Role of mesoscale eddies on the variability of biogenic flux in the northern and central Bay of Bengal

Mesoscale cyclonic eddies (cold core) are though known to enhance the phytoplankton biomass in the Bay of Bengal, their contribution to the carbon export to the deep ocean are yet to be quantified. Using biogenic flux data obtained from the sediment traps, located at 17 degrees 27N, 89 degrees 13E (northern Bay of Bengal trap: NBBT) and 13 degrees 07N, 84 degrees 24E (central Bay of Bengal trap: CBBT), we explored the variability of biogenic flux in response to cyclonic eddies. Temporal variation of the biogenic flux at NBBT (1994-1998) and CBBT (1993-1996) showed four distinct peaks with no well-defined seasonal pattern. The inverse relationship between the high flux events and sea surface height anomaly (SSHA) along with the dominant periodicity of 10-15 weeks from the Chi-square analysis of SSHA confirmed the role of eddies in the observed higher biogenic fluxes. During the eddy events, enhanced opal flux suggested eddy-driven new production, while lower carbonate to opal ratio along with high organic carbon indicated large export via diatoms. Finally, we show that 42% of the total organic carbon collected at mid-depth (approximate to 1000 m) in the Bay of Bengal is contributed by eddy-driven processes via diatom bloom making it a regional sink for CO2.