Media release

From: Springer Nature

Marine heatwaves last longer in deeper water

The duration and intensity of marine heatwaves may persist for longer in deeper water, according to a study published in Nature Climate Change. The findings indicate that subsurface biodiversity may be at a high risk of exposure to cumulative heat from these events.

Marine heatwaves have biological and socio-ecological impacts, and are increasing with climate change. To date, the impacts and projections of these events have mostly focused on sea-surface temperatures, however localized observations suggest that marine heatwaves may lead to subsurface warming that could persist for up to two years after surface events end.

Using global sea temperature reanalysis data and observations, Eliza Fragkopoulou and colleagues estimate the duration and intensity of marine heatwave events from 1993–2019 at depths up to 2,000 metres. The authors find that the highest heatwave intensity was found not at the surface, but at the subsurface between 50–250 metres depth. However, despite the intensity then decreasing with further depth, the duration of events increases approximately up to twofold compared to the surface. The authors combined these data with biodiversity data on species ranges and suggest subsurface biodiversity could be at highest risk from cumulative intensity (a thermal stress proxy) in the upper 250 metres. They identify high-risk ocean regions at different depths, including large portions of the Indian and North Atlantic oceans, where high cumulative heatwave intensity overlaps with areas of predicted high species sensitivity to thermal stress.

The authors suggest that as the frequency of these events is expected to increase with climate change, further research is needed to explore how they will impact subsurface marine ecosystems.