Zachariae Isstrom Glacier in Accelerated Retreat
Posted by feww on November 16, 2015
Greenland’s ZI losing 5 billion tons of mass per year: Report
The northeast Greenland glacier Zachariae Isstrom (ZI) has come unmoored from a stabilizing sill and is crumbling into the North Atlantic Ocean at an accelerated rate of 5 billion tons per year, according to a report published in the current issue of Science.
ZI, which holds “a 0.5-meter sea-level rise equivalent,” entered a phase of accelerated retreat in fall 2012, says the report.
“The acceleration rate of its ice velocity tripled, melting of its residual ice shelf and thinning of its grounded portion doubled, and calving is now occurring at its grounding line. Warmer air and ocean temperatures have caused the glacier to detach from a stabilizing sill and retreat rapidly along a downward-sloping, marine-based bed. ”
“Zachariae Isstrom is being hit from above and below,” said senior author Eric Rignot, a researcher at Earth system science at UCI. “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.”
Its “equal-ice-volume” neighbor Nioghalvfjerdsfjorden, which is also melting rapidly, though retreating at a slower rate along an upward-sloping bed, drain a sector about 200,000 km² in size, or 12% of the Greenland Ice Sheet, says the report
“These two glaciers together drain the northeast Greenland ice stream, the only large, dynamic feature that extends continuously deep to the ice sheet interior near Greenland’s summit. This marine-based sector holds a 1.1-m sea-level rise equivalent.”
“Not long ago, we wondered about the effect on sea levels if Earth’s major glaciers were to start retreating,” says Rignot. “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.”
The report is published in the current issue of Science, posted at http://www.sciencemag.org/ [Science. ISSN 0036-8075 (print), 1095-9203 (online) ]