Big melt in Antarctica

May 18, 2007

Courtesy of Far North Science
By Doug O'Harra

Here's more heating news, this time from the cryosphere of the Far South, a region thought to be much cooler than the Far North and not as responsive to greenhouse gas influences.

NASA's QuikScat satellite detected extensive areas of snowmelt, shown in yellow and red, in west Antarctica in January 2005. NASA/JPL

A team of rocket scientists from NASA's Jet Propulsion Laboratory and university researchers detected a massive snow meltdown on the ice covering West Antarctica, ultimately sloshing up an area larger than the state of California.

It was caused by warm temperatures in January 2005 - the peak of the austral summer.

"This was the first widespread Antarctic melting ever detected with NASA's QuikScat satellite and the most significant melt observed using satellites during the past three decades," NASA reported in a news release about the finding.

The team was led by JPL's Son Nghiem and Konrad Steffen, director of the Cooperative Institute for Research in Environmental Sciences at the University of Colorado, Boulder, led the team. Their study, "Snow Accumulation and Snowmelt Monitoring in Greenland and Antarctica," appears in the recently published book Dynamic Planet.

QuikScat satellite data helps scientists measure whether ice sheets in Antarctica and Greenland accumulate snow and gain mass QuikScat / NASA-JPL

QuikScat satellite data helps scientists measure whether ice sheets in Antarctica and Greenland accumulate snow and gain mass - or melt enough during summer that they actually lose mass. In this study, the team tracked snowfall and melt in Antarctica and Greenland from July 1999 through July 2005.

What they found about that brief warm spell in January 2005 was stunning - air temperatures that reached 41 °F, above-freezing air that lasted more than a week at a time.

"The observed melting occurred in multiple distinct regions, including far inland, at high latitudes and at high elevations, where melt had been considered unlikely," they reported in a news release. "Evidence of melting was found up to 900 kilometers (560 miles) inland from the open ocean, farther than 85 degrees south (about 500 kilometers, or 310 miles, from the South Pole) and higher than 2,000 meters (6,600 feet) above sea level."

"Antarctica has shown little to no warming in the recent past with the exception of the Antarctic Peninsula, but now large regions are showing the first signs of the impacts of warming as interpreted by this satellite analysis," Steffen said.

"Increases in snowmelt, such as this in 2005, definitely could have an impact on larger-scale melting of Antarctica's ice sheets if they were severe or sustained over time."

A different JPL study found in 2006 that overall Antarctica ice sheets had lost mass for the first time.

Here's how the QuikScat process worked:

The satellite's scatterometer instrument sends radar pulses to the ice sheet surface, measuring the echoed pulses that bounce back. When snow melts and then refreezes, it changes to ice, just as ice cream crystallizes when it is left out too long and is then refrozen. QuikScat can differentiate this icy fingerprint in the snow cover and can map on a continental scale the extent of strong snowmelt and the subsequently formed ice layer. Available ground station measurements validate the satellite results.

The 2005 melt was intense enough to create an extensive ice layer when water refroze after the melt. However, the melt was not prolonged enough for the melt water to flow into the sea.

"Water from melted snow can penetrate into ice sheets through cracks and narrow, tubular glacial shafts called moulins," Steffen said. "If sufficient melt water is available, it may reach the bottom of the ice sheet. This water can lubricate the underside of the ice sheet at the bedrock, causing the ice mass to move toward the ocean faster, increasing sea level."

Antarctica holds most of the Earth's freshwater locked in ice and snow. If that water were to melt and be released to the ocean, global sea level could rise by scores of meters. Ocean currents, climate, storm patterns and seawater salinity would be altered on a vast scale. Antarctica JPL / Ben Holt, Sr.

The NASA-Colorado team has detected no additional melting through March 2007, according to Nghiem. But they need to keep watching.

"Satellite scatterometry is like an X-ray that sees through snow and finds ice layers beneath as early as possible," he said. "It is vital we continue monitoring this region to determine if a long-term trend may be developing."

Most of Far North Science is written and edited by Doug O'Harra, a writer and journalist based in Anchorage, Alaska.