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New Antarctic ice core reveals secrets of climate change

A new Antarctic ice core that's more than 10,000 feet long suggests that West Antarctica may have begun melting more than 2,000 years earlier than believed. The secret? Sea ice.

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"The thought prior to our work is that Antarctica began to warm about 18,000 years ago, after the Northern Hemisphere had started to warm" about 24,000 years ago, says Fudge.

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Climatologists debated exactly how the north triggered the south, though most agreed that the global ocean conveyor belt played a role, but they agreed that "Antarctica took its signal from the north to get it going." Fudge's team agrees that warming kicked into high gear 18,000 years ago, but they found evidence of warming in West Antarctica beginning between 2,000 and 4,000 years before the northern "trigger."

It now appears that both the northern and southern hemispheres were affected by orbital changes that made for longer summer days. In Antarctica, the increased sunlight melted the sea ice.

Sea ice has huge implications for climate change, for one simple reason: air above ice can get much, much colder than air above flowing water. "There's this great ability to amplify changes with sea ice. This is what we see happening in the northern hemisphere today, with the sea ice loss near the North Pole: You change the temperature a little, that changes the amount of sea ice a little, which then changes the amount of sea ice a lot. It creates a feedback loop," says Fudge.

Don't confuse sea ice with icebergs, warns Fudge. Icebergs are chunks of continental glaciers that calve into the ocean and float away. Sea ice is more like lake ice, or river ice: even when the whole surface doesn't freeze over, a rime of ice can grow on the edge of a lake or river. Similarly, a continent-scale "rime" of sea ice grows around the edge of Antarctica every winter, reaching 3 to 6 feet thick and expanding over 5 million square miles.

Two miles, straight down

The team took the first, short ice cores from the site in 2005, and then began this drilling project in 2006. Because of Antarctica's brutally short summers, they only had 30 to 35 drill days each year, so it took until December 2011 to extract the more than 2 miles of ice that made up the 68,000-year record, which they're still analyzing.

"You can only drill about 3 meters of ice each time you send the drill down," says Fudge, "so by the time you're drilling the deepest ice, you're 2 miles down, so you have to send the drill down 2 miles, grab 10 feet, come back up 2 miles, and then send it back down an extra 10 feet to grab the next one... It takes about 3 hours for one drill run." Then the ice begins its 6-month journey, first by plane to the coast, then by ship to Los Angeles, then overland to Denver, when the analysis finally begins – all while keeping it deep-frozen.

"It is not an inexpensive process, so we feel a great responsibility," Fudge acknowledges. "I think the paper we just published is the first of many really tremendous records that are changing our perception about how our climate system works."


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