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Antarctic sea-ice decline is delayed by ocean eddies

Climate change is progressing rapidly, leaving traces all over the planet. The impact of global warming is particularly dramatic in the Arctic: during the past decades, the sea-ice has declined massively in the face of rising temperatures. According to the latest simulations, by 2050 the Arctic could be consistently ice-free during summers.

Surprisingly though, on the other side of the planet, the Antarctic sea-ice seems to have evaded the global warming trend, and has remained largely unchanged since 1979. However, contrary to actual observations, existing climate model-based simulations indicate significant sea-ice loss in the Antarctic too.

According to a new study led by the Alfred Wegener Institute for Polar and Marine Research (AWI), this Antarctic “sea-ice paradox” could be explained by the fact that current simulations fail to take into account the role of ocean eddies in delaying Antarctic sea-ice decline.

“This so-called Antarctic sea-ice paradox has preoccupied the scientific community for some time now,” said study first author Thomas Rackow, a senior scientist at AWI. “The current models cannot yet correctly describe the behavior of the Antarctic sea-ice; some key element seems to be missing.” 

By employing the AWI Climate Model (AWI-CM), a high-resolution computer simulation used to model changes in climate, Dr. Rackow and his colleagues managed to map processes from the Southern Ocean in much more detail than previous researchers.

“We used a broad range of configurations for our simulations. In the process, it became clear that only those simulations with a high-resolution description of the Southern Ocean encircling the Antarctic produced delayed sea-ice loss similar to what we are seeing in reality,” explained Dr. Rackow. “When we then extended the model into the future, even under a highly unfavorable greenhouse-gas scenario the Antarctic sea-ice cover remains largely stable until mid-century. After that point the sea-ice retreats rather rapidly, just as the Arctic sea-ice has been doing for decades.”

According to the scientists, the delay in Antarctic sea-ice decline could be explained by the activity of ocean eddies – currents with diameters of 10 to 20 km – which allow the ocean to transport additional heat taken up from the atmosphere north, towards the Equator. This northward heat transport is closely linked to the underlying overturning circulation in the upper kilometer of the ocean, which in the Southern Ocean is influenced both by wind and these eddies. As a result, the ocean surrounding the Antarctic warms slower, and the sea ice remains stable for longer.

“Our study supports the hypothesis that climate models and projections of the Antarctic sea-ice will be far more reliable as soon as they are capable of realistically simulating a high-resolution ocean, complete with eddies. Thanks to the ever-increasing performance of parallel supercomputers and new, more efficient models, next-generation climate models should make this a routine task,” concluded Dr. Rackow.

The study is published in the journal Nature Communications.

By Andrei Ionescu, Staff Writer

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