In Antarctica, melting may beget ice

Disintegration of floating glaciers could be responsible for freezing of seawater

Melting may not be the destroyer of all ice. Melting ice shelves may actually spur the growth of sea ice in Antarctica.

ICE BY MELTING Antarctica’s sea ice has grown in recent years because ice-shelf melting creates a cold, fresh sea surface that easily freezes, new simulations suggest. Acaro/Wikimedia Commons

The extent of Antarctica’s sea ice (white) reached a record high in September 2012 (shown). New simulations suggest that the melting of ice shelves (pale gray) creates a cold, fresh sea surface that easily freezes. Jesse Allen/NASA Earth Observatory, NSIDC

While Arctic sea ice has dwindled, the extent of Antarctic sea ice has expanded by nearly 2 percent per decade since 1985. As the oceans have warmed in the same time period, deep ocean currents have carried heat to the deep waters surrounding Antarctica. The warmth may be melting the base of ice shelves, sections of Antarctica’s ice sheet that float over the ocean.

That melting floods the ocean with cold freshwater, suggest Richard Bintanja of the Royal Netherlands Meteorological Institute and colleagues. Less dense than saltwater, the frigid freshwater stays on the surface and easily freezes. Over time, this process could lead to the formation of more and more sea ice near the continent, the team says.

Climate and ocean simulations confirm that the melting of ice shelves is a plausible mechanism for the growth of sea ice, the researchers report March 31 in Nature Geoscience. And the explanation accounts for more sea-ice growth than another possible explanation, that stronger winds around the continent have cooled the region, Bintanja says.

Melting ice shelves may have a small effect on sea ice in the far north, too, Bintanja says. Differences in geography between the poles help explain why the Arctic is losing ice even as the Antarctic gains. Antarctica’s sea ice develops along the perimeter of the continent and has more room to grow than the Arctic’s sea ice, which is encircled by land.

Oceanographer David Holland of New York University says the idea deserves testing. At the moment, there’s no way to know how much water the melting ice shelves dump into the Southern Ocean. The study, he says, “points out the need to establish an observational network of sub-ice-shelf melting.” Such data would allow scientists to build more realistic climate-ocean simulations, he says.

Erin Wayman

Erin Wayman is the magazine managing editor. She has a master’s degree in biological anthropology from the University of California, Davis and a master’s degree in science writing from Johns Hopkins University.

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