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September 6, 2018
A topographic map of the rocky surface under the glacier. The brown peak is the inactive volcano Mount Resnik. The blue bar shows the missing layers, also known as unconformity, that move in a straight line to the sea. Vertical walls are tracks where the snowmobile has mapped ice sheets.Nicholas Holschuh / University of Washington
A region in western Antarctica behaves differently than most of the continent's ice: a large patch of ice is thickening, unlike other parts of West Antarctic that are losing ice. The continuation of this tendency to thicken affects the overall quantity that the melting or collapse of glaciers could raise the level of the world's oceans.
A study conducted by the University of Washington has uncovered a new index of the behavior of this region: a volcano under the ice cap has left a record of almost 6,000 years. The hidden track in the middle of the cap indicates that the current thickening is only a short-term feature that might not affect the glacier in the long run. It also suggests that similar clues to the past may be hidden deep within the ice sheet itself.
A panoramic image of McMurdo Station (left) and the Ross Sea, towards which the ice streams of the Siple Coast flow.Ryan Nichol, UCL Physics and Astronomy / Wikimedia
"What is exciting about this study is that we show how the icecap structure is a powerful record of what has happened in the past," said Nicholas Holschuh, Postdoctoral Researcher in Earth Sciences. and space. He is the first author of the article published on September 4 in The Cryosphere.
The data comes from the ice above Mount Resnik, an inactive 1.6-kilometer (mile-high) volcano currently lying within 300 meters of ice. The volcano is just upstream of the thickening of the Kamb Ice Stream, which is part of a dynamic coastal ice region that flows into the Ross Sea in Antarctica.
This map shows the average changes in the thickness of the Antarctic ice cap during the last decade. Other data confirm that the most important thickening occurs near the ice creek Kamb. Kamb and the nearby water courses pour into the Ross Sea.Nick Holschuh / University of Washington
Studies show that the Kamb Ice Stream flowed quickly in the past, but more than a century ago, it was drained by the other four major ice currents, which, according to glaciologists, occurs every hundred years. years. Meanwhile, the ice inside Kamb's ice stream is starting to swell and it's unclear what will happen next.
"The closure of the Kamb Ice Run began well before the satellite era," said Holschuh. "We need longer-term indicators to understand its behavior in order to understand the importance of this closure for the future of ice in the region."
The article analyzes two radar surveys of the region's ice. One of them was collected in 2002 by co-authors Robert Jacobel and Brian Welch, using the penetrating radar system of St. Olaf College in Minnesota and the other in 2004 by the co – author Howard Conway, professor of research on Earth and space. Sciences.
Conway noticed the missing layers and asked his colleagues to investigate.
The upper panel shows the map of ice layers around Mount Resnick. The lower panel shows a rupture in the layers (white line) imaged 30 kilometers downstream of Mount Resnik, resulting from changes in ice flow due to the volcano.Nicholas Holschuh / University of Washington
"Only when we spent probably six months with this dataset did we begin to gather the fact that this thing we could see in the ice cap was forming in response to the subglacial volcano." said Holschuh.
The study shows that the mysterious element comes from the ice covering Mount Resnik. The authors believe that the height of the volcano pushes the relatively thin ice sheet to the point of modifying the local wind fields and affects the deposition of snow. As the icecap passes over the volcano, a section lacks a few annual layers of snow.
"These missing layers are common in East Antarctica, where precipitation is less abundant and strong winds can strip surface snow," said Holschuh. "But it's really one of the first times we've seen those missing layers in West Antarctica. This is also the first time that a discrepancy has been used to reconstruct the movement of the ice cap of the past. "
Over time, glacial records show that this feature has followed a straight path to the sea. Over the 5,700-year record, the five major coastal ice streams have reportedly accelerated and slowed down several times. the water in the base lubricates the flow of the glacier, then turns away periodically, blocking one of the ice currents.
"Despite the fact that there were all these dramatic changes on the coast, the ice that was flowing inside was not really affected," Holschuh said.
What the feature shows is that a change occurred a few thousand years ago. UW's previous research shows a rapid retreat at the edge of the ice sheet until about 3,400 years ago, part of the recovery after the last ice age. The track of the volcano also shows a thinning of the ice about this time.
"This means that the interior of the ice sheet reacts to large-scale climate forcing from the last glacial maximum until today," Holschuh said. "Large-scale weather forcing is therefore very consistent between the interior and the coast, but the shorter-term processes are really apparent in the coastal record but are not visible on the inside.
Holschuh warns that it is only one point of data and that it must be confirmed by other observations. He is part of an international team of Antarctic scientists looking to combine the hundreds of radar analyzes of the Antarctic and Greenland glaciers that were originally done to measure the thickness of the ice. These data may also contain unique details on the internal structure of the glacier, which can be used to recreate the history of ice cap movement.
The equipment used to map the ice sheets consists of a snowmobile (left) that pulls a sled with radar penetrating the ice.Nicholas Holschuh / University of Washington
"These persistent historical ice flow tracers are probably everywhere," said Holschuh. "The more we can unravel the stories of past movements related to ice cap structure, the more realistic we can be in our predictions of how it will respond to future climate change."
The research was funded by the National Science Foundation and NASA. The other co-author is Knut Christianson, Assistant Professor of Earth and Space Science at UW.
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For more information, contact Holschuh at [email protected]. Images and videos are available for direct download at www.bit.ly/VolcanoUnderGlacier.
NSF Grant: OPP-9814574, OPP-0087345, NASA: NNX16AM01G
Tag (s): climate change • College of the Environment • Department of Earth and Space Sciences • Glaciers • Polar Science
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