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Home / Science / Upturned "Rivers" of Warm Seawater Attack Antarctic Ice Shelfs [Video]

Upturned "Rivers" of Warm Seawater Attack Antarctic Ice Shelfs [Video]



  East Getz Ice Shelf

Satellite images show Polynyas (open water regions) located at the ends of the basal channels below the shear ridges of the East Getz Ice Shelf form . A new study in Science Advances highlights how warm seawater and ice dynamics weaken the edges of Antarctic ice shelves, making them more prone to breakup. Credit: Karen Alley / The College of Wooster and NASA MODIS / MODIS Antarctic Ice Shelf Image Library at the National Snow and Ice Data Center, CU Boulder.

Newly understood factors make ice shelves more prone to breakup, according to the College of Wooster. University of Colorado in Boulder Study.

Upside-down "rivers" of warm seawater erode the breaklines of thick, floating Antarctic ice shelves from below and help to create conditions that cause the ice shelf to break and sea level rise, according to a new study.

The results, published in Science Advances on October 9, 201

9, describe a new process that is important for the future of the Antarctic ice and the continent's contribution to the rise of the oceans. Models and forecasts do not yet take into account the newly understood and worrying scenario that is already underway.

"Warm water circulation attacks the undersides of this ice shelf at its most vulnerable spots," said Alley, who is Ph. D. at the University of Colorado Boulder, National Snow and Ice Data Center, part of CIRES. Alley is now an Assistant Professor of Earth Sciences at the College of Wooster in Ohio. "These effects are important," she said. We need to do it. "

At the edges of land-based ice sheets, ice sheets float on the sea, and about three-quarters of the Antarctic continent is surrounded by these expanses of ice sheet When braked by these bedrock obstructions, ice shelves slow the flow of ice from the continent's interior to the ocean, but when a ice shelf retreats or falls apart, the ice on land flows much faster into the ocean and increases the speed of sea-level rise.

Scientists' new work focuses on two factors of conspiracy to weaken ice shelf: First, flowing ice often stretches and rips at its edges or "shear edges" Especially when it's flowing fast, Alley said. "In MODIS and other satellite imagery you can see all these crevasses. "

When these rugged features flow towards the ocean and become part of floating ice shelves, they are susceptible to erosion by warm water tails from below. The team reported.

Hot and fresh water is more buoyant than cold and salty water. Therefore, it tends to "find" high spots in floating ice and sometimes forms a kind of "upside-down river" which can be miles and tens of meters wide for miles. Alley and her colleagues first mapped these rivers or "basal canals" a few years ago and discovered them as wrinkles or sacks in otherwise smooth ice surfaces.

Now they have put everything together and shown that large basal channels form more on the shear edges – the weakest parts – of fast-flowing ice shelves. While the ice is still on land, large ridges form on the shear ridges that develop into thin spots as the ice flows onto the ocean. Warm seawater finds these thin spots along the base of the ice shelf, further eroding and weakening the edges and making ice shelves more susceptible to retreat and collapse.

In the past, researchers did not know that warm feathers are so common among ice shelf edges. Alley's team used satellite imagery to show that at the ends of the shear edges of many of the fastest-changing Antarctic glaciers warm water rises to the surface, melting sea ice and forming open waters called "Polynyas". The study found these polynyas forming in the same places year after year, which means that warm water is actually channeled under thin, weak shear edges of the ice shelf.

These processes appear to occur on ice shelves in both Antarctica and Greenland, so Alley's focus is on Antarctic glaciers.

The research team has published earlier work on the harmful effects of meltwater on the surface of ice shelves. "Now we see a new process where warm water flows from below into the shelf," said co-author Ted Scambos, senior CIRES scientist at CU Boulder. "Like scratching a glass plate, the shelf is weakened by the trough, and in a few decades the ice sheet is free to venture out into the ocean faster."

Scambos and Alley return to Antarctica this fall to work on ice dynamics to continue the continent; Scambos is a senior scientist at Thwaites International Glacier Collaborative.

Reference: "Troughs Developed in Icecream Shear Limits Require Ice Shelfs for Oceanic Separation" by Karen E. Alley, Ted A. Scambos and Richard B. Alley and Nicholas Holschuh, October 9, 2019, Advances in science .
DOI: 10.1126 / sciadv.aax2215

Video: Karen Alley / Wooster and NASA MODIS / MODIS Antarctic Ice Shelf Image Archive / NSIDC. [19659018] (function (d, s, id) {
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