Satellite and in situ observations of a phytoplankton bloom from coastal Bay of Bengal: role in pCO₂ modulation

Abstract

A phytoplankton bloom was monitored in coastal waters of Bay of Bengal and its influence in water column properties was investigated. Significant draw down of CO₂ was noted within the vicinity of the bloom associated with high chlorophyll biomass. Microscopic analysis revealed diatoms as the dominant population. Skeletonema costatum a diatom, reached cell density of 36,898 cells l⁻¹ within the bloom. The lowest surface pCO₂ observed was 287 μatm at the southern end of the transect covarying with surface chlorophyll of 1.090 μg l⁻¹ . At the northern end the surface pCO₂ went as low as 313 μatm. The pCO₂ levels below the mixed layer increased twice of that of surface value (∼600 μatm). The chlorophyll values observed by Ocean Colour Monitor-2 were modestly related with the in situ measurements. The primary productivity derived from growth rate, assimilation number and maximum surface chlorophyll was 160.6 mg C m⁻² day⁻¹ leading to a modest sequestration ∼of 0.08 Gg of carbon per day by the surface waters. Our observations reflects the potential role of diatom blooms on coastal carbon dynamics therefore should be carefully monitored in realm of anthropogenic changes.