25 May 2023
 | 25 May 2023

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

Sam Ditkovsky, Laure Resplandy, and Julius Busecke

Abstract. The global ocean is losing oxygen with warming. Observations and Earth system model projections suggest, however, 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 leads to far more prominent OMZ contraction and redistribution regimes than in the Pacific Ocean. As a result, only the outermost OMZ layers (oxygen > 180 μmol/kg) 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 South Indian 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). We extend the existing conceptual framework used to explain the Pacific OMZ response to interpret the response in the Indian Ocean.

Sam Ditkovsky et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2023-1082', Anonymous Referee #1, 27 Jun 2023
    • AC1: 'Reply on RC1', Sam Ditkovsky, 10 Aug 2023
  • RC2: 'Comment on egusphere-2023-1082', Anand Gnanadesikan, 29 Jun 2023
    • AC2: 'Reply on RC2', Sam Ditkovsky, 10 Aug 2023
  • RC3: 'Comment on egusphere-2023-1082', Anonymous Referee #3, 10 Jul 2023
    • AC3: 'Reply on RC3', Sam Ditkovsky, 10 Aug 2023

Sam Ditkovsky et al.


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Short summary
The global ocean is losing oxygen due to warming. The Indian Ocean is however gaining oxygen in large parts of the basin, and its naturally occurring oxygen minimum zone is not expanding. This rather unexpected response is explained by the unique ocean circulation of the Indian Ocean, which is bounded by a continent to the north but connected to the Pacific Ocean by the Indonesian Throughflow.