Preprints
https://doi.org/10.5194/egusphere-2024-2210
https://doi.org/10.5194/egusphere-2024-2210
06 Aug 2024
 | 06 Aug 2024

Subsurface manifestation of Marine Heatwaves in the South West Indian Ocean

Clea Baker Welch, Neil Malan, Daneeja Mawren, Tamaryn Morris, Janet Sprintall, and Juliet Clair Hermes

Abstract. Marine heatwaves (MHW) are extreme events of prolonged, anomalously warm ocean temperatures. Globally, marine heatwaves are increasing in frequency and intensity and are responsible for long-term impacts on marine ecosystems, which have devastating socio-economic consequences. A key gap in our understanding of MHWs is how they manifest in the subsurface. This paper uses satellite sea surface temperature (SST) data and in situ subsurface temperature observations from Expendable Bathythermographs (XBTs) to investigate the anomalous water temperature characteristics associated with surface identified MHWs in the South West Indian Ocean (SWIO) and how they progress through the water column. We find that the SWIO, which is dominated by the presence of mostly warm anticyclonic eddies, is characterised by moderate MHWs, and that the frequency, duration and intensity of these events are largely associated with mesoscale activity. Surface-detected MHW case studies demonstrated a strong subsurface temperature anomaly signal, with maximum intensity below the mixed layer depth. The spatial distribution of anticyclonic, warm-core eddies closely matched the distribution of the MHWs. This provides a possible mechanism for the deep extent of these surface MHWs. Improving our understanding of the interaction between mesoscale features and subsurface MHW characteristics will benefit prediction of MHWs and management of the regions’ biodiversity.

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Journal article(s) based on this preprint

05 Aug 2025
| Highlight paper
Subsurface manifestation of marine heat waves in the southwestern Indian Ocean
Clea B. Welch, Neil Malan, Daneeja Mawren, Tamaryn Morris, Janet Sprintall, and Juliet C. Hermes
Ocean Sci., 21, 1695–1708, https://doi.org/10.5194/os-21-1695-2025,https://doi.org/10.5194/os-21-1695-2025, 2025
Short summary Co-editor-in-chief
Clea Baker Welch, Neil Malan, Daneeja Mawren, Tamaryn Morris, Janet Sprintall, and Juliet Clair Hermes

Interactive discussion

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2024-2210', Anonymous Referee #1, 03 Sep 2024
    • AC1: 'Reply on RC1', Clea Welch, 31 Jan 2025
  • RC2: 'Comment on egusphere-2024-2210', Anonymous Referee #2, 18 Nov 2024
    • AC2: 'Reply on RC2', Clea Welch, 31 Jan 2025
  • EC1: 'Comment on egusphere-2024-2210', Meric Srokosz, 04 Feb 2025
    • AC3: 'Reply on EC1', Clea Welch, 05 Feb 2025

Interactive discussion

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2024-2210', Anonymous Referee #1, 03 Sep 2024
    • AC1: 'Reply on RC1', Clea Welch, 31 Jan 2025
  • RC2: 'Comment on egusphere-2024-2210', Anonymous Referee #2, 18 Nov 2024
    • AC2: 'Reply on RC2', Clea Welch, 31 Jan 2025
  • EC1: 'Comment on egusphere-2024-2210', Meric Srokosz, 04 Feb 2025
    • AC3: 'Reply on EC1', Clea Welch, 05 Feb 2025

Peer review completion

AR: Author's response | RR: Referee report | ED: Editor decision | EF: Editorial file upload
AR by Clea Welch on behalf of the Authors (31 Jan 2025)  Author's response   Author's tracked changes   Manuscript 
ED: Referee Nomination & Report Request started (04 Feb 2025) by Meric Srokosz
RR by Anonymous Referee #1 (17 Feb 2025)
RR by Anonymous Referee #2 (19 Feb 2025)
ED: Publish subject to minor revisions (review by editor) (19 Feb 2025) by Meric Srokosz
AR by Clea Welch on behalf of the Authors (06 Mar 2025)  Author's response   Author's tracked changes   Manuscript 
ED: Publish as is (10 Mar 2025) by Meric Srokosz
AR by Clea Welch on behalf of the Authors (02 Apr 2025)  Author's response   Manuscript 

Journal article(s) based on this preprint

05 Aug 2025
| Highlight paper
Subsurface manifestation of marine heat waves in the southwestern Indian Ocean
Clea B. Welch, Neil Malan, Daneeja Mawren, Tamaryn Morris, Janet Sprintall, and Juliet C. Hermes
Ocean Sci., 21, 1695–1708, https://doi.org/10.5194/os-21-1695-2025,https://doi.org/10.5194/os-21-1695-2025, 2025
Short summary Co-editor-in-chief
Clea Baker Welch, Neil Malan, Daneeja Mawren, Tamaryn Morris, Janet Sprintall, and Juliet Clair Hermes
Clea Baker Welch, Neil Malan, Daneeja Mawren, Tamaryn Morris, Janet Sprintall, and Juliet Clair Hermes

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Short summary
Marine heatwaves (MHWs) are prolonged periods of extreme ocean temperatures with significant impacts on marine ecosystems. Much research has focused on surface MHWs, but less is known about their subsurface extent. This study uses satellite and in situ data to investigate MHWs in the Southwest Indian Ocean (SWIO). We find that MHWs in the SWIO are typically moderate in severity, closely linked to mesoscale eddies, and that strong temperature anomalies extend below surface-identified MHWs.
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