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3/28/95     Cruise Update from R/V Thompson

We finished the oligotrophic station (10N) a few days ago and are
beginning the transect back into the coast. The seas are calm,
the winds light, and the sun strong.  

Like Process-1, we are running the stations clockwise. We completed the 
northeastern transect in good time, and collected good data.
There were only a few hangups, but Mike Grogan and Tony Burke did
double-duty keeping operations on track and troubleshooting equipment
problems. A mysterious intestinal virus put several
of the crew and scientific party to bed for a few days, and although it
seemed hard to keep up the pace of stations, we managed to complete all
the work. Some of the first results we saw were from Guy Rosinbaum,
collecting aerosol samples. He found a tremendous decrease in the
amount of particulate matter in the atmosphere compared to Process-1.

The general trend going south was oligotrophy: increasing
stratification, clearer water, and increasing water temperatures.
Nitrate declined from 5-6 uM in the surface waters near the Gulf of
Oman to about 0.1-0.2, and then by station 11 became undetectable. By
station 8, ammonium had also vanished from the surface layer. Chlorophyll
declined from 0.5-0.9 ug/l in the north to 0.1 at station 11 the end of 
the NE transect. Near-surface maxima in chlorophyll gave way to a sharp
subsurface maximum at a depth of about 2-3% of surface irradiance. The
subsurface maximum is also a particle maximum, thus unlike many open 
ocean areas, it is not only a photoadaptation phenomenon.

Opposite the general offshore trends noted above, Dennis Hansell and Nancy
Hayward say that DOC concentrations _increase_ offshore, from 75 to  85 uM
in the mixed layer, reflecting higher nutrients and upwelled water closer
to shore. pCO2 and TCO2 declined offshore, in the case of pCO2, from 400
to 370 ppm, according to Dan O'Sullivan and Esa Peltola.  

Anne Gauzens and Juanita Urban report many more herbivorous copepods 
to the north (Eucalanus, Oithona), than on Process1, while further south 
the community consists of smaller forms. They say that the copepods are
producing fecal pellets at the rate of 1 per hour, each pellet having a
carbon concentration of 0.6 ug, or 1.4 ugC per day per copepod
(lower than EqPac). Anne also notes that in her copepod grazing experiments,
chlorophyll increases only when copepods are present (not in the
e controls). This is the same result as on Process 1, and she and Mike
Roman have hypothesized that the copepods crop the protozoans allowing the
nanophytoplankters to increase.

Rates of herbivory and bactivory are significant, although somewhat
lower than on Process-1, according to Dave Caron and Peter Countway. The
largest fraction of phytoplankton is < 5um, and loss rates are up to 0.7
per day, declining with depth. Similar rates and trends hold for bactivory.

The rate of primary production (Mike Hiscock, Carol Knudson, John Marra) is
very high, around 2 gC/m2/d, and similar to Process1, although the rate
declines to less than half that value by the station at 10 N. Still
these are very high rates, perhaps driven by high values of
nutrients, temperature and irradiance. Nitrogen production
experiments are proceeding, and Ray Sambrotto and Bonnie Mace also note
high levels of urea and large utilization of this nitrogen species.  
Bacterial production done by Hugh Ducklow and Matt Church, ranges over 
200-400 mgC/m^2/d in surface waters.  

We conducted a simple "grow-out" experiment (incubating a sample of
near-surface water from station 2 for a few days), and produced  a 
fairly heavy culture of Phaeocystis (about 50 colonies per 0.3 l) and
Rhizosolenia after two days. We recently began an experiment to see if 
common zooplankters eat the Phaeocystis. 

At station 08 (about 1000 km out), we noticed a secondary
fluorescence maximum at 150 m. At station 11 (The "Twin Peaks" station) Jeff 
Kinder managed to trip a bottle in the maximum. Mikel Latasa (UH) noticed
that his filter for this sample was a light blue-green. Dave Caron said
that the secondary max was also seen on Process-1, and identified as 
consisting of a population of Prochlorococcus. Dave confirmed that
assesment for this sample using his epifluorescence microscope. Chuck 
Trees made an absorption spectrum of the filtered material, and said
that it was unusual in having a double-peak at 440-500 (with one maximum 
at 490), and a broad peak in the red region of the spectrum. Mikel also
noted that the concentration of chlorophyll measured by the Turner was no
different than zero because of a very high Fa (acid) value, indicating that 
a substantial fraction of the pigment was chl-b. We incubated a sample for
24h with 14C at 1%Io, but Carol said the uptake was very small. Samples 
for nutrients, gases, POC, DOC, and bacteria, were, of course, also taken
for later analysis.

The secondary fluorescence peak also coincides with a salinity minimum. The 
literature suggests that the salinity minimum is a water mass formed along
the coast of India during the NE monsoon, and spreads at depth in the
eastern Arabian Sea. The cells in the layer certainly appear viable
(although their PS rate must be very low), so it is uncertain whether they
are a remnant of subduction, or growing happily at a few milliEin m^-2 d^-1.

The oxygen minimum zone extends from about 200-1000 m, and the
concentrations, according to Ron Patrick of the Hydro team, are
near zero. Still, Anna Fahrenkopf ((UDel) says there are large quantities 
of iodide in the OMZ, 50x greater than the Atlantic or Pacific, and from
comparable stations during the SW monsoon. Iodate reduction may be
greater than nitrate reduction and experiments are underway to isolate the
responsible agents. Among nitrogen species, however, nitrite  went
"off-scale" according to Kathy Krogslund of the Hydro team, at one station
reaching concentrations of 6 uM. The nitrite max is in the upper part of 
the OMZ,  between 250-350m.  Marcia Gowing and Karen Wishner collected
a great set of MOCNESS samples at various oxygen levels in the OMZ and
noted substantial faunal differences layers-to-layer.

Becky Reitmeyer (UH) reports that Fe and Al concentrations are 0.5-1 nm in the
surface layers. They are lower than on Process-1, which is what she and
Chris Measures expected (and agrees with Guy's dust samples, and decrease
going offshore. 

Mary-Jo Richardson-Gardner has an ac-3 absorption-meter/transmissometer
in-line with the ship's uncontaminated seawater line. Notable in the data
is a diurnal signal in transmittance of about 1.5-2% in amplitude. 

Brent Lewis has been collecting samples for metals (in the OMZ), and John
Andrews is doing the same for the Thorium series, to be analyzed in their
respective labs after the cruise.

The CTD team (Jeff Kinder, Richard Korman, Mike Grogan and Tony Burke) 
continue to produce high quality hydrographic data and, and the same goes
for the chemical analysis team of Ron Patrick, Kathy Krogslund, Dennis
Guffy, Walter Schmitt, Howard Rutherford and Rhonda Kelly. The deck
and sampling operations are smooth, consistent, and professional, and much
appreciated by the PI's. The data is on-line very soon after the water is 
collected, and we have had the opportunity to visualize some of the data
collected thus far. With lots of help from Cheng Ho back at LDEO, we have
been able to produce depth-distance sections of the CTD and nutrient data, 
using THOMPSON's Sparc station and GMT system. 

The sections give us a good overall picture of the water column and how it
has changed going south. Overall, it appears that water at
depth is moving north, and the temperature, salinity and density contours all
suggest upwelling near Oman. The NE section shows about the same increase in
surface temperature going south seen in the AVHRR images that are sent
to the ship by Mark Luther. The nutrient data also support upwelling;
the sections showing the offshore decreasing gradient in surface nitrate.
The fluorescence data (roughly, chlorophyll biomass) show a maximum 
at about 600 km out from Oman, corresponding to stations 5 and 6.

We have observed some human impacts. During a transit, Eric (the 3rd
mate) on his watch saw a large sea turtle swimming with its hind leg
entangled in a drift net, and dragging an also entangled dead shark. 

Haven't seen any marlin, yet, although sharks (mostly white-tip) and squid
have been hanging out at night in the ship's lights, and tuna schools have
been passing by.

A color front zipped by as we transited to to Station 13, and crossing it
may have put us in a gradient region near the North Equatorial Current.
According to THOMPSON Captain Glenn Gomes, our drifter traveled 8 nm WNW in
12h on 24 March.

We've all enjoyed the tremendous support, assistance, friendliness, and
good cheer of the Captain and crew of the THOMPSON. We're running
smoothly and we're ready for the second transect of stations. 

John Marra is Chief Scientist on Process Cruise 2.