Growing underwater heat blob speeds demise of Arctic sea ice

https://www.sciencemag.org/news/2020/08/growing-underwater-heat-blob-speeds-demise-arctic-sea-ice#

Source: By Paul Voosen, Science Magazine. 

Excerpt: In March, soon after arriving aboard the Polarstern, a German icebreaker frozen into Arctic sea ice, Jennifer Hutchings watched as ice broke up around the ship, weeks earlier than expected. ...Arctic sea ice is itself an endangered species. ...The trend is clear: Summer ice covers half the area it did in the 1980s, and because it is thinner, its volume is down 75%. With the Arctic warming three times faster than the global average, most scientists grimly acknowledge the inevitability of ice-free summers, perhaps as soon as 2035. ...Now, he and others are learning that a warming atmosphere is far from the only factor speeding up the ice loss. Strengthening currents and waves are pulverizing the ice. And a study published last week suggests deep heat in the Arctic Ocean has risen and is now melting the ice from below. Unlike the Atlantic or Pacific oceans, the Arctic gets warmer as it gets deeper. Bitter winters and chilly, buoyant freshwater from Eurasian rivers cool its surface layers, which helps preserve the underside of the ice. But at greater depths sits a warm blob of salty Atlantic water, thought to be safely separated from the sea ice. As the reflective ice melts, however, it is replaced by darker water, which absorbs more of the Sun’s energy and warms. Those warming surface waters are likely migrating down into the blob, which robotic temperature probes, moorings, and oceanographic surveys show is steadily warming and growing. With enough heat to melt the Arctic’s ice three to four times over, the blob could devour the ice from below if the barrier of the cold surface layers ever dissipates. Measurements from the eastern Arctic Ocean, published last week in the Journal of Climate, show the blob, usually found 150 meters below or deeper, has recently moved up to within 80 meters of the surface. Increased turbulence means some of that heat is now melting ice, says Igor Polyakov, an oceanographer at the University of Alaska, Fairbanks. “This heat has become, regionally, the key forcing for sea ice decay.”....