Is the biological productivity in the Bay of Bengal light limited

Abstract

Recent measurements of chlorophyll, primary productivity (PP) and nutrients along the central Bay of Bengal (BOB) during summer, fall and spring inter-monsoons showed that the northern bay becomes less productive compared to the south in summer and fall intermonsoon, in spite of the nutrient input to the upper ocean by way of river influx as well as eddy-pumping. Along the western boundary also, highest PP in the northern bay did not occur during summer or in the fall intermonsoon, but occurred in the spring intermonsoon. The reason for this was explored using diffuse attenuation (K d (490)) and photosynthetically active radiation (PAR) which indicates the influence of the river flux in curtailing the downward penetration of solar radiation and cloud cover respectively. During summer and fall intermonsoon, biological productivity in the northern BOB is severely limited by the reduced downward penetration of solar radiation due to the large quantities of sediment brought by the adjoining rivers. Though the cloud cover reduces PAR in the northern BOB, this has only a secondary effect in comparison to the light limitation due to turbidity, which showed an order of magnitude increase in the northern Bay.