What drives the biological productivity of the northern Indian Ocean?
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Date
2009Author
PrasannaKumar, S.
Narvekar, J.
Nuncio, M.
Gauns, M.
Sardessai, S.
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The northern Indian Ocean consists of two unique tropical basins: the Arabian Sea and the Bay of Bengal. The Arabian Sea is one of the most highly productive regions of the world ocean, while the Bay of Bengal is a basin of low productivity. In this chapter we summarize the biological productivity of these two basins and explore the reasons for this dissimilarity in light of the prevailing atmospheric forcing and associated oceanic processes based on in situ and remote sensing data. The high biological productivity of the Arabian Sea was driven by seasonally changing physical processes in accordance with the semiannual switching of atmospheric forcing. In summer the high biological productivity was triggered by a combination of wind-driven mixing, Ekman pumping associated with the cyclonic wind stress curl, and advection of nutrient-rich waters from the upwelling regions off Somalia and Arabia into the central Arabian Sea, whereas the winter blooms were triggered by winter convection and nutrient injection into the euphotic zone. In contrast, the biological productivity of the Bay of Bengal, situated in a similar latitude and subjected to similar wind forcing, was regulated by a set of different mechanisms. The large freshwater influx during summer inhibits the upward transport of nutrients to the euphotic zone by wind mixing thereby curtailing the biological productivity. The mesoscale eddies, which are ubiquitous in the Bay of Bengal, controlled the bulk of the observed biological productivity. In addition, the tropical cyclones occurring during spring and fall intermonsoons also trigger high biological productivity over short periods
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