(Image credit: Joughin et al./Science Advances)
Pine Island Glacier, one of those fastest-shrinking glaciers at Antarctica, hastened its slide into the sea between 2017 and 2020, when one-fifth of its associated ice shelf broke off as enormous icebergs, a new analysis reveals.
The glacier sped up another period lately, between the 1990s and 2009, when warm ocean currents ate away at the underside of the ice shelf, destabilizing its structure and causing the glacier to accelerate open water, according to a 2010 report in the journal Geophysical Research Letters.
The ice shelf lies at the seaward edge of the glacier and scrapes against the land on each side, in addition to a number of the seafloor under, thus slowing the stream of glacial ice into the Amundsen Sea off of West Antarctica. As this frozen barrier pumped away over the course of two years, the glacier’s move toward the sea hastened by 1.5 miles (2.5 kilometers) per year to 2.5 miles (4 kilometers ) per year, in accordance with the 2010 study.
But whereas melting of the ice caused this previous acceleration, this time around, a more surprising, dramatic procedure drove the speed-up, according to another study published Friday (June 11) from the journal Science Advances. Basically, since the glacier moved, surface-level cracks and deep rifts appeared in its own ice shelf; this network of cracks gave out at several places, periodically causing huge chunks of the ice shelf to break loose, first writer Ian Joughin, a glaciologist at the University of Washington (UW) Applied Physics Laboratory, told Live Science.
As the ice shelf’s region shrank by roughly 20% — representing a loss of 251 square miles (651 square km) of region — that the glacier’s rate increased by 12% close to its border, the team found. In high profile videos of this glacier, stitched together from satellite information, the sides of the ice shelf could be observed grating against the coastline, while big cracks split out across the center of the shelf and then suddenly snap.
Calving, when icebergs break with an ice shelf,”has been known to be important for a long time, but this study demonstrates that floating ice loss from some locations has a much more dramatic impact on the glacier than if it breaks off in other regions,” Christine Dow, Canada research chair in glacier hydrology and ice dynamics in the University of Waterloo in Ontario, advised Live Science within an email.
“This is an interesting finding and explains a lot of recent change in the glacier. However, a bit more work is required to find out how fast the glacier will collapse,” said Dow, who wasn’t involved in the new analysis. For example, it’s uncertain exactly what drives the formation of the cracks that are annoying, whether they will appear more often in the long run or the way the stream of water underneath the glacier itself may contribute to this process, ” she said.
The finding does hint that the Pine Island ice shelf may fall more rapidly than previously projected — within the course of decades, rather than centuries, Joughin said. This may hasten the entire glacier’s collapse, consequently. However, as Dow mentioned, the specific timing of the breakdown remains uncertain. “The changes are rapid and concerning, but not immediately catastrophic,” he noted. “Nothing’s going to happen overnight.”
Satellite images capture ice shelf retreat
Pine Island Glacier and the neighboring Thwaites Glacier contain enough ice to raise global sea levels by approximately 4 feet (1.2 meters), should all that exposed ice fall into the sea, in accordance with the NASA Earth Observatory. Currently, Pine Island Glacier leads roughly 0. 006 inches (0. 167 millimeters) of sea-level rise each year, but that rate may gain later on, Joughin said.
Past research revealed how melting in the so-called grounding line — the point where the floating ice shelf first loses contact with the seafloor — drove previous accelerations of this glacier. These speed-ups happened in”fits and starts” as the grounding line retreated, because this loss of ice caused the glacier to jut forward before it got snagged on a brand new ridge in the seafloor, Joughin explained. And after this collection of accelerations, the glacier’s speed remained rather stable between 2009 and mid-2017.
To comprehend what the glacier was up to recently, Joughin and his colleagues used images from the Copernicus Sentinel-1 satellites, which can be worked by the European Space Agency and equipped with synthetic aperture radar (SAR). SAR images look like black-and-white photographs, but rather than taking a photo of visible light, SAR satellites endeavor radio waves in the landscape and document the signals which bounce back, Joughin said.
Starting in 2015, the Copernicus Sentinel-1 satellites took snapshots of Pine Island Glacier every 12 days, then after fall 2016, they began collecting data daily. The researchers analyzed all the data collected between January 2015 and September 2020 and utilized the great number of images to make detailed videos of this ice flow.
The group found that the calving speed of the ice shelf more than doubled in the time period and that starting from September 2017, the disintegrating plate dropped significant contact with the coastline on its southern border. This seemed to coincide with a sudden acceleration of this glacier, which continued to accelerate as more icebergs calved from the plate during the subsequent three decades. At precisely the same time, available information indicated”no obvious change in the ocean temperature variability” in the area, hinting that melt-driven reduction of the ice shelf likely was not to blame, the group noted.
To better understand what triggered the acceleration from 2017 to 2020, the team crafted an ice flow model of the glacier and ice shelf, considering local environmental conditions. They analyzed what the version would do if not one of the outermost shelf had broken off into the sea, and they found that the speed-up wasn’t as dramatic as what they found in the SAR footage. The team then attempted lopping off huge chunks of the shelf, as happened in actual life, and also the glacier hastened so.
“The only change I made is that I removed that part of the ice shelf,” Joughin said. “The speed of the model was very close to that which was observed in nature.”
That stated, even though the model came very near representing the SAR footage, there’s”still a mismatch” at the true and modeled flow rates of the floating ice, especially toward the ice shelf’s seaward edge, Dow said. This signals that some physiological systems may be acting on the ice flow however are still missing from your mod