Deep-Sea Heatwaves Intensify: Impact on Marine Life & Fisheries

 Marine heatwaves are experiencing increased duration and intensity in deeper waters, posing potential threats to sensitive marine species. This escalation is attributed to climate change, which has amplified the frequency of these extreme events. Notably, the world's oceans have absorbed 90% of the excess heat generated by carbon emissions from human activities since the start of the industrial age.

Marine heatwaves, characterized by unusually high water temperatures, have been observed to be more frequent and intense. Alarmingly, these heatwaves can cause severe damage to marine species that cannot migrate to cooler waters to escape the unbearable warmth. This is especially true for corals in the Great Barrier Reef and kelp forests off southern Australia and the northeastern Pacific.

A novel study published in Nature Climate Change investigates the impacts of temperature surges in deeper waters. Lead author Eliza Fragkopoulou described the study as "the first of its kind to delve into marine heatwaves below the surface". She added that most existing studies have focused on the ocean surface, leaving a knowledge gap about the characteristics of marine heatwaves in the deep ocean.

Using a combination of on-site observations and modeling techniques, the team of researchers analyzed data from global marine heatwaves from 1993 to 2019, including data up to 2,000 meters below the surface. The study revealed that heatwave intensity was highest at 50 to 200 meters below the surface, with instances of being up to 19% stronger than surface heatwaves.

In addition, the study found that the duration of marine heatwaves also increases with depth, with warming persisting up to two years after surface temperatures return to normal. The researchers utilized a proxy measure of thermal stress, known as cumulative intensity, and mapped this against biodiversity distribution at their maximum heat limits to identify areas where marine life is potentially more vulnerable to changes.

These high-stress conditions were found to overlap in up to 22% of global oceans. However, the regional variability of marine heatwaves and varying oceanic conditions makes measuring biodiversity exposure complex, as their duration can vary by location.

Eliza Fragkopoulou, from the Centre of Marine Sciences at Portugal's University of Algarve, stated that the most significant impact on biodiversity is likely from the surface to a depth of 250 meters. The largest portions of the ocean categorized as highly exposed were found in the North Atlantic and Indian oceans, at depths between 1,000 and 2,000 meters.

A separate study published in Nature last month suggested that some marine species are more resilient to heatwaves than others. It found that ocean fish can withstand marine heatwaves without a significant impact on their population. Fragkopoulou emphasized the need for further research on deep-sea heatwaves to better understand their potential impacts on tourism and fisheries.