As part of the MaHeWa project, two Argo floats were deployed around New Caledonia in late November 2025, in the context of an ongoing marine heatwave.
A first float was deployed on 30 November 2025 from the research vessel Antea during the KASEAOPE3 mission, south of New Caledonia.
A second float was deployed from the Amborella, the Government of New Caledonia’s vessel, north of the archipelago.
These deployments took place during a marine heatwave currently classified as moderate to strong, with sea surface temperature anomalies reaching up to +3°C.
Tracking the marine heatwave… below the surface
Satellite observations provide measurements of sea surface temperature but offer limited information on subsurface conditions, where marine organisms live, move and experience thermal stress.
The deployed Argo floats will allow scientists to:
measure temperature, salinity and pressure down to 2,000 m depth;
document the vertical structure of the ongoing marine heatwave through daily profiles down to 500 m over a 15-day period;
monitor the evolution of the water column throughout the event, from the surface to the ocean interior.
These repeated profiles will provide essential data to better understand how heat accumulates and dissipates in the ocean around New Caledonia.
Opportunistic and strategic deployments
The floats were deployed from the stern platforms of the vessels, through coordinated operations between the scientific teams and ship crews.
Beyond the objectives of the MaHeWa project, these deployments also contribute to the global Argo observing system, an international reference for ocean monitoring.
In line with the MaHeWa project objectives, these observations will support analyses conducted within WP1.
Current marine heatwave conditions around New Caledonia
According to OSTIA analyses from 25 November 2025 (Copernicus Marine Service):
the region shows a positive mean sea surface temperature anomaly;
several areas west, south and south-west of Grande Terre reach +3°C anomalies;
marine heatwave categories range from moderate to strong, with localized severe cores in the south-west.
These conditions highlight the need for subsurface monitoring of the event, which is precisely the purpose of deploying these two Argo floats, in both the northern and southern regions of New Caledonia.
Photos credits : Inès mangolt.
