Geochemical evidence for anoxic deep water in the Arabian sea during the last glaciation

Abstract

Various paleoceanographic studies have indicated that the deep ocean was probably depleted in dissolved oxygen during the last glacial period (~18 kyr B.P.; δ¹⁸O, stage 2) compared to present time. However, direct evidence of low oxygen content in the deep waters has been lacking. Here, we report geochemical evidence of near anoxic conditions in the deep Arabian Sea during the entire last glacial cycle (δ¹⁸O; stages 2, 3 and 4). Anoxia is inferred from the concomitant enrichment of organic carbon and authigenic uranium in the glacial sections of a core from the deep eastern Arabian Sea. The anoxic conditions during the last glacial period, probably caused by a change in deep water circulation, evidently enhanced preservation of organic matter and simultaneous removal of uranium from seawater.