Upwelling induced productivity and coastal eutrophication in the eastern Arabian Sea since the late Marine Isotope Stage 3

We present the multiproxy record of relative abundances of benthic foraminifera, planktic foraminiferGlobigerina bulloides, and dissolution and replacement features in the tests of foraminifera from Core SK291/GC17, located on the outer continental shelf of the eastern Arabian Sea (EAS). The sediment cores encompass an age range of ~40,000 to 3,500 calibrated years before present (cal yr BP). Distinctly high relative abundance ofG. bulloidessuggests strong upwelling and associated high productivity caused by intense Indian summer monsoon (ISM) winds in the EAS during ~40,000-29,000 cal yr BP, i.e., the late Marine Isotope Stage 3 (MIS 3). As the sea level was about 60-80 m lower than the recent time, increased continental influx driven by high monsoonal precipitation caused a eutrophic condition in the shallow EAS. This eutrophication led to an oxygen-deficient state at the sediment-water interface, evident from the dominance of dysoxic-suboxic and synchronous subjugation of oxic benthic foraminifera. Partial pyritization of foraminifera tests was observed during this interval, suggesting iron-rich continental influx to the study area. During the Last Glacial Maximum (LGM), a lower mean sea level and weak upwelling caused a mesotrophic and relatively well-oxygenated condition at Core SK291/GC17. The gradual rise of sea level till the early-middle Holocene increased the distance between the studied core and the coastline, thus reducing the influence of terrigenous influx. Further, the studied core has been below the upper horizon of the Oxygen Minimum Zone since the early Holocene, which is corroborated by the decline of the oxic group of benthic foraminifera and the low diversity index.