May 15th, 2007 11:28 EST
NASA and University Scientists Have Found Clear Evidence of Snow melting in West Antarctica
WASHINGTON - A team of NASA and university scientists has found clear
evidence that extensive areas of snow melted in west Antarctica in
January 2005 in response to warm temperatures. 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. The affected regions encompass a
combined area as big as California.
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.
The melting occurred in multiple distinct regions, including far
inland, at high latitudes and at high elevations, where melt had been
considered unlikely. 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. Maximum air temperatures at the time of the melting were
unusually high, reaching more than 41 F in one of the affected areas.
They remained above melting for approximately a week.
"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
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 over the
subsequently formed ice layer. Available ground station measurements
validate the satellite result.
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."
Changes in the ice mass of Antarctica, Earth`s largest freshwater
reservoir, are important to understanding global sea level rise.
Large amounts of Antarctic freshwater flowing into the ocean also
could affect ocean salinity, currents and global climate.
Nghiem said while no further melting had been detected through March
2007, more monitoring is needed. "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."
QuikScat data are helping scientists better understand how Antarctica
and Greenland`s ice sheets gain or lose mass. "We need to know what`s
coming in and going out of the ice sheets," Nghiem said. "QuikScat
data, combined with data from NASA`s IceSat and Gravity Recovery and
Climate Experiment satellites, along with aircraft and ground
measurements, all contribute to more accurate estimates of how the
polar ice sheets are changing."
The study, "Snow Accumulation and Snowmelt Monitoring in Greenland and
Antarctica," appears in the recently published book "Dynamic Planet."
For more information about this study, contact Jim Scott of the
University of Colorado, Boulder, at 303-492-3114 or Adriana Raudzens
Bailey of the Cooperative Institute for Research in Environmental
Sciences, Boulder, at 303-492-6289.
For more information on QuikScat, visit: