Seafloor marine heatwaves are becoming more frequent, but are rarely captured by current models

Models of sea temperature are crucial for predicting and responding to the environmental impacts of climate change. Elevated temperatures can affect the behaviour and life cycles of marine organisms and potentially cause tissue damage or death. Such impacts have been observed in species ranging from seagrass and plankton to crustaceans and fish. This threat to marine ecosystems has policy and management implications for conservation, fisheries, aquaculture and other sectors.

Global sea temperature models typically have limited accuracy at regional scale, particularly around continental shelves. The shallow waters and unique configurations of these areas need higher resolution models to be properly understood. Traditional models are also often restricted to the sea surface, without providing predictions for heatwaves near the seabed.

Seabed ecological communities may be especially sensitive to heatwaves because temperatures on the seafloor are normally stable. That means that a relatively small temperature increase is likely to be classed as a heatwave. This contrasts with sea surfaces, which typically experience more variable temperatures, meaning fluctuations are more likely to remain within the normal range. Seabed organisms are also often less mobile, and so less able to seek out favourable conditions in other locations.

Understanding the impact of climate change on future seafloor temperatures is crucial for conservation planning, according to a group of researchers from the UK and Italy. To better understand temperature change on the ocean floor. This research – funded by Horizon Europe¹ - studied the coastal shelf of northwestern Europe, including the North Sea, coastal waters around the UK and Ireland, and the northern Bay of Biscay. These regions are some of the most heavily fished in the world and also provide cultural and ecological services.

The researchers used five detailed regional models to predict future changes in the ocean and the impacts on temperature. These models accounted for the features of the shelf and provided predictions for surface and seafloor temperatures for each season of the year. The models are based on a climate change scenario of high emissions, named by the Intergovernmental Panel on Climate Change as “Representative Concentration Pathway 8.5”. A study cited by the researchers suggests this is a realistic scenario given the current trends in “global climate policies and industrial development”.

The researchers focused on heatwaves: periods of at least five days in which the temperature was unusually high for the time of year. They defined this as being higher than 90% of the temperatures recorded around that time over the reference period (1990–2009). They ran the models from the present day to the end of this century.

Under the high emissions pathway being modelled – the real-world likelihood of which is debated – heatwaves were predicted to occur over most of the year by 2100. The research suggests that the frequency and intensity of heatwaves would increase more rapidly on the seafloor than at the surface, and that heatwaves are likely to be more common over autumn, winter and spring than over summer. This is due to historically higher temperature variability in summer, meaning that warmer periods at this time of year are less likely to qualify as heatwaves. The researchers also found that some areas, such as around northwest Ireland and off the southwest coast of Norway, appear more resilient to seafloor heatwaves.

Ultimately, these findings highlight the importance of including sub-surface temperatures and seasonal predictions in climate change models of sea temperatures. They also suggest that sea temperature models should be designed to predict year-round temperature changes; currently they typically focus on summer months as these have the highest absolute temperatures. Since most other coastal shelf systems are likely to experience similar warming effects, according to the researchers, they suggest that more work should be done to model these in future. They emphasise the importance of understanding how future predicted heatwaves may affect seafloor communities and how non-summer heatwaves affect organisms and ecosystems at all depths.

Footnotes:

1. The associated Horizon 2020 project is COMFORT: Our common future ocean in the Earth system – quantifying coupled cycles of carbon, oxygen, and nutrients for determining and achieving safe operating spaces with respect to tipping points. https://cordis.europa.eu/project/id/820989

Source:

Wilson, R. J., Artioli, Y., Galli, G., Harle, J., Holt, J., Queirós, A. M., and Wakelin, S. (2025) Seafloor marine heatwaves outpace surface events in the future on the northwestern European shelf. Ocean Science 21:1255–1270. https://doi.org/10.5194/os-21-1255-2025

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“Science for Environment Policy”: European Commission DG Environment News Alert Service, edited by the Science Communication Unit, The University of the West of England, Bristol.

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The contents and views included in Science for Environment Policy are based on independent, peer reviewed research and do not necessarily reflect the position of the European Commission. Please note that this article is a summary of only one study. Other studies may come to other conclusions.