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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