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Oceans Adversely Affected by Heatwaves

The effects of marine heatwaves are more intense between 50 and 250 metres than in the most superficial waters, concluded researchers from the University of Algarve, warning that this poses a greater risk to biodiversity.

In a study published in the scientific journal Nature Climate Change, the work team led by researchers from the Centre for Marine Sciences (CCMAR) of the Algarve University (UAlg) maintains that the duration and intensity of marine heatwaves “may persist for longer in deeper waters” and that “subsurface biodiversity may be subject to greater risk” due to temperature change.

“Until now, predictions and impacts of these events have focused on the sea surface, however, localized observations suggest that marine heatwaves may occur below the surface and persist for years,” the researchers said in a statement announcing the study’s publication.

The UAlg points out that CCMAR researcher Eliza Fragkopoulou and the rest of the team used “global sea temperature observations and reanalysis data,” from “past weather forecasts” with “modern weather models,” to estimate the duration and intensity of marine heatwaves.

The analysis covered the period between 1993 and 2019 and depths up to 2,000 metres, allowing the researchers to find that “the greatest intensity of marine heatwaves does not occur at the surface, but rather in the subsurface, specifically between 50 and 250 meters deep.”

“Against our initial expectations, we found that marine heatwaves are more intense below the surface and that their duration can double when compared to the surface,” said Eliza Fragkopoulou.

The authors of the study then cross-referenced the temperature data with the distribution of marine species and concluded that “subsurface biodiversity could be at risk, due to a higher cumulative intensity (indicator of thermal stress) of heat waves in the first 250 meters” of the sea.

“Around the world, we have identified regions of greatest risk to marine biodiversity, including significant parts of the Indian and North Atlantic Oceans, where the high cumulative intensity of heat waves coincides with areas where a high sensitivity of species experience from heat stress,” explained Jorge Assis, a CCMAR research leader.

The researchers warned of the need to develop more research in this area, due to the increase in the intensity and frequency of heat waves at sea, caused by climate change and global warming.

“Extreme temperature events are expected to redistribute marine species, taking them from the surface to the deep ocean. However, there are other factors that can prevent this redistribution, with unpredictable consequences,” warned Miguel Bastos Araújo, from the National Museum of Natural Sciences (MNCN-CSIC), who was also part of the research team.

Samantha Gannon

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