WHP Ref. No.: AR11/ACM25/ACM26
Last updated: March 1992

Cruise Plan for The Subduction Experiment

Chief Scientist: 	Robert A. Weller, Woods Hole Oceanographic Inst.
Cruise: 		Oceanus 250 Legs 1 and 2
Dates: 		January 25, 1992 to February 25, 1992
Ship: 		RV Oceanus

Overview

R/V Oceanus cruise number 250, Leg 1 departed Woods Hole,
Massachusetts on 25 January 1992 to recover and redeploy five surface
moorings as part of the Office of Naval Research (ONR) funded ASTEX
and Subduction Experiments. This cruise involved personnel and
equipment from both the Woods Hole Oceanographic Institution (WHOI)
and Scripps Institution of Oceangraphy (SIO).  Table 1 lists the
Subduction I mooring deployment and recovery information. (The first
setting of moorings were deployed in June/July 1991 during Oceanus
cruise number 240. A separate cruise summary report is available.)
Table 2 lists the Subduction ll mooring deployment information.
During Oceanus cruise 250 the Suduction I moorings were replaced with
five new surface moorings that are intended to stay on station for a
period of eight months. A total of 102 recording instruments were
deployed on the five Subduction ll moorings. There are 9
meteorological packages, 34 current meters, 58 temperature data
loggers and one Acoustic Doppler Current Profiler. The schedule as
shown below is to replace the moorings in October 1992 and then
recover them in June 1993. While transiting between mooring sites
hourly XBTs and meteorological observations were taken. This report
describes the work that was accomplished during Oceanus 250 Legs 1
and 2, including summaries of the instrumentation that was recovered
and deployed, and underway activites, i.e. XBT sections,
meteorological observations and ALACE launches. A brief chronology of
the cruise events is included.

Table 1:  Subduction I  Mooring Deployment and Recovery Positions

Buoy     Mooring #   Deployment Time (UTC)  Recovery Time     Position (GPS)
NE        914        18 Jun 1991 1642       14 Feb 1992 2315  33 00.07N
                                                              21 59.75W
C         915        23 Jun 1991 0026       11 Feb 1992 1120  25 31.90N
                                                              28 59.75W
SW        916        25 Jun 1991 1312       02 Feb 1992 0727  18 00.03N
                                           *04 Feb 1992 1844  33 59.96W
SE        917        29 Jun 1991 0137       20 Oct 1991 0000  18 00.13N
                                          **08 Feb 1992 0843  22 00.00W
NW        918        03 Jul 1991 1323       15 Sep 1991 2035  32 54.61N
                                         ***23 Feb 1992 1022  33 53.50W

*    SW Mooring broke free on 3 Nov 1991.  Top 110m recovered 2 Feb 1992, 
     remainder of mooring recovered 4 Feb 1992.
**   SE Mooring broke free on 10 Oct 1991.  Top 50m recovered 30 Oct 1991, 
     remainder of mooring recovered 8 Feb 1992.
***  NW Mooring broke free on 3 Aug 1991.  Top 400m recovered 15 Sep 1991,
     remainder of mooring recovered 23 Feb 1992.


Table 2:  Subduction II  Mooring Deployment Positions

Buoy     Mooring #   Deployment Time (UTC)  Position (GPS)
SW        924        05 Feb 1992 1318       17 59.93N
                                            34 00.65W
SE        925        09 Feb 1992 0244       17 59.72N
                                            22 00.29W
C         926        12 Feb 1992 1915       25 31.95N
                                            28.57.23W
NE        927        20 Feb 1992 1547       33 01.98N
                                            22 00.27W
NW        928        23 Feb 1992 2328       32 54.42N
                                            33 53.35W

Scientific Goals

Subduction is the mechanism by which water masses formed in the mixed
layer and near surface layer of the ocean through air-sea
interactions find their way into the upper thermocline. The basic
idea that fluid in the ocean's interior originates at the sea surface
is an old one, dating from Iselin and Montgomery in the late 1930's,
but only recently have simple models begun to provide a framework for
a dynamical understanding of the processes involved in subduction. In
essence, the study of the subduction processes and mechanisms
involves an understanding of the complete three-dimensional
circulation in the upper ocean and the coupling of the mixed layer to
the interior of the ocean. The work proposed under the auspices of
the Subduction ARI will attempt to understand subduction and its
underlying mechanisms through a combination of Eulerian and
Lagrangian measurements of velocity, measurements of the tracer
distributions and hydrographic properties and modelling. Measurements
will be made on synoptic scales in frontal regions as well as on
larger scales appropriate to the structure of the quasi-steady
wind-driven and thermohaline circulation.
The large scale structure of the surface wind and thermal forcing and
the upper ocean response will be observed by a moored array of
surface meteorological packages, current meters and acoustic doppler
profilers. The meteorological data collection is supported jointly by
the Subduction and Atlantic Stratocumulus Transition Experiment
(ASTEX) programs.

Cruise Participants

Robert A. Weller, Chief Scientist	(WHOI)
Richard P. Trask                 	(WHOI Research Specialist)
William Ostrom                   	(WHOI Senior Research Assistant)
Bryan Way                        	(WHOI Engineering Assistant)
Paul Bouchard                    	(WHOI Engineering Assistant)
Neil McPhee                      	(WHOI Engineering Assistant)
Nancy Pennington                 	(WHOI Senior Research Assistant)
Nan Galbraith                    	(WHOI Information Systems
						 Associate)
Lloyd Regier                     	(SIO Design Engineer)
Glenn Pezolli                    	(SIO Development Technician)

Underway Measurements

From the time the ship left Woods Hole meteorological data from a
shipboard IMET system mounted on the bow mast were recorded on
optical disk. The IMET parameters included, wind speed, wind
direction, air temperature, seawater temperature, relative humidity,
precipitation, shortwave radiation, and barometric pressure. One
minute averages were recorded. In addition to the data being
collected by the IMET sensors, an independent set of hourly
meteorological observations were collected and recorded by hand.
These included wet and dry bulb temperatures (using a Bendix
psychrometer), sea surface temperature (using a bucket thermometer),
visual cloud cover estimates, and wind speed, wind direction, and
barometric pressure from the ship's sensors, as well as chaps sPeed
and direction.

A total of 11 SIO Autonomous LAgrangian Circulation Explorers were
deployed during OC-250. 

Three hundred XBTs were deployed during OC-250. The T-7 probes were
purchased from Spartan of Canada. XBT data was logged on a NEC APC IV
which has a Spartan data aquisition microprocessor card installed.
The digital data is simultaneously logged in memory and plotted on
the screen. In all there were very few probes that failed to produce
reasonable data. 

Cruise Track and Mooring Stations

Oceanus Cruise Number 250 departed Woods Hole on Saturday, January
25, 1992 at 11 :30 UTC. The purpose of the cruise was to recover and
redeploy the array of five surface moorings deployed in June/July
1991 as part of the ONR funded ASTEX and Subduction Experiment. This
is the second of four scheduled mooring cruises planned for this
experiment.

Southwest Mooring

The Oceanus arrived at the drifting toroid buoy at 0515 UTC on
Sunday, February 2, 1992 at position 15ƒ 13.09' N, 44ƒ 47.48' W. The
buoy's marine lantern was first sited at a distance of approximately
5 miles . After a brief opportunity for fishing, the buoy and parted
mooring were brought aboard. An XBT (#44) was taken while along side
the buoy prior to recovery. A total of 6 SIO Vector Measuring Current
Meters (VMCMs at 1 Om, 30m, 50m, 70m, 90m, and 110m), 2 WHOI Brancker
temperature recorders (80m,100m) and 1 SIO Brancker temperature
recorder (60m) were recovered. The last item to be recovered was the
110 meter current meter.

With the upper part of the mooring aboard the Oceanus got underway at
07:30 UTC for the original Southwest mooring site at 18ƒ 00.03'N, 33ƒ
59.96'W. The ship arrived at the site on 4 February 1992 at 1152 UTC.
Upon arriving at the site the location of the anchor was checked by
ranging on the acoustic release from approximately 2 miles away. The
range obtained confirmed the original anchor position obtained during
the setting cruise in June/July 91. The ship was then positioned
one-half mile down wind of the anchor position and the release was
fired at 1235 UTC. Recovery of the bottom of the mooring was
initiated at 1430 UTC. By 1843 UTC the entire parted mooring was on
board. The entire mooring was therefore recovered.

With the mooring aboard attention was turned to preparing for
redeployment. The deck was cleared and off spooling the wire on the
winch was begun. Simultaneously three acoustic releases were wire
tested using the CTD winch. Two SIO releases and one WHOI release
were tested to a depth of 1000 meters. These operations were followed
by rewinding the wire and nylon for the next mooring. While the
winding was taking place the ship was positioned 7 miles to the south
southwest. This was downwind of the target and slightly south to
compensate for a small northerly current.

The deployment of the upper instrumentation (10 and 30m VMCMs) and
buoy (in that order) went quite smoothly. With the buoy in the water
the ship initially had just enough way on to maintain steerage. As
more instrumentation and wire were deployed the speed through the
water was increased to .5 knot and then to 1.0 knot. Mid way through
the deployment the mooring was towed while 1800 meters of nylon and
500 meters of polypropylene were wound onto the winch. The plan was
to continue to tow until the water depth was within 40 meters of the
planned depth. Unfortunately during our approach the water was
several hundred meters shallower than what was needed. Towing had to
continue at a slow pace until the design depth was obtained. As the
ship approached the original target the water depth increased for a
sufficient distance to permit the deployment of the mooring. The
anchorwas deployed at 1318 UTC on 5 February 1992.

Following the anchor deployment the ship was repositioned to watch
the Toroid ride through the water as the anchor went to the bottom.
The toroid behaved considerably different during this deployment than
in previous deployments in June/July 91. The speed through the water
was much less (.7 kt), the buoy was not heeled over as much.

Two hours of intense meteorological observations were made as the
buoy settled into position. Meteorological observations were obtained
by the hand held and bridge sensors and logged with the IMET data
every 15 minutes. At the same time the VAWR Argos transmissions were
received directly from the buoy via the Telonics receiver aboard
ship. These data were compared at the end of the two hour period. All
observations compared well. These observations are used as a check of
instrument performance and as a final calibration point before
leaving the site. An acoustic release survey followed. The ship got
underway for the Southeast mooring location (18ƒ N and 22ƒ W) at 1750
UTC 5 February 1992. The meteorological watch was resumed and hourly
XBTs were started at 1900 UTC.

Southeast Mooring

The R/V Oceanus arrived at the Southeast site at 0507 UTC on 8 Feb
1992. This mooring was originally set on 29 June 1991 and had parted
on 10 October 1991. Since all that remained were the subsurface
components with no recovery aids such as a flashing light we waited
until daylight to release it.

While we waited a three point acoustic release survey was conducted.
The results of that survey showed that the release was within 150
meters of the position determined when the mooring was set. Also
during the wait for daylight time was spent determining the set and
drift of the ship which would aid in the deployment.

The acoustic release was fired at 0853 UTC 8 February 1992 and the
mooring was sighted at 0936. Recovery was initiated at the release
end of the mooring and proceeded very smoothly. The entire mooring
was on board by 1155 UTC.

The deck was cleared, glass balls transferred, and the discus buoy to
be deployed was moved into deployment position. A test lowering of
three acoustic releases followed along with the off spooling of the
recovered mooring and the rewinding of the new mooring

Deployment of the Southeast mooring began at 2224 UTC on 8 February
1992. The ship was positioned 4 miles to the southwest of the target.
This starting position was downwind and slightly to the north to
compensate for a southerly drift experienced earlier. The deployment
went along quite smoothly. Since the bottom was very flat and exact
positioning was not important the deployment proceeded right through
to anchor drop without any towing aside from that which was needed to
wind the remainder of the mooring onto the winch. The anchor was
deployed at 0244 UTC on 9 February 1992. Following the deployment,
four hours were spent taking meteorological observations every 15
minutes while standing by the surface buoy. An acoustic release
survey was then conducted. At the conclusion of the release survey
the ship got underway for the Central moorina site.

Central Mooring

The R/V Oceanus arrived at the Central mooring site at 1100 UTC on 11
February 1992 At a distance of approximately 1.5 miles an acoustic
range to the release was taken to ascertain whether the anchor was in
the same position as when it was deployed. The range obtained
confirmed the original anchor position. The ship then got into
position to make an approach for recovery. With the buoy just off the
bow of the ship the release commands were sent and confirmation of
release received. The ship then moved in for recovery. The buoy
appeared in good condition and came aboard without any damage. There
was a minimal amount of growth on the buoy indicating the anti
fouling paint worked well during the eight months it was in the
water. On some sections of the hull the paint had worn away and it is
unclear whether the same application of paint would work for a much
longer deployment. The same was noticed with the VMCMs that were
recovered. All the VMCMs appeared in good condition.

The mooring was off spooled and the new mooring components were wound
onto the winch beginning with the wire to nylon shot. The buoy bridle
and bridle mounted instruments were given a coat of anti-fouling
paint. At the completion of the preparatory work a decision was made
to rest for the remainder of the evening and begin the deployment
after breakfast the following day.

The deployment of the second setting of the Central mooring began at
1037 UTC on 12 February 1992. The ship was positioned 5 miles
downwind (east-southeast of the site) and proceeded at an average
speed of about .6 knots over the bottom. After the wire to nylon shot
was deployed it was necessary to tow the mooring for about 2 hours
while the remainder of the mooring was wound onto the winch. The last
cluster of balls were deployed along with the release and the mooring
was towed for about 30 minutes until the appropriate water depth was
obtained. The anchor was deployed at 1915 UTC, 12 February 92.
Following the deployment an acoustic release survey was conducted.
The ship then returned to within .25 miles of the surface buoy.
Meteorological observations were made every 15 minutes until 0100
UTC13 February 92 at which time the Oceanus got underway for the
Northeast mooring. Hourly meteorological observations were resumed
and hourly XBTs were started at 0200 UTC.

Northeast Mooring

The ship arrived at the Northeast mooring at 2253 UTC on 14 February
92 . At a distance of approximately 1.5 miles an acoustic range to
the release was taken to ascertain whether the anchor was in the same
position as when it was deployed. The range obtained confirmed the
original anchor position. The ship then got into position to make an
approach for recovery. With the buoy just off the bow of the ship the
release commands were sent. The ship then moved in for recovery. The
buoy was brought aboard without any problems.

There were considerably more goose neck barnacles on the underside of
the Northeast buoy than was observed on the Central buoy and the 10
meter VMCM also had quite a few growing on it as well. The VMCMs at
10 and 30 meters and the test sting at 20 meters had the majority of
growth.

Following the recovery of the Northeast mooring the R/V Oceanus got
underway for Madiera. The ship arrived in Funchal, Madiera at 0800Z
on 16 February 92. Work immediately began to turnaround the two
recovered buoys and instrumentation for deployment on the Northeast
and Northwest moorings. The upper part of the Northeast mooring was
wound onto the winch. The remaining reels were secured on deck. In
all there were three full days of work getting everything ready for
the second leg.

The Oceanus departed Madiera at 0800 UTC on 19 February 1992 enroute
to the Northeast mooring. The ship arrived at the Northeast site at
0600 UTC on 20 February 92. As the ship approached the site a brief
depth survey was conducted. While on location the set and drift of
the ship was established to determine the start position for the
mooring work. While steaming into the wind (northeast) at
approximately 1 knot the ship was set to the northwest. A start
position four miles to the southeast of the target was decided upon.

The deployment commenced at 0915 UTC and proceeded very smoothly.
Since the bottom was very flat and it was not necessary to hit any
particular target the mooring anchor was deployed as soon as it was
prepared. The anchor was deployed at 1547 UTC on 20 February 1992.
After the mooring had settled out an acoustic release survey was
conducted. Following the acoustic survey, meteorological observations
were taken every 15 minutes for four hours while the ship was within
.25 miles of the surface buoy. The Oceanus then got underway for the
Northwest buoy at 2152 UTC on 20 February 1992. Hourly XBTs were
resumed at 2300 UTC.

Northwest Mooring

The ship arrived at the Northwest mooring site at 0230 UTC on 23
February 1992. Since this mooring had parted in August 1991 there was
nothing on the surface and it was preferable to wait until daylight
before recovery was attempted. While waiting the ship interrogated
the release to determine if it was still operable and to see if it
was in the same location as when deployed. The release responded
without any trouble and appeared to be in the same position. A depth
survey was conducted to determine the depth variability in the
immediate target area. The new mooring design for the northwest site
permitted a +60 meters depth window around the design depth without
producing any significant effect on the mooring's performance. The
area within those limitations was identified as the "strike zone".
Deployment anywhere within the "strike zone" would be permissible.
Time was also spent determining the set and drift of the ship at the
drop site and the start position.

With daylight the ship was positioned .3 miles downwind of the anchor
position and the release was fired at 0854 UTC. The mooring was
sighted at 0909 UTC and was completely recovered by 1119 UTC.

A set and drift exercise conducted during the off spooling and
winding indicated that the ship should be positioned to the southeast
of the site and steam to the west. A slight northerly current would
set the ship to the northwest. The ship was positioned 4 miles
downwind of the mooring site to begin deployment.

The deployment began at 1756 UTC on 23 February 1992. The upper
temperature instruments and buoy were deployed very smoothly. The
mooring was towed for approximately 45 minutes while the
nylonpolypropylene shot was wound onto the winch. Deployment resumed
and the mooring was again towed with the glass balls and release
outboard. The anchor was deployed at 2328 UTC on 23 February 1992.

After the mooring had settled out an acoustic release survey was
conducted. Meteorological observations were taken everY 15 minutes
for four hours while the ship was positioned .25 miles downwind of
the buoy. At 0545 UTC 24 February 1992 the ship got underway for
Ponta Delgada, Azores. Hourly XBTs were resumed at 0900 UTC with the
last XBT deployed at 2000 UTC.

The ship arrived in the Azores on 26 February 1992 at 0900 UTC.
