Marine heatwaves last longer in deeper water: study

PARIS: Marine heatwaves may last longer and be more intense in deeper water, potentially threatening sensitive species as climate change makes the extreme events more frequent, researchers said on Monday.

Oceans have absorbed 90 percent of the excess heat produced by the carbon pollution from human activity since the dawn of the industrial age. Marine heatwaves -- episodes of abnormally high water temperatures -- have become more frequent and intense.

These can have a particularly severe impact on species that cannot migrate to escape intolerably warm waters, like corals in the Great Barrier Reef and kelp forests off southern Australia and the northeastern Pacific.

In a new study published in the journal Nature Climate Change, researchers looked at impacts of temperature spikes in deeper waters, which lead author Eliza Fragkopoulou said was “the first attempt to look into marine heatwaves below the surface”.

“Marine heatwaves and their effects have been studied mostly at the ocean surface and we did not know much about their characteristics in the deep ocean,” she told AFP. Using on-site observations and modelling, researchers examined global marine heatwaves from 1993 to 2019, including data up to 2,000 metres below the surface.

The duration also increased with depth, with warming persisting up to two years after temperatures returned to normal on the surface, the study said. The scientists looked at a proxy measure of thermal stress known as cumulative intensity and mapped that against distribution of biodiversity at the edge of their maximum heat limits to see areas where marine creatures are potentially more vulnerable to changes.