As climate change has intensified heat waves, the world is struggling to cope. Earlier this month, US space agency Nasa said this year’s summer was Earth’s hottest since global records began in 1880. Now, researchers have found that marine heatwaves last longer and can be more intense in deeper water, which could threaten the survival of certain marine species.
A marine heatwave is a period of unusually high ocean temperatures, which significantly impacts marine biodiversity. Over the years, oceans have absorbed 90% of the excess heat produced by carbon pollution from human activity since the industrial age. Now, marine heatwaves have become more frequent due to climate change, an AFP report explains.
Marine heatwaves can significantly impact vulnerable species that cannot migrate to escape warm waters like corals of the Great Barrier Reef. The new study, published in the journal Nature Climate Change, examined the temperature spikes in deeper waters, which lead author Eliza Fragkopoulou said was "the first attempt to look into marine heatwaves below the surface", as reported by AFP.
"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," Fragkopoulou told AFP. The researchers used on-site observations and modelling to examine global marine heatwaves from 1993 to 2019, including data up to 2,000 metres (6,562 feet) below the surface.
The findings showed that the intensity was highest at 50 to 200 metres below the surface, often up to 19% more intense compared to the surface heatwave. Furthermore, the duration also increased in deeper areas, which were continuously warm for up to two years after the surface temperature was back to normal. The marine heatwaves’ effect on biodiversity was likely greatest from the surface to a depth of 250 metres, the study found.
According to the AFP report, the parts that were highly exposed to marine heatwaves were in the North Atlantic and Indian oceans, at depths between 1,000 and 2,000 metres.
In 2021, almost 1 billion sea creatures died on the coast of Vancouver as the Pacific region hit record-setting temperatures, as reported by NPR. Talking to AFP, Fragkopoulou warned that the impact of marine heatwaves on deep-sea biodiversity is still largely unknown and there is an urgent need for more and better monitoring of the global ocean.