The recent data from the HOPE buoy, deployed in New Caledonia, are enriching MaHeWa’s analyses on the effects of marine heatwaves (MHWs) by revealing very high-frequency dynamics of surface planktonic biomass — capable of quadrupling within hours — which in turn accelerates the formation of carbon-rich “marine snow” that sinks toward the deep ocean.
In the tropical “ocean deserts” covering 60% of the marine surface, diazotrophs such as Trichodesmium create massive blooms acting as natural fertilizers, fixing atmospheric nitrogen to boost the food chain and carbon storage — mechanisms typically observed seasonally (November to April).
In July 2025, a persistent MHW detected through our forecasting tools developed in partnership with Mercator Ocean is believed to have triggered unusual wintertime efflorescences of Trichodesmium in the middle of the austral winter, creating temporary “oases” that positively contribute to carbon fixation in the open ocean, while at the same time raising concerns about the resilience of already vulnerable coastal coral reefs.
The HOPE team’s field and laboratory experiments — involving PhD students Ambroise Delisée and Matthieu Savarino, together with microbiologist Mercedes Camps — are quantifying the sedimentation of this marine snow and estimating its potential for long-term CO₂ sequestration.
Counterintuitively, MHWs could temporarily enhance CO₂ sequestration in the ocean.
Joint HOPE–MaHeWa studies will provide further insights in the coming months.
For MaHeWa, these biological findings help refine our risk assessment of MHW impacts on coastal and now semi-offshore ecosystems, thanks to the HOPE buoy, thereby supporting proactive adaptation strategies to climatic disturbances — particularly during the winter season.
