Nutrients, plankton, and productivity in a warm-core ring in the Western Gulf of Mexico.
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Argos drift buoy trajectory data showed that a region of anticyclonic circulation about 100 km in diameter was present over the upper continental slope of the NW corner of the Gulf of Mexico in September-October, 1988. Guided by these data, Texas A&M University scientists joined by colleagues from Mexico's Direccion General de Oceanografia Naval surveyed the area from October 17-22 on R/V Gyre cruise 88G-05 with a dense grid of conductivity- temperature-depth and expendable bathythermograph stations. The presence of a subsurface salinity maximum greater than 36.5 psu within the upper 150m of this anticyclone indicated that it had originated as a warm-core eddy of the Loop Current; however, a maximum of only 36.54 psu at o=25.5 in contrast to as much as 36.88 psu at this density surface in a fresh ring indicated that this feature had spent many months in the western gulf since its separation from the Loop Current. Biologically, the warm-core ring was oligotrophic: its surface waters were generally depleted in nitrate to depths of more than 100 m, and chlorophyll standing stocks (< 20 mg/m squared), primary productivity (< 0.4 mg C/(m cubed)(h), and zooplankton biomass (only 4 mL 100/m cubed day and 6 mL 100/m cubed night in the upper 200 m) were all extremely low.