Seafloor Ties La Nina to Antarctic Melt

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Researchers can tell you that the Western Antarctic Peninsula is warming faster than just about anyplace else on the planet — ice shelves are breaking up, glaciers are retreating — but when they try to fit the trend into the bigger picture of natural variability they don’t have much to go on. Satellites have been monitoring the region only a few decades and the instrument record is short and skimpy.

Robotic Sub to Probe Antarctic Ice Melt

So a new study of an ocean sediment core taken from deep water just offshore — described in the latest issue of the journal Nature — is drawing attention not so much for its unexpected results, but for the gaping hole it is beginning to fill.

Some 43 meters (141 feet) long, the core analyzed by Amelia Shevenell at University College London and US colleagues gives a continuous profile of sea surface temperatures of the Southern Ocean out near the tip of the peninsula going back 12,000 years — the warm, relatively stable climate era known as the Holocene.

Before the recent warming, a long-term cooling trend — driven by regional effects of orbital cycles — is punctuated by abrupt, shorter-term changes driven by more earthly connections: westerly winds and the El Niño Southern Oscillation, the scientists report.

During the past 2,000 years, the peninsula seems strongly effected by the El Niño-La Niña cycle in the tropical Pacific Ocean that periodically spreads warm and cool sea surface temperatures along the equator. The authors report that during cool La Niña conditions — such as the strong episode currently gripping the eastern tropical Pacific — westerly winds intensify and move farther south, warming the Western Antarctic Peninsula.

How El Niño Shapes Antarctic Ice

Climate scientists are likely to be taking a closer look at this connection. If climate models are correctly projecting that our warming climate will bring a stronger and more frequent El Niño-La Niña cycle, the ice load along the peninsula could become more unstable, threatening a faster rise in global sea levels.

IMAGE: View west towards Gerlache Strait from Cayley Glacier, Antarctic Peninsula. Credit: Eugene Domack, Hamilton College, New York

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