Friction means Antarctic glaciers more sensitive to climate change than we thought

Antarctic glacier
Antarctic glacier. Credit: British Antarctic Survey

One of the biggest unknowns in understanding the effects of climate change today is the melting rate of glacial ice in Antarctica. Scientists agree rising atmospheric and ocean temperatures could destabilize these ice sheets, but there is uncertainty about how fast they will lose ice.

The West Antarctic Ice Sheet is of particular concern to scientists because it contains enough ice to raise global sea level by up to 16 feet, and its physical configuration makes it susceptible to melting by warm ocean water. Recent studies have suggested that the collapse of certain parts of the is inevitable. But will that process take several decades or centuries?

Research by Caltech scientists now suggests that estimates of future rates of melt for the West Antarctic Ice Sheet—and, by extension, of future sea-level rise—have been too conservative. In a new study, published online on March 9 in the Journal of Glaciology, a team led by Victor Tsai, an assistant professor of geophysics, found that properly accounting for Coulomb friction—a type of friction generated by solid surfaces sliding against one another—in computer models significantly increases estimates of how sensitive the ice sheet is to temperature perturbations driven by climate change.

Unlike other ice sheets that are moored to land above the ocean, most of West Antarctica's ice sheet is grounded on a sloping rock bed that lies below sea level. In the past decade or so, scientists have focused on the coastal part of the ice sheet where the land ice meets the ocean, called the "grounding line," as vital for accurately determining the melting rate of ice in the southern continent.

"Our results show that the stability of the whole ice sheet and our ability to predict its future melting is extremely sensitive to what happens in a very small region right at the grounding line. It is crucial to accurately represent the physics here in numerical models," says study coauthor Andrew Thompson, an assistant professor of environmental science and engineering at Caltech.

Part of the seafloor on which the West Antarctic Ice Sheet rests slopes upward toward the ocean in what scientists call a "reverse slope gradient." The end of the ice sheet also floats on the ocean surface so that ocean currents can deliver warm water to its base and melt the ice from below. Scientists think this "basal melting" could cause the grounding line to retreat inland, where the ice sheet is thicker. Because ice thickness is a key factor in controlling ice discharge near the coast, scientists worry that the retreat of the grounding line could accelerate the rate of interior ice flow into the oceans. Grounding line recession also contributes to the thinning and melting away of the region's ice shelves—thick, floating extensions of the ice sheet that help reduce the flow of ice into the sea.

According to Tsai, many earlier models of ice sheet dynamics tried to simplify calculations by assuming that is controlled solely by viscous stresses, that is, forces that apply to "sticky fluids" such as honey—or in this case, flowing ice. The conventional models thus accounted for the flow of ice around obstacles but ignored friction. "Accounting for frictional stresses at the ice sheet bottom in addition to the viscous stresses changes the physical picture dramatically," Tsai says.

In their new study, Tsai's team used computer simulations to show that even though Coulomb friction affects only a relatively small zone on an ice sheet, it can have a big impact on ice stream flow and overall ice sheet stability.

In most previous models, the ice sheet sits firmly on the bed and generates a downward stress that helps keep it attached it to the seafloor. Furthermore, the models assumed that this stress remains constant up to the grounding line, where the ice sheet floats, at which point the stress disappears.

Tsai and his team argue that their model provides a more realistic representation—in which the stress on the bottom of the ice sheet gradually weakens as one approaches the coasts and grounding line, because the weight of the ice sheet is increasingly counteracted by water pressure at the glacier base. "Because a strong basal shear stress cannot occur in the Coulomb model, it completely changes how the forces balance at the grounding line," Thompson says.

Tsai says the idea of investigating the effects of Coulomb friction on ice sheet dynamics came to him after rereading a classic study on the topic by American metallurgist and glaciologist Johannes Weertman from Northwestern University. "I wondered how might the behavior of the ice sheet differ if one factored in this water-pressure effect from the ocean, which Weertman didn't know would be important when he published his paper in 1974," Tsai says.

Tsai thought about how this could be achieved and realized the answer might lie in another field in which he is actively involved: earthquake research. "In seismology, Coulomb friction is very important because earthquakes are thought to be the result of the edge of one tectonic plate sliding against the edge of another plate frictionally," Tsai said. "This ice sheet research came about partly because I'm working on both glaciology and earthquakes."

If the team's Coulomb model is correct, it could have important implications for predictions of ice loss in Antarctica as a result of . Indeed, for any given increase in temperature, the model predicts a bigger change in the rate of ice loss than is forecasted in previous models. "We predict that the ice sheets are more sensitive to perturbations such as temperature," Tsai says.

Hilmar Gudmundsson, a glaciologist with the British Antarctic Survey in Cambridge, UK, called the team's results "highly significant." "Their work gives further weight to the idea that a marine ice sheet, such as the West Antarctic Ice Sheet, is indeed, or at least has the potential to become, unstable," says Gudmundsson, who was not involved in the study.

Glaciologist Richard Alley, of Pennsylvania State University, noted that historical studies have shown that ice sheets can remain stable for centuries or millennia and then switch to a different configuration suddenly.

"If another sudden switch happens in West Antarctica, could rise a lot, so understanding what is going on at the grounding lines is essential," says Alley, who also did not participate in the research.

"Tsai and coauthors have taken another important step in solving this difficult problem," he says.


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Sediment wedges not stabilizing West Antarctic Ice Sheet

Journal information: Journal of Glaciology

Citation: Friction means Antarctic glaciers more sensitive to climate change than we thought (2015, March 10) retrieved 22 October 2019 from https://phys.org/news/2015-03-friction-antarctic-glaciers-sensitive-climate.html
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Mar 10, 2015
Models.........(yawn)........wake me up in a century or two.

Mar 10, 2015
Who has a "Science Officer"?

L Ron Hubbard?

Barney Google?

Perhaps a little reading about the state of our world-wide glaciers, responsible for the water used by two billion people, is in order.


Mar 10, 2015
BS, ice is growing.

Mar 10, 2015
Hmm... it's interesting how AGW Cult "science" CO2 is only melting the West Antarctic where there happens to be significant geothermal activity.

Mar 10, 2015
According to the most recent research, the ice sheet in question is being affected by geothermal heating from below due to volcanic activity. The instability of this particular glacier was already recognized in the 60s, and is most likely due to processes that began thousands of years ago. Moreover, If global warming were a factor we'd be seeing similar effects throughout Antarctica, but that is definitely not the case. To attribute the instability of this one glacier to climate change is a typical example of alarmist hype.


Mar 10, 2015
I guess Victorag is unaware of the tropical diseases already in the birds in Alaska, and the acidification of the oceans, threatening the base of the Marine Food Chain.

Mar 10, 2015
To gaming ogre:

"A European satellite has shown ice sheets shrinking at 120 cubic miles a year in Antarctica and Greenland"

120 CUBIC MILES of ice into the sea. In one year, . . and it is increasing.

http://www.thegua...reenland

Mar 10, 2015
According to the most recent research, the ice sheet in question is being affected by geothermal heating from below due to volcanic activity. The instability of this particular glacier was already recognized in the 60s, and is most likely due to processes that began thousands of years ago. Moreover, If global warming were a factor we'd be seeing similar effects throughout Antarctica, but that is definitely not the case. To attribute the instability of this one glacier to climate change is a typical example of alarmist hype.

This is utterly wrong. While there is volcanic activity under the glaciers in West Antarctica, they have been steady and continuous in their eruption activity, and there is no evidence, at all, of any geothermal heating beyond what would be expected from localized, specific areas. The melt, if any, of such eruptions has no measurable effect on the ice sheets, and the localized eruption melt has no discernible effect on the stability of the ice sheet. .cont.

Mar 10, 2015
Furthermore, according to the most recent research, the geothermal activity under the WA ice sheets has actually diminished since the 60's.

It is also a ridiculous position to take, to suggest that the WA and EA ice sheets respond to geothermal warming equally. That is like saying the East coast of the US responds to changes in volcanoes in Oregon.

And finally, it is a typical denialist tactic to downplay anything that doesn't meet the confirmation biased evidence of their denial of the science, and place undeserved attribution to the most obscure of events if it meets their preconceived ideas of what they think should be happening.

Mar 10, 2015
@antigoracle as well, u really are a dimwit aren't u - so immensely out of date & repeating rubbish !

gaming_ogre claimed
BS, ice is growing.
Anything at all to support, what appears to be a stupid & misleading claim and to counter the findings in this link:-
http://www.washin...is-year/

Can any denier answer this simple AGW issue:-

"How can adding a greenhouse gas to the atmosphere, such as CO2 with known & irrefutable thermal properties of absorbance/re-radiation, somehow NOT increase thermal resistivity ?"

If that simple issue cannot be addressed by antigoracle & gaming_ogre & other dimwits, some of which claim to have uni degrees, then why bother to paint yourself as so very stupid in the banal, unscientific posts you make, drawing attention to your lack of eduction and immensely happy to look foolish ?

Mar 10, 2015
Victorag claimed
According to the most recent research, the ice sheet in question is being affected by geothermal heating from below due to volcanic activity. The instability of this particular glacier was already recognized in the 60s, and is most likely due to processes that began thousands of years ago. Moreover, If global warming were a factor we'd be seeing similar effects throughout Antarctica, but that is definitely not the case. To attribute the instability of this one glacier to climate change is a typical example of alarmist hype.
No. There is not enough energy from geothermal, if U imagine there is then shown a link to proof of data ?

Besides Arctic is mostly surrounded by land whilst Antarctic completely by water.

Their dynamics, albedo, proximity to human heat sources & weather patterns are COMPLETELY different you berk !

Please get an education, then U will be immune to being an unpaid mouthpiece & might learn some physics & gain freedom !

Mar 10, 2015
Interesting. But 99% of all glacial retreat from the last ice age occurred before the industrial age.

Mar 10, 2015
Interesting. But 99% of all glacial retreat from the last ice age occurred before the industrial age.

So?

Frankly 95% of it occurred before the end of the Younger Dryas. The glaciers and ice sheets were actually increasing, up until the 1880's or so. Since then, the remaining 4% has disappeared.

Do you always make empty points?

Mar 11, 2015
Interesting. But 99% of all glacial retreat from the last ice age occurred before the industrial age.
@samohta
And 100% of all asteroid/meteor strikes on earth have happened in the past as well, too

that doesn't mean that there will be NO asteroid/meteor strikes in the future just because it has only happened in the past

that argument is no different than saying we will never have another CME towards earth because the historical record shows that 100% of ALL registered and recorded CME's towards earth are in our past

your argument is nonsense and illogical from the start


Mar 11, 2015
One of the biggest unknowns in understanding the effects of climate change today is the melting rate of glacial ice in Antarctica.
Yeah, how does it do that when it generally never gets above freezing? Is it magic?

Mar 11, 2015
One of the biggest unknowns in understanding the effects of climate change today is the melting rate of glacial ice in Antarctica.
Yeah, how does it do that when it generally never gets above freezing? Is it magic?


BAHAHAHAHA!!!!! Yea ubaumoron, it's magic! This one goes into the "stupidest ubamoron questions ever asked" file!!! BAHAHAAHAAAA!!!!

Mar 11, 2015
ubavontuba asked a doozy
Yeah, how does it do that when it generally never gets above freezing? Is it magic?
"Generally" is your word here, care to qualify it re an actual quanta/metric in relation to your claim EG % ?

AND

Seems u imagine Antarctica isn't surrounded by (liquid) water

AND that winds only blow from the cold regions to the warmer over water.

Had a look at the wind patterns around Antarctica year round ?

Got any concise science to add or definitively refute:-
http://www.thegua...reenland

AND my long lasting question to arbitrary deniers & hopefully those with 'some' physics:-

"How can adding a greenhouse gas to the atmosphere, such as CO2 with well known & never disproved thermal properties, somehow NOT increase thermal resistivity ?"

Do U ubavontuba understand the universal relationship between resistivity & potential & how to actually measure that potential ?

ctd

Mar 11, 2015
ubavontuba asked with implicit claim
Yeah, how does it do that when it generally never gets above freezing? Is it magic?
Unfortunately you are showing you (again) you haven't learned about "latent heat of fusion".

ie. The energy difference between ice & water at 'freezing' temp of zero deg C !

Also, bear in mind, any heat source from below the ice has a greater thermal path to space as the air above the ice also warms, its an issue of "thermal resistivity", in this case it might be small but, there is no evidence it subtracts far more evidence it ADDs by virtue of GHG's effect to INCREASE thermal resistivity...

Also bear in mind oceans heat content STILL rising & see example in this link, red areas in southern hemisphere around Antarctica !
http://www.remss....ry_temps

From the very site you cherry pick less than a 30yr period from woodfortrees...

Mar 14, 2015
BAHAHAHAHA!!!!! Yea ubaumoron, it's magic! This one goes into the "stupidest ubamoron questions ever asked" file!!! BAHAHAAHAAAA!!!!
Your response is even stupider, as it is apparent you couldn't answer the question.


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