Mechanism of the biological response to winter cooling in the northeastern Arabian Sea
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Date
1996Author
Madhupratap, M.
PrasannaKumar, S.
Bhattathiri, P.M.A.
DileepKumar, M.
Raghukumar, S.
Nair, K.K.C.
Ramaiah, N.
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The Arabian Sea is one of the most biologically productive ocean regions, mainly due to the upwelling of nutrients during the summer (southwest) monsoon. But the northern Arabian Sea continues to sustain fairly high biological production after the upwelling season and during much of the winter (northeast) monsoon. The processes that enable this high winter productivity have hitherto been poorly understood, being variously attributed to surface cooling effects or wind-driven changes in ocean circulation. Here we present physical, chemical and biological data that indicate that sea cooling drives convection processes that lead to the upwelling of nutrients into the surface waters of the north-eastern Arabian Sea during winter, and that this mechanism of nutrient supply is a dominant control on winter primary productivity. Observed seasonal changes in bacterial and microzooplankton populations may provide an explanation for the Arabian Sea 'paradox' that mesozooplankton biomass remains more or less invariable throughout the year
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