Vast region of Antarctica melted, refroze in 2005, says NASA

LONDON — An inland area of snow in west Antarctica the size of California melted in January 2005 in response to warm temperatures, according to a team of NASA and university scientists, who used radar to make their observations.

The melting occurred in multiple distinct regions but the affected regions encompass a combined area as big as California, NASA said. If the melt water had made its way to the sea could have affected ocean salinity, currents and global climate, NASA said in a statement.

The melt occurred in response to an extended period of about a week when air the temperature reached 41 degrees F (5 degrees C). It occurred far inland, at high latitudes and at high elevations, where melt had previously been considered unlikely.

The melting was discovered by NASA's QuikScat satellite, which uses radar to differentiate between snow and ice. The ice was formed when the melt water refroze, NASA said.

This was the first widespread Antarctic melting detected using QuikScat and the most significant melt observed using satellites during the three decades of observation. Evidence of melting was found up to 560 miles inland from the open ocean, farther than 85 degrees south (about 310 miles from the South Pole) and higher than 6,600 feet above sea level.

Son Nghiem of NASA's Jet Propulsion Laboratory, Pasadena, Calif., and Konrad Steffen, director of the Cooperative Institute for Research in Environmental Sciences at the University of Colorado, Boulder, led the team. Using data from QuikScat, they measured snowfall accumulation and melt in Antarctica and Greenland from July 1999 through July 2005.

"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," said Steffen. "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." The satellite's scatterometer instrument sends radar pulses to the ice sheet surface, measuring the echoed pulses that bounce back. QuikScat can differentiate between ice and snow and map it on a continental scale. Ground station measurements were used to validate the satellite result.

"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," said Steffen.

Nghiem said while no further melting had been detected through March 2007, more monitoring is needed. "It is vital we continue monitoring this region to determine if a long-term trend may be developing."

The study, "Snow Accumulation and Snowmelt Monitoring in Greenland and Antarctica," appears in the recently published book "Dynamic Planet." For more information on QuikScat, visit: http://winds.jpl.nasa.gov