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4 Apr 1995 19:00:19 +0000 (GMT)

Cruise Update from Chief Scientist, John Marra


We're now ready to  begin the "final four" stations; the one we just
departed, station 26 at about 17N/60E, a designated LONG one. The other
day we swung by the WHOI buoy, and it looked good. The Omani flag was
still attached, and the anemometer was spinning. The sea around the
mooring was "boiling" with fish (Captain Gomes' description).

We are seeing the expected gradient toward more productive waters as we
go away from the oligotrophic stations to the south. Chuck Trees said
that the euphotic zone decreased from 90 to 60 m in less than a degree
of latitude, accompanied by a change in the color of the water. Now the
euphotic zone is < 50 m in blue-green water. We thought the
fluorescence maximum would shoal but that hasn't happened much. Instead
it has become broader, the increase beginning at about 30 m and
extending down to 100 m with a peak at 40 m of about 2.5-4.5 Volts
(scale = 0-5), depending on time of day, and corresponding to about
0.5-1.0 ug Chl per liter. We've also begun to notice an oxygen maximum
in the top part of the fluorescence maximum.  Primary production
continues high. At 10N (the oligotrophic station) we went below 1 gC
per m^2 per day (that's about 0.1 mol C per m^2 per day for the
conversionally-challenged), but is back up to about 2.

Karen Wishner devised a means to sample some of the neuston that we are
seeing on occasion, and caught an unidentified siphonophore, a snail,
and a barnacle. All, by one mechanism or another, inhabit the air-water
interface. She and Marcia are noticing _Calanoides_ in diapause
("hibernating" at depth), evidenced by the presence of oil in their
bodies. Sharon has studied Calanoides, and the net-tow results may help
her explain more of its life cycle with respect to the southwest
monsoon.

Anne Gauzens and John Marra devised an experiment to see what eats
Phaeocystis (grown earlier), and Anne picked out several volunteers
from among the copepod community. One in particular, _Undinula_, Anne
thought might be a good candidate, and after the experiment, out of
five species, only Undinula showed signs of having ingested the Phaeo
colonies.  Another experiment with Undinula showed a large production
of fecal pellets ('fresh' according to Juanita Urban). A 14C-labelling
experiment is currently being analyzed.

Dave Caron finds abundant Sarcodines (Forams, Acantharians,
particularly), and even saw in a microscope sample an Acanth release
swarmers. Dennis is finding that, overall, distribution of DOC is
greater (by 5 uM) in the offshore stations, but was lowest at the
oligotrophic station at 10N.  There appears to be a broad maximum at
13-15N, with lower values north and south of this zone. As we get
closer to the coast, Guy is finding the dust concentrations picking
up.

We continue to chase down the nitrite story. Kathy Krogslund sees three
separate maxima (with high-resolution bottle trips), a small one in the
chlorophyll maximum (perhaps related to light-limited nitrate uptake),
and two at 250-400 m in the oxygen minimum zone at greater than 4 uM.
The nitrite maxima mirror minima in nitrate, implicating
denitrification.

The CTD team continues to provide excellent data and support, as does
the Hydro Team. The TM-rosette is working great, mistrips are about
0.2% of the total.

In a few hours we'll arrive at station 27, and after a MOC, initial CTD
and TM-rosette casts, we'll have two Slurps, a Bongo, a Monster, and a
NoonShot.

John Marra is sci-01@thompson.ocean.washington.edu