A persistent eddy in the Central Arabian Sea: potential trophic significance

Abstract

Arabian Sea is an area of strong currents, complicated flow patterns with several eddies and semi annually reversing monsoon winds. This paper deals with a cold eddy highly rich in phytoplankton in the Central Arabian Sea, centered around: 14° 25' N and 69° 20' E during January - March 1998. The eddy was about 100 km in diameter with a depth of about 4000 m and maximum chlorophyll-a concentration was 1 mg m⁻³ compared with 0.2 mg m⁻³ in the surrounding areas. Average optical depth of the area was 12 m. The occurrence of the eddy and the related oceanographic variables were inferred from SeaWiFS derived chlorophyll-a (Chl-a), NOAA Pathfinder AVHRR derived sea surface temperature, sea surface height from TOPEX altimeter and collateral information. The cold eddy formation is probably due to longshore density variation in the ocean. Due to negative sea level anomalies, associated surface divergence and upwelling process, the region of cold eddy is known to be highly productive. The cold eddy in the same location was observed during January 2000. The persistence of the eddy for more then a month indicates that this area is a rich forage ground for tuna fishery.