Ideas on how ice forms in Antarctica turned upside down by new research

Scientists working in the most remote part of Antarctica say that some Antarctic ice can grow in thickness from the bottom up when subglacial water refreezes.

This bottom-up growth of Antarctic ice is in contrast to the typical way in which Antarctic ice sheets are known to form. Antarctica is a frozen continent largely covered by thick ice sheets. Ice sheets form as falling snow accumulates year after year, as the snow becomes compressed into ice by the weight of the upper layers.

In 2006, researchers from Columbia University’s Earth Institute showed that lakes of liquid water lie beneath large areas of Antarctic ice. Over 200 subglacial lakes have been discovered beneath Antarctica’s frozen surface. Deeply buried ice can melt due to heat radiating naturally from underlying rock or due to heat produced by friction from moving ice sheets.

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). (Image Credit: Bell et al., 2011)

In 2008 – 2009, scientists embarked on an expedition to study the subglacial water and overlying ice in East Antarctica’s Gamburtsev Mountains. The Gamburtsev range is larger than the European Alps and is buried deep beneath the ice. To study this area of Earth, scientists used laser scanners, magnetometers and radar antennas mounted to a DHC-6 Twin Otter aircraft.

The scientists were surprised to discover that refrozen ice makes up 24 percent of the ice sheet base around Dome A, a high point of the East Antarctic ice sheet. In some places, refrozen ice contributed to slightly more than half of the ice thickness.

In essence, a sizable portion of the ice sheet appears to be forming from the bottom up. That is in contrast to the well known way that Antarctic ice accumulates, from the top down.

In a second interesting finding, the scientists discovered that refrozen ice can deform the ice sheet upward. Robin Bell, a geophysicist at Columbia University’s Lamont-Doherty Earth Observatory and a project co-leader said in a press release.

When we first saw these structures in the field, we thought they looked like beehives and were worried they were an error in the data. As they were seen on many lines, it became clear that they were real. We did not think that water moving through ancient river valleys beneath more than one mile of ice would change the basic structure of the ice sheet.

In the future, the scientists hope to use data on East Antarctica’s ice sheet thickness to locate areas of ancient ice that can be drilled to remove cores and analyzed to recreate a long-term climate record. A clear understanding of ice sheet formation – both from the bottom up as this new research indicates, and in the typical way of accumulating from snowfall, from above – will be critical for predicting how ice sheets might respond to a warming climate and contribute to rising sea levels in this century and beyond.

March 3, 2011

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