Nutrient biogeochemistry of the eastern Arabian Sea during the southwest monsoon retreat

Hydrography of the eastern Arabian Sea and associated chemical and biological responses were studied during the withdrawal phase of summer monsoon 2003. The shelf region off the southwest coast of India (10A degrees N-15A degrees N) continued to exhibit upwelling of colder (< 28.5 A degrees C), nutrient rich (nitrate > 2.0 mu M, phosphate > 0.8 mu M, silicate > 4.0 mu M) and relatively low oxygenated waters (similar to 180 mu M). The vertical advection of nutrients, coupled with anthropogenic terrestrial inputs, enhanced the levels of chlorophyll and primary productivity near the coastal margin off Cochin. The influence of both natural and anthropogenic nutrient loadings on the coastal system of the western continental shelf of India leads to eutrophication and hypoxia with negative impacts on the environment in general and fisheries in particular.