Some Ice Sheets in Greenland slowing their movement

In the face of decades of increasing temperatures and surface melting, the movement of the southwest portion of the Greenland Ice Sheet that terminates on land has been slowing down, according to a new study being published by the journal Nature on Oct. 29.

Researchers derived their results by tracking ice sheet movement through Landsat satellite images taken from 1985 to 2014 across a roughly 3,088-square-mile (8000-square-kilometer) region in southwest Greenland. They found that, between 2007 and 2014, ice movement slowed in 84 percent of the study area, during a period of high surface melt, compared to the years between 1985 and 1994. The average slowdown was 12 percent, or 32.8 feet (10 meters) per year.

The finding is contrary to the widely held view that a greater amount of surface melting will result in faster-moving ice sheets, as the movement of both ocean- and land-terminating ice sheets is caused in part by surface meltwater, which makes its way to the bedrock through openings in the ice and acts as a lubricant. The amount of meltwater draining from the ice sheet in four out of the five years between 2007 and 2012 has been the most substantial of the last 50 years.

Researchers found that while the larger summertime meltwater volume of recent years has led to greater lubrication of the ice sheet base, speeding up its flow as expected, by the end of summer the meltwater has also established channels at the base that act as efficient drainage systems to lessen the water under the ice sheet, slowing it down by winter.