The crucial heat absorption of the Southern Ocean

The continuously circling Southern Ocean stands out among oceans as a crucial heat absorber, according to new modelling.

Oceans have been a key buffer to the last 50 years of human-induced climate change, absorbing around 90% of excess heat.

“The Southern Ocean dominates this ocean heat uptake, due in part to the geographic set-up of the region,” says Maurice Huguenin, a PhD candidate at the University of New South Wales and lead author on a paper describing the research, published in Nature Communications.

“Antarctica, which is surrounded by the Southern Ocean, is also surrounded by strong westerly winds.

“These winds influence how the waters absorb heat, and around Antarctica they can exert this influence while remaining uninterrupted by land masses – this is key to the Southern Ocean being responsible for pretty much all of the net global ocean heat uptake,” Huguenin explains.

Because these winds blow essentially uninterrupted, they keep drawing water from the ocean depths to the surface. This water then gets pushed north, absorbing atmospheric heat, before being sent downwards again at latitudes roughly between 45° and 55° S.

World map with red arrows point down on southern ocean, black arrows pointing north and blue arrows pointing up
Global ocean heat uptake, heat loss and heat transport over the last half century, run through different historical simulations. The red and blue vertical arrows indicate heat gain and loss in each basin. The black (slanted) arrows show the heat transport rates. Credit: Huguenin et al

The researchers’ modelling showed that this made the Southern Ocean the most important heat absorber.

But co-author Professor Matthew England, also at UNSW, emphasises that this effect has consequences too.

“Sea levels are rising because heat causes water to expand and ice to melt. Ecosystems are experiencing unprecedented heat stress, and the frequency and intensity of extreme weather events is changing,” says England.

More on the Southern Ocean: Small, but mighty important

The researchers urge for more monitoring of the remote Southern Ocean.

“We still have a lot to learn about ocean warming beyond the 50 years highlighted in our study,” says Huguenin.

“All future projections, including even the most optimistic scenarios, predict warmer oceans in the future.”

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