A paper published recently in Nature using two ACCESS models, has revealed the drivers of a marine heatwave that swept across the North Atlantic Ocean during the summer of 2023, causing severe impacts on climate and ecosystems.
“The intensity of the warming in that single summer was equivalent to about two decades worth of warming for the North Atlantic,” says lead author Professor Matthew England from UNSW Sydney.
North Atlantic sea surface temperature (SST) anomalies relative to 1981–2010.
This study relied on two ACCESS ocean model simulations of the Australian Community Climate and Earth System Simulator Ocean Model Version 2 (ACCESS-OM2) that were run from 1958 forward in time up to and beyond the period of the North Atlantic marine heatwave. The project was a joint collaboration between authors from UNSW, ANU, the Bureau of Meteorology and Potsdam Institute for Climate Impact Research (PIK) in Germany.
“The ACCESS models were critical to unpack the reasons for this unprecedented warming. These models are global in scale and reproduce the marine heatwave in the right locations and magnitude. These models allow us to calculate heat budget terms that are impossible to derive from the incomplete observations we have available,” says Professor England.
The researchers used observationally constrained atmospheric reanalyses alongside ocean observations and model simulations to show that air–sea heat fluxes acting on an extremely shallow surface mixed layer, rather than anomalous ocean heat transport, were responsible for this extreme ocean warming event.
Future research to understand these processes will be undertaken using new versions of Australia’s ACCESS models, which are now maintained by the national research infrastructure ACCESS-NRI.
“We are now exploring the same processes but for Southern Ocean marine heatwaves, as the processes controlling the North Atlantic marine heatwave are also relevant to marine heatwaves in our region,” says Professor England.
Understanding these processes is critical as current projections show that the severity of marine heatwaves is set to worsen in the future.
The models used in the study were available through the Consortium for Ocean-Sea Ice Modelling in Australia (COSIMA). Runs were undertaken with the assistance of resources from the National Computational Infrastructure (NCI). ACCESS-NRI and NCI are enabled by the Australian Government, Department of Education, through the National Collaborative Research Infrastructure Strategy (NCRIS).
Original article: https://www.nature.com/articles/s41586-025-08903-5