As part of WP1, which focuses on exposure to thermal stress, an Argo float was deployed on 30 November 2025 from the research vessel Antea during the KASEAOPE3 mission, in order to document the ongoing marine heatwave south of New Caledonia. This event is currently classified as moderate to strong, with temperature anomalies reaching +3°C at the surface according to OSTIA analyses from 25 November 2025 (Copernicus Marine Service). This deployment offers a unique opportunity to observe the vertical structure of the warming associated with this MHW.
While satellites provide information on sea-surface temperature, they do not reveal what is happening deeper in the water column, where marine organisms live and directly experience thermal stress. The Argo float will measure temperature, salinity and pressure down to 2,000 metres. It will collect daily profiles down to 500 metres over 15 days, documenting the vertical evolution of the marine heatwave and monitoring the dynamics of the water column from the surface to the ocean interior.
The resulting data will help assess how heat accumulates or dissipates in the region, supplying essential information for analyses conducted under WP1 tasks 1.1 and 1.2. These observations will support the identification of zones that are most exposed or sheltered from marine heatwaves, a key objective for understanding risk patterns across the territories studied in MaHeWa.
The deployment was carried out at night from the aft deck of Antea, thanks to efficient coordination between the scientific team of the KASEAOPE3 mission and the crew on board. This action also contributes to the global Argo network, an international reference programme for ocean monitoring. The collected data will complement those used within WP1 and strengthen observational capabilities for tracking MHWs both at large scale and in coastal systems.
According to OSTIA analyses dated 25 November 2025 (Copernicus Marine Service), the region presents a positive mean anomaly, with some areas in the south, west and southwest of Grande Terre reaching +3°C at the surface. Marine heatwave categories range from moderate to strong, with localised severe cores in the southwest. These conditions confirm the importance of monitoring the event at depth, which is precisely what the Argo float will enable.
Photo credit: Inès Mangolte.
