Changes in surface conditions and associated hypoxia since the late Marine Isotope Stage 3, eastern Arabian Sea

This study presents multiproxy record of benthic foraminiferal assemblages, relative abundances of planktic foraminifer Globigerina bulloides, stable isotope ratios in benthic foraminifer Uvigerina peregrina, and signature of pyritization from Core SK291/GC17, located at a water depth of 182 m in the eastern Arabian Sea (EAS). The sediment core covers an age from ∼40,000 to 3500 calibrated years before present (cal yr BP). Distinctly high abundance of G. bulloides, suggests strong upwelling and high productivity driven by intense Indian summer monsoon (ISM) winds in the EAS during ∼40,000–29,000 cal yr BP, corresponding to the late Marine Isotope Stage 3 (MIS3). As the sea level was lower than the recent time in the MIS3, closer proximity of the core to the coast aided high continental influx, which led to eutrophic, oxygen deficient condition at the sediment-water interface. This hypoxic condition is evident from the subjugation of oxic benthic foraminifera and their very low species diversity. Framboidal pyrite aggregates were observed during the MIS 3, suggesting iron-rich continental influx to the study core followed by pyritization in the anoxic environment. During the Last Glacial Maximum (LGM), a lower sea level and weak ISM caused relatively mesotrophic (and better oxygenated) condition over Core SK291/GC17. The extreme eutrophic and associated hypoxic condition in the late MIS 3 at Core SK291/GC17 was never experienced in the younger intervals, with G. bulloides percentages showing continuous decrease.