Pine Island Glacier, one of the fastest shrinking glaciers AntarcticaHastened its slip into the ocean between 2017 and 2020, with one-fifth of the associated ice shelves collapsing as giant icebergs, new research reveals.
Glaciers accelerated at another time in the recent history of warm ocean currents consuming underneath between the 1990s and 2009. ice According to the journal’s 2010 report, shelves destabilize their structure and accelerate glaciers towards open waters. Geophysics Research Letter..
Ice shelves are located on the sea-side edge of the glacier, scraping off the land on both sides and part of the seafloor beneath it, slowing the glacier’s ice flow into the Amundsen Sea off the coast of West Antarctica. According to a 2010 survey, glacier migration to the sea accelerated from 1.5 miles (2.5 km) to 2.5 miles (4 km) per year as the frozen barrier melted over the course of 20 years.
But while ice shelf melting has caused this past acceleration, this time a more abrupt and dramatic process speeds up, according to a new study published in the journal on Friday (June 11). Promoted Science Advances.. In essence, as the glacier moved, surface-level cracks and deep crevices appeared on the ice shelf. Ian Joughin, a glaciologist at the University of Washington’s (UW) Applied Physics Laboratory, told Live Science that this network of destruction has occurred in several places and huge chunks of ice shelves are regularly released. Said it was done.
It was found that when the area of the ice shelf shrank by about 20% (representing a loss of 251 square miles (651 square kilometers) of area), the glacier velocity increased by 12% near its edge. High-resolution video of glaciers stitched together from satellite data shows the sides of the ice shelf gridded with respect to the coastline, but a large crack in the center of the ice shelf causes a sudden snap. ..
Delivery when the iceberg leaves the ice shelf “has long been known to be important, but this study found that the loss of floating ice from one location was more important than when it broke elsewhere. It has shown to have a much more dramatic impact on the region. ” Christine Dow, research chairman of Glacier Hydrology and Ice Dynamics at the University of Waterloo, Ontario, told Live Science by email.
“This is an interesting discovery and explains many of the recent changes in glaciers, but it takes a little more work to see how fast glaciers collapse,” he said, not involved in the new study. Said Dow. For example, the exact cause of the formation of annoying cracks is unknown, whether it will appear more often in the future, or how the flow of water beneath the glacier itself contributes to this process.
The survey results are from Pine Island Ice shelf According to Joffin, it could collapse faster than previously predicted — in decades, not centuries. This can accelerate the collapse of the entire glacier. However, as Dow said, the exact timing of the failure remains uncertain. “Changes are rapid and worrisome, but not immediately catastrophic,” he said. “Nothing will happen overnight.”
Satellite image captures ice shelf retreat
The Swaite Glacier, adjacent to the Pine Island Glacier, contains enough ice to raise the world’s sea level by about 4 feet (1.2 meters) if all fragile ice collapses into the sea. According to NASA Earth Observatory.. Currently, the Pine Island Glacier contributes about 0.006 inches (0.167 millimeters) of sea level rise each year, but its speed may increase in the future, Joughin said.
past the study It showed how melting at the so-called ground line (the point where floating ice shelves first lose contact with the seafloor) facilitated the previous acceleration of the glacier. These speedups occurred “fit and start” when the ground wire retracted. This is because the loss of ice pushed the glacier forward until it caught on a new ridge on the ocean floor, Joughin explained. And after this series of accelerations, glacier velocities were fairly stable from 2009 to mid-2017.
To understand what the glacier is doing lately, Joughin and his colleagues used images from the Copernicus Sentinel-1 satellite, operated by the European Space Agency and equipped with Synthetic Aperture Radar (SAR). The SAR image looks like a black-and-white photograph, but instead of taking a snapshot of visible light, the SAR satellite projects radio waves into the landscape and records the bouncing signal, Joughin said.
Since 2015, the Copernicus Sentinel-1 satellite has taken snapshots of the Pine Island Glacier every 12 days and began collecting data every 6 days since the fall of 2016. The researchers examined all the data collected between January 2015 and September 2020 and used a large number of images to create a detailed video of the ice flow.
The team found that ice shelf birth rates more than doubled in that time frame, and that since September 2017, the collapsed ice shelves have lost significant contact with the southern coastline. This seemed to be consistent with the sudden acceleration of the glacier. The glacier continued to accelerate as more icebergs delivered from the shelves over the next three years. at the same time, Available data The team showed that “there was no apparent change in seawater temperature fluctuations” in the region, suggesting that it is likely not due to the thinning of ice shelves.
To better understand what caused the acceleration from 2017 to 2020, the team created a model of glacier ice flow and ice A shelf that takes into consideration the environmental conditions of the area. They tested what the model would do if the outermost shelves weren’t broken into the ocean and found that the speedup wasn’t as dramatic as what we saw in the SAR footage. The team then tried to cut off a huge chunk of shelves, as it happened in real life, and the glacier accelerated accordingly.
“The only change I made was to remove that part of the ice shelf,” said Joughin. “The speed of the model was very close to the speed observed in nature.”
That said, the model has come very close to reflecting SAR footage, but is “still inconsistent” with the actual and modeled velocities of floating ice, especially towards the sea-side edge of the ice shelf. there is. This suggests that some physical systems may be acting on the ice stream, but are still missing from the model, she said.
“It’s not yet clear how important these missing parts are to determine the future of the Pine Island Glacier,” Dow told Live Science.
For example, Dow’s own research group is currently investigating how the flow of water below glaciers plays a role in the rate of melting of ice above. This subglacier water accumulates due to friction from moving glaciers and geothermal heat from glaciers. Earth Less than; Eventually, freshwater slides out from under the glacier into the cavity under the ice shelf, mixing the salty seawater found there. This could cause more hot water to move towards the ground wire, which could lead to a “faster retreat” of the ice shelf, but the new model does not take this process into account, Dow said.
And there’s another missing puzzle piece that scientists have to deal with. What causes the iceberg to eventually become snap-free when deep destruction appears on the ice shelf?
Scientists can model melt-driven thinning fairly well, but “the part about shelf collapse goes into fracture mechanics.” This is also a tricky physical factor. earthquake Prediction, Joughin said. “The bottom line is … it’s hard to say when something bursts or breaks,” he said. He said that as icebergs become more accurate in predicting when they will deliver from ice shelves, scientists will be able to more accurately predict subsequent glacier acceleration and associated sea level rise.
But even if glaciers accelerate again in the near future, their contribution to sea level rise should not suddenly soar to catastrophic levels in the territory of a few feet a year, Joughin said. Again, glaciers now contribute about 0.006 inches of sea level rise annually, so “triple it to just 0.5 mm. [0.02 inches] One year. “
Originally published in Live Science.
Dramatic images capture rapid slides of Antarctic glaciers
Source link Dramatic images capture rapid slides of Antarctic glaciers