Antarctic ice melt

Colossal icebergs careening along the Antarctic coastline can shut down the deep, cold currents that help drive ocean circulation, a new study reports.

These aren’t everyday icebergs, even by Antarctica’s mighty standards — these huge icebergs are the size of small European countries. Unleashed by fracturing glaciers, they interfere with the Antarctic Ocean’s sea-ice factories, called polynyas, according to the study.

The open-water polynyas persist year-round, allowing bitter winter winds to freeze seawater into freshwater ice, leaving behind dense, salty seawater that sinks to the ocean depths. These sinking currents, called the Antarctic Bottom Water, are a major driver of oceanic circulation, said study co-author Guillaume Massé, a paleoclimatologist at the University of Laval in Quebec, Canada.

The scientists studied the recent history of one of the Antarctic Bottom Current’s most important polynyas, near East Antarctica’s Mertz Glacier. About one-quarter of the cold current comes from this polynya, according to earlier studies. By analyzing microscopic plankton fossils and geochemical tracers in seafloor sediments, the researchers could determine whether the polynya was covered or ice-free. […]