In Greenland, Another Major Glacier Comes Undone
A new study by NASA and university researchers spells more trouble for Greenland's Ice Sheet and global sea levels.
It's big. It's cold. And it's melting into the world's ocean.It's Zachariae  Isstrom, the latest in a string of Greenland glaciers to undergo rapid change  in our warming world. A new NASA-funded study published today in the journal  Science finds that Zachariae Isstrom broke loose from a glaciologically stable  position in 2012 and entered a phase of accelerated retreat. The consequences  will be felt for decades to come.The reason? Zachariae  Isstrom is big. It drains ice from an area of 35,440 square miles (91,780  square kilometers). That's about 5 percent of the Greenland Ice Sheet. All by  itself, it holds enough water to raise global sea level by more than 18 inches  (46 centimeters) if it were to melt completely. And now it's on a crash diet, losing  5 billion tons of mass every year. All that ice is crumbling into the North  Atlantic Ocean."North  Greenland glaciers are changing rapidly," said lead author Jeremie Mouginot, an  assistant researcher in the Department of Earth System Science at the  University of California, Irvine. "The shape and dynamics of Zachariae Isstrom  have changed dramatically over the last few years. The glacier is now breaking  up and calving high volumes of icebergs into the ocean, which will result in  rising sea levels for decades to come."Mouginot and  his colleagues from NASA's Jet Propulsion Laboratory, Pasadena, California; and  the University of Kansas, Lawrence, set out to study the changes taking place  at Zachariae Isstrom.The team used data  from aerial surveys conducted byNASA's Operation IceBridgeand satellite-based  observations acquired by multiple international space agencies (NASA,ESA,CSA,DLR,JAXAandASI) coordinated by thePolar Space Task Group. The NASA satellite data used are from the  joint NASA/USGS Landsat program. The various tools used -- including a highly  sensitive radar sounder, gravimeter and laser profiling systems, coupled with  radar and optical images from space -- monitor and record changes in the shape,  size and position of glacial ice over long time periods, providing precise data  on the state of Earth's polar regions.The  scientists determined the bottom of Zachariae Isstrom is being rapidly eroded  by warmer ocean water mixed with growing amounts of meltwater from the ice  sheet surface. "Ocean warming has likely played a major role in triggering [the  glacier's] retreat," Mouginot  said, "but we need more oceanographic observations in this critical sector of  Greenland to determine its future.""Zachariae Isstrom is being hit from above and below," said the  study's senior authorEric Rignot, Chancellor's Professor of Earth system science at UCI, and Joint  Faculty Appointee at JPL. "The  top of the glacier is melting away as a result of decades of steadily  increasing air temperatures, while its underside is compromised by currents  carrying warmer ocean water, and the glacier is now breaking away into bits and  pieces and retreating into deeper ground."Adjacent  to Zachariae Isstrom is another large glacier, Nioghalvfjerdsfjorden, which is  also melting rapidly but is receding at a slower rate because it's protected by  an inland hill. The two glaciers make up 12 percent of the Greenland ice sheet  and would boost global sea levels by more than 39 inches (99 centimeters) if  they fully collapsed.The  sector where these two glaciers reside is one of three major marine-based  basins in Greenland, along with Jakobshavn Isbrae in central west Greenland and  the Petermann-Humboldt sector in central north Greenland. The latter two  sectors hold enough water to raise global sea level by 2 feet (0.6 meters)  each, and both are also undergoing significant changes at present. The authors conclude  it is likely that Nioghalvfjerdsfjorden and Petermann-Humboldt glaciers will  lose their ice shelves in coming years, further increasing Greenland's future  contributions to global sea level rise."Not  long ago, we wondered about the effect on sea levels if Earth's major glaciers in  the polar regions were to start retreating," Rignot noted. "We no longer need  to wonder; for a couple of decades now, we've been able to directly observe the  results of climate warming on polar glaciers. The changes are staggering and  are now affecting the four corners of Greenland."In  2015, NASA kicked off a new six-year field campaign, Oceans Melting Greenland,  which will examine ocean conditions around Greenland affecting the Ice Sheet.  For more information on OMG, visit:https://omg.jpl.nasa.gov/portal/Ongoing  research into the health of ice sheets and glaciers in Greenland and  Antarctica is supported by funding fromNASA's Cryospheric Sciences Program.For more  information on the study, visit:http://news.uci.edu/research/massive-northeast-greenland-glacier-is-rapidly-melting-uci-led-team-finds/