Distinct oxygenation modes of the Gulf of Oman during the past 43,000 years – a multi-proxy approach

Abstract. Climatic conditions and its change shape the strength and extent of the oxygen minimum zone (OMZ). The presence and variability of the OMZ in the Arabian Sea is of importance for their ecosystem. The state of oxygenation has, for instance, an impact on the pelagic and benthic faunal community or the nitrogen and carbon cycles. The understanding of the dynamics of the OMZ, its marine environmental is of importance due to its climate feedbacks. In this study, we combined three independent proxies to reconstruct the oxygenation state of the water column and bottom water in the Gulf of Oman for the past about 43 ka for the first time. We used nitrogen isotopes (δ¹⁵N) as well as the alkane ratio (lycopane + n-C₃₅)/n-C₃₁ and benthic foraminiferal faunal analysis to reconstruct the strength of the OMZ in the water column and bottom water oxygenation, respectively. Our results show that the Gulf of Oman experienced strong pronounced OMZ and bottom water deoxygenation during the Holocene. Contrary, during the Last Glacial Maximum (LGM)/ Marine Isotope Stage (MIS) 2 the Gulf of Oman was very well ventilated with a highly diverse benthic foraminiferal community. This may have been caused by stronger wind-induced mixing and better ventilation by oxygen-rich water masses. Our results also show moderate oxygenation during MIS 3 with deoxygenation events during most of the warmer Dansgaard-Oeschger (D/O) events. We propose two distinct oxygenation modes for the Gulf of Oman: 1) a stable period of either strongly pronounced water column OMZ and bottom water deoxygenation or well-oxygenated water column and bottom water conditions and 2) an unstable period of oscillating oxygenation states between moderately oxygenated (stadials) and deoxygenated (interstadial, D/O events) conditions.