Hydrographic changes in the southern Bay of Bengal during the last ～ 65,000 y inferred from carbon and oxygen isotopes of foraminiferal fossil shells

摘要

We present δ~(13)C and δ~(18)O records of planktonic (Globigerinoides ruber) and benthic foraminifera (Cibi-cidoides spp.) from two deep sea sediment cores (SK157-15 and SK157-16) from the southern Bay of Bengal. The chronology of these gravity cores was established using eleven AMS radiocarbon ages from mixed species of planktonic foraminifera (Globigerinoides ruber and Globigerinoides sacculifer) and oxygen isotope stratigraphy. Large variations in δ~(13)C and δ~(18)O of planktonic and benthic foraminifera in these cores are suggestive of significant changes in surface and deep water masses for the ～65 ka BP. The δ~(18)O values in planktonic foraminifera in both these cores are significantly higher relative to sediment cores from the western Bay of Bengal and the Andaman Sea because of the reduced influence of riverine fresh water fluxes. Benthic δ~(13)C values in cores SK157-15 and SK157-16 exhibit significant variations in source water characteristics during the Holocene and the last glaciation. Large decrease in δ~(13)C values of bottom dwelling benthic foraminifera (Cibicidoides spp.) during the Last Glacial Maximum (LGM) and ～50-65 ka BP suggest drastic reduction in North Atlantic Deep Water (NADW) fluxes into the southern Bay of Bengal and concurrent increase of deep water formed in the Southern Ocean (SODW) with significantly low δ~(13)C values.