Glaciologists Unveil Most Precise Map of Antarctic Ice Flow
A new map of Antarctic ice velocity has been created using 25 years' worth of satellite data by glaciologists from the University of California, Irvine (UCI) and NASA’s Jet Propulsion Laboratory.
To chart the movement of ice sheets across the surface of the land mass, the researchers combined input from six satellite missions: the Canadian Space Agency’s Radarsat-1 and Radarsat-2; the European Space Agency’s Earth remote sensing satellites 1 and 2 and Envisat ASAR; and the Japan Aerospace Exploration Agency’s ALOS PALSAR-1.
Previous mapping efforts relied heavily on “feature” and “speckle tracking” methods, which detect the motion of parcels of ice on the ground over time. This approach has been proven effective in estimating ice flow speed. To measure significantly slower ice sheet movement in the vast interior regions, the team augmented these techniques with synthetic-aperture radar phase interferometry, which detects the subtle motion of natural reflectors of radar signals in snow/ice independent of the size of the parcel of ice illuminated by the radar.
This gives a precision of up to two orders of magnitude better than speckle tracking. A drawback is that it requires a lot more data, namely multiple passes at different angles over the same point on the ground – a problem that was solved by a consortium of international space agencies pointing Earth-monitoring spacecrafts to this part of the world.
The team was able to compose a map that resolves ice movement to a level of 20 centimeters (a little over half a foot) per year in speed and five degrees in annual flow direction for more than 70 percent of Antarctica.
A joint NASA and Indian Space Research Organization satellite, launching in late 2021, will be the first interferometric-mode SAR mission designed to look solely toward the South Pole. It will provide a coast-to-coast view of Antarctica every 12 days.
“With this level of precision in the interior regions, we’ll be able to reconstruct high-resolution spatial details in the bed topography beneath the ice through inversion techniques over far broader areas than in previous attempts – essential to improving ice sheet models and projections of sea level rise from Antarctica,” said co-author Eric Rignot, chair and Donald Bren Professor of Earth System Science at UCI and a JPL senior research scientist.
Antarctica losing six times more ice annually now than 40 years ago
Antarctica experienced a sixfold increase in yearly ice mass loss between 1979 and 2017, according to a study published by glaciologists from the University of California, Irvine, NASA’s Jet Propulsion Laboratory and the Netherlands’ Utrecht University earlier this year. The accelerated melting caused global sea levels to rise more than half an inch during that time.
“That’s just the tip of the iceberg, so to speak,” said lead author Professor Eric Rignot of UCI. “As the Antarctic ice sheet continues to melt away, we expect multi-meter sea level rise from Antarctica in the coming centuries.”
The team was able to discern that between 1979 and 1990, Antarctica shed an average of 40 gigatons of ice mass annually. (A gigaton is one billion tons.) From 2009 to 2017, about 252 gigatons per year were lost.
The pace of melting rose dramatically over the four-decade period. From 1979 to 2001, it was an average of 48 gigatons annually per decade. The rate jumped 280 percent to 134 gigatons for 2001 to 2017. Sectors losing the most ice mass are adjacent to warm ocean water.
Giant Cavity
A study by scientists from UCI and NASA’s Jet Propulsion Laboratory released earlier this year revealed a gigantic cavity on the underside of Thwaites Glacier in West Antarctica. The hole is reportedly two-thirds the area of Manhattan, about 1,000 feet tall and expanding. The researchers expected to find gaps between ice and bedrock at Thwaites’ bottom where ocean water could flow in and melt the glacier from below, but the size and explosive growth rate of the newfound hole surprised them. It’s thought to be big enough to have contained 14 billion tons of ice, most of which has melted over the last three years.