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From Ken Brink

2/17/95    SeaSoar Cruise Update from R/V THOMPSON

The second Arabian Sea SeaSoar cruise left Muscat February 8 on the R/V Thompson. The goal of the effort is to understand changes in upper ocean physical and biological structure over the courseof an annual cycle. (The first cruise took place November-December 1994). Participating groups are led by Brink (SeaSoar), Wood/Sherry (phytoplankton distribution and abundance), Yentsch/Phinney (particulate counts and pigments), Jones (nutrients and hydrography) and Tindale/Rosinbaum (aerosols). In addition, we have two very helpful Omanis on board. So far, we have conducted about 8 days of SeaSoaring and done 8 hydrographic stations. The SeaSoar pattern consists of an alongshore line, turning offshore at about 18 deg onto the main JGOFS line, two "radiator" patterns (125 km square) and a "bowtie" pattern through the moored array. While there is a persistenxt relict mixed layer of about 75-100m depth, the actual mixed layer seems to be typically 40m or shallower, with only a faint temperature and salinity contrast across its base. Conditions are relatively eutrophic: surface nurtrients are generally substantial (> 0.3-1.0 micromolar) and Secchi depths are typically 12-14m. Phytoplankton cell sizes appear to represent typically larger species than during our last cruise. Spatial biological distributions show some clear correlation with physical structures (such as a substantial change in picoplankton abundances across a density front). At depth, nutrient measurements suggest active denitrification (nitrite concentrations around 3-5 micromolar at 150-250m). Weather conditions are mild, and the sailing is very smooth. At present, the port Z drive is operating, but it will be shut off again toward the end of the cruise. Otherwise the ship is operating well. The ship's complement is again friendly and extremely helpful. We are all happy to be having such a productive cruise. Ken Brink Kenneth Harold Brink is