Some Antarctic ice is forming from bottom

Columbia Unversity’s Earth Institute: Scientists working in the remotest part of Antarctica have discovered that liquid water locked deep under the continent’s coat of ice regularly thaws and refreezes to the bottom, creating as much as half the thickness of the ice in places, and actively modifying its structure. The finding, which turns common perceptions of glacial formation upside down, could reshape scientists’ understanding of how the ice sheet expands and moves, and how it might react to warming climate, they say. The study appears in this week’s early online edition of the leading journal Science; it is part of a six-nation study of the invisible Gamburtsev Mountains, which lie buried under as much as two miles of ice.

…“We usually think of ice sheets like cakes--one layer at a time added from the top. This is like someone injected a layer of frosting at the bottom--a really thick layer,” said Robin Bell, a geophysicist at Columbia University’s Lamont-Doherty Earth Observatory and a project co-leader. “Water has always been known to be important to ice sheet dynamics, but mostly as a lubricant. As ice sheets change, we want to predict how they will change. Our results show that models must include water beneath.” The Antarctic ice sheet holds enough fresh water to raise ocean levels 200 feet; if even a small part of it were to melt into the ocean, it could put major coastal cities under water.

The scientists found that refrozen ice makes up 24% of the ice sheet base around Dome A, a 13,800-foot-high plateau that forms the high point of the East Antarctic ice sheet, at 3.8 million square miles roughly the size of the continental United States. In places, slightly more than half the ice thickness appears to have originated from the bottom, not the top. Here, rates of refreezing are greater than surface accumulation rates.

….Because the ice is in motion, understanding how it forms and deforms at the base is critical to understanding how the sheets will move, particularly in response to climate changes, researchers say. “It’s an extremely important observation for us because this is potentially lifting the very oldest ice off the bed,” said Jeff Severinghaus, a geologist at Scripps Institution of Oceanography in San Diego who was not involved in the study. He said it could either mean older ice is better preserved – or, it could “make it harder to interpret the record, if it’s shuffled like a deck of cards.”

…"Scientific results from the Antarctic Gamburtsev Province Project data set are already transforming our understanding of ice sheet behavior,” said Dr. Alexandra Isern, program director for Antarctic earth sciences in the National Science Foundation’s Office of Polar Programs. “This understanding is critical for the development of climate models that can accurately describe how our planet will react to increased global temperatures."…

From the Earth Institute's website: Radar image (B) shows the Gamburtsev Mountains (bottom of image) overlain by the ice sheet, which has been deformed by a bulge of refrozen ice (center). (Courtesy Bell et al., 2011)