Glacial Expansion of Deoxygenation in the Arabian Sea

The mechanisms by which ongoing climate change influences ocean Oxygen Minimum Zones (OMZs) are insufficiently understood, making it essential to examine their long-term variations under substantial climatic forcing. Here, we present the first planktic foraminifera iodine-to-calcium records in two Arabian Sea sediment cores: one located within the core of the modern OMZ in the north and other on its southeastern flank, enabling us to infer the lateral extent of the OMZ across the last glacial cycle. Our results indicate persistently stronger deoxygenation in the northern Arabian Sea throughout the last glacial cycle. The OMZ expanded southward during the Last Glacial Maximum—likely driven by reduced ventilation and increased productivity from enhanced winter mixing of nutrients. During deglaciation, it retreated northward as southern-sourced intermediate waters intruded and productivity declined. We suggest that changes in ventilation and productivity, rather than water temperature, exerted the dominant control on Arabian Sea OMZ variability.