. Additionally, the Sample Delivery System
program would freeze drawing sample in Deliver Sample or Prepare
Pipette mode and caused a few sample bottles to be emptied. This
resulted in a few lost samples. Furthermore, due to a novice operator,
during analysis of station 34 the Metrohm 876 Dosimat Plus calibration
was changed and samples were run with the incorrect calibration.
However, the lead technician was able to find this error and corrected
the mistake. Only 6 samples were analyzed using the icorrect dosimat
calibration function but were recalculated to correct for this error.


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

Dickson laboratory Certified Reference Material (CRM) Batch 178 and
180 were used to determine the accuracy of the total alkalinity
analyses. The total alkalinity certified value for these batches are:

* Batch 187 2204.98 ± 0.37 µmol/kg (32;16)

* Batch 192 2213.70 ± 0.53 µmol/kg (32;16)

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).

At least one reference material was analyzed at every A20 stations
resulting in 142 reference material analyses. On A20, the measured
total alkalinity value for each batch is:

* Batch 187 2205.54 ± 1.79 µmol kg-1 (107) [mean ± std. dev. (n)]

* Batch 192 2214.45 ± 1.58 µmol kg-1 (33) [mean ± std. dev. (n)]

If greater than 24 Niskin bottles were sampled at a station, three
Niskin bottles on that station were sampled twice to conduct duplicate
analyses. If 24 or less Niskin bottles were sampled at a station, one
or two Niskins on that station were sampled twice for duplicate
analyses. The standard deviation for the duplicates measured on A20
is:

Duplicate Standard Deviation ± 2.10 µmol kg–1 (111) [± std. dev. (n)]

The total alkalinity measurements for each A20 stations have been
compared to measurements taken from the neighboring A20 2021 stations.

1689 total alkalinity values were submitted for A20. Further dilution
corrections need to be applied to this data and will not be applied
until onshore, therefore this data is to be considered premilinary.


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

PI’s
   * Rik Wanninkhof (NOAA/AOML)

   * Richard A. Feely (NOAA/PMEL)

Technicians
   * Charles Featherstone (NOAA/AOML)

   * Andrew Collins (NOAA/PMEL)


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

Samples for DIC measurements were drawn (according to procedures
outlined in the PICES Publication, *Guide to Best Practices for Ocean
CO2 Measurements* [Dickson2007]) from Niskin bottles into 294 ml
borosilicate glass bottles using silicone tubing. The flasks were
rinsed once and filled from the bottom with care not to entrain any
bubbles, overflowing by at least one-half volume. The sample tube was
pinched off and withdrawn, creating a 6 ml headspace, followed by 0.12
ml of saturated HgCl_2 solution which was added as a preservative. The
sample bottles were then sealed with glass stoppers lightly covered
with Apiezon-L grease and were stored at room temperature for a
maximum of 12 hours.


Equipment
---------

The analysis was done by coulometry with two analytical systems (AOML
3 and AOML 4) used simultaneously on the cruise. Each system consisted
of a coulometer (CM5017 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 ([Johnson1985],
[Johnson1987], [Johnson1993], [Johnson1992], [Johnson1999]).

The two DICE systems (AOML 3 and AOML 4) were set up in a seagoing
container modified for 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 swept into the titration cell of
the coulometer with 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 OH^- ions at the anode. The OH^- ions
react with the H^+ and the solution turns blue again. A beam of light
is shone through the solution, and a photometric detector at the
opposite side of the cell senses the change in transmission. Once the
percent transmission reaches its original value, the coulometric
titration is stopped, and the amount of CO_2 that enters the cell is
determined by integrating the total change during the titration.


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

Calculation of the amount of CO2 injected was according to the CO2
handbook [DOE1994]. The concentration of CO2 ([CO2]) in the samples
was determined according to:

   [\text{CO}_2] = \text{Cal. Factor} * \frac{(\text{Counts} -
   \text{Blank} * \text{Run Time}) * K
   \mu\text{mol}/\text{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.

The instrument has a salinity sensor, but all DIC values were
recalculated to a molar weight (µmol/kg) using density obtained from
the CTD’s salinity. The DIC values were corrected for dilution due to
the addition of 0.12 ml of saturated HgCl_2 used for sample
preservation. The total water volume of the sample bottles was 294 ml
(calibrated by Esa Peltola, AOML). The correction factor used for
dilution was 1.00041. 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 average
correction was 1.26 µmol/kg for AOML 3 and 1.58 µmol/kg for AOML 4.

The coulometer cell solution was replaced after 24-28 mg of carbon was
titrated, typically after 9-12 hours of continuous use. The blanks
ranged from 12-35.


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

The stability of each coulometer cell solution was confirmed three
different ways.

1. Gas loops were run at the beginning of each cell

2. CRM’s supplied by Dr. A. Dickson of SIO, were analyzed at the
   beginning of the cell before sample analysis.

3. 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%) by means of an 8-port valve [Wilke1993] 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 determined with the use of
standards (Certified Reference Materials (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 to the data base have been corrected to this batch 187 CRM
value. The CRM certified value for this batch is 2002.85 µmol/kg.

The precision of the two DICE systems can be demonstrated via the
replicate samples. Approximately 11% of the niskins sampled were
duplicates 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
difference for these duplicates on AOML 3 and 4 respectively are 1.74
µmol/kg and 1.38 µmol/kg - No major systematic differences between the
replicates were observed.

The pipette volume was determined by taking aliquots of distilled
water from volumes at known temperatures. The weights with the
appropriate densities were used to determine the volume of the
pipettes.

Calibration data during this cruise:

+---------+---------------------+------------+----------------+-----------+----------------------+
| UNIT    | Ave Gas Cal Factor  | Pipette    | Ave CRM        | Std Dev   | Ave Difference Dupes |
|=========|=====================|============|================|===========|======================|
| AOML3   | 1.00448             | 27.990 ml  | 2003.23, N= 42 | 0.67      | 1.74                 |
+---------+---------------------+------------+----------------+-----------+----------------------+
| AOML4   | 1.00422             | 29.387 ml  | 2004.32, N= 43 | 1.27      | 1.38                 |
+---------+---------------------+------------+----------------+-----------+----------------------+


Instrument Repairs
------------------

AOML 3 had a relay switch failure before Station 17. The relay switch
and micro acid pump were replaced and the instrument functioned well
for the rest of the cruise. AOML 4 had the 5V power supply fail during
Station 65. The power supply was replaced with a new one and the
instrument functioned well for the remainder of the cruise.


Underway DIC Samples
--------------------

Underway samples were collected from the flow thru system in the
hydro-lab during transit. Discrete DIC samples were collected
approximately every 4 hours before the line of 90 CTD stations
commenced with duplicates every fifth sample. A total of 38 discrete
DIC samples including duplicates were collected while underway. The
average difference for replicates of underway DIC samples was 0.68
µmol/kg and the average STDEV was 0.30.


Summary
-------

The overall performance of the analytical equipment was good during
the cruise. Including the duplicates, a total of 2245 samples were
analyzed from 90 CTD casts for dissolved inorganic carbon (DIC), which
equates to a DIC value for 68% of the niskins tripped. A total of 38
discrete DIC samples including duplicates were collected from the
underway system and analyzed while in transit. The DIC data reported
to the database directly from the ship are to be considered
preliminary until a more thorough quality assurance can be completed
shore side.

[DOE1994] 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.

[Dickson2007] Dickson, A.G., Sabine, C.L. and Christian, J.R. (Eds.),
              (2007): *Guide to Best Practices for Ocean CO2
              Measurements*. PICES Special Publication 3, 191 pp.

[Feely1998] Feely, R.A., R. Wanninkhof, H.B. Milburn, C.E. Cosca, M.
            Stapp, and P.P. Murphy (1998): *“A new automated underway
            system for making high precision pCO2 measurements aboard
            research ships.”* Anal. Chim. Acta, 377, 185-191.

[Johnson1985] Johnson, K.M., A.E. King, and J. McN. Sieburth (1985):
              *“Coulometric DIC analyses for marine studies: An
              introduction.”* Mar. Chem., 16, 61-82.

[Johnson1987] 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.

[Johnson1992] 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.

[Johnson1993] 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.

[Johnson1999] 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 interna consistency of underway surface TCO2
              concentrations.* Marine Chemistry 67:123–44.

[Lewis1998] Lewis, E. and D. W. R. Wallace (1998) Program developed
            for CO2 system calculations. Oak Ridge, Oak Ridge National
            Laboratory. http://cdiac.ornl.gov/oceans/co2rprt.html

[Wilke1993] 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


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

PI
   * Dr. Andrew Dickson

   * Dr. Frank Millero

Technicians
   * Daniela Nestory

   * Albert Ortiz


Sampling
--------

Samples were collected in 250 mL Pyrex glass bottles and sealed using
grey 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 poisoned with 0.02% of the sample volume of saturated
mercuric chloride (HgCl_2). Samples were collected only from Niskin
bottles that were also being sampled for both total alkalinity and
dissolved inorganic carbon in order to completely characterize the
carbon system. Additionally, duplicate samples were collected from all
stations for quality control purposes.


Analysis
--------

pH 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 725-735nm.
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
2.0mM and a total ionic strength of 0.7 M. A total of two batches were
used during A20. The pHs of these batches were adjusted with 0.1 mol
kg^-1 solutions of HCl and NaOH (in 0.6 mol kg^-1 NaCl background) to
approximately 7.81, 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_{\text{iso}}) were determined for each
measurement, where:

   R = \frac{A_{578} - A_{\text{base}}}{A_{434} - A_{\text{base}}}

and

   A_{\text{iso}} = A_{488} - A_{\text{base}}

The change in R for a given change in A_{\text{iso}}, \Delta R/\Delta
A_{\text{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_{\text{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_{\text{iso}} (bR + a)


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

At the beginning of the cruise two of the Kloehn V6 pumps were found
to have leaky ports as indicator dye was found seeping into the cell
port from the dye port. The Kloehn V6 pump was replaced and posed no
issues for the remainder of the cruise.  During station 27, Agilent
8453 spectrophotometer’s self-test failed the RMS noise test. This
resulted in a change of the dueterium bulb and immediately resolved
the issue. Samples were run the day the bulb may have malfunctioned.
However the reference seawater that was analyzed at the end of that
day was remianed accurate. Thus no inaccurate measurements were taken
while the dueterium bulb was performing suboptimally. Furthermore, the
sample cell was broken due to stress on the sample inlet glass tubes,
but the operator and lead tech were able to rig the cell to remain
operable.


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

The precision of the data was assessed from measurements of duplicate
analyses, replicate analyses (two successive measurements on one
bottle), and certified reference material (CRM) Batch 192 (provided by
Dr. Andrew Dickson, UCSD). two or three duplicates and one or two
replicate measurements were performed on every station when at least
twenty-four Niskins were sampled. If less than twenty-four Niskins
were sampled, only one or two duplicates and one replicate measurement
were performed. CRMs were measured at the beginning and ending of each
day.

The precision statistics for A20 are:

+----------------------------+--------------------------+
| Duplicate precision        | ± 0.0009 (n=173)         |
+----------------------------+--------------------------+
| Replicate precision        | ± 0.0017 (n=104)         |
+----------------------------+--------------------------+
| B192                       | 7.7491 ± 0.00185 (n=52)  |
+----------------------------+--------------------------+
| B192 within-bottle SD      | ± 0.0005 (n=52)          |
+----------------------------+--------------------------+

2026 pH values were submitted for A20. 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, N_2O, and SF_6
==============================

PIs
   * Mark J. Warner (UW)

Analysts
   * Mark J. Warner (UW)

   * Rolf E. Sonnerup (UW)

   * Carla L. Mejías-Rivera (UPR)

Warning:

  Note that N_2O measurements are a Level 3 measurement. The
  concentrations were measured on the same water samples collected for
  the Level 1 CFC/SF_6 measurements. The N_2O analysis is still under
  development. Please contact the PI for any use of these data.

Samples for the analysis of dissolved CFC-11, CFC-12, SF_6, and N_2O
were collected from approximately 1427 of the Niskin water samples
during the expedition. When taken, water samples for tracer analysis
were the first samples drawn from the 10-liter bottles. Care was taken
to co-ordinate the sampling of the tracers with other samples to
minimize the time between the initial opening of each bottle and the
completion of sample drawing. In most cases, dissolved oxygen,
dissolved inorganic carbon, and pH samples were collected within
several minutes of the initial opening of each bottle. To minimize
contact with air, the tracer samples were collected from the Niskin
bottle petcock into 250-cc ground glass syringes through plastic 3-way
stopcocks. The syringes were stored in the dark in a large ice chest
in the laboratory at 3.5° - 6° C until 30-45 minutes before analysis
to reduce the degassing and bubble formation in the sample. At that
time, they were transferred to a water bath at approximately 35° C to
warm the samples prior to analysis in order to increase the stripping
efficiency.

Concentrations of CFC-11, CFC-12, SF_6, and N_2O in air samples,
seawater and gas standards were measured by shipboard electron capture
gas chromatography (EC-GC). This system from the University of
Washington was located in a portable laboratory on the fantail.
Samples were introduced into the GC-EC via a purge and trap system.
Approximately 200-ml water samples were purged with nitrogen and the
compounds of interest were trapped on a Porapak Q/Carboxen
1000/Molecular Sieve 5A trap cooled by an immersion bath to -60oC.
During the purging of the sample (6 minutes at 170 ml min-1 flow), the
gas stream was stripped of any water vapor via a Nafion trap in line
with an ascarite/magnesium perchlorate dessicant tube prior to
transfer to the trap. The trap was then isolated and heated by direct
resistance to 175oC. The desorbed contents of the trap were back-
flushed and transferred onto the analytical pre-columns. The first
precolumn was a 40-cm length of 1/8-in tubing packed with 80/100 mesh
Porasil B. This precolumn was used to separate the CFC-11 from the
other gases. The second pre-column was 13 cm of 1/8-in tubing packed
with 80/100 mesh molecular sieve 5A. This pre-column separated the
N_2O from CFC-12 and SF_6. Three analytical columns in three gas
chromatographs with electron capture detectors were used in the
analysis. CFC-11 was separated from other compounds by a long column
consisting of 36 cm of Porasil B and 150 cm of Carbograph 1AC
maintained at 80°C. CFC-12 and SF_6 were analyzed using a column
consisting of 2.33 m of molecular sieve 5A and 1.5 m of Carbograph 1AC
maintained at 80°C. The analytical column for N_2O was 30 cm of
molecular sieve 5A in a 120°C oven. The carrier gas for this column
was instrumental grade P-5 gas (95% Ar / 5% CH4) that was directed
onto the second precolumn and into the third column for the N_2O
analyses. The detectors for the CFC-11, and for CFC-12 and SF_6 were
operated at 300ºC. The detector for N_2O was maintained at 320 ºC.

The analytical system was calibrated frequently using a standard gas
of known gas composition. Gas sample loops of known volume were
thoroughly flushed with standard gas and injected into the system. The
temperature and pressure was recorded so that the amount of gas
injected could be calculated. The procedures used to transfer the
standard gas to the trap, precolumns, main chromatographic columns and
EC detectors were similar to those used for analyzing water samples.
Three sizes of gas sample loops were used. Multiple injections of
these loop volumes could be made to allow the system to be calibrated
over a relatively wide range of concentrations. Air samples and system
blanks (injections of loops of CFC-free gas) were injected and
analyzed in a similar manner. The typical analysis time for samples
was 740 sec.

For atmospheric sampling, an ~100 meter length of 3/8-in OD Dekaron
tubing was run from the portable laboratory to the bow of the ship. A
flow of air was drawn through this line to the main laboratory using
an Air Cadet pump. The air was compressed in the pump, with the
downstream pressure held at ~1.5 atm. using a back-pressure regulator.
A tee allowed a flow (100 ml min-1) of the compressed air to be
directed to the gas sample valves of the CFC/SF_6/N_2O analytical
system, while the bulk flow of the air (>7 l min-1) was vented through
the back-pressure regulator. Air samples were generally analyzed when
the relative wind direction was within 50 degrees of the bow of the
ship to reduce the possibility of shipboard contamination. The pump
was run for approximately 30 minutes prior to analysis to insure that
the air inlet lines and pump were thoroughly flushed. The average
atmospheric concentrations determined during the cruise (from a sets
of 4 or 5 measurements analyzed when possible) were 222.8 ± 5.6 parts
per trillion (ppt) for CFC-11 (n=27), 497.5 ± 3.4 ppt for CFC-12
(N=37), 10.6 ± 0.2 ppt for SF6 (N=19), and 307.1 ± 12.1 parts per
billion for N2O (N=18) Note that a larger aliquot was required for
higher precision N_2O analysis, and this higher aliquot resulted in
SF_6 peak areas outside the range of the calibration curve used for
seawater samples.

Concentrations of the CFCs in air, seawater samples and gas standards
are reported relative to the SIO98 calibration scale [Prinn00].
Concentrations in air and standard gas are reported in units of mole
fraction in dry gas, and are typically in the parts per trillion (ppt)
range for CFCs and SF_6 and parts per billion (ppb) for N_2O.
Dissolved CFC concentrations are given in units of picomoles per
kilogram seawater (pmol kg-1), SF_6 in femtomoles per kilogram
seawater (fmol kg-1), and N_2O in nanomoles per kilogram seawater
(nmol kg-1). CFC concentrations in air and seawater samples were
determined by fitting their chromatographic peak areas to multi-point
calibration curves, generated by injecting multiple sample loops of
gas from a working standard (UW WRS 32399) into the analytical
instrument. Full-range calibration curves were run at the beginning
and end of the cruise, as well as during long transits/weather delays
when possible. Single injections of a fixed volume of standard gas at
one atmosphere were run much more frequently (at intervals of 2 hours)
to monitor short-term changes in detector sensitivity. Estimated limit
of detection is 2 fmol kg-1 for CFC-11, 1 fmol kg-1 for CFC-12 and
0.01 fmol kg-1 for SF_6.

The efficiency of the purging process was evaluated by re-stripping
water samples and comparing the residual concentrations to initial
values. These re-strip values were less than 1% for CFC-11 and
essentially zero for CFC-12 and SF_6. Based on the re-strips of
numerous samples where the stripper blank was low and relatively
constant, the mean values for N_2O were approximately 5-10%  during
the cruise.

On this expedition, based on the analysis of 35 duplicate samples (i.e
two syringe samples collected from the same Niskin), we estimate
precisions (1 standard deviation) of 2.2% or 0.0031 pmol kg-1
(whichever is greater) for dissolved CFC-11, 0.58% or 0.0011 pmol kg-1
for CFC-12 measurements, 0.016 fmol kg-1 or 1.9% for SF_6 (Stations
24-90), and 1.67% or 0.27 nmol kg-1  for N_2O.


Analytical Difficulties
-----------------------

The major issue affecting the data quality was that SF_6 was not being
fully retained on the trap at the beginning of the cruise at the
initial flow rates used for stripping (200 cc min-1). It took some
time to diagnose this problem as none of the other compounds were
affected. While a new trap was packed, the stripping flow was reduced
to 170 cc min-1 resulting in partial retention of SF_6 on the
analytical trap. Peak areas for an injection of a single large gas
sample loop were about 60-80 K counts during this time period. The
resulting precision for SF_6 was on the order of 10% based upon
duplicate samples. The SF_6 data are flagged as 3 during this time
period, meaning they are of questionable quality. The trap was
replaced after Station 23, and the SF_6 peak areas for the injection
of the large loop increased to 380-400K counts with the precisions
reported above. SF_6 data from Stations 1-23 should only be
interpreted for qualitative trends.

The trap appeared to be cooling/heating unevenly for Stations 23 and
24 which affected the N_2O measurements.  The temperature of the trap
needs to be below -45ºC or N_2O can pass through the MS 5A.

Data quality for CFC-11 is affected by a compound which elutes
slightly later from the trap into the detector.  The chromatographic
peaks for the two compounds are often fused. Post-cruise processing
should result in higher reported precisions.

[Prinn00] Prinn, R. G., Weiss, R.F., Fraser, P.J., Simmonds, P.G.,
          Cunnold, D.M., Alyea, F.N., O’Doherty, S., Salameh, P.,
          Miller, B.R., Huang, J., Wang, R.H.J., Hartley, D.E., Harth,
          C., Steele, L.P., Sturrock, G., Midgley,  P.M., McCulloch,
          A., 2000. A history of chemically and radiatively important
          gases in air deduced from ALE/GAGE/AGAGE.  Journal of
          Geophysical  Research, 105, 17,751-17,792


Dissolved Organic Carbon and Total Dissolved Nitrogen
=====================================================

PI
   * Dennis Hansell (UM)

Technician
   * Abby Tinari

Analysts
   * Lillian Custals

Support
   NSF


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

The goal of the DOM project is to evaluate dissolved organic carbon
(DOC) and total dissolved nitrogen (TDN) concentrations along the A20
zonal transect.


Sampling
--------

DOC profiles were taken from approximately every two out of three
stations from 26 of 36 Niskin bottles ranging the full depth of the
water column (55 of 90 stations; ~1294 DOC/TDN samples). All samples
collected above 250 meters were filtered through an inline filter
holding a combusted GF/F filter attached directly to the niskin. This
was done to eliminate particles larger than 0.7 µm from the sample. To
reduce contamination by the filter or filter holder, a new filter and
holder was used for every station. All samples were rinsed 3 times
with about 5 mL of seawater and collected into combusted 40 mL glass
EPA vials. Samples were fixed with 100 µL of 4M Hydrochloric acid and
stored at room temperature on board. Samples were shipped back to
University of Miami for analysis via high temperature combustion on
Shimadzu TOC-V or TOC L analyzers.

Sample vials were prepared before the cruise by combustion at 450°C
for 12 hours to remove any organic matter. Vial caps were cleaned by
soaking in DI water overnight, followed by a 3 times rinse with DI
water and left out to dry.

Sampling goals for this cruise were to continue high resolution, long
term monitoring of DOC distribution throughout the water column, in
order to help better understand biogeochemical cycling in global
oceans.


Standard Operating Procedure for DOC analyses – Hansell Lab UM
--------------------------------------------------------------

DOC samples will be analyzed via high temperature combustion using a
Shimadzu TOC-V or Shimadzu TOC-L at an inshore based laboratory at the
University of Miami. The operating conditions of the Shimadzu TOC-V
have been slightly modified from the manufacturer’s model system. The
condensation coil has been removed and the headspace of an internal
water trap was reduced to minimize the system’s dead space. The
combustion tube contains 0.5 cm Pt pillow on top of Pt alumina beads
to improve peak shape and to reduce alteration of combustion matrix
throughout the run. CO_2 free carrier gas is produced with a Whatman®
gas generator [Carlson2010]. Samples are drawn into a 5 mL injection
syringe and acidified with 2M HCL (1.5%) and sparged for 1.5 minutes
with CO_2 free gas. Three to five replicate 100 µL of sample are
injected into a combustion tube headed to 680°C. The resulting gas
stream is passed through several water and halide traps, including an
added magnesium perchlorate trap. The CO_2 in the carrier gas is
analyzed with a non-dispersive infrared detector and the resulting
peak area is integrated with Shimadzu chromatographic software.
Injections continue until at least three injections meet the specified
range of a SD of 0.1 area counts, CV \leq 2\% or best 3 of 5
injections.

Extensive conditioning of the combustion tube with repeated injection
of low carbon water (LCW) and deep seawater is essential to minimize
the machine blanks. After conditioning, the system blank is assessed
with UV oxidized low carbon water. The system response is standardized
daily with a four-point calibration curve of potassium hydrogen
phthalate solution in LCW. All samples are systematically referenced
against low carbon water and deep Sargasso Sea (2600 m) reference
waters and surface Sargasso Sea water every 6 – 8 analyses (Hansell
1998). The standard deviation of the deep and surface references
analyzed throughout a run generally have a coefficient of variation
ranging between 1-3% over the 3-7 independent analyses (number of
references depends on the size of the run). Daily references waters
were calibrated with DOC CRM provided by D. Hansell (University of
Miami; [Hansell2005]).


DOC Calculation
~~~~~~~~~~~~~~~

   \mu\text{MC} = \frac{\text{average sample area} - \text{average
   machine blank area}}{\text{slope of std curve}}


Standard Operating Procedure for TDN analyses – Hansell Lab UM
--------------------------------------------------------------

TDN samples will be analyzed via high temperature combustion using a
Shimadzu TOC-V or Shimadzu TOC-L at an inshore based laboratory at the
University of Miami. The operating conditions of the Shimadzu TOC-V
were slightly modified from the manufacturer’s model system. The
condensation coil was removed and the headspace of an internal water
trap was reduced to minimize the system’s dead space. The combustion
tube contained 0.5 cm Pt pillows placed on top of Pt alumina beads to
improve peak shape and to resuce alteration of combustion matrix
throughout the run. Carrier gas was produced with a Whatman® gas
generator [Carlson2010] and ozone was generated by the TNMI unite at
0.5L/min flow rate. Three to five replicate 100 µL of sample were
injected at 130 mL/min flow rate into the combustion tube headed to
680°C, where the TN in the sample was converted to nitric oxide (NO).
The resulting gas stream was passed through an electronic
dehumidifier. The dried NO gas then reacted with ozone producing an
excited chemiluminescence NO_2 species [Walsh1989] and the
fluorescence signal was detected with a Shimadzu TNMI
chemiluminescence detector. The resulting peak area was integrated
with Shimadzu chromatographic software. Injections continue until the
at least three injections meet the specified range of a SD of 0.1 area
counts, CV \leq 2\% or best 3 of 5 injections.

Extensive conditioning of the combustion tube with repeated injections
of low carbon water (LCW) and deep seawater is essential to minimize
the machine blanks. After conditioning, the system blank was assessed
with UV oxidized low nitrogen water. The system response was
standardized daily with a four-point calibration curve of potassium
nitrate solution in blank water. All samples were systematically
referenced against low nitrogen water and deep Sargasso Sea reference
waters (2600 m) and surface Sargasso Sea water ever 6-8 analyses
[Hansell1998]. Daily references water were calibrated with deep CRM
provided by D. Hansell  (University of Miami; [Hansell2005]).


TDN calculation
~~~~~~~~~~~~~~~

   \mu\text{MN} = \frac{\text{average sample area} - \text{average
   machine blank area}}{\text{slope of std curve}}

[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.


Carbon Isotopes in Seawater (14/13C)
====================================

PI
   * Roberta Hansman (WHOI)

   * Rolf Sonnerup (UW)

Technician
   * Abby Tinari

A total of 288 samples were collected from stations collected along
the A20 transect. 32 samples (full) each were taken from 6 of the 90
stations and 16 (partial) samples each were taken from a separate 6 of
the 90 stations. Full and partial sampling alternated approximately
every 6 stations. Samples were collected in 500 mL airtight glass
bottles. Using silicone tubing, the flasks were rinsed 3 times with
seawater. While keeping the tubing at the bottom of the flask, the
flask was filled and flushed by allowing it to overflow 1.5 times its
volume. Once the sample was taken, about 10 mL of water was removed to
create a headspace and 100 µL of saturated mercuric chloride solution
was added to the sample. To avoid contamination, gloves were used when
handling all sampling equipment and plastic bags were used to cover
any surface where sampling or processing occurred.

After each sample was taken, the glass stoppers and ground glass joint
were dried and Apiezon-M grease was applied to ensure an airtight
seal. Stoppers were secured with a large rubber band wrapped around
the entire bottle. Samples were stored in AMS crates in the ship’s dry
laboratory. Samples were shipped to WHOI for analysis.

The radiocarbon/DIC content of the seawater (DI14C) is measured by
extracting the inorganic carbon as CO_2 gas, converting the gas to
graphite and then counting the number of 14C atoms in the sample
directly using an accelerated mass spectrometer (AMS).

Radiocarbon values will be reported as 14C using established
procedures modified for AMS applications. The 13C/12C of the CO_2
extracted from seawater is measured relative to the 13C/12C of a CO_2
gas standard calibrated to the PDB standard using and isotope radio
mass spectrometer (IRMS) at NOSAMS.


LADCP
=====

PI
   * Dr. Andreas Thurnherr


Data Acquisition and QC
-----------------------

In order to collect full-depth profiles of horizontal and vertical
ocean velocity, two Acoustic Doppler Current Profilers (ADCPs), one
facing upward (uplooker) and the other downward (downlooker), as well
as a Deep Sea Power And Light rechargeable 48V battery and cables were
installed on the CTD rosette. This lowered ADCP (LADCP) system was
provided by the Lamont-Doherty Earth Observatory. The LADCP system is
self contained, requiring on-deck cable connections to charge the
battery and for communicating with the ADCPs. The battery charger was
affixed to an elevated cable run in the CTD bay and connected to a
long power cord extension terminating on a bench in the wet lab next
to the bulkhead door leading to the CTD bay. On the bench, the LADCP
data acquisition computer, a Mac Mini, as well as two bench-top power
supplies for the ADCPs were installed.

Between casts the LADCP system in the CTD bay was left connected to
the (unpowered) battery charger, as well as to the two deck cables
leading to the data acquisition computer and to the bench-top power
supplies. The male plug of the (disconnected) adapter cable between
the battery and the LADCP star cable was dummied up. While the deck
cables in the wet lab were permanently connected to the acquisition
computer with RS232-to-USB adapters, the corresponding power
connectors were left disconnected from the bench-top power supplies.
With this setup there is no voltage on any of the LADCP cables on the
rosette.

A few minutes before the CTD was moved out of the bay for deployment
the battery was disconnected from the charger and connected to the
ADCPs via an adapter cable and the star cable, both permanently
installed on the rosette. The male connector of the battery charger
cable was dummied up. In order to start data acquisition,the
instruments were woken up by the acquisition computer, the data from
the previous cast deleted from their built-in memory cards, and the
instruments were programmed to start pinging. Finally the two deck
cables were disconnected from the pig-tails that were also permanently
installed on the rosette in order to protect the expensive star cable
from unnecessary wear. The deck cables and pig tail connectors were
dummied up and the latter were secured to the rosette with a velcro
strap to avoid whipping during the casts. Once everything was set up,
the CTD operator and/or the marine tech were notified that the LADCP
system was ready for deployment. Deployment information was logged on
LADCP log sheets once the CTD system had entered the water.

After the CTD had been secured in the bay after each cast the velcro
securing the dummied up pig-tail ends  to the rosette was removed, the
dummied up pig-tail ends were rinsed with fresh water, the dummy plugs
were removed, and the pig tails were connected to the deck cables.
Using the acquisition computer, LADCP data acquisition was stopped
Afterand the data download was initiated. Afterwards the two bench top
power supplies were connected to the deck cables in the lab, the
battery was disconnected from the adapter cable on the rosette, the
male end of the battery adapter cable on the rosette with two exposed
pins now carrying 48V (from the bench-top power supplies) was dummied
up, and the battery cable was attached to the (still unpowered)
charger cable. Afterwards power was applied to the battery charger in
the wet lab and the time noted on the LADCP log sheet.

After the data from the cast had finished downloading (after about 20
minutes on deep casts), the bench top power supplies were disconnected
from the deck cables in the lab. Then the data files were checked by
integrating the measured vertical velocities in time, which yields
estimates for the maximum depth (zmax) and the end depth (zend) of the
profile, both of which were recorded on the log sheet. After the
battery was fully charged (usually about an hour after charging was
initiated, as indicated by LEDs on the charger) the charger was
disconnected from power in the wet lab and the time was noted on the
log sheet. At this stage, the LADCP system was ready for the next
cast.

Communication between the acquisition computer and the ADCPs was
handled by a new acquisition software (acquire2), implemented as a set
of UNIX shell commands designed to minimize the possibility of
operator errors. Three different commands are used:

*Lstart* – This command wakes the instruments, lists their memory
contents, clears the memory (after operator confirmation) and programs
the instruments to start pinging by uploading command files. CTD
station and cast numbers must be provided by the operator since the
LADCP files use an independent numbering scheme. (CTD station and cast
information, as well as the LADCP profile number were noted on the
LADCP log sheet.)

*Ldownload* – This command interrupts the running data acquisition,
downloads the data and backs up the data files to a network drive.

*Lcheck* – This command integrates the measured vertical velocities
from both ADCPs to estimate zmax and zend, which are displayed
together with other useful profile statistics before the data files
are backed up (again) on the network drive.

While these three commands are all that is needed for LADCP data
acquisition, a fourth command (Lreset) is available for resetting the
ADCPs after swapping instruments and in case of communications
problems, of which there were none during this cruise.

During the night watch the LADCP data were processed for horizontal
velocity using the LDEO_IX processing software and for vertical
velocity using the LADCP_w processing software, both installed on the
acquisition computer. Important diagnostic plots were printed out,
inspected, and filed in a ring binder. In addition to these processing
diagnostics, LADCP data quality was continuously monitored by creating
section plots, some of which can be found in the narrative section of
this cruise report. Over most of the section the LADCP data quality
appears to be excellent, although there is a coverage gap in the deep
waters of stations 32-45 caused by insufficient acoustic backscatter
due to lack of particles in the water column in the center of the
subtropical gyre. Inspection of the LADCP data from the 2012
occupation of A20 indicates similar problems in the same region, which
are not flagged in the archived data, however. A more comprehensive
post-cruise LADCP QC will be carried out by Thurnherr in his lab
before submission of the new data to the archives.

   [image]Data gap caused by insufficient acoustic backscatter for
   stations 32-45.


Instrumentation
---------------

A single 300kHz TRDI Workhose Monitor ADCP (WH300, s/n 12734), fitted
with a custom self-recording accelerometer/magnetometer package, was
installed as the uplooker during all casts. The data from the
accelerometer/magnetometer package will be downloaded after the
instruments return to the lab and used for QC and final processing if
needed.

Several different instruments were installed as downlookers during
different casts. For the shakedown cast (900) a prototype Nortek
Signature 100 ADCP (Sig100) was used. This instrument was provided as
a loaner for testing. It was integrated into the LDEO LADCP system
during pre-cruise quarantine, requiring a re-write of the data
acquisition software and fabrication of an underwater adapter cable.
While the instrument had performed well on the bench in Falmouth, ping
synchronization stopped working reliably on the vessel. Since high-
quality LADCP data can be collected without ping synchronization
(requiring the detection and removal of the measurements affected by
interference) the shakedown cast was carried out with the two ADCPs
pinging independently. While the WH300 performed well, the Sig100 did
not yield good data as indicated by bad values for zmax and zend. The
instrument was therefore replaced with a 150kHz TRDI Workhorse (WH150,
s/n 19394) with a recently manufacturer-refurbished transducer.

While the WH150 performed reasonably well, some of the processing
diagnostic from the uplooker WH300 were noticably cleaner. Therefore,
before station 18 the WH150 was replaced with a second WH300 (s/n
24497). This instrument performed very similar to the WH150, in
particular showing the same (weak) anomalies in the processing
diagnostics, which are therefore likely related to the installation
location (about 5 feet below the pivot point of the rosette) of the
downlooker instrument. As there was no apparent difference in the
quality of the processed profiles before and after station 18 the
WH300 (s/n 24497) was left installed until profile 31.

In the mean time the Sig100 data from the shakedown profile together
with additional diagnostics were sent to the manufacturer for
analysis. Nortek engineers indicated that the poor data quality was
caused by electrical noise and, in particular, by a missing ground
path between the electronics and the pressure case. The instrument was
modified to provide such a ground path and installed again on the
rosette for station 32. Since the data from this station were
noticeably improved, compared to the shakedown profile, it was decided
to leave the instrument on for another two profiles using different
configurations (with and without ping synchronization) as well as with
a different, simpler, newly fabricated underwater adapter cable
lacking the synchronization connections. At the same time, a more
careful analysis of the Sig100 data files was carried out, revealing
that the quality of the recorded velocities was still considerably
worse than those from the TRDI instruments. Therefore, the Sig100 was
removed from the rosette and replaced by the WH150 used before on
stations 1-17.

While this instrument performed well for a few casts its range
deteriorated gradually but quite quickly to the point of not returning
any bins with valid velocities at depth on station 41. The instrument
was therefore replaced (again) for station 42 with the WH300 s/n 24497
which had been used before on station 18-31. While this instrument
yielded very good data, several profiles showed strange echo-amplitude
anomalies affecting a small number of the recorded ensembles. When, on
station 52, the data from this instrument additionally contained an
unexplained gap of 1.5s, it was decided to swap the downlooker with
another spare (WH300 s/n 24477). This final instrument performed well
and was left in place for the remainder of the cruise (profiles
53-90). While WH300 s/n 24497 is suitable as a spare it was
nevertheless decided decided to ship another instrument to port in the
USVI for the following cruise (A22).

While the Sig100 ADCP was not used any more, toward the end of the
cruise a detailed engineering assessment of the data From the
prototype Sig100 was provided by Nortek engineers, with the following
summary:

Unfortunately, the instrument proved to be missing key noise-reduction
hardware, including shielding plates, filter boards and ground
connection, that caused noticeable range loss below 2000 m water
depth. And additional issue also artificially increased the noise in
the first 100-150 m. An on-site modification after the initial
shakedown cruise (sic) significantly reduced the noise (correction of
ground connection), but proved to be insufficient to correct all
issues and reach the design specifications. However, data analysis
does suggest near-instrument cells are still valid and that a properly
built instrument should have a range of approximately 100 m in deep,
low scattering conditions, with no velocity bias.

While this overall optimistic assessment is encouraging, additional
work during post-cruise QC will be required to test the assertion that
the velocity data from the near instrument cells (bins) are indeed
valid.


Chipods
=======

PI
   * Jonathan Nash


Overview
--------

Chipods are instrument packages that measure turbulence and mixing in
the ocean. Specifically, they are used to compute turbulent
diffusivity of heat (K) which is inferred from measuring dissipation
rate of temperature variance (\chi) from a shipboard CTD. Chipods are
self-contained, robust and record temperature and derivative signals
from FP07 thermistors at 100 Hz; they also record sensor motion at the
same sampling rate. Details of the measurement and our methods for
processing \chi can be found in [Moum_and_Nash2009]. In an effort to
expand our global coverage of deep ocean turbulence measurements, the
ocean mixing group at Oregon State University has supported chipod
measurements on all of the major global repeat hydrography cruises
since December 2013.


System Configuration and Sampling
---------------------------------

Three chipods were mounted on the rosette to measure temperature (T),
its time derivative (dT/dt), and x and z (horizontal and vertical)
accelerations at a sampling rate of 100 Hz. Two chipods were oriented
such that their sensors pointed upward. The third one was pointed
downward.

The up-looking sensors were positioned higher than the Niskin bottles
on the rosette in order to avoid measuring turbulence generated by
flow around the rosette and/or its wake while its profiling speed
oscillates as a result of swell-induced ship-heave. The down-looking
sensors were positioned as far from the frame as possible and as close
to the leading edge of the rosette during descent as possible to avoid
measuring turbulence generated by the rosette frame and lowered ADCP.

The chipods were turned on by connecting the sensors to the pressure
case at the beginning of the cruise. They continuously recorded data
until the end of the leg.

   [image]Upward-looking chipod sensors attached to the rosette.

   [image]Downward-looking chipod sensor attached to the rosette.

   [image]Highly sensitive temperature probe, which is sampled at
   100Hz.

+------------------+--------------------+-----------------+------------------------+
| Logger Board SN  | Pressure Case SN   | Up/Down Looker  | Cast Used              |
|==================|====================|=================|========================|
| 2018             | Ti 44-2            | Up              | 901-90                 |
+------------------+--------------------+-----------------+------------------------+
| 2024             | Ti 44-7            | Up              | 901-90                 |
+------------------+--------------------+-----------------+------------------------+
| 2032             | Ti 44-15           | Down            | 901-90                 |
+------------------+--------------------+-----------------+------------------------+


Issues
------

After recovering rosette on cast 02901, chipod S/N 2024 sensor end was
poking out of its pressure case, with both o-rings were exposed and
the interior full of seawater. Before cast 03001, the entire sensor
and housing were replaced, using the same logger.

   [image]Flooded chipod with sensor separated from pressure case.

After cast 06901, the end cap for one of the chipods was lost. A
replacement was printed using TGT’s 3D printer.

[Moum_and_Nash2009] Moum, J., and J. Nash, Mixing Measurements on an
                    Equatorial Ocean Mooring, Journal of Atmospheric
                    and Oceanic Technology, 26(2), 317–336, 2009


Discrete pCO2
=============

PIs
   * Rik Wanninkhof (NOAA/AOML)

Analysts
   * 14. Patrick Mears (CIMAS/RSMAS)


Sampling
--------

Samples were drawn from 11-L Niskin bottles into 500 ml glass bottles
using nylon tubing with a Silicone adapter that fit over the drain
cock. Bottles were first rinsed three times with ~25 ml of water. They
were then filled from the bottom, overflowing a bottle volume while
taking care not to entrain any bubbles. About 5 ml of water was
withdrawn to allow for expansion of the water as it warms and to
provide space for the stopper and tubing of the analytical system.
Saturated mercuric chloride solution (0.24 ml) was added as a
preservative. The sample bottles were sealed with glass stoppers
lightly covered with grease and were stored at room temperature for a
maximum of fourteen hours prior to being run.

The analyses for pCO2 were done with the discrete samples at 20ºC. A
primary water bath was kept within 0.03ºC of the analytical
temperature; a secondary bath was kept within 0.3ºC the analytical
temperature. The majority of the samples were analyzed in batches of
twelve bottles, which took approximately 3.5 hours including the six
standard gases. When twelve bottles were moved into the primary water
bath for analyses, the next twelve bottles were moved into the
secondary water bath. No sample bottle spent less than two hours in
the secondary water bath prior to being moved to the analytical water
bath. Duplicate samples from the same Niskin were drawn to check the
precision of the sampling and analysis.

1260 samples were drawn from 63 CTD casts. 62 sets of duplicate
bottles were drawn at numerous depths. The average relative standard
error was 0.15%, while the median relative error was 0.09%.

   [image]fCO2 (uatm) section plot of the GO-Ship A20 section.

An error in a USB hub connection resulted in the analysis program
becoming frozen and draining one of the samples on station 9. A loose
connection with the potentiometer controlling the sample water and gas
flow resulted in a few delays but did not cause the loss of any
samples. At the Southern most stations the surface water had measured
values less than the lowest standard.


Underway Sampling
-----------------

Underway samples were collected from the underway seawater line
located in the aft wetlab that is connected to the same seawater line
as the underway pCO2 system located in the hydrolab. The seawater is
pumped from a bow seawater inlet located approximately 5.3 meters
below the waterline through a sea chest where instruments measure and
record temperature and salinity.

From the UW seawater line, 37 samples including duplicates were drawn
during the transit from Port Everglades, Florida to Woods Hole and
from Woods Hole to the first station.


Analyzer Description
--------------------

The principles of the discrete pCO2 system are described in
[Wanninkhof1993] and [Chipman1993]. The major difference in the
current system is the method of equilibrating the sample water with
the constantly circulating gas phase. This system uses miniature
membrane contactors (Micromodules from Memrana, Inc.), which contain
bundles of hydrophobic micro-porous tubes in polycarbonate shells (2.5
x 2.5 x 0.5 cm). The sample water is pumped over the outside of the
tubing bundles in two contactors in series at approximately 25 ml/min
and to a drain. The gas is recirculated in a vented loop, which
includes the tubing bundles and a non-dispersive infrared analyzer
(LI-COR™  model 840) at approximately 32 ml/min.

The flow rates of the water and gas are chosen with consideration of
competing concerns. Faster water and gas flows yield faster
equilibration. A slower water flow would allow collection of smaller
sample volume; plus a slower gas flow would minimize the pressure
increase in the contactor. Additionally, the flow rates are chosen so
that the two fluids generate equal pressures at the micro-pores in the
tubes to avoid leakage into or out of the tubes. A significant
advantage of this instrumental design is the complete immersion of the
miniature contactors in the constant temperature bath. Also in the
water bath are coils of stainless steel tubing before the contactors
that ensure the water and gas enter the contactors at the known
equilibration temperature.

The instrumental system employs a large insulated cooler (Igloo Inc.)
that accommodates twelve sample bottles, the miniature contactors, a
water circulation pump, a copper coil connected to a refrigerated
circulating water bath, an immersion heater, a 12-position sample
distribution valve, two thermistors, and two miniature pumps. The
immersion heater works in opposition to the cooler water passing
through the copper coil. One thermistor is immersed in the water bath,
while the second thermistor is in a sample flow cell after the second
contactor. The difference between the two thermistor readings was
consistently less than 0.02ºC during sample analyses. In a separate
enclosure are the 8-port gas distribution valve, the infrared
analyzer, a barometer, and other electronic components. The gas
distribution valve is connected to the gas pump and to six standard
gas cylinders.

To ensure analytical accuracy, a set of six gas standards (ranging
from 288 to 1534 ppm) was run through the analyzer before and after
every sample batch. The standards were obtained from Scott-Marin and
referenced against primary standards purchased from C.D. Keeling in
1991, which are on the WMO-78 scale.

A custom program developed using LabView™ controls the system and
graphically displays the CO2 concentration as well as the
temperatures, pressures and gas flow during the 15-minute
equilibration. The analytical system was running well enough that the
equilibration period was shortened to 12 minutes for the second half
of the cruise. The CO2 in the gas phase changes greatly within the
first minute of a new sample and then goes through nearly two more
oscillations. The oscillations dampen quickly as the concentration
asymptotically approaches equilibrium. The flows are stopped, and the
program records an average of ten readings from the infrared analyzer
along with other sensor readings. The data files from the discrete
pCO2 program are reformatted so that a Matlab program designed for
processing data from the continuous pCO2 systems can be used to
calculate the fugacity of the discrete samples at 20ºC. The details of
the data reduction are described in [Pierrot2009].

   [image]CO2 oscillations during start of first sample in set of
   twelve

The instrumental system was originally designed and built by Tim
Newberger and was supported by C. Sweeney and T. Takahashi. Their
skill and generosity has been essential to the successful use and
modification of this instrumental system. Francesca Alatrorre provided
greatly needed assistance in collecting samples.


Standard Gas Cylinders
^^^^^^^^^^^^^^^^^^^^^^

+------------+--------------------------+
| Cylinder # | ppm CO_2                 |
|============|==========================|
| JB03282    | 288.46                   |
+------------+--------------------------+
| JB03268    | 384.14                   |
+------------+--------------------------+
| CB11243    | 591.61                   |
+------------+--------------------------+
| CA05980    | 792.51                   |
+------------+--------------------------+
| CA05984    | 1036.95                  |
+------------+--------------------------+
| CA05940    | 1533.7                   |
+------------+--------------------------+

[Chipman1993] Chipman, D.W., J. Marra, and T. Takahashi, 1993: Primary
              production at 47ºN and 20ºW in the North Atlantic Ocean:
              A comparison between the 14C incubation method and mixed
              layer carbon budget observations. Deep-Sea Res., II, v.
              40, pp. 151-169.

[Wanninkhof1993] Wanninkhof, R., and K. Thoning, 1993: Measurement of
                 fugacity of CO2 in surface water using continuous and
                 discrete sampling methods. Mar. Chem., v. 44, no.
                 2-4, pp. 189-205.

[Pierrot2009] Pierrot, D., C. Neill, K. Sullivan, R. Castle,
              R.Wanninkhof, H. Luger, T. Johannessen, A. Olsen, R.A.
              Feely, C.E. Cosca, 2009: Recommendations for autonomous
              underway pCO2 measuring systems and data-reduction
              routines . Deep-Sea Res., II, v. 56, pp. 512-522.


Underway pCO2
=============

PIs
   * Simone Alin (NOAA/PMEL)

Analysts
   * Andrew Collins (NOAA/PMEL)

The partial pressure of CO2 (pCO2) in the surface ocean was measured
throughout the duration of this expedition with a General Oceanics
8050 underway system.Uncontaminated seawater was continuously passed
(~2.8 l/min) through a chamber where the seawater concentration of
dissolved CO2 was equilibrated with an overlying headspace gas. The
CO2 mole fraction of this headspace gas (xCO2) was measured
approximately every three minutes via a non-dispersive infrared
analyzer (Licor 7000). Roughly every three hours, the system measured
four gas standards with known CO2 concentrations certified by the NOAA
Earth Science Research Laboratory in Boulder, CO ranging from ~300 –
900 ppm CO2. Additionally, a tank of 99.9995% ultra-high purity
nitrogen gas was measured as a baseline 0% CO2 standard. Following
measurements of standard gases, six measurements of atmospheric xCO2
were made of air supplied through tubing fastened to the ships
starboard jackstaff. Twice a day, the infrared analyzer was calibrated
via a zero and span routine using the nitrogen gas and the highest
concentration (872.6 ppm) CO2 standard. In addition to measurements of
seawater xCO2, atmospheric xCO2, and standard gases, several variables
were monitored to evaluate system performance (e.g. gas and water flow
rates, pump speeds, equilibrator pressures, etc). For more detail on
the general design of this underway pCO2 system, see [Pierrot2009].

A Seabird (SBE) 38 temperature sensor located at the ship’s seawater
intake provided measurements of in situ seawater temperature, while a
SBE 45 thermosalinograph monitored temperature and salinity in the bow
of the ship before the seawater reached the pCO2 system. An Aanderaa
4330 optode plumbed in line with the pCO2 system water supply measured
dissolved oxygen (DO) continuously. Additionally, a modified SeaFET
system was also plumbed in line which measured pH throughout the
duration of the cruise.

During the transit from Woods Hole to the first hydrographic station,
discrete samples (n=37) for measurements of dissolved inorganic
carbon, total alkalinity, pH, DO, nutrients (nitrate, nitrate, silica,
phosphate), and salinity were drawn from the ships uncontaminated
seawater supply every four hours. These were analyzed onboard and will
be used for comparison to measurements collected by the underway
system.

A preliminary round of processing was performed on this dataset using
Matlab routines developed by Denis Pierrot of the Atlantic Oceanic and
Meteorological Lab in Miami, FL. In two brief instances, the underway
system was shut down for minor maintenance to be performed. During our
initial transit to the first CTD station, the system was shut down
while passing through the Canadian Exclusive Economic Zone. A ~12-hour
data gap occurred (20-March) when the cable sending the ship’s SCS
data (position, intake temperature, etc) was loose; this data will be
recovered and merged with the dataset during the next round of
processing. Of 13,056 measurements, four were assigned a WOCE quality
flag of 4 (bad measurement), while none were assigned a quality flag
of 3 (questionable measurement) during this initial round of
processing. Measurements of gas standards were within 1% of their
certified value throughout the duration of the expedition, save for
one brief period where the Licor demonstrated some drift (Figure 1).

Preliminary review of collected data suggest that the main control on
the surface seawater carbonate system was temperature (Figure 2).
Excursions from thermodynamic controls on pCO2, pH and DO were
measured during the brief time spent on the continental shelf near the
coast of South America, where extremely low values of pCO2 were
measured. Concomitant changes were observed in pH, DO, DIC, and other
variables. The likely causes of these low values are likely due to
dilution of seawater by riverine input (e.g. Amazon; surface
salinities dropped below 20 PSU), and potentially by fixation of
dissolved carbon via primary production. However, further evaluation
of these data and the supplementary suite of discrete measurements
that were collected is needed before the controls on pCO2, pH and DO
can be fully elucidated.

This dataset should be considered preliminary; additional quality
control and quality assurance is needed before these data can be
considered final.

   [image]Difference between measurements made by the non-dispersive
   infrared analyzer (Licor 7000) of gas standards and the known
   certified value of those standards (in ppm CO2).

   [image]Spatial distribution of the relevant parameters (sea surface
   temperature [SST, oC], sea surface salinity [PSU], fCO2 [ppm], pH,
   and DO [M]) measured by the underway pCO2 system during the 2021
   GO-SHIP A20 research expedition.

[Pierrot2009] Pierrot, D., Neill, C., Sullivan, K., Castle, R.,
              Wanninkof, R.W., Lüger, H., Johannessen, T., Olsen, A.,
              Feely, R.A., Cosca, C.E.; 2009. Recommendations for
              autonomous underway pCO2 measuring systems and data-
              reduction routines. Deep-Sea Research II 56 (2009)
              512–522


Float Deployments
=================


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

PIs:
   * Kenneth Johnson (MBARI)

   * Steven Riser (UW)

   * Jorge Sarmiento (Princeton)

   * Lynne Talley (UCSD/SIO)

   * Susan Wijffels (WHOI)

Shipboard personnel:
   * Andreas Thurnherr (LDEO)

   * Elizabeth Ricci (UW SSSG)

   * Stephen Jalickee (UW SSSG)

   * Stephanie O’Daly (UAF)

8 biogeochemical (BGC) Argo floats were deployed on A20 as part of the
Global Ocean Biogeochemistry (GO-BGC) program (https://go-bgc.org),
which is funded by NSF Award 1946578. These BGC Argo floats on A20
were the first in this program, which is slated to grow to 500 floats
globally over the next 5 years. GO-BGC contributes to international
and US BGC-Argo, and all floats conform to Argo mission requirements.
Data are freely available through the Argo data portals and from the
GO-BGC website. BGC-Argo floats are helping to resolve seasonal cycles
of many key properties that are relevant to global biogeochemical
processes.

The Atlantic sector for GO-BGC is led by the WHOI Argo group (Susan
Wijffels, Roo Nicholson; planning Pelle Robbins), who planned the
float deployment locations to span the length of both A20 and A22.

The floats have a 10-day cycle. After an initial test dive, the floats
descend to a parking depth of 1000 m, and then drift for 10 days with
the ocean currents; after the 10-day drift, the floats dive to 2000 m
and then ascend to the surface, during which data are measured and
saved. The 2000 m-surface data profiles are then sent to shore via
Iridium Satellite communication, using an antenna located at the top
of the float. The floats deployed were UW-modified Teledyne Webb Apex
floats. The floats are equipped with CTD, oxygen, nitrate, FLBB bio-
optical, and pH sensors.

These 8 floats and 4 additional floats for the subsequent A22 voyage
were readied at U. Washington (S. Riser Argo lab), and shipped to
Woods Hole Oceanographic Institution (WHOI). In Woods Hole, UW Argo
engineer Greg Brusseau tested each float prior to loading on R/V
Thompson. WHOI provided excellent high-bay lab space with an adjacent
outdoor parking lot where it was possible to test the floats, to
satisfy the Covid19 pandemic isolation requirements.

Before the deployment of each float, the FLBB and the nitrate sensors
were carefully cleaned using lens wipes, DI water and lens paper. The
floats are self-activating, so no initial operations were required
before their deployment to activate them. Co-chief scientist Andreas
Thurnherr and Thompson marine technicians Elizabeth Ricci and Stephen
Jalickee were in charge of the GO-BGC float deployments. Additional
assistance was provided by Stephanie O’Daly and the ABs on watch. The
procedure required the use of a line strung through the deployment
collar of the float. Each deployment occurred off the fantail while
the ship was steaming at about 2 knots. Deployments were smooth with
the exception of float 5906440 (UW ID 19107), during which the line
tangled and the float was freed with a hook; a slight line hangup also
occurred for float 5906434 (UW ID 19970).

Float deployments occurred after the completion of a CTD station. For
all deployments, samples of nutrients, salinity, POC/HPLC, DIC, pH and
alkalinity were taken at each depth, at least down to 2000 m. The HPLC
and POC samples were taken from Niskin bottles tripped as duplicates,
at the surface and at the chlorophyll maximum depths (DCM), or the
base of the mixed layer if the DCM was not present. The samples were
filtered by SIO/ODF team (Susan Becker and Alexandra Fine), and will
be sent frozen to the U.S. for analysis (NASA for HPLC and SIO/UCSD
for POC).

The floats were adopted by different schools and organizations in the
U.S. as part of the outreach program “Adopt-a-float” (https://www.go-
bgc.org/outreach/adopt-a-float). Each class named the float and
received the details (and pictures) of their deployment from Andreas
Thurnherr, via GO-BGC personnel onshore George Matsumoto (MBARI).
Together with their teachers, the students will follow the float data,
which can be easily downloaded and plotted from the website.

Seven of the floats began reporting data immediately, beginning with
the engineering profile followed within a day by the first profile.
The second float deployed (5906341, UW ID 19061) reported its
engineering profile, but has not produced full profiles as of the end
of the cruise. It appears that all sensors are working well, with the
exception of pH on float 5906343 (UW ID 19881), which provided only a
partial first profile. This was not related to issues with the float
deployment.

The location and date of the float deployments are indicated in the
table below, with WMO and UW ID numbers and the CTD cast at the
deployment location.


Summary of deployment details for the GO-BGC profiling floats.
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

+---------+-------+-----------+----------+---------------------+---------------+-------------------------+------------------+
| WMO ID  | UW ID | Longitude | Latitude | Date and Time (UTC) | CTD Station # | Comments                | Deployer         |
|=========|=======|===========|==========|=====================|===============|=========================|==================|
| 5906342 | 19142 | -52.33    | 40.0657  | 03/24/2021 2347     | 18            | Clean                   | Stephen Jalickee |
+---------+-------+-----------+----------+---------------------+---------------+-------------------------+------------------+
| 5906341 | 19061 | -52.33    | 35.8859  | 03/27/2021 0800     | 25            | Clean; No first profile | Elizabeth Ricci  |
+---------+-------+-----------+----------+---------------------+---------------+-------------------------+------------------+
| 5906440 | 19107 | -52.33    | 31.66    | 03/29/2021 1240     | 32            | Line tangled            | Elizabeth Ricci  |
+---------+-------+-----------+----------+---------------------+---------------+-------------------------+------------------+
| 5906435 | 19512 | -52.33    | 27.64    | 03/31/2021 1515     | 39            | Clean                   | Elizabeth Ricci  |
+---------+-------+-----------+----------+---------------------+---------------+-------------------------+------------------+
| 5906340 | 19364 | -52.33    | 24.14    | 04/02/2021 1215     | 45            | Clean                   | Elizabeth Ricci  |
+---------+-------+-----------+----------+---------------------+---------------+-------------------------+------------------+
| 5906339 | 19588 | -52.33    | 20.06    | 04/04/2021 1340     | 52            | Clean                   | Elizabeth Ricci  |
+---------+-------+-----------+----------+---------------------+---------------+-------------------------+------------------+
| 5906343 | 19881 | -52.33    | 15.97    | 04/06/2021 1400     | 59            | Clean; pH partial       | Elizabeth Ricci  |
+---------+-------+-----------+----------+---------------------+---------------+-------------------------+------------------+
| 5906434 | 19970 | -52.33    | 11.89    | 04/08/2021 1425     | 66            | Clean                   | Elizabeth Ricci  |
+---------+-------+-----------+----------+---------------------+---------------+-------------------------+------------------+


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

PIs
   * Susan Wijffels (WHOI)

   * Steven Jayne (WHOI)

   * Pelle Robbins (WHOI)

A total of 7 core Argo floats were deployed on this cruise. Co-chief
scientist Andreas Thurnherr and Thompson marine technicians Elizabeth
Ricci and Stephen Jalickee were in charge of the deployments.
Additional assistance was provided by Stephanie O’Daly and the ABs on
watch. All floats were deployed without problems using instructions
provided by Jessica Kiosk and at the locations provided before the
cruise by Pelle Robbins(WHOI Argo group).


summary of the deployment details of the Core Argo floats
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

+--------------+--------------+--------------+--------------+--------------+--------------+--------------+--------------+
| ID           | S/N          | Date         | Time         | CTD Station  | Latitude     | Longitude    | Water Depth  |
|==============|==============|==============|==============|==============|==============|==============|==============|
| A1           | 7617         | 04/01        | 0625         | 41           | 26.47N       | 52.33W       | 5200m        |
+--------------+--------------+--------------+--------------+--------------+--------------+--------------+--------------+
| A2           | 7667         | 04/05        | 0330         | 54           | 18.89N       | 52.33W       | 5153m        |
+--------------+--------------+--------------+--------------+--------------+--------------+--------------+--------------+
| A3           | 7625         | 04/05        | 2351         | 57           | 17.14N       | 52.33W       | 4300m        |
+--------------+--------------+--------------+--------------+--------------+--------------+--------------+--------------+
| A4           | 7601         | 04/06        | 2106         | 60           | 15.39N       | 52.33W       | 5270m        |
+--------------+--------------+--------------+--------------+--------------+--------------+--------------+--------------+
| A5           | 7602         | 04/06        | 1100         | 62           | 14.22N       | 52.33W       | 5170m        |
+--------------+--------------+--------------+--------------+--------------+--------------+--------------+--------------+
| A6           | 7626         | 04/08        | 0043         | 64           | 13.06N       | 52.33W       | 5100m        |
+--------------+--------------+--------------+--------------+--------------+--------------+--------------+--------------+
| A7           | 7605         | 04/09        | 0420         | 68           | 10.71N       | 52.33W       | 4910m        |
+--------------+--------------+--------------+--------------+--------------+--------------+--------------+--------------+


Sofar Drifter Deployments
=========================

A total of 11 Sofar Ocean Technologies “Spotter” drifters were
deployed on this cruise (Table 1). Co-chief scientist Andreas
Thurnherr and Thompson marine technicians Elizabeth Ricci and Stephen
Jalickee were in charge of the deployments. Additional assistance was
provided by Stephanie O’Daly and the ABs on watch. The drifters were
deployed by dropping them over the side with the vessel in motion.

The following description of the drifter program has been provided by
Sofar Ocean Technologies: Sofar Ocean Technologies is deploying a
global free-floating metocean sensor array which develops new
assimilation strategies to improve global ocean weather forecast
models. The network of Sofar buoys make observations of real-time
ocean conditions including surface winds, waves and currents, and
transmit the data back to shore through an integrated satellite
connection. Sofar is working to expand its coverage in the Atlantic,
Indian, and Southern Oceans by utilizing Ship of Opportunity partner
groups, with all data from the globnal network publically available in
real time through the Sofar Weather Dashboard. Data exports are also
available to partner groups as part of our research grants program,
either directly to deployment partners, or through our Climate
Initiative. Sofar’s work is funded in part by the US Office of Naval
Research, which has sponsored several research projects including an
upcoming effort to directly observe hurricane activity in the Atlantic
in order to improve hurricane forecasting and operational tracking
systems.


Summary of the deployment details of the Sofar
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

+--------------+--------------+--------------+--------------+--------------+--------------+--------------+--------------+
| ID           | S/N          | Date         | Time         | Station      | Latitude     | Longitude    | Depth        |
|==============|==============|==============|==============|==============|==============|==============|==============|
| D1           | 1197         | 03/24        | 0730         | 16           | 41.10N       | 52.33W       | 5120m        |
+--------------+--------------+--------------+--------------+--------------+--------------+--------------+--------------+
| D2           | 1191         | 03/24        | 2337         | 18           | 40.07N       | 52.33W       | 5220m        |
+--------------+--------------+--------------+--------------+--------------+--------------+--------------+--------------+
| D3           | 1181         | 03/25        | 1509         | 20           | 39.08N       | 52.23W       | 5280m        |
+--------------+--------------+--------------+--------------+--------------+--------------+--------------+--------------+
| D4           | 1192         | 03/26        | 0645         | 22           | 37.89N       | 52.33W       | 5350m        |
+--------------+--------------+--------------+--------------+--------------+--------------+--------------+--------------+
| D5           | 0442         | 03/26        | 0350         | 23           | 37.22N       | 52.34W       | 5370m        |
+--------------+--------------+--------------+--------------+--------------+--------------+--------------+--------------+
| D6           | 1195         | 03/27        | 0759         | 25           | 35.88N       | 52.33W       | 4450m        |
+--------------+--------------+--------------+--------------+--------------+--------------+--------------+--------------+
| D7           | 1190         | 03/27        | 1555         | 26           | 35.22N       | 52.33W       | 5460m        |
+--------------+--------------+--------------+--------------+--------------+--------------+--------------+--------------+
| D8           | 1188         | 03/28        | 0624         | 28           | 34.05N       | 52.33W       | 5050m        |
+--------------+--------------+--------------+--------------+--------------+--------------+--------------+--------------+
| D9           | 1184         | 03/28        | 2136         | 30           | 32.89N       | 52.33W       | 5560m        |
+--------------+--------------+--------------+--------------+--------------+--------------+--------------+--------------+
| D10          | 1170         | 03/29        | 1949         | 33           | 31.14N       | 52.34W       | 5560m        |
+--------------+--------------+--------------+--------------+--------------+--------------+--------------+--------------+
| D11          | 1193         | 03/31        | 0040         | 37           | 28.81N       | 52.33W       | 5110m        |
+--------------+--------------+--------------+--------------+--------------+--------------+--------------+--------------+


Sargassum
=========

PI
   * Dennis McGillicuddy


Overview
--------

Occupation of GO-SHIP lines A20 by R/V Thomas G. Thompson offered an
exceptional opportunity to sample the Great Atlantic Sargassum Belt
[Wang2019]. Satellite imagery indicates another significant bloom
began just before the cruise, with the abundance of Sargassum in
February of 2021 near the top of that observed in Februaries of the
last five years, second only to February 2018. Given the seasonality
of the phenomenon, Sargassum abundance was expected to increase during
the course of the cruise.

Recent evidence suggests a long-term shift in the elemental
stoichiometry of the seaweed (particularly N:P), which may reflect
changes in nutrient supply fueling these blooms [Lapointe_submitted].
Sargassum tissue samples in the high-abundance region of the tropical
and southern subtropical Atlantic are very few in number, with
opportunistic sampling by the R/V Thomas G. Thompson in August 2019
providing most of the measurements of which we are aware.

Clearly more observations are needed to test the hypothesis of a long-
term shift in N:P and its implications for nutrient supply and
Sargassum bloom dynamics. A20 extended into the high-abundance region,
and the core hydrographic and inorganic nutrient measurements will be
extremely valuable for interpreting satellite-based Sargassum
abundance. The critical need for opportunistic sampling is Sargassum
tissue.


Procedure
---------

Seaweed sampling was conducted by dipnet affixed to a standard
recovery pole. A standard sample is 30-40g, an amount that fits easily
into a quart-sized Ziploc bag. When sufficient biomass was available,
12 samples per station were collected, 6 dried and 6 frozen, each
comprised of triplicates for the two species S. fluitans and S. natans
which are easily distinguishable by their pods and leaves. In the
event that sufficient biomass was not available, dried samples were
prioritized.

Samples to be dried were rinsed with DI water, shaken dry, and placed
in drying oven on parchment paper with name of designated species and
station. Drying oven temperature were set between 55 and 65 C and
checked periodically with a thermometer inserted into top dryer vent.
Once sample was “bone dry” or crispy (typically 24-48 hours), sample
were placed in Ziploc bag and labeled with species, station location
collected, and date of collection.

Samples to be frozen were separated by species and placed in Ziploc
bags, labeled with a code referencing date, location, type. Excess
water was removed (with paper towel) prior to sealing bags and bags
were stored in a freezer and covered with a black blanket to keep
samples dark. Additional sample details were recorded on log sheets,
including date, time, location, GPS, etc.

[Lapointe_submitted] Lapointe, B. E., R. A. Brewton, L. W. Herren, M.
                     Wang, C. Hu, D. J. McGillicuddy, S. Lindell, F.
                     J. Hernandez, and P. L. Morton, submitted:
                     Nutrient content and stoichiometry of pelagic
                     Sargassum reflects increasing nitrogen
                     availability in the Atlantic Basin. Nature
                     Communications.

[Wang2019] Wang, M., C. Hu, B. B. Barnes, G. Mitchum, B. Lapointe, and
           J. P. Montoya, 2019: The great Atlantic Sargassum belt.
           Science, 365, 83-87.


Marine Microgels
================

PI
   * Dennis Hansell

Marine microgels are poorly understood, small particulate entities in
the ocean. In terms of abundance, they are commonly micron size and
smaller. Their formation is by self-assembly and ionic bridging
between organic macromolecules. Their role and dynamics in the ocean
are only poorly known, but they are prospectively a sink for high
molecular weight dissolved organic matter, making that material
available as small particles as a substrate for heterotrophic
microbes. Few oceanic distributions have been established for
microgels, yet it is from distributions that controls can be inferred.
Samples are being taken at 3 locations (two stations each) during the
current (2021) occupation of A20 in the North Atlantic. These data, in
the context of hyrographic and DOC data, will provide more insights on
the pool.


NITRATE \delta^15N AND \delta^18O
=================================

PI:
   * Daniel Sigman (Princeton University)

Samplers:
   * Francesca Alatorre

   * Cassondra DeFoor

   * Paige Hoel

   * Elana Perez

Nitrate (NO_3^-) is the primary form of fixed nitrogen (N) in the sea
and an essential macronutrient, the supply of which can limit primary
production and carbon export from the surface ocean. The dual isotopes
of NO_3^- (\delta^15N and \delta^18O) record biogeochemical and
physical processes on different time scales. In general, nitrate
consuming processes tend to raise the \delta^15N and \delta^18O of
nitrate equally while nitrate producing processes tend to decouple the
dual isotopes. Since different processes leave different imprints on
the isotopic composition of nitrate, the dual isotopes can be used to
separate and quantify the impact of multiple N fluxes acting on the
nitrate pool.

Seawater samples for nitrate isotope analyses were collected from all
depths at about every two degrees of latitude. Two 30mL samples were
collected from each niskin bottle fired at depths shallower than 300
m. One 30mL sample was taken from all other depths. All bottles were
rinsed once with half their full volume before being filled with
seawater. The samples were stored onboard at -20°C in order to
preserve them for land based analysis.


Analysis
--------

The denitrifier method [Casciotti2002] [Sigman2001] will be used to
analyze NO_3^-, \delta^15N, and \delta^18O. Briefly, this method
converts all NO_3 to nitrous oxide (N_2O) via denitrifying bacteria
before the sample is analyzed by an IRMS. Samples were collected at
stations 9, 16, 19, 22, 24, 28, 33, 38, 44, 46,49, 51, 54, 56, 59,62,
64, 67, 69, 77, 88. At station 9 a problem with the CTD cable
prevented bottles from tripping in the upper 100 m, therefore samples
for the upper 100 m were collected on station 10.


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.


Francesca Alatorre
------------------

My experience aboard the R/V Thomas G Thompson for the US-GO SHIP, leg
A20 has been one of the most exciting adventures of my academic
career. Over the course of a little over a month, I have learned about
the nuances of hydrographic and oceanographic research and how my
interest in this field of research continues to grow steadily. I
worked on board the R/V TGT as a CTD watchstander. My daily duties
included: preparing the CTD rosette for launch while on predetermined
station coordinates, monitoring the CTD package’s decent and using its
software to sample water at various depths, sampling salinity and pCO2
from up to 36 bottles and depths, and maintaining console and sample
logs that detail important information from each cast. In the
beginning, I was extremely intimated by the intricacies of the general
CTD operations; it was quite a lot to take in. But I was incredibly
lucky to be on the night shift with the CTD analyst who previously was
a watchstander himself, and he walked me through all procedures until
I was comfortable myself with fulfilling my duties.

Although over the course of this GO SHIP cruise, my belonging was
questioned several times in regards to being the only undergraduate
(from a university not known for their oceanography research) and
among the few people of color aboard. The frequency of the
microaggresions were unfortunately occurring on a daily basis by the
other researchers on board. Regardless of the combined and deliberate
effort to put me down and intimate me as a scientist and future
researcher, I feel even more affirmed on my path to become an
oceanographer. This experience has also afforded me the opportunity to
meet some incredible, caring, and wonderful people that added to this
journey rather than detract. Overall, this journey was an incredible
learning experience about the Atlantic Ocean and about the details of
how hydrography data is analyzed, collected, and processed; especially
with the use of CTD rosette/package for collection. I sincerely hope
to soon be able to work again on a research vessel like the R/V Thomas
G. Thompson in the near future.


Cassondra DeFoor
----------------

I sailed on the Thomas G. Thompson from Woods Hole, Massachusetts to
St. Thomas, US Virgin Islands on the A20 leg for US GO-SHIP. All of
the crew members had to quarantine two weeks prior to boarding due to
the COVID-19 pandemic. We boarded this ship eager to break our social
isolation and collect samples from the Northern Atlantic on March
15th, 2021. I held the position of a CTD watch/stander for my first
journey at sea. My duties included preparing the Niskin bottles and
rinsing the sensors to the various instruments on the rosette prior to
each cast, communicating with the winch operators to lower the rosette
to ten meters above the ocean floor and then to each consecutive depth
where we would close a Niskin bottle, ensuring that oxygen sensitive
samples such as chlorofluorocarbon, oxygen, partial pressure of carbon
dioxide, dissolved inorganic carbon, and pH, were sampled within 15
minutes of depressurizing each bottle, and taking samples for salinity
analysis. This was the ideal position to introduce me to the world of
oceanographic cruises. I learned valuable information about how
samples are taken, what data is regularly monitored, and how to care
for a Rosette, CTD, and Niskin bottles. I quickly realized it takes a
village to make an oceanographic cruise successful and each person on
ship has a vital job. It was also a great opportunity for me to learn
about the field through masters and doctoral students, professional
oceanographers, and the ship crew who spend a large portion of their
time at sea.

Aside from the science, I enjoyed the serenity and easy-going nature
of life at sea. We were very lucky to not have experienced much rough
weather which made for an enjoyable journey. I spent much of my time
disconnected from the internet and instead reading, playing solitaire
and cribbage, and learning how to tie knots. Some of my favorite
memories include visiting the bridge to watch the bow nod along with
the waves, doing yoga outside on the stern on a sunny day, and playing
the various records on the record player in the computer lab. Going to
sea is an essential part of this career so I am grateful to have had
the opportunity to sail on a US GO-SHIP leg this early in my journey.
It solidified my desire to continue my pursuit as a chemical
oceanographer. I hope that this is the first of many cruises that I
take part in during my career.


Paige Hoel
----------

I don’t know when exactly the GO SHIP A20 cruise began to feel like
home. I retrace my steps to the first day on the ship, when I got lost
finding my stateroom and did seemingly endless circles through the
doors and staircases and hallways all over the ship. It didn’t feel
like home then. But hours later, I knew I was in the right place at
the right time.

Being around the scientists, the crew, the blue and endless ocean,
just felt right. Like so many others on this cruise, I was coming out
of my entirely remote and virtual new world of science, excited to
interact with others for the first time, not just scientifically, but
socially, for the first time in a while. As I spoke to everyone about
their research, bit by bit I began to understand how unique and
wonderful oceanographic cruises are. I was not only in an environment
where I could nerd out about the ocean, but where everyone else around
me was actively doing so. Socially, intellectually, scientifically,
this cruise seems to have really been a goldilocks just right
scenario. I am typing this in the main lab, listening to a sink
gurgling and the alkalinity system breathing. I am home.

I can not yet say with certainty what this cruise has meant to me. I
first dreamed of going on an oceanographic cruise around four years
old. It was a national geographic documentary about oceanographer
Robert Ballard that sparked my imagination in oceanography, and desire
to do the science at sea. My love for oceanography grew with me. I
applied to many cruises as an undergraduate and graduate student. No
luck. I pressed on.

My fascination found a happy home in the world of biogeochemical
modeling. My graduate studies found a happy home at UCLA in the
Atmospheric and Oceanic Science department. Although I was fulfilled
and fascinated by my research on waste water modeling and
phytoplankton models, I felt a slight twang of melancholy when other
oceanographers would speak about their times at sea, cruises both
upcoming and past. My desire to go never faded, but my understanding
of what types of oceanographers actually need to go on these cruises
broadened. Modelers don’t need to go on cruises. In fact, one of the
primary purposes of modeling is to create data in the absence of
direct observations. Why on earth would I NEED to go on a cruise?

The opportunity to be a CTD watch stander popped up on our lab groups
slack channel. I spoke to my advisor, who said any oceanographer, no
matter their specific discipline, can glean so much from a cruise. I
applied, I was accepted, and now I am at the end of this journey I
have dreamed about for the last 21 years.

The tasks have felt a little mindless at times. The CTD watch stander
does not need to think critically. But the role is mission critical,
and I am endlessly thankful for the opportunity to have been at the
intersection of scientists, crew, and our shared love, the ocean. As a
watch stander I coordinated depths, samples, and paid attention to
every small detail needed to ensure great samples. Without great
samples, the scientific mission of the cruise cannot be met. Even if I
had a tiny influence in making those amazing measurements, I am
immensely proud.

GO SHIP provided me the opportunity to see the full lens of
oceanography, the beautiful challenge of creating a snapshot of one
piece of water, and given me a deep and profound appreciation for each
carbon measurement I have ever used. GO SHIP gave me a home, an
oceanographic home, in the middle of the Atlantic, moving at a speed
of 12 knots, down 52.33 degrees west.


Carla Mejías-Rivera
-------------------

Towards the end of my doctoral studies, I applied to the GO-SHIP A20
cruise eager to acquire additional knowledge in the field of chemical
oceanography and to experience what is like to participate in a
research expedition in open ocean. As a Chemist, I was especially
interested to work with the CFC/SF6 tracers group. I was sure that
having this opportunity was going to help me expand my knowledge in
the field by learning a new research topic and providing me with
numerous experiences that will surely clarify and open new options for
my future in the field of oceanography.

My duties during the expedition consisted of collecting and analyzing
water samples for CFC-12, CFC-11, SF_6 and N_2O. Sample collection for
tracers was a completely new experience for me. Instead of collecting
seawater into bottles, these samples are collected into a 250ml glass
syringe, employing special care to avoid even the smallest bubble,
since bubbles can alter the tracers’ analysis. This was a challenging
skill to acquire at the beginning but once learned, sampling was very
fun. Samples in the syringes were then taken to the lab for analysis.
They were injected, one at a time, into an instrument that extracts
the tracers from the sample, separates, concentrates, and sends them
into three different gas chromatographers. After processing, I had the
opportunity to view the profiles and learn how to interpret the
fundamental features. While looking at the data profiles and visually
comparing them to the previous GO-SHIP expedition in the same transect
(2012), we could not avoid seeing ourselves as “translators” of the
ocean’s message through chemical analysis… isn’t it wonderful!?! So
many stories can be told by looking at this data, some could serve as
lessons learned, others could bring hope, but all equally fascinating.

While at sea, having the opportunity to meet other scientists and crew
and get to know their work was overall very enriching and exciting.
This opportunity was not only great for my professional development
but also personally fulfilling. I am very grateful for all the people
that made this possible, for those who shared their knowledge, for the
amazing human beings I met, for all the lessons learned, and for the
time I spent onboard the R/V Thomas G. Thompson.


Elena Perez
-----------

The past 4 weeks at sea sailed by oooweee! From March 16 to April 16,
2021 I’ve learned many a valuable lesson while onboard the R/V
Thompson for the A20 line of US GO-SHIP cruises. Most importantly, I
learned that being a CTD watchstander does not mean we have to stand
for 12 hours a day. In fact, most of our work was done sitting in the
computer lab: monitoring CTD casts and talking with the winch
operators. When we weren’t in the computer lab, we were usually in the
staging bay. One of us would be helping sample salts/nitrates/pCO2.
And the other person had to take on the tough duty of sample cop.
Responsibilities of sample cop include: wrangling scientists into
line, making sure there was enough water in the Niskin bottles for all
of us, and prepping that there CTD for the next cast.

Overall, this experience has given me valuable insights into field
work of oceanography. As an incoming graduate student, it’s been great
to observe with my own eyes the physics, biology, and chemistry of the
oceans that I’ll likely be learning about this fall 2021 in
classrooms.

Beyond the science, I immensely enjoyed boat life (except when I was
missing the creature comforts of life on land, e.g. dogs, good WiFi
connection, etc.). I’ve listed below some of the best parts of boat
life, in my opinion, in no particular order.

1. The best stargazing I’ve ever beared witness to. When you’re 1,000+
   miles from land with very very dark skies you’re bound to see the
   Milky Way, a few satellites, and a handful of shooting stars if you
   stay out long enough

2. The sunrises everyday convinced me that night shift is way better
   than day shift. I’ve never seen so many sunrises in a row, and
   never seen a sunrise with 360º views all around.

3. Playing cribbage during downtime/when our shift was over. Cribbage
   is now the unofficial game of the R/V Thomas G. Thompson.

4. Decorating and watching the deployment of 8 of the first-ever
   biogeochemical Argo floats.

5. The bluest water I’ve ever seen. I loved sitting on the stern (or
   the bow, I’m not picky) and just watching the water and sargassum
   go by

6. Emptying all the Niskin bottles after everyone is done sampling.

7. All the birds. Although I haven’t seen an albatross yet :/ I might
   just have to go on another cruise so I can catch a glimpse of one
   of these legendary birds
