Coccolith Chemistry as Proxy of Coccolithophorid Productivity Response to Monsoon Cycles

Coccolithophorid algae are important to the marine biologic carbon pump because their coccoliths are believed to be the dominant ballast increasing the transfer efficiency of organic carbon into the deep sea. Efforts to reconstruct coccolithophorid production from CaCO3 accumulation are complicated by variable dissolution, hence we use sediment traps to explore coccolith chemistry (Sr/Ca and stable isotopes) as a proxy for coccolithophorid production. In biogenically dominated fluxes of the Arabian Sea, coccolith Sr/Ca covaries with primary productivity, coccolithophorid calcification, and coccolith export to shallow 1000m traps. However in Bay of Bengal traps lithogenic fluxes during the southwest monsoon dramatically increase export of all coccoliths during the southwest monsoon, although Sr/Ca and productivity of some species is highest in Northeast monsoon. In Quaternary coccoliths from the Bay of Bengal and Arabian Sea Sr/Ca variations closely track precessional monsoon cycles. In the Arabian Sea, strong summer monsoons drive high productivity due to increased upwelling intensity. In contrast in the Bay of Bengal high productivity during monsoon maxima likely reflects either shifts in chemical weathering intensity or in groundwater nitrate release due to increased vegetation and runoff.