Ventilation of the Bay of Bengal oxygen minimum zone by the Southwest Monsoon Current

Sheehan, Peter M. F., Webber, Benjamin G. M., Sanchez-Franks, Alejandra and Queste, Bastien Y. (2025) Ventilation of the Bay of Bengal oxygen minimum zone by the Southwest Monsoon Current. Ocean Science, 21 (4). 1575–1588. ISSN 1812-0784

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Abstract

Oxygen minimum zones occupy large areas of the tropical subsurface oceans and substantially alter regional biogeochemical cycles. In particular, the removal rate of bio-available nitrogen (de-nitrification) from the water column in oxygen minimum zones is disproportionate to their size. The Bay of Bengal is one of the strongest OMZs in the global oceans; however, variable sources of oxygen prevent the onset of large-scale de-nitrification. The various oxygen- supply mechanisms that maintain oxygen concentrations in the OMZ above the denitrification threshold are currently unknown. Here, using a combination of multi-platform observations and model simulations, we identify an annual supply of oxygen to the Bay of Bengal in the high-salinity core of the Southwest Monsoon Current, a seasonal circulation feature that flows northwards into the Bay during the SouthAsian southwest monsoon (i.e. June to September). Oxygen concentrations within the Southwest Monsoon Current (80 to 100 μmol kg−1) are higher than those of waters native to the Bay (i.e. < 20 μmol kg−1). These high-oxygen waters spread throughout the central and western Bay of Bengal, leading to substantial spatio-temporal variability in observed oxygen concentrations. Moreover, the northward oxygen transport of the Southwest Monsoon Current is a spatially and temporally distinct event that stands out from background oxygen transport. Model results indicate that, interannually, oxygen supply to the Bay varies with the strength of the Southwest Monsoon Current more closely than with its oxygen concentration. Consequently, we suggest that predictability of the annual oxygen flux is likely aided by understanding and predicting the physical forcing of the Southwest Monsoon Current. Our results demonstrate that the current, and in particular its high-salinity, high-oxygen core, is a feature relevant to the processes and communities that drive denitrification within the Bay of Bengal that has heretofore not been considered

Item Type:	Article
Additional Information:	Data availability: Seaglider observations (Webber et al., 2019)) are available from the British Oceanographic Data Centre: https://doi.org/10.5285/996bf53d-5448-297a-e053-6c86abc0b996. The code for MEDUSA-2 (Yool et al., 2013a) is available from the repository of Geoscientific Model Development: http://gmd.copernicus.org/articles/6/1767/2013/gmd-6-1767-2013-supplement.zip (last access: 23 July 2025, Yool et al., 2013a). The GLORYS12 ocean physics reanalysis is available from the Copernicus Marine Data Centre; here, we use GLOBAL_MULTIYEAR_PHY_001_030, which is available under the following DOI: https://doi.org/10.48670/moi-00021 (Madec, 2008; Lellouche et al., 2021). Satellite-altimeter-derived surface currents are also available from the Copernicus Marine Data Centre; here, we use SEALEVEL_GLO_PHY_L4_MY_008_047, which is available under the following DOI: https://doi.org/10.48670/moi-00148 (CLS, 2025). The observation-based climatology from the World Ocean Atlas 2023 (Locarnini et al., 2024; Reagan et al., 2024; Garcia et al., 2024) is available from https://www.ncei.noaa.gov/data/oceans/woa/WOA23/DATA/ (NOAA, 2025). Funding information: This research has been supported by the Natural Environment Research Council (grant nos. NE/L013827/1, NE/L013835/1 and NE/W003813/1), the European Research Council H2020 programme (grant no. 741120), the Office of Naval Research Global (grant no. N62909-21-1-2008) and the Svenska Forskningsrådet Formas (grant no. 2022-01536).
Uncontrolled Keywords:	sdg 14 - life below water ,/dk/atira/pure/sustainabledevelopmentgoals/life_below_water
Faculty \ School:	Faculty of Science > School of Environmental Sciences University of East Anglia Research Groups/Centres > Theme - ClimateUEA
UEA Research Groups:	Faculty of Science > Research Groups > Centre for Ocean and Atmospheric Sciences Faculty of Science > Research Groups > Climatic Research Unit
Depositing User:	LivePure Connector
Date Deposited:	16 Jun 2025 10:30
Last Modified:	18 Aug 2025 00:45
URI:	https://ueaeprints.uea.ac.uk/id/eprint/99506
DOI:	10.5194/egusphere-2024-3681

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