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Date: Wed, 20 Dec 1995 20:26:52 +0000 (GMT)
12/21/95 Process 7 Cruise Report
Greetings from the Middle East - the Arabian Sea to be precise! As you prepare
for your holiday season, rest assured that we are out here diligently collecting
samples and data to be analyzed during the coming year. Unlike the federal
government, we have not shut down operations. As you sit down to your Christmas
feasts, we will be finishing up the last Long station on the southern transect.
We'll pause to have our own feast, sing a few carols, exchange gifts, enjoy the
starry night, and maybe pull in a few more tuna. The Christmas ornament contest
revealed some incredible talent, ingenuity and creativity! Top prize went to a
small machined brass candle and candlestick holder. Other winners and notables
were a miniature nativity scene, a CTD rosette with angels whirling around the
outside, Santa with his sleigh and reindeer, a wooden medallion with a carving
of the ship on one side, origami, Santa riding a CTD rosette, and Frosty the
Snowman with LED buttons, nose, and a winking eye. You wouldn't believe how odd
lab items can be turned into attractive ornaments!
On the science front, things couldn't be going smoother. The MocNess and other
nets are providing great samples, the CTD operation runs like clockwork, and the
primary productivity array is always snagged on the first try by Mike Grogan.
The latest report from Lou Codispoti and the hydro-team falls in the "no-news is
good news category. Things are progressing smoothly with approximately 125 CTD
casts completed. As on previous legs, phosphate and silicate were always
abundant in the photi c zone compared to the sum of nitrate, nitrite and
ammonium. South of about 15 degrees, inorganic nitrogen concentrations were
frequently less than 0.1 micromolar suggesting nutrient limitation of
phytoplankton growth. As we proceeded northwest, nitrate concentrations of more
than 1 micromolar were common in the surface layers and coincided with
detectable ammonium and nitrite concentrations suggesting that phytoplankton
growth was not limited by major plant nutrients. Mixed layers on the order of 50
m de ep suggest that light limitation might be more important in this area.
These conditions are reminiscent of conditions encountered during process Leg 1,
which occurred during January-February, except that surface nutrient
concentrations may not be quite as high during the present cruise.
At oligotrophic stations, Lisa Campbell reports that phytoplankton community
growth rates were equal to or exceeded those obtained during the SW monsoon.
Also, in contrast to the coastal stations, nutrient addition experiments at the
oligotrophic station s indicate growth may be limited by nutrient availability.
What we had earlier characterized as a minimum in small, optically-sensed
particles at the top of the Oxygen Minimum Zone (OMZ) based on 200 m casts from
past cruises is actually the normal decrease with depth for particle
concentrations. The minimum is actually the top of an increase in particle
concentration associated with the OMZ that peaks around 250m and decreases to
normal deep-water values by 500 m. At stations 10-18 there was often a
pronounced fluorescence peak at 130 m. The particle and fluor escnece peaks do
not seem to be advective features, yet they are well below the 1% light level.
At station 18, fluorescence values at the 120 m peak were as high as values in
the upper 50 m. The deep fluorescence peaks were not prominant in this area du
ring the SW monsoon. Hopefully samples for bacteria, flow cytometry,
microzooplankton, and aggregate distributions will shed some light on these
anomalous distributions. As we move northwest on the southern transect we are
seeing more and more marine snow with the TAMU Large Aggregate Profiling System
in the upper 100 m with a sharp drop at the small-particle "minimum." There
appear to be few large aggregates in the OMZ, but their abundance increases
somewhat below the OMZ.
Favorable weather has been a tremendous help in acquisition and processing of
good radiometric profile data at each daylight station, and providing real-time
support for the primary productivity project; also, Dan Sullivan is attempting
to measure in-situ spectral absorption and beam attenuation to complement
discrete sampling and filtering for spectral particulate absorption.
Marsha Gowing reports that the previously described sampling program for
microzooplankton and phytoplankton distribution and abundance continued at
stations 8-23. Phytoplankton tows in the mixed layer consistently contained
acantharians, Rhizosolenia (wi th Richelia at station 11), Planktoniella
(occasionally with epibionts), and Chaetoceros (occasionally with epibiotic
ciliates). Filamentous cyanobacteria occurred at stations 8-11 and 16, and
Phaeocystis colonies were noted at stations 17 and 23. Station 21 was
characterized by a bloom of Noctiluca.
Biomass of zooplankton has seemed low compared with the southwest monsoon until
station 21 according to Sharon Smith. In many places, there were so few
scatterers below 100 meters that the acoustic Doppler current profiler was
unable to record any curren t. At station 17 (14deg27'N, 65degE) we encountered
a patch of salps, the first we've seen this year (or ever in my experience out
here). Now, at station 24, we again find the swimming crab Charybdis smithii at
the surface, but no sign of the upwelling- associated copepod Calanoides
carinatus. At the beginning of this cruise, C. carinatus was still at the
surface nearshore (station 1-3). Calanoides carinatus probably has completed
its ontogenetic migration to depth. The overall impression we have of t he
upper layer zooplankton this cruise is of small calanoids and cyclopoids in the
company of large numbers of predators, especially species of Euchaeta.
Sampling is proceding well for all other groups, too, but they are heavily
involved in the marathon of Long stations at the end of the cruise. Our two
Omani observers, Ali Al Harassi and Khalfan Al Rashdi, have been an integral
component of the sampling and analysis program and have been as diligent and
effective as anyone on the ship, and that is saying a lot, because the
cooperation and efforts of everyone have been impressive. We hope everything is
going as well for you as it is out here! We just hope the good weather persists
while we clean out and pack up the ship. We won't be "home for Christmas" in
person, but we'll be there in spirit. We wish you all the best from all of us!
Wilford D. Gardner is firstname.lastname@example.org