Washington, Nov 7 : A NASA-led research team has used satellite data to make the most precise measurements to date of changes in the mass of mountain glaciers in the Gulf of Alaska.
This is a region expected to be a significant contributor to global sea level rise over the next 50-100 years.
The team, that comprised of Geophysicist Scott Luthcke of NASA's Goddard Space Flight Center, Greenbelt, Maryland, and colleagues, knew from well-documented research that changes in the cryosphere - glaciers, ice caps, and other parts of the globe covered year-round by ice - are a key source of most global sea level rise.
The team worked to develop a satellite-based method that could accurately quantify glacial mass changes across seasons and years, and even discern whether individual glacier regions are growing or shrinking.
The study's authors found that the annual ice mass lost from glaciers in the Gulf of Alaska has been 84 gigatons annually, about five times the average annual flow of the Colorado River through the Grand Canyon and equal to the entire amount of water in the Chesapeake Bay.
"The Gulf of Alaska region is 20 times smaller than the ice-covered area of Greenland, yet it contributes nearly half as much freshwater melt as Greenland and accounts for about 15 percent of present-day global sea level rise stemming from melting ice," said Luthcke, lead author of the study.
"Considering that the Gulf of Alaska makes such a disproportionate contribution, it is vital that we know more about the nature of glacial change there," he added.
Using data collected by the GRACE satellites from 2003-2007, as well as unique processing and analysis techniques, Luthcke and colleagues were able to measure the mass of the glaciers every 10 days across an area spanning 18,919 square miles, about the equivalent of Vermont and New Hampshire combined.
The team found the largest ice mass losses occurring in the Yakutat, Glacier Bay, and St. Elias regions.
Those observations are consistent with recent studies from aircraft-based altimeters and other satellites.
"The consistent and direct measurement of ice-mass change made possible by the GRACE data and the analysis techniques applied in this study provide unprecedented observations that further our knowledge of the region's complex ice evolution," said Luthcke.
The most rapid glacial melt, according to Luthcke and colleagues, came in response to the summer heat wave of 2004, when the region's glaciers shed 374 gigatons of ice, or about 98 cubic miles of ice.
"With such rapid change taking place in such a critical area, we need to be able to more reliably observe how these glaciers are responding," said Luthcke.