ScienceDaily, December 9, 2011
An unusually hot
melting season in 2010 accelerated ice loss in southern Greenland by 100
billion tons -- and large portions of the island's bedrock rose an additional
quarter of an inch in response.
That's the finding
from a network of nearly 50 GPS stations planted along the Greenland coast to
measure the bedrock's natural response to the ever-diminishing weight of ice
above it.
Every year as the
Greenland Ice Sheet melts, the rocky coast rises, explained Michael Bevis, Ohio
Eminent Scholar in Geodynamics and professor in the School of Earth Sciences at
Ohio State University. Some GPS stations around Greenland routinely detect
uplift of 15 mm (0.59 inches) or more, year after year. But a temperature spike
in 2010 lifted the bedrock a detectably higher amount over a short five-month
period -- as high as 20 mm (0.79 inches) in some locations.
In a presentation
December 9 at the American Geophysical Union meeting in San Francisco, Bevis
described the study's implications for climate change.
"Pulses of
extra melting and uplift imply that we'll experience pulses of extra sea level
rise," he said. "The process is not really a steady process."
Because the solid
earth is elastic, Bevis and his team can use the natural flexure of the
Greenland bedrock to measure the weight of the ice sheet, just like the
compression of a spring in a bathroom scale measures the weight of the person
standing on it.
Bevis is the
principal investigator for the Greenland GPS Network (GNET), and he's confident
that the anomalous 2010 uplift that GNET detected is due to anomalous ice loss
during 2010: "Really, there is no other explanation. The uplift anomaly
correlates with maps of the 2010 melting day anomaly. In locations where there
were many extra days of melting in 2010, the uplift anomaly is highest."
In scientific
parlance, a melting day "anomaly" refers to the number of extra
melting days -- that is, days that were warm enough to melt ice -- relative to
the average number of melting days per year over several decades.
In 2010, the
southern half of Greenland lost an extra 100 billion tons of ice under
conditions that scientists would consider anomalously warm.
GNET measurements
indicate that as that ice melted away, the bedrock beneath it rose. The amount
of uplift differed from station to station, depending on how close the station
was to regions where ice loss was greatest.
Southern Greenland
stations that were very close to zones of heavy ice loss rose as much as 20 mm
(about 0.79 inches) over the five months. Even stations that were located far
away typically rose at least 5 mm (0.2 inches) during the course of the 2010
melting season. But stations in the North of Greenland barely moved at all.
From 2007 to 2009,
GNET installed GPS stations in the bedrock that lay exposed around the ice
sheet margins along the Greenland coast. The research team is using Earth's
natural elasticity to "weigh" the ice. As previous Ohio State studies
of Antarctica revealed, ice weighs down bedrock, and when the ice melts away,
the bedrock rises measurably in response.
GNET and similar
GPS networks around the world could thus allow scientists to continue to
measure ice loss after the Gravity Recovery and Climate Experiment (GRACE)
satellites are retired in 2015. (GRACE is a joint project of NASA and the
German Aerospace Center.)
Bevis' coauthors in
the School of Earth Sciences at Ohio State include Abel K. Brown, Eric C.
Kendrick, Jason E. Box, Dana John Caccamise, Hao Zhou, Jian Wang, and Terry J.
Wilson.
Their colleagues
include John M. Wahr of the University of Colorado, Boulder; Shfaqat Abbas
Khan, Finn Bo Madsen, and Per Knudsen of the Danish Technical University in
Copenhagen; Michael J Willis of Cornell University; Tonie M. van Dam and
Olivier Francis of the University of Luxembourg; Bjorn Johns, Thomas Nylen, and
Seth White of UNAVCO, Inc, in Boulder; Robin Abbott of CH2M HILL Polar
Services, in Boulder; and Rene Forsberg of the Space Institute, Denmark.
GNET
is funded by the National Science Foundation.
Story Source:
The above story is reprinted from materials provided by Ohio State University.
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