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“Fantastic” seabed backs record Antarctic retreat

It is among the best images on the seabed obtained anywhere around the Antarctic
It is among the best images on the seabed obtained anywhere around the Antarctic

Scientists are learning how quickly the Antarctic ice margin can retreat into a warming world.

They have identified functions on the seabed that indicate that the ice edge was on the way back up to 50 meters per day at the end of the last ice age.

It is about ten times faster than what is observed by satellites today.

The discovery is important because it imposes realistic constraints on the computer simulations used to project future changes in the region.

“In numerical models you play with the parameters ̵

1; and they can do very strange things,” said Prof Julian Dowdeswell. “But what this information says is that in fact prices far higher than we get even in the satellite register today were possible in the not far from the geological past.”

The director of the Scott Polar Research Institute (SPRI) in Cambridge, UK, led an expedition to the Larsen region on the Antarctic peninsula last year.

His team used autonomous underwater vehicles (AUV) with high-resolution mapping capabilities to investigate the sediment at the bottom of the western Weddell Sea.

What the robots saw was a delicate pattern with ridges that looked like a series of ladders where each track was about 1.5 m high and spaced between 20-25 m.

The researchers interpret that these ridges are functions generated at the ice floor.

This zone is the point where the ice that flows from the Antarctic into the sea becomes fluid and begins to flow. The rocks are created when the ice at this location repeatedly clumps the sediment as the tide rises and falls.

The AUVs flew only 60 meters above sea level in about 500 meters of water
The AUVs flew only 60 meters above sea level in about 500 meters of water

For the pattern to have been produced and preserved, the ice must have been in retreat (forward ice would destroy the ridges). And the tide “clock” therefore provides a speed for this reversal.

Prof Dowdeswell explained: “We have a maximum of 90 of these rolls with a distance of 20-25m – which gives us, if extrapolated, a speed of 40-50m per day. Again, if extrapolated – it is a speed over 10 km per retreat year And the really interesting thing about it is that it is a speed that is quite an order of magnitude higher than even the fastest retreat of the basics of the Pine Island-Thwaites system today. “

Pine Island and Thwaite’s glaciers are two of Antarctica’s fastest-changing ice bodies whose ice margins are melted by warm seawater beneath them.

The ridges that the AUVs are located about 40 km from the cliffs that lie in front of the ice edge in Larsen’s sector today. The marks are considered to be about 12,000 years old. Then the ice would have been much more extensive than it is today, but which today would have experienced rapid changes as the global climate emerged from the deepest freeze.

The western Weddell Sea is not an easy place to work because of its abundant sea ice
The western Weddell Sea is not an easy place to work because of its abundant sea ice

Dr. Alistair Graham from the University of South Florida, USA, works with AUV data. He was not involved in this research.

He said he thought the interpretation was compelling but that there would probably be some skepticism in the community that the rolls were really formed daily with the tide.

“The information in the magazine is absolutely fantastic,” he told BBC News.

“The ability to map with a resolution of one meter from an AUV really lifts a veil on the seabed structure and composition. We’ve been able to get snapshots of these kinds of images in the past, by sending an AUV under Pine Island Glacier, for example, but these images from the Dowdeswell team are the best so far from Antarctica.

“What this paper also emphasizes to me is that there are still great lessons to be learned from looking at the history of ice history at the poles. For somewhere like Thwaites Glacier, where we are desperate to understand its future trajectory, understand what it did for centuries and The millennia leading up to the observations we make today will be a critical part of determining how much ice is lost and how fast it progresses.

“We have similar high-resolution images from an AUV that was distributed at Thwaites Glacier last year that we are currently working on, and that hopefully will address some of these pressing issues.”

The new research is published in the journal Science. The Weddell Sea Expedition 2019 was an international effort led by SPRI and partly funded by the Flotilla Foundation and Marine Archeology Consultants Switzerland.

The AUVs are operated by the US and UK Ocean Infinity.

The distance between
The distance between the “rollers” is about 20-25 meters

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