The largest icebergs usually hug the Antarctic coast for decades before wandering into deep ocean water, where they melt and fall to pieces. To listen for clues about how such icebergs eventually break apart, geophysicists Douglas MacAyeal of the University of Chicago and Emile Okal of Northwestern University planted seismographs on the surface of iceberg B15A, a 71-mile-long block of ice with the distinction of being the world's largest free-floating object. Their recording turned up the sounds of the iceberg being battered to bits against the Antarctic shore over a couple days in October 2005. The big surprise came when the researchers tracked down the origin of that battering.
By measuring ocean swells of different wavelengths, the duo traced the destructive turbulence to a storm in the Gulf of Alaska that, a few days earlier, had kicked up 40-foot-high seas. Like the proverbial butterfly that flapped its wings in Beijing and caused a hurricane halfway around the world, the Alaskan storm's waves spread out across the Pacific Ocean and broke apart an iceberg more than 8,000 miles away. "It was jaw dropping," says MacAyeal.
If global warming leads to an increase in monster storms, MacAyeal adds, then the entire Antarctic ice skirt could be in jeopardy: Larger sea swells could pulverize its huge icebergs and floating ice shelves. The ice skirt plays a critical role in keeping the land-based Antarctic ice cap in place. Destroy the floating ice and the ice cap (which holds enough water to raise sea levels by 200 feet) would collapse unimpeded into the sea.