WHP Ref. No.:  AR11
WOCE ExpoCode: 90VE43_1
Last updated:  September 1991

CRUISE REPORT FOR THE SUBDUCTION EXPERIMENT

Chief Scientist: Robert A. Weller, Woods Hole Oceanographic Institution
Cruise:          Oceanus 240 leg 3
Dates:           June 17, 1991 to July 5, 1991
Ship:            R/V oceanus
Portd of call:   Funchal, Madeira to Ponta Delgada, Azores


OVERVIEW

R/V Oceanus cruise number 240, leg 3 departed Funchal, Madeira on 
17 June 1991 to deploy five surface moorings as part of the Office of Naval 
Research (ONR) funded Subduction and ASTEX Experiments.  This cruise 
involved both personnel and equipment from the Woods Hole Oceanographic 
Institution (WHOI) and Scripps Institution of Oceanography (SIO).   While 
transitting between moorings sites hourly XBTs and half hourly meteorological 
observations were taken.  The five surface moorings that were deployed are 
intended to stay on station for a period of eight months at which time they 
will be recovered and replaced with new moorings.  Table 1 contains the 
mooring positions and seployment times.  A total of 88 recording 
instruments were deployed on the five Subduction moorings.  There are 9 
meteorological packages, 32 current meters, 54 temperature data loggers, 
one Acoustic Doppler Current Profiler and one conductivity data logger.  
The schedule is to replace the moorings in February and October 1992 and 
then recover them in June 1993.


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 involved 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 approprate 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.


TABLE 1:  Subduction Mooring Deployment and Positions

Buoy  Mooring #  Deployment  Time (UTC)     Position (GPS)
-------------------------------------------------------------
NE      914      18-JUN-1991   16:42     33 00.07N  21 59.75W
C       915      23-JUN-1991   00:26     25 31.90N  28 57.17W
SW      916      25-JUN-1991   13:12     18 00.03N  33 59.96W
SE      917      29-JUN-1991   01:37     18 00.13N  22 00.00W
NW      918      03-JUL-1991   13:23     32 54:61N  33 53.50W


PERSONNEL

Robert A. Weller,     Chief Scientist  (WHOI)
Jeff Sherman          (SIO design engineer)
Richard P. Trask      (WHOI research specialist)
Nancy J. Pennington   (WHOI senior research assistant)
Gennaro H. Crescenti  (WHOI meteorologist)
Bryan S. Way          (WHOI engineering assistant)
Paul R. Bouchard      (WHOI engineering assistant)
William Ostrom        (WHOI senior research assistant)
Neil McPhee           (WHOI engineering assistant)
Stephen Abbott        (SIO development technician)
Glenn S Pezzoli       (SIO development technician)
Christine Murray      (SIO development technician)


WATER SAMPLING AND UNDERWAY MEASUREMENTS

Water samples were collected near the Central mooring position for 
Jim Ledwell (WHOI).  Since there was no hydro wire on board the ship a reel 
of 1/4" kevlar was wound on the TSE mooring winch.  Nine depths had 
previously been marked on the kevlar where Niskin bottles were to be placed.  
The Kevlar was deployed with a weight off the sterm and Niskin bottles 
were attached at the appropriate depths (50, 100, 150, 100, 250, 300, 350, 
400 and 450 meters). The Niskin bottles were tripped at 0135 UTC on 23 June 
1991 at position 25^32.817' N, 28^55.498' W.  The surface wire angle at the 
time the samples were collected was measured to be approximately 30 degrees.

Meteorological observations of air temperature, relative humidity, 
relative wind speed and directon, ship's speed and directon, barometric 
pressure and sea surface (bucket) temperature were recorded every 30 
minutes while underway.

After leaving Madeira on June 19, while enroute to the Central 
mooring site and throughout the remainder of the cruise hourly XBTs were 
taken.  The data was logged on a PC using a Sparton of Canada Ltd. XBT 
processor card.  The type of XBTs were Sippican T-7 probes, which provide 
temperature data to a depth of 750 meters. XBTs were not lauched when 
within approximately 10 miles of a mooring site. 


CRUISE TRACK AND MOORING STATIONS

Leg 3 of Oceanus cruise number 240 departed Funchal, Madeira on 
June 17th, 1991 at 0714 UTC to deploy five surface moorings for the ONR 
fundede Subduction and ASTEX Experiments.


During the transit to the NorthEast mooring meteorological 
observations were recorded every 30 minutes.  the first mooring to be 
deployed was the NorthEast mooring at position 33N, 22W. Upon arrival at 
the site a depth survey was conducted.  The bottom was found to be 
relatively flat with the mooring site having a coorected depth of 5264 
meters. ( Throughout the depth surveys, mooring deployments, and subsequent 
acoustic release/anchor surveys, GPS was used for all navigation.)  The 
mooring deployment began 7 nautical miles downwind (southeast) of the 
target.  The near-surface instrumentation were deployed first followed by 
the surface buoy and the remainder of the mooring.  Careful attention was 
paid to the target site so as to get the anchor as close to it as possible. 
 The anchor was deployed at 1642 UTC on 18 June 1991.  Following the 7.5 
hour deployment an acoustic release/anchor survey was conducted.  Based on 
this survey the GPS anchor position for the NorthEast Subduction mooring 
(WHOI mooring numeber 914) is 33 00.07'N, 21 59.75'W.  During the anchor 
survey the ship was positioned 1/4 mile downwind of the surface buoy and 
measurements of sea surface temperature, air temperature, relative humidity, 
barometric pressure, wind speed and direction were made every 5 minutes 
for 30 minutes.  The ship's position at the start of the meteorological 
observations was 32^59.362'N , 22^00.151'W.


Following the anchor survey the ship returned to Madeira to load 
equipment that could not git during the first part of the cruise.  One 
toroid surface buoy and three anchors with flip plates and seven wire 
baskets were loaded in Madira.  During the loading of the wire baskets the 
doing they damaged the VAWR and one solar panel on the southeast toroid 
surface buoy.  The wind speed and direction head on the VAWR was replaced 
with a spare as well as the damaged solar panel.  Upon completion of 
loading and fueling in Madeira the ship departed at 2000 on 19 June 1991 
enroute to the Central mooring site.

While enroute to the Central mooring site and throughout the 
remainder the cruise hourly XBTs were taken starting at position 31,17.67N, 
19,16.37W.  In addition to collecting XBT data, the half hour 
meteorological data was again logged.  Oceanus arrived at the Central 
Subduction mooring site at 1030 UTC on June 22, 1991.  The depth survey was 
started upon arrival.  The original proposed mooring site (25.5N, 29W) was 
found to have an irregular sloping bottom and a decision was made to move 
the site to the northeast about s nautical miles where the bottom is flat 
and uniform.  Oceanus moved to a position 7 miles down wind (southwest) of 
the new mooring site in preparation for starting the mooring deployment. 
The mooring deployment work lasted 10.5 hours.  The anchor was finally 
deployed at 0027 UTC on June 23, 1991.  The acoustic release/anchor survey 
for the Central mooring (WHOI mooring number 915) was completed.  The 
surveyed GPS anchor position is 25,31.90N, 28,57.17W which has a corrected 
water depth of 5670 meters.  Immediately following the mooring deployment 
water samples were collected for Jim Ledwell (WHOI).  Prioi to leaving the 
Central mooring site the Oceanus was positioned 1/4 mile down wind of the 
surface buoy.  Shipboard metorological observations were logged every 5 
minutes for 30 minutes using the same procedures as were used for the 
NorthEast mooring.  These intensive meteorological observations were made 
at 25,31.53N. 28,57.91W.

Oceanus arrived at the SouthWest mooring site at 2330 UTC on 24 
June 1991.  A depth survey of the site was begun immediately.  The original 
mooring site and the area around it was found to be relatively flat with a 
corrected water depth of 5307 meters.  The ship was positioned 6 miles 
downwind of the proposed mooring site and preparations were made for the 
deployment of the SouthWest Subduction mooring.  The procedure used to 
deploy the SIO toroid mooring was nearly identical to that used to deploy 
the discus moorings.  The mooring deployment lasted 8.5 hours.  An acoustic 
release/anchor survey was conducted.  based on the results of this survey 
the GPS anchor position for the Southwest Subduction mooring (WHOI Mooring 
number 916) is 18,00.03N, 33,59.96W.

Oceanus arrived at the SouthEast mooring site at 1835 UTC on June 
28,1991.  A depth survey was conducted and the bottom was found to be 
relatively flat with the proposed mooring site (18N, 22W) having a 
corrected depth of 3295 meters.  Following the depth survey the ship was 
positioned 4 nautical miles down wind/down swell to a position south 
southeast of the site.  the mooring deployment lasted 5.5 hours.  The ship 
remained near the buoy for several hours before moving off to conduct the 
anchor survey.  The results of the survey indicated the GPS anchor position 
for the Southeast Subduction mooring (WHOI mooring number 917) was 18, 00.
13N, 22,00.00W.

While enroute to the North West mooring site the Oceanus passed by 
the Central discus mooring for a brief inspection and collection of 
shipboard meteorological observations.  The ship arrived at the Central 
mooring at 0620 UTC on July 1,1991.  Prior to getting on station the buoy 
was detected on radar approximately 7 miles away and the marine lantern 
could be seen 4 miles away.  While on station shipboard meteorological 
observations were taken every 5 minutes for 45 minutes.  Since everything 
appeared functional the ship was again underway for the NorthWest site by 
0730 UTC.  The ship arrived at the NorthWest site on 3 July 1991 at 0030 
UTC.  A depth survey was started as the ship arrived at the site and it was 
soon evident that the bathymetry was extremely irregular and considerably 
shallower than had been expected.  After a detailed radiator pattern survey, 
a new site was chosen.  The corrected water depth at the new site was 
3607 meters.  The ship was then positioned at the site.  since there was 
little weight under the buoy when first deployed it had a greater tendency 
to rall than did the other toroids.  the anchor was kicked over at 1323 UTC 
in 5608 meters of water.  the final mooring deployment lasted 6 hours.  
shipboard meteorological observations were every 5 minutes for 30 minute 
while the ship remained about 1/4 mile downwind of the buoy.  the VAWR data 
telemetry was compared with shipboard observations and everything appeared 
operational.  the GPS anchor position for the NorthWest Subduction mooring 
(WHOI mooring number 918) is 32,54.61N, 33,53.50W.

Following the anchor survey the ship headed for the Azores, arriving 
Ponta Delgada on 5 July 1991 at 0828 UTC.

   

