The Arabian Sea hosts one of the most intense and perennial oxygen minimum zones (OMZs) in the world ocean, where water-column denitrification removes a substantial fraction of global marine fixed nitrogen. This review synthesizes ecological and isotopic evidence from bulk sedimentary nitrogen isotopes (δ15N), foraminifera-bounded nitrogen isotopes (FB-δ15N), benthic foraminiferal assemblages, and geochemical proxies to reconstruct changes in Arabian Sea denitrification and oxygenation from the Last Glacial Maximum (LGM- ~26.5 - 19 ka) through the Holocene (~11.7 ka to present). Multi-proxy evidence shows that the glacial Arabian Sea OMZ was moderately better oxygenated than present, with reduced water-column denitrification evidenced by low bulk δ15N values and more diverse, oxic-tolerant benthic foraminiferal communities. The transition from the last glacial period was marked by a significant peak in δ15N, indicating increased denitrification due to enhanced monsoon-driven productivity and reduced ventilation of intermediate waters. Throughout the Holocene, the OMZ became more pronounced, as evidenced by consistently high δ15N levels and low-diversity of benthic communities adapted to low-oxygen conditions. A significant ongoing discussion revolves around the interpretation of bulk sediment δ15N compared to FB-δ15N records, with the latter indicating similar denitrification rates during the LGM and late Holocene. We have identified two distinct oxygenation patterns over the last ~43,000 years: stable phases (LGM, Holocene) and unstable phases (MIS 3) characterized by centennial- to millennial-scale fluctuations, likely influenced by Dansgaard-Oeschger cycles and variations in the Atlantic Meridional Overturning Circulation.
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