Back in the summer of 2023, the sea ice surrounding Antarctica cratered. At various points, more than 1.5 million fewer square kilometers were covered with ice than the previous low, set just the year prior. It hasn’t really come back.
That 2023 record still stands out, but 2024 wasn’t all that much better for Southern Ocean sea ice. This year still only trails those record lows for ice formation futility. And now, a new study published Monday in Proceedings of the National Academy of Sciences offers a distressing explanation: starting around 2015, the surface of that ocean has gotten substantially saltier.
“Antarctica is no longer the stable, frozen continent we once believed it to be,” wrote lead author Alessandro Silvano, of the University of Southampton in the UK, in an accompanying piece for The Conversation. “It is changing rapidly, and in ways that current climate models didn’t foresee. Until recently, those models assumed a warming world would increase precipitation and ice-melting, freshening surface waters and helping keep Antarctic sea ice relatively stable. That assumption no longer holds.”
The researchers used satellite observations to determine that the ocean around Antarctica began to get significantly saltier just as sea ice extent started to crash. This creates a feedback loop: saltier water is denser, so it sinks more readily through the ocean’s layers; this stirs up those layers and brings heat — and more salt — up from the depths; that heat helps melt more ice, which darkens the ocean’s surface and allows more heat to be absorbed from the sun. Lather, rinse, repeat.
Losing Antarctic sea ice is a global problem. “What’s happening at the bottom of the world is rippling outward, reshaping weather systems, ocean currents and life on land and sea,” Silvano wrote. It will allow more total heat to stay inside the Earth system, help accelerate warming further. It will harm wildlife like penguins that rely on the ice, all the way down to tiny krill that feed on algae beneath the ice. And perhaps most importantly, the findings upend what had been expected from melting ice — in theory it should have “freshened” the ocean, as more and more fresh water entered.
“If we don’t update our scientific models, we risk being caught off guard by changes we could have prepared for,” Silvano wrote. “Indeed, the ultimate driver of the 2015 salinity increase remains uncertain, underscoring the need for scientists to revise their perspective on the Antarctic system and highlighting the urgency of further research.”
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