A giant cavity: two thirds of the Manhattan area and nearly 300 meters high, which grow at the bottom of the Thwaites Glacier in the western Antarctic, is one of several disturbing discoveries that are going reported in a new study led by NASA on the disintegrating glacier. The findings highlight the need for detailed observations of the lower part of Antarctic glaciers in calculating the speed of sea levels in response to climate change.
The researchers hoped to find some gaps between the bottom of the ice and the rocks at the bottom of Thwaites, where ocean water could flow and melt the glacier from below. The size and growth rate of the new hole, however, surprised them. It is large enough to contain 14,000 million tons of ice, and most of this gel melts in the last three years.
"We have been suspicious for years that Thwaites was not very tied to the bottom rock," said Eric Rignot, from the University of California, Irvine, and the Jet Propulsion Laboratory at NASA in Pasadena, California. Rignot is co-author of the new study, published in Advances of science. "Thanks to a new generation of satellites, we can finally see the detail," he said.
The cavity was revealed by a radar that penetrates the ice into NASA's IceBridge operation, an airborne campaign starting in 2010 that studies connections between the polar regions and the global climate. The researchers also used data from a constellation of synthetic opening radars of the Italian and German domains. These high resolution data can be processed using a technique called radar interferometry to discover how the surface of the lower floor has moved between the images.
"[The size of] a cavity under a glacier plays an important role in the grave, "said the main author of the study, Pietro Milillo of JPL." As more heat and water go down the glacier, it melts more fast ".
The numerical models of ice sheets use a fixed shape to represent a cavity under the ice, instead of allowing the cavity to change and grow. The new discovery implies that this most likely limitation causes these models to underestimate the speed with which Thwaites is losing ice.
Regarding the size of Florida, the Thwaites glacier is currently responsible for about 4% of the rise in the global level of the sea. It has enough ice to raise the world ocean a little more than 2 feet (65 centimeters) and the backstops of neighboring glaciers that would increase sea levels an additional 8 feet (2.4 meters) if you lose all the gel
Thwaites is one of the toughest places to get on Earth, but it's getting to be better known than ever. The National Science Foundation of the United States and the British National Environmental Research Council are creating a five year field project to answer the most critical questions about their processes and features. The Thwaites International Glacier League will begin its field experiments in the summer of the South Hemisphere 2019-20.
How scientists measure the loss of ice
There is no way to control Antarctic glaciers from the long-term soil level. On the other hand, scientists use data from satellite or airborne instruments to observe features that change as a glacier melts, such as flow velocity and surface height.
Another changing feature is the glacier land line: the place near the edge of the continent where it extends from the bed and begins to float to the sea water. Many Antarctic glaciers extend for miles beyond their dirt lines, floating over the open ocean.
In the same way that a boat on the ground can float again when the weight of its cargo is removed, a glacier that loses ice weight can float on the ground where it used to stick. When this happens, the ground line is removed in the interior. This exposes more part of the bottom of the glacier to the sea water, increasing the likelihood that the melting speed will accelerate.
An irregular retreat
For Thwaites, "we are discovering different withdrawal mechanisms," Millilo said. The different processes in several parts of the facade of 100 kilometers long (160 kilometers in length) of the glacier are putting the rates of withdrawal from the ground line and the loss of ice away from the synchronization.
The huge cavity is located under the main trunk of the glacier on its western side, the farthest side of the Western Antarctic Peninsula. In this region, as the tide rises and falls, the ground line retreats and advances in an area of 2 to 3 miles (3 to 5 kilometers). The glacier has been disappeared from a crest to the rock of the ground at a constant rate of about 0.4 to 0.8 miles (0.6 to 0.8 kilometers) the year of of 1992. Despite this stable rate of withdrawal from the land line, the fusion rate on this side of the glacier is extremely high.
"On the eastern part of the glacier, the removal of the land line passes through small channels, perhaps one kilometer wide, such as the fingers that reach below the glacier to melt it from the bottom," goes say Milillo In this region, the rate of removal of the land line doubled from 0.4 miles (0.6 kilometers) in the year from 1992 to 2011 at 0.8 miles (1.2 kilometers) the year from 2011 to 2017. Even with this accelerated retreat, however, the fusion rates on this side of the glacier are lower than on the west side.
These results point out that the interactions between ice and ocean are more complex than previously understood.
Milillo hopes the new results will be useful for researchers at the Thwaites Glacier International Collaboration as they prepare for their field work. "These data are essential for field parties to focus on the areas where the action is, because the ground line quickly retreats with complex spatial patterns," he said.
"Understanding the details about how the ocean undoes this glacier is essential to project its impact on the rise in sea levels in the coming decades," said Rignot.
The Milillo document and its co-authors of the journal Science Advances are titled "Heterogeneous removal and ice melting of the Thwaites Glacier, Western Antarctic." The authors were from the University of California, Irvine; the German Aerospace Center of Munich, Germany; and the Grenoble Alpes university in Grenoble, France.