A warm-water time bomb could spell disaster for Arctic sea ice | Artificial intelligence

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By Andy Coghlan

The Arctic is in hot water, literally, following the discovery that heat has been accumulating rapidly in a salty layer of the Arctic Ocean 50 metres down. Currently, it’s being held at that depth by a less dense layer of freshwater overhead, but if the two layers start to mix it could melt all seasonal sea ice, accelerating the already-rapid loss of polar ice cover.

Researchers discovered the heat time–bomb after analysing publicly available data on ice cover, and at different depths on sea temperature, heat content and saltiness over the past three decades. The data was gathered around the Canadian Basin, a major basin of the Arctic Ocean fed by waters from the North Chukchi Sea, just north of the Bering Strait between Alaska and Siberia.

Over this timespan, the heat content of the salty layer doubled, from 200 to 400 million joules per square metre, enough to reduce overall Arctic ice thickness by 80 centimetres.

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The root cause is global warming, which has seen temperatures in the Arctic rise by 2 degrees from pre-industrial levels–twice the global average—leading to record-low sea ice coverage. The researchers found that with sea ice retreating, heat absorption by exposed surface waters has increased fivefold in 30 years, mainly from direct sunlight, which no longer gets reflected by ice.

And with no ice in the way, strong northerly winds push these newly-warmed surface waters at the Arctic fringes down to the depths where they’re now accumulating under the Arctic. The fear is that the freshwater “lid” keeping them there could fall apart.

“It could be lost through increased mechanical mixing of the water layers, especially driven by the winds,” says Mary-Louise Timmermans at Yale University and head of the team. “With continued sea-ice losses, we’d have more wind-driven mixing, and that would erode this natural barrier,” she says.

Loss of a protective “freshwater” layer is already happening elsewhere around the Arctic in the Barents Sea north of Scandinavia, allowing warmer Atlantic waters to flow in and potentially destroy an entire Arctic ecosystem in the North Barents Sea within a decade.

Journal reference: Science Advances, DOI: 10.1126/sciadv.aat6773