Deep ocean marine heatwaves may be under-reported, study says

Heatwaves deep in oceans may be "significantly under-reported", highlighting an area of marine warming that has been largely overlooked, a joint study by Australia's national science agency (CISRO) and the Chinese Academy of Sciences has found.

The study, which was published on Thursday in the Nature scientific journal, found that 80% of marine heatwaves below 100 metres are independent of surface events.

It said researchers used observational data from more than two million ocean temperature profiles from global oceans.

"These findings deepen our understanding of the frequency and intensity of extreme temperature events under the ocean surface and possible implications," CISRO's Ming Feng said.

Marine heatwaves are prolonged temperature events that can cause severe damage to marine habitats, such as impacts to coral reefs and species displacement, the study said.

These events are becoming more common due to global warming, causing "catastrophic ecological and socioeconomic impacts," it said.

The majority of previous studies on marine heatwaves have focused on surface signals based on widely available satellite observations of sea-surface temperature.

The finding of separate, deeper warming was particularly worrying, the research found, because it affects the habitat of so many creatures and what they feed on.

"Extreme temperature events below the sea surface are of greater ecological concern because they affect the habitat of most marine primary producers and consumers," it said.

The research also highlighted the influence of ocean currents, in particular eddies, on marine heatwaves, indicating they are a major driver of subsurface events, CISRO said.

Ocean eddies can impact acidification, oxygen levels and nutrient concentrations in the ocean.

Understanding the drivers of subsurface marine heatwaves such as eddies will help to improve assessment of these events in a warming climate and help to predict them in future, it said.