Antarctica's Pine Island Glacier Vulnerable to La Niña Events, Researchers Find

Pine Island Glacier melting is more vulnerable to climatic variations caused by La Niña events than previously assumed, a new study reported.

The present study was conducted by researchers at British Antarctic Survey along with their colleagues at University of Washington and other institutions. The team found that the melting of the ice-shelf decreased by 50 percent between the years 2010 and 2012.

La Nina might have led to this decrease in melting, according to the researchers. La Niña is characterized by cold temperatures in the Equatorial Pacific, while El Niño event means a rise in the temperature in the Pacific. Previously, it was assumed that El-Nino and La Nina events affect only tropical climate.

The present study shows that they might even affect Antarctic sea ice loss.

The Pine Island Glacier

Pine Island Glacier makes up about 10 percent of West Antarctic Ice Sheet and is one of the biggest routes for Antarctic ice to reach the Amundsen Sea. The glacier's ice shelf has been thinning for about four decades now, which has led to massive ice losses in the area.

An ice shelf is a large, floating block of ice that forms where a glacier meets a coastline.

It is known that most of the ice shelf melting in the region is due to the "deep oceanic inflow of Circumpolar Deep Water (CDW)", which flows near the Pine Island Glacier.

The warm water from the ocean seeps-in, melting the glacier from beneath. In 2009, a research team recorded higher volume and temperature of the CDW. The rise in warm water meant that the ice-shelf was melting rapidly. However, data from January 2012, showed that the glacier melt during 2011-12 was lowest ever recorded. Also, the top of the layer that separates cold water from the warm water (thermocline) was about 250 meters deeper than the layer recorded in the previous years, according to a news release.

The changes in ice-shelf topography prevented warm water from seeping in and helped cold water cool the underbelly of the glacier.

Researchers found that fluctuations in temperatures could be explained the dramatic cooling of the ocean surrounding the glacier. According to the team, increase in winds flowing eastward caused by the La Nina event (that occurred in2 012) was behind the reduction in ice-melt in the region. Usually, the winds flow westward in this region.

"We had thought that the wind variability played an interesting, but relatively small role, but the new data supports our idea and shows that it has a strong effect," Eric Steig, a UW professor of Earth and space sciences, according to a news release. "The wind field in late 2011 and early 2012 had changed dramatically compared to previous years - the dominant westerly winds in the surrounding area were easterly almost all through late 2011 and early 2012, and those changes were related to the very large 2011 La Nina event."

The study is published in the journal Science.