Water flowing through ice sheets speeds up warming

WASHINGTON - A new study has suggested that water flowing through ice sheets via crevasses, fractures and large drains called moulins can carry warmth into ice sheet interiors, greatly accelerating the thermal response of an ice sheet to climate change.

The University of Colorado study has shown ice sheets like the Greenland Ice Sheet can respond to such warming on the order of decades rather than the centuries projected by conventional thermal models.

Ice flows more readily as it warms, so a warming climate can increase ice flows on ice sheets much faster than previously thought, said the study authors.

“We are finding that once such water flow is initiated through a new section of ice sheet, it can warm rather significantly and quickly, sometimes in just 10 years, ” said lead author Thomas Phillips, a research scientist with Cooperative Institute for Research in Environmental Sciences (CIRES).

Melt water flowing through the openings can create “ice caves” and networks of “pipes” that can carry water through the ice and spreading warmth, the authors concluded.

To quantify the influence of melt water, the scientists modelled what would happen to the ice sheet temperature if water flowed through it for eight weeks every summer-about the length of the active melt season.

The result was a significantly faster-than-expected increase in ice sheet warming, which could take place on the order of years to decades depending on the spacing of crevasses and other ‘pipes’ that bring warmer water into the ice sheet in summer.

“The key difference between our model and previous models is that we include heat exchange between water flowing through the ice sheet and the ice,” said Harihar Rajaram of CU.

Several factors contributed to the warming and resulting acceleration of ice flow, including the fact that flowing water into the ice sheets can stay in liquid form even through the winter, slowing seasonal cooling.

In addition, warmer ice sheets are more susceptible to increases of water flow, including the basal lubrication of ice that allows ice to flow more readily on bedrock.

A third factor is melt water cascading downward into the ice, which warms the surrounding ice. In this process the water can refreeze, creating additional cracks in the more vulnerable warm ice, according to the study.

Taken together, the interactions between water, temperature, and ice velocity spell even more rapid changes to ice sheets in a changing climate than currently anticipated, the authors concluded.

The findings were published online in Geophysical Research Letters. (ANI)