Unique ocean circulation pathways reshape the Indian Ocean oxygen minimum zone with warming

<p>The global ocean is losing oxygen with warming. Observations and Earth system model projections, however, suggest that this global ocean deoxygenation does not equate to a simple and systematic expansion of tropical oxygen minimum zones (OMZs). Previous studies have focused on the Pacific O...

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Main Authors: S. Ditkovsky, L. Resplandy, J. Busecke
Format: Article
Language:English
Published: Copernicus Publications 2023-11-01
Series:Biogeosciences
Online Access:https://bg.copernicus.org/articles/20/4711/2023/bg-20-4711-2023.pdf
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author S. Ditkovsky
L. Resplandy
J. Busecke
author_facet S. Ditkovsky
L. Resplandy
J. Busecke
author_sort S. Ditkovsky
collection DOAJ
description <p>The global ocean is losing oxygen with warming. Observations and Earth system model projections, however, suggest that this global ocean deoxygenation does not equate to a simple and systematic expansion of tropical oxygen minimum zones (OMZs). Previous studies have focused on the Pacific Ocean; they showed that the outer OMZ deoxygenates and expands as oxygen supply by advective transport weakens, the OMZ core oxygenates and contracts due to a shift in the composition of the source waters supplied by slow mixing, and in between these two regimes oxygen is redistributed with little effect on OMZ volume. Here, we examine the OMZ response to warming in the Indian Ocean using an ensemble of Earth system model high-emissions scenario experiments from the Coupled Model Intercomparison Project Phase 6. We find a similar expansion–redistribution–contraction response but show that the unique ocean circulation pathways of the Indian Ocean lead to far more prominent OMZ contraction and redistribution regimes than in the Pacific Ocean. As a result, only the outermost volumes (<span class="inline-formula">oxygen&gt;180</span> <span class="inline-formula">µmol kg<sup>−1</sup></span>) expand. The Indian Ocean experiences a broad oxygenation in the southwest driven by a reduction in waters supplied by the Indonesian Throughflow in favor of high-oxygen waters supplied from the southern Indian Ocean gyre. Models also project a strong localized deoxygenation in the northern Arabian Sea due to the rapid warming and shoaling of marginal sea outflows (Red Sea and Persian Gulf) and increases in local stratification with warming. We extend the existing conceptual framework used to explain the Pacific OMZ response to interpret the response in the Indian Ocean.</p>
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spelling doaj.art-20ceafad45394afb962e0e340d9840142023-11-29T11:29:29ZengCopernicus PublicationsBiogeosciences1726-41701726-41892023-11-01204711473610.5194/bg-20-4711-2023Unique ocean circulation pathways reshape the Indian Ocean oxygen minimum zone with warmingS. Ditkovsky0L. Resplandy1J. Busecke2Program in Atmospheric and Oceanic Sciences, Princeton University, Princeton, NJ, USADepartment of Geosciences and High Meadows Environmental Institute, Princeton University, Princeton, NJ, USALamont-Doherty Earth Observatory, Columbia University, New York, NY, USA<p>The global ocean is losing oxygen with warming. Observations and Earth system model projections, however, suggest that this global ocean deoxygenation does not equate to a simple and systematic expansion of tropical oxygen minimum zones (OMZs). Previous studies have focused on the Pacific Ocean; they showed that the outer OMZ deoxygenates and expands as oxygen supply by advective transport weakens, the OMZ core oxygenates and contracts due to a shift in the composition of the source waters supplied by slow mixing, and in between these two regimes oxygen is redistributed with little effect on OMZ volume. Here, we examine the OMZ response to warming in the Indian Ocean using an ensemble of Earth system model high-emissions scenario experiments from the Coupled Model Intercomparison Project Phase 6. We find a similar expansion–redistribution–contraction response but show that the unique ocean circulation pathways of the Indian Ocean lead to far more prominent OMZ contraction and redistribution regimes than in the Pacific Ocean. As a result, only the outermost volumes (<span class="inline-formula">oxygen&gt;180</span> <span class="inline-formula">µmol kg<sup>−1</sup></span>) expand. The Indian Ocean experiences a broad oxygenation in the southwest driven by a reduction in waters supplied by the Indonesian Throughflow in favor of high-oxygen waters supplied from the southern Indian Ocean gyre. Models also project a strong localized deoxygenation in the northern Arabian Sea due to the rapid warming and shoaling of marginal sea outflows (Red Sea and Persian Gulf) and increases in local stratification with warming. We extend the existing conceptual framework used to explain the Pacific OMZ response to interpret the response in the Indian Ocean.</p>https://bg.copernicus.org/articles/20/4711/2023/bg-20-4711-2023.pdf
spellingShingle S. Ditkovsky
L. Resplandy
J. Busecke
Unique ocean circulation pathways reshape the Indian Ocean oxygen minimum zone with warming
Biogeosciences
title Unique ocean circulation pathways reshape the Indian Ocean oxygen minimum zone with warming
title_full Unique ocean circulation pathways reshape the Indian Ocean oxygen minimum zone with warming
title_fullStr Unique ocean circulation pathways reshape the Indian Ocean oxygen minimum zone with warming
title_full_unstemmed Unique ocean circulation pathways reshape the Indian Ocean oxygen minimum zone with warming
title_short Unique ocean circulation pathways reshape the Indian Ocean oxygen minimum zone with warming
title_sort unique ocean circulation pathways reshape the indian ocean oxygen minimum zone with warming
url https://bg.copernicus.org/articles/20/4711/2023/bg-20-4711-2023.pdf
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