Preprints
https://doi.org/10.5194/egusphere-2025-3281
https://doi.org/10.5194/egusphere-2025-3281
16 Jul 2025
 | 16 Jul 2025

Characterization of Past Marine Heatwaves around South Pacific Island Countries: What really matters?

Shilpa Lal, Sophie Cravatte, Christophe Menkes, Jed Macdonald, Romain LeGendre, Ines Mangolte, Cyril Dutheil, Neil Holbrook, and Simon Nicol

Abstract. Marine heatwaves (MHWs) can have devastating and lasting impacts on marine ecosystems. We investigated past MHW characteristics around 12 southwestern Pacific Island countries and territories (PICTs) using two observed sea surface temperature products and an ocean reanalysis product. PICTs are highly dependent on their marine resources for their livelihoods: a better understanding of MHW characteristics is needed for planning and adaptation to risks associated with MHWs. Our research builds on previous studies where MHWs have been detected and described using a point-based definition. We first revisit past MHW characteristics based on their spatial extent, vertical extent and seasonality. We show that filtering MHWs by size (spatial extent) and seasonality can greatly affect their characterisation and help trace their physical drivers. We then characterise past events inside each EEZ (Economic Exclusive Zone) and at the coast with MHW indices tailored to benefit Pacific Island stakeholders. We consider two types of events: large-scale events, covering a large part of the EEZ, likely to affect pelagic fisheries, and events affecting coastal zones and ecosystems. We distinguish between events occurring in the hot season (November to April), and in the cold season (May to October). We show that all 12 PICTs experienced MHWs in the past 30 years that are getting more frequent with greater spatial extents, longer durations, but with less intensity. New Caledonia, Vanuatu, Fiji and Tonga appear to be more exposed to MHWs with longer duration, higher maximum intensity, and deeper extent compared to other countries.

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Shilpa Lal, Sophie Cravatte, Christophe Menkes, Jed Macdonald, Romain LeGendre, Ines Mangolte, Cyril Dutheil, Neil Holbrook, and Simon Nicol

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  • RC1: 'Comment on egusphere-2025-3281', Anonymous Referee #1, 27 Sep 2025
  • RC2: 'Comment on egusphere-2025-3281', Anonymous Referee #2, 02 Oct 2025
Shilpa Lal, Sophie Cravatte, Christophe Menkes, Jed Macdonald, Romain LeGendre, Ines Mangolte, Cyril Dutheil, Neil Holbrook, and Simon Nicol
Shilpa Lal, Sophie Cravatte, Christophe Menkes, Jed Macdonald, Romain LeGendre, Ines Mangolte, Cyril Dutheil, Neil Holbrook, and Simon Nicol

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Short summary
This paper characterizes historical (1981–2023) marine heatwaves in the tropical southwestern Pacific, where they pose a challenge for marine resource dependent Islands. Heatwaves are distinguished as a function of their spatial extent, signature at the coast, and seasonality, to allow a better understanding of their impacts on ecosystems. Marine heatwaves are getting longer and more frequent, with greater spatial extents. Our results aim to inform the Pacific Islands on their vulnerability.
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