From 2017 to 2020, the Antarctica's Pine Island Glacier ice shelf lost approximately one-fifth its area, mainly in three dramatic breaks.Pine Island Glacier is one of the most rapidly-shrinking glaciers of Antarctica. It hastened its slide to the sea between 2017-2020, when one-fifth its associated ice shelf was exposed as huge icebergs. A new study finds that this happened.According to a 2010 report published in Geophysical Research Letters, the glacier also accelerated between the 1990s to 2009 when warm ocean currents destabilized the structure of the ice shelf. The result was that the glacier moved toward open water.The ice shelf is located at the seaward edge the glacier. It scrapes against both the land and some of the seafloor below, slowing down the flow of glacial water into the Amundsen Sea off West Antarctica. According to the 2010 study, the glacier's movement towards the sea increased from 1.5 miles (2 km) per annum to 2.5 miles (4 km/annum) over the period of 20 years.Related: 10 signs the Earth's climate has gone off-trackAccording to Science Advances, the acceleration was caused by melting of the ice shelf. However, the new study, published Friday, June 11, in Science Advances, shows that this time, the acceleration was driven by a sudden and dramatic process. The glaciologist Ian Joughin from the University of Washington's Applied Physics Laboratory explained that the glacier was moving and created surface-level cracks as well as deep rifts in its ice shelves. These fractures eventually caused large chunks of the ice shelves to burst, causing them to move.The team discovered that the glacier's speed rose by 12% close to its edge as the area of the ice shelf shrank by 20%. This represented a loss in area of 251 sq. miles (651 km)). High-resolution video of the glacier is stitched from satellite data. The sides can be seen grating against coastline while large cracks open across the middle of the shelf before snapping suddenly.Calving is when icebergs are freed from an ice shelf. However, this study shows that floating ice loss in some areas has a more significant impact on glaciers than if it occurs in other locations. Christine Dow, Canada research chair for glacier hydrology, ice dynamics, University of Waterloo, Ontario, shared her findings with Live Science via email."This interesting finding explains a lot about recent changes in the glacier. Dow, however, said that more research is needed to determine how quickly the glacier will crumble. Dow was not part of the new study. She said that it is unclear what causes the troublesome cracks to form, whether they will be more frequent in the future, or how the water below the glacier might contribute to the process.Joughin stated that this finding suggests that the Pine Island Ice Shelf may be able to collapse faster than expected over the course of decades rather than centuries. This could accelerate the entire glacier's meltdown. However, Dow noted that the exact time of this collapse is still unknown. He noted that "The changes are rapid, concerning, and not immediately catastrophic." "Nothing is going to happen overnight."This photograph of Pine Island Glacier was taken from the east side, looking westward, in January 2010. Image credit: Ian Joughin/University of WashingtonSatellite images capture retreat from ice shelvesAccording to NASA Earth Observatory, Pine Island Glacier (and Thwaites Glacier), contain enough ice to raise global ocean levels by approximately 4 feet (1.2 metres) if all of that fragile ice melts into the sea. Pine Island Glacier currently contributes approximately 0.006 inches (0.167 milimeters) to sea-level rise every year, but Joughin stated that this rate could increase in the future.Studies in the past showed that melting at the "grounding line", the point where floating ice shelves first lose contact with the seafloor, was responsible for previous accelerations. Joughin explained that these speed-ups happened in "fits & starts" as the grounding lines retreated. This loss of ice caused glacier to move forward until it was snagged on the seafloor. Between 2009 and mid 2017, the glacier's speed remained relatively stable after these accelerations.Joughin and his team used images from Copernicus Sentinel-1 satellites to understand the recent activities of the glacier. These satellites are operated by European Space Agency (ESA) and have synthetic aperture radar (SAR). SAR images are similar to black-and-white photos, but instead taking a photo of visible light, SAR satellites project radio waves onto the landscape and record the signals back, Joughin explained.The Copernicus Sentinel-1 satellites began taking snapshots of Pine Island Glacier every twelve days in 2015. They then started collecting data every six-days after fall 2016. Researchers analyzed all data from January 2015 to September 2020, and then used the many images to create detailed videos about the ice flow.Related: Antarctica (photos).The team discovered that the calving rates of the ice shelf increased more than twice in this time period. Also, that since September 2017, the shelf began to lose significant contact with its southern shoreline. This was accompanied by a rapid acceleration of the glacier. The speed increased as more icebergs calved off the shelf over the next three year. The team also noted that data showed "no apparent change in the ocean temperature variability in the region", suggesting that melting of the ice shelves wasn't the culprit.The team created an ice flow model that included the glacier and the ice shelf to better understand the causes of the acceleration between 2017 and 2020. They also took into consideration local environmental conditions. The team tested the model to see what it would do if the outermost shelf was not broken into the sea. They found that the acceleration wasn't quite as dramatic as they had seen in the SAR footage. The team tried to remove large chunks of the shelf as it happened in real life. The glacier then accelerated accordingly.Joughin stated that the only thing Joughin had done was to remove that portion of the ice shelf. "The model ran at a speed very similar to what was observed in nature."Dow stated that although the model was very close to matching the SAR footage, there was "still a mismatch” between the true and modeled flow rates of floating ice. This is especially evident towards the seaward edge of the ice shelf. She said that this suggests that there may be physical systems acting on the ice flow, but they are missing from the model.Dow stated to Live Science that it is not clear how crucial those missing pieces are in determining the future Pine Island Glacier's fate.Dow's research group, for instance, is currently studying the role of water flow below the glacier in melting rates of the ice. The subglacial water is accumulated due to friction between the moving glacier, and geothermal warmth from the earth below. Eventually, the fresh water will slip out of the glacier into the cavity beneath the shelf and mix with the seawater. Dow pointed out that this may cause more warm water to flow toward the grounding line, and possibly lead to a faster retreat of the ice shelves. However, the new model does not take this into consideration.Scientists must also solve a missing puzzle piece: What causes icebergs not to snap?Although scientists are able to model melt-driven thinning quite well, the "part about the shelf breaking down gets into fracture mechanics," Joughin stated. This tricky physical factor also plays into earthquake prediction. He said that it is difficult to predict when an item will burst or break. Scientists would be better equipped to predict when icebergs will calve from the ice shelf, and to predict the sea-level rise.Joughin stated that even though the glacier is expected to speed up in the near future its contribution to sea level rise won't spike to an alarmingly high level of several feet per year. He noted that the glacier contributes approximately 0.006 inches to sea-level rise annually. "Even if we tripled that, it would only be half-a-millimeter [0.02 in] per year."Original publication on Live Science
