The Bay of Bengal is traditionally considered to be a less productive basin compared to the Arabian Sea. We explore the reasons for this in the central Bay during summer. Copious rainfall and river water freshen the upper layers of the Bay by 3–7 psu during summer, and SST was warmer by 1.5–2°C than in the central Arabian Sea. This leads to a strongly stratified surface layer. The weaker winds over the Bay are unable to erode the strongly stratified surface layer, thereby restricting the turbulent wind‐driven vertical mixing to a shallow depth of <20 m. This inhibits introduction of nutrients from below, situated close to the mixed layer bottom, into the upper layers. While advection of nutrients rich water into the euphotic zone makes the Arabian Sea highly productive, this process is unlikely in the Bay of Bengal.
Reliable data on biological characteristics from the Bay of Bengal are elusive. In this paper, we present results on physics, chemistry and biology simultaneously measured
The Bay of Bengal is traditionally considered to be a less productive basin compared to the Arabian Sea. Despite the contrasting chlorophyll and primary productivity pattern, sediment trap data shows that annual fluxes of organic carbon reach comparable rates in both the basins. The traditional mechanisms of nutrient supply to the upper ocean waters cannot account for this. We propose eddy pumping as a possible mechanism of vertical transfer of nutrients across the halocline to the oligotrophic euphotic zone during summer monsoon when upper ocean is highly stratified. This would induce rapid biological uptake and in turn significantly increase biological production. In the northern Bay, riverine input acts as an additional source of nutrients and augments the subsurface nutrient injection to the euphotic zone by eddy pumping. Notwithstanding this, the lower than expected primary production in the north suggests the possible role of riverine sediment in limiting the sunlight for photosynthesis.
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