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Glacial cavity indicates that ice melts faster than we thought

A gigantic cavity – two-thirds of Manhattan's territory and almost 300m above the top of Thwaites Glacier in West Antarctica is one of several worrying findings reported in the new NASA-led disintegrating glacier study.

The results show the need for detailed observations on Antarctic glaciers, calculating how fast the global sea level will respond to climate change.

Researchers expect that at the bottom of Thwaites there will be some gaps between the ice and the rock, where ocean water can flow and melt the glacier from below. However, the size of the newly created hole and the explosive growth rate surprised them. It is large enough to contain 14 billion tonnes of ice, and most of this ice has melted in the last three years.

"For years, we've been thinking that Thwaites is not firmly attached to the base underneath it," says Eric Rignot of the University of California, Irvine and NASA's Jet Propulsion Laboratory. Rignot is a co-author of a new study published today for the development of science. "Thanks to the new generation of satellites, we can finally see the details," he adds.

NASA's IceBridge operation, which began in 2010 and explored the link between the polar region and the global climate, revealed a cavity in NASA's IceBridge. The researchers also used data from the Italian and German synthetic aperture radar constellation. These very high resolution data can be processed by a technique called radar interferometry to discover how the earth's surface below has moved between images.

"[The size of] Coal beneath the glacier plays an important role in melting, ”says study leader Pietro Milillo of JPL. "As the glacier takes more heat and water, it melts faster."

Numerical ice sheet models use a fixed form to depict the cavity under the ice rather than allowing the cavity to change and grow. The new discovery means that this limitation is likely to cause underestimation of these models, how quickly Thwaites loses ice.

The size of Florida, Thwaites Glacier, is currently responsible for about 4 percent of the global sea level rise. It has enough ice to lift the world ocean a little over 2 feet (65 centimeters) and an adjacent glacier that would raise the sea level by another 2.4 meters if all the ice were lost.

Thwaites is one of the most difficult places to reach on Earth, but it has become better known than ever before. The US National Science Foundation and the British National Environmental Research Council set up a five-year rural project to answer the most important questions about its processes and features. International Thwaites Glacier Collaboration will launch field experiments in the southern hemisphere in summer 2019-20.

How scientists evaluate ice loss

In the long term, it is not possible to monitor the Antarctic glaciers from the ground level. Instead, scientists use satellite or air instrument data to observe features that change as glaciers, such as its flow rate and surface height.

Another variable feature is the glacial earthing line – a place near the edge of the continent where it rises from the bed and begins to swim in the sea water. Many Antarctic glaciers rise to miles outside of their ground lines flying over the open ocean.

Just like a grounded boat, one can swim again when the weight of the load is removed, the glacier that loses the weight of the ice can swim over the ground where it is glued. When this happens, the grounding line resets inland. It exposes the bottom of the glacier to the sea water, increasing the likelihood that it will melt at speed.

Irregular resignation

Thwaites: "We discover various retreat mechanisms," says Millilo. The various processes in the various glacier ice levels of 100 miles (160 kilometers) make the landing line retreat and the rate of ice loss from synchronization.

The huge cavity is located below the glacial main frame on the western side – further down the western Antarctic peninsula. In this region, when the tide rises and falls, the grounding line departs and moves about 3km to 5km. Since 1992, the glacier has fallen since 1992 from the bedrock to 600 m to 800 meters. Despite the steady speed of the grounding, the melting speed on this side of the glacier is extremely high.

"On the eastern side of Glacier, the retreat of the earthing line takes place in small channels, maybe a kilometer wide, like fingers that reach under the glacier to melt it from below," says Milillo. In this region, the pace of landing has been doubled from around 600 million per year between 1992 and 2011 to 1.2 km per year from 2011 to 2017. t Even with this accelerating retreat, the melting speed on this side of the glacier is lower on the western side.

These results show that the interaction of the ice ocean is more complicated than previously understood.

Milillo hopes that the new results will be useful to International Thwaites Glacier Collaboration researchers in preparation for their field work. "Such data are essential for the field parties to focus on the areas where the action is taking place, because the grounding line quickly retreats to complex spatial models," he says.

"Understanding how the ocean melts, this glacier is essential to plan its impact on sea level rise over the coming decades," adds Rignots.

Milillo and his co-authors study in the Science Advances magazine are named "Heterogeneous Retreat and Thwaites Glacier Ice Melt, West Antarctica". Co-authors were at the University of California, Irvine; German Aviation and Space Center in Munich, Germany; Grenoble Alps University, Grenoble, France.

The picture shows: Thwaites Glacier.
Credits: NASA / OIB / Jeremy Harbeck

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