The ice shelf on Antarctica鈥檚 Pine Island Glacier lost about one-fifth of its area from 2017 to 2020, mostly in three dramatic breaks. The timelapse video incorporates satellite images from January 2015 to March 2020. For most of the first two years, the satellite took high-resolution images every 12 days; then for more than three years it captured images of the ice shelf every six days. Images are from the Copernicus Sentinel-1 satellites operated by the European Space Agency on behalf of the European Union.
Credit: Joughin et al./Science Advances
For decades, the ice shelf helping to hold back one of the fastest-moving glaciers in Antarctica has gradually thinned. Analysis of satellite images reveals a more dramatic process in recent years: From 2017 to 2020, large icebergs at the ice shelf鈥檚 edge broke off, and the glacier sped up.
Since floating ice shelves help to hold back the larger grounded mass of the glacier, the recent speedup due to the weakening edge could shorten the timeline for Pine Island Glacier鈥檚 eventual collapse into the sea. The from researchers at the 天美影视传媒 and British Antarctic Survey was published June 11 in the open-access journal Science Advances.
鈥淲e may not have the luxury of waiting for slow changes on Pine Island; things could actually go much quicker than expected,鈥� said lead author , a glaciologist at the UW Applied Physics Laboratory. 鈥淭he processes we鈥檇 been studying in this region were leading to an irreversible collapse, but at a fairly measured pace. Things could be much more abrupt if we lose the rest of that ice shelf.鈥�
Pine Island Glacier contains approximately 180 trillion tons of ice 鈥� equivalent to 0.5 meters, or 1.6 feet, of global sea level rise. It is already responsible for much of Antarctica鈥檚 contribution to sea-level rise, causing about one-sixth of a millimeter of sea level rise each year, or about two-thirds of an inch per century, a rate that鈥檚 expected to increase. If it and neighboring Thwaites Glacier speed up and flow completely into the ocean, releasing their hold on the larger West Antarctic Ice Sheet, global seas could rise by several feet over the next few centuries.
These glaciers have attracted attention in recent decades as their ice shelves thinned because warmer ocean currents melted the ice鈥檚 underside. From the 1990s to 2009, Pine Island Glacier鈥檚 motion toward the sea accelerated from 2.5 kilometers per year to 4 kilometers per year (1.5 miles per year to 2.5 miles per year). The glacier鈥檚 speed then stabilized for almost a decade.
Results show that what鈥檚 happened more recently is a different process, Joughin said, related to internal forces on the glacier.
From 2017 to 2020, Pine Island鈥檚 ice shelf lost one-fifth of its area in a few dramatic breaks that were captured by the Copernicus Sentinel-1 satellites, operated by the European Space Agency on behalf of the European Union. The researchers analyzed images from January 2015 to March 2020 and found that the recent changes on the ice shelf were not caused by processes directly related to ocean melting.
鈥淭he ice shelf appears to be ripping itself apart due to the glacier鈥檚 acceleration in the past decade or two,鈥� Joughin said.
Two points on the glacier鈥檚 surface that were analyzed in the paper sped up by 12% between 2017 and 2020. The authors used an ice flow model developed at UW to confirm that the loss of the ice shelf caused the observed speedup.
鈥淭he recent changes in speed are not due to melt-driven thinning; instead they’re due to the loss of the outer part of the ice shelf,鈥� Joughin said. 鈥淭he glacier鈥檚 speedup is not catastrophic at this point. But if the rest of that ice shelf breaks up and goes away then this glacier could speed up quite a lot.鈥�
It鈥檚 not clear whether the shelf will continue to crumble. Other factors, like the slope of the land below the glacier鈥檚 receding edge, will come into play, Joughin said. But the results change the timeline for when Pine Island鈥檚 ice shelf might disappear and how fast the glacier might move, boosting its contribution to rising seas.
鈥淭he loss of Pine Island鈥檚 ice shelf now looks like it possibly could occur in the next decade or two, as opposed to the melt-driven subsurface change playing out over 100 or more years,鈥� said co-author , an ocean physicist at British Antarctic Survey. 鈥淪o it’s a potentially much more rapid and abrupt change.鈥�
Pine Island鈥檚 shelf is important because it鈥檚 helping to hold back this relatively unstable West Antarctic glacier, the way the curved buttresses on Notre Dame cathedral hold up the cathedral鈥檚 mass. Once those buttresses are removed, the slow-moving glacier can flow more quickly downward to the ocean, contributing to rising seas.
鈥淪ediment records in front of and beneath the Pine Island ice shelf indicate that the glacier front has remained relatively stable over a few thousand years,鈥� Dutrieux added. 鈥淩egular advance and break-ups happened at approximately the same location until 2017, and then successively worsened each year until 2020.鈥�
Other co-authors are and at the UW; and Mark Barham at British Antarctic Survey. The study was funded by the U.S. National Science Foundation, NASA and the U.K. Natural Environment Research Council.
For more information, contact Joughin at ian@apl.washington.edu and Dutrieux at pitr1@bas.ac.uk
NSF: OPP-1643285, NASA grant: NNX17AG54G