Significant terrigenous dilution affects the biogenic deposits in the Bay of Bengal during the last deglaciation-glaciation

The coupling relationship between biogenic deposits and productivity might vary in different stages or regions. To explore the responses of biogenic deposits to productivity since the last glacial period, we analyzed multi-biogenic data in Core YDY09 from the Bay of Bengal (BoB) over the past 30 ka. We firstly observed that the trends of biogenic deposit records (radiolarians, BSi, and CaCO3) were in antiphase to the surface productivity during the Last Glacial Maximum (LGM), Heinrich Stadial 1 (HS1) and late deglacial period (LdGp; 15-10 ka) in the northeastern Indian Ocean. We conclude that the decoupling between high surface productivity and low biogenic deposits during the LGM and LdGp was due to the significant dilution caused by large-scale terrigenous inputs. Unlike the LGM when low sea levels induced huge terrestrial material inputs, the LdGp had a rapidly rising sea level while the strong Indian summer monsoon may play a key role. Conversely, the high biogenic deposits during the HS1 were possibly due to weak terrigenous dilution because of the Intertropical Convergence Zone (ITCZ) rainfall weakening. The strong terrigenous dilution during the LGM and weak terrigenous dilution during the HS1 in the BoB were consistent with those in the northern South China Sea (SCS) except for the unique LdGp. Our findings would increase the understanding of the decoupling mechanisms between biogenic deposits and productivity in the global marginal seas.