Abstract
AbstractAt suboxic oxygen concentrations, key biogeochemical cycles change and denitrification becomes the dominant remineralization pathway. Earth system models predict oxygen loss across most ocean basins in the next century; oxygen minimum zones near suboxia may become suboxic and therefore denitrifying. Using an ocean glider survey and historical data, we show oxygen loss in the Gulf of Oman (from 6–12 to <2 μmol kg−1) not represented in climatologies. Because of the nonlinearity between denitrification and oxygen concentration, resolutions of current Earth system models are too coarse to accurately estimate denitrification. We develop a novel physical proxy for oxygen from the glider data and use a high‐resolution physical model to show eddy stirring of oxygen across the Gulf of Oman. We use the model to investigate spatial and seasonal differences in the ratio of oxic and suboxic water across the Gulf of Oman and waters exported to the wider Arabian Sea.
Highlights
Oxygen is necessary to sustain aerobic life; it regulates biogeochemical cycling and structures marine ecosystems
Using an ocean glider survey and historical data, we show oxygen loss in the Gulf of Oman not represented in climatologies
This study has shown that the midwater decline in oxygen content of the NWAS after IIOE has led to persistent suboxic conditions in the Oxygen minimum zones (OMZ) (150 m–950 m) in the absence of Persian Gulf Water (PGW)
Summary
Oxygen is necessary to sustain aerobic life; it regulates biogeochemical cycling and structures marine ecosystems. Modeling work by Lachkar et al (2016) shows that PGW eddies transport oxygen to the wider OMZ, reducing denitrification, increasing surface nitrogen supply, and suppressing OMZ expansion They emphasize the need to better understand the processes as existing parameterizations of eddy-driven oxygen fluxes are insufficient to resolve the submesoscale variability observed in oxygen concentrations and its impacts on nitrogen budgets. We demonstrate using historical climatology and an ocean glider time series that the core of the OMZ in the Gulf of Oman has shifted from a hypoxic to a suboxic regime We illustrate that this shift is not represented in widely used climatologies and may negatively impact accuracy of projections of deoxygenation in ESM.
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