Intense storms that sweep over the Southern Ocean enable the ocean to absorb more heat from the atmosphere. New research from the University of Gothenburg shows that today’s climate models underestimate how storms mix the ocean and thereby give less reliable future projections of our climate.

The Southern Ocean is a vast expanse of ocean encircling the Antarctic continent, regulating Earth’s climate by moving heat, carbon, and nutrients out in the world’s oceans.

It provides a critical climate service by absorbing over 75 per cent of the excess heat generated by humans globally. The Southern Ocean’s capacity to reduce climate warming depends on how efficiently it can absorb heat from our atmosphere.

In a new study in Nature Geoscience, researchers from the University of Gothenburg show that storms play a key role in controlling how the Southern Ocean exchanges heat with the atmosphere. The team finds that intense winds churn the ocean, drawing colder deep water upward and pushing warmer surface water downward. The surface stays cooler and can take up more heat from the atmosphere.

Storms lower surface temperature

“Our research shows that summers with stronger storm activity generate lower surface temperatures across the Southern Ocean. Hence, a stormy ocean can absorb more heat from the atmosphere, then in calm weather,” says Marcel du Plessis, Researcher in oceanography at the University of Gothenburg and main author of the study.

How much heat the ocean absorbs from the atmosphere influences everything from how high temperatures will be on land, to the extent of sea ice and the severity of marine heatwaves.

The research team have been studying storm patterns around Antarctica over the last few decades and can now link changes in storm intensity and their windiness to changes in our climate and atmospheric circulation. In general, it is observed that storms are becoming stronger, due to an increase in the atmospheric pressure difference between Antarctica and the Subtropics.

Climate models are inaccurate

Current climate models, which underpin the climate projections used to guide policy, tend to underestimate the strength of Southern Ocean storms and thereby simulate an overly warm ocean.

“That is why our findings are important, because a better representation of storm processes is essential for more accurate future climate projections,” says Marcel du Plessis. 

Conducting research in the Southern Ocean is complicated, challenging, and costly. In the study, the researchers used a combination of advanced autonomous underwater and surface robots that measured the ocean temperature and salinity, and atmospheric conditions above the waves. They combined the results from these robotic observations with multi-year model and satellite data to disentangle these complex storm and ocean heat exchange processes.

Different processes in winter

“This is the first time we can clearly link Southern Ocean storms to changes in ocean warming and our climate variability over the past 20 years. Such results mean we can better understand how the ocean is warming today and thereby predict how our Earth’s climate may change in the future”, says Sebastiaan Swart, Professor of Oceanography, at the University of Gothenburg.

It’s in the Antarctic summer that storms have their strongest impact on ocean heat uptake. In winter, completely different processes take place. This will be the next challenge for researchers to observe and understand.