Warm ocean water attacking edges of Antarctica's ice shelves

Warm ocean water attacking edges of Antarctica's ice shelves
Satellite images show polynyas (open-water regions) forming at the ends of basal channels beneath shear margins of the East Getz Ice Shelf. A new study in Science Advances illuminates how warm ocean water and ice dynamics conspire to weaken the edges of Antarctica's ice shelves, making them more vulnerable to breakup Credit: Karen Alley/The College of Wooster and NASA MODIS/MODIS Antarctic Ice Shelf Image Archive at the National Snow and Ice Data Center, CU Boulder.

Upside-down "rivers" of warm ocean water are eroding the fractured edges of thick, floating Antarctic ice shelves from below, helping to create conditions that lead to ice-shelf breakup and sea-level rise, according to a new study.

The findings, published today in Science Advances, describe a new process important to the future of Antarctica's ice and the continent's contribution to rising seas. Models and forecasts do not yet account for the newly understood and troubling scenario, which is already underway.

"Warm water circulation is attacking the undersides of these ice shelves at their most vulnerable points," said Alley, who earned her Ph.D. at the University of Colorado Boulder, in the National Snow and Ice Data Center, part of CIRES. Alley is now a visiting assistant professor of Earth Sciences at The College of Wooster in Ohio. "These effects matter," she said. "But exactly how much, we don't yet know. We need to."

Ice shelves float out on the ocean at the edges of land-based ice sheets, and about three-quarters of the Antarctic continent is surrounded by these extensions of the . The shelves can be hemmed in by canyon-like walls and bumps in the ocean floor. When restrained by these bedrock obstructions, ice shelves slow down the flow of ice from the interior of the continent toward the ocean. But if an ice shelf retreats or falls apart, ice on land flows much more quickly into the ocean, increasing rates of .

The scientists' new work focuses on two factors conspiring to weaken ice shelves. First, flowing ice often stretches and cracks along its edges or "shear margins," especially when it's flowing quickly, Alley said. "In MODIS and other , you see all these crevasses."

As those craggy features flow toward the ocean and become part of floating ice shelves, they're vulnerable to erosion from below, by warm plumes of ocean water, the team reported.

Satellite images (videos below) show polynyas (open-water regions) forming at the ends of basal channels beneath shear margins of the East Getz Ice Shelf. A new study in Science Advances illuminates how warm ocean water and ice dynamics conspire to weaken the edges of Antarctica's ice shelves, making them more vulnerable to breakup Credit: Karen Alley/The College of Wooster and NASA MODIS/MODIS Antarctic Ice Shelf Image Archive at the National Snow and Ice Data Center, CU Boulder.

Warm and is more buoyant than cold and salty water, so it has a tendency to "find" high spots in floating ice, sometimes forming a type of "upside-down river" that can grow miles wide and tens of miles long. Alley and her colleagues first mapped those rivers or "basal channels" a few years ago, spotting them as wrinkles or sags in otherwise smooth ice surfaces.

Now, they've put it all together, showing that large basal channels are more likely to form at the shear margins—the weakest parts—of fast-flowing ice shelves. While the ice is still on land, large troughs form in the shear margins, becoming thin spots when the ice flows onto the ocean. Warm ocean water finds those thin spots along the base of the ice shelf, further eroding and weakening margins, making ice shelves more vulnerable to retreat and collapse.

In the past, researchers didn't know that warm plumes were so common beneath ice-shelf margins. Alley's team used satellite imagery to show that, at the ends of shear margins on many of Antarctica's fastest-changing glaciers, warm water rises to the surface, melting sea ice and forming areas of open water called "polynyas." The study found these polynyas forming year after year in the same spots, which means that warm water is indeed channelizing beneath thin, weak ice-shelf shear margins.

These processes appear to happen on ice shelves in both Antarctica and Greenland, Alley said, though the new work focuses on Antarctic glaciers.

The research team published earlier work focused on the damaging effects of meltwater on the surface of the ice shelves. "Now we're seeing a new process, where warm cuts into the shelf from below," said co-author Ted Scambos, a CIRES senior scientist at CU Boulder. "Like scoring a plate of glass, the trough renders the shelf weak, and in a few decades, it's gone, freeing the ice sheet to ride out faster into the ."

Scambos and Alley are heading back to Antarctica this fall, to continue work on the continent's ice dynamics; Scambos is a lead scientist in the International Thwaites Glacier Collaborative: https://thwaitesglacier.org/


Explore further

Warming ocean water undercuts Antarctic ice shelves

More information: "Troughs developed in ice stream shear margins precondition ice shelves for ocean-driven breakup" Science Advances (2019). advances.sciencemag.org/content/5/10/eaax2215
Journal information: Science Advances

Citation: Warm ocean water attacking edges of Antarctica's ice shelves (2019, October 9) retrieved 20 October 2019 from https://phys.org/news/2019-10-ocean-edges-antarctica-ice-shelves.html
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Oct 09, 2019
The AGW Cult, now with their "polynyas" stories about gloBull warming, only where there is extensive geothermal activity from volcanoes that formed during the Pliocene.
https://www.thegu...tarctica

Oct 09, 2019
oh deer auntieoral
you are wasting so mush of yout already useless existence
grovelling before your saudi master
fondly kissing his silk slippers

get off your well-callused knees
open your eyes
& look around you
the world is moving on

the natural climate changes getting super-sized by human destructive waste

Oct 09, 2019
Go take you meds Willis and have a little nap and when the "stupid" pills have done their magic, ensure the nurse straps to your mouth, your spittoon. Then, perhaps, you'll be able to muster some semblance of an argument, as this site is getting plastered with your drool shorting the circuits on your keyboard.

Oct 09, 2019
@antigoracle.
The AGW Cult, now with their "polynyas" stories about gloBull warming, only where there is extensive geothermal activity from volcanoes that formed during the Pliocene.
https://www.thegu...tarctica
Realise that the volcanoes have been there for millions of years already. The new factor is that warm currents from the warmer latitudes are now getting warmer due to AGW effects, thus making the ice shelf structures weaker than would have been if the warm water only came from the effects of long pre-existing geothermal inputs from volcanoes that have been there for millions of years (to which the Antarctic Ice Sheet system has been in balance for all that time). The point now is that AGW warming 'inputs' (via warmer ocean currents coming from elsewhere) is an added input which is obviously being observed now to be destabilising that long-existing balance. Please try to 'connect ALL the dots', mate. Ok? :)

Oct 09, 2019
Where is all this sea level rise we keep hearing about?

Banks still giving out 30 year mortgages in Miami. Miami is not a FEMA site. WTF?

Oct 09, 2019
oh rc, you are such a xomedian

your droll encouragement to auntieoral to grow up
& stop cowering from reality
with any possible expectation
that she has any ethical standards
or moral character?

priceless humor!

Oct 09, 2019
I didn't think the article was very clear on where the warm water is coming from. It mentions 'warm and fresh' water. I'm not looking for a childish argument - genuine question.

Oct 09, 2019
old coot
i'll bet you doughnuts to dollars
that most pf those endangered properties?
are being flipped on a regular basis
as each sap-buyer/crooked gambler/investor casino
s figuring on dumping the deed to the next sucker/gambler up

all expecting to have fled the rigged game with their skimmed profits
by the time the final attempt to sell?
falls through as waves lap across the house carpeting

in a rigged game, if you do not know who the intended mark is?
tag! your it...

o_c you are just so gullible,
it's making me feel sorry for you

cut it out, damn you!

Oct 09, 2019
heracli. the meaning that i take away from this article is that the rising ocean water is coming from several sources

the oceans are themselves heating up
i.e. when heated, water expands
shall we sing a chorus of "Steam Heat!"
both polar ice caps are melting
combining with the warmer sea water to increase storm surges during hurricanes,& typhoons

in addition, higher ocean levels? (res, plural, dynamic system) higher tides to beat on the coastlines

then us suicidally-inclined anthropophagous dolts
are pumping all the fresh water out from underneath our homes
gotta keep those golf courses green!
which lowers the land we want to inhabit, above the rip tides
to destructive tidal waves & storm surges

plus encouraging contamination of our limited supply of drinking water
with sea water sewage & industrial wastes

thus vividly displaying that we, homo dunderhead, are a evolutionary dead-end

& won't that be a relief for any surviving species?

Oct 10, 2019
Go take you meds Willis and have a little nap and when the....babble babble chest thump chest thump...
aaa Monkeyyy goracle.... swinging the those branches with full force today i see... Now now... those asylum walls is not talking to you it's all in your mind (hint...inside those 2 peas) try and focus them... ;)

Oct 10, 2019
Mental illness on full display...

The AGW Cult, now with their "polynyas" stories...

Oct 10, 2019
I didn't think the article was very clear on where the warm water is coming from. It mentions 'warm and fresh' water. I'm not looking for a childish argument - genuine question.
They don't know, but they can see the warm currents coming in and out with satellites.

The paper is open access at the address given in this article. It is at https://advances....eaax2215


Oct 10, 2019
Mental illness on full display...

The AGW Cult, now with their "polynyas" stories...


Goracle and his puppets banging his head against the Asylum walls, the chest thumping all over the show, always funny LOL ;)

Oct 10, 2019
Where is all this sea level rise we keep hearing about?

Banks still giving out 30 year mortgages in Miami. Miami is not a FEMA site. WTF?


Not even a single foolish question in response to the reality of NO NOTICEABLE SEA LEVEL RISE... YET. But plenty of negative marks, LOL, what childish fools.


Oct 10, 2019
well old_coot, as usual from you denierbot-loonies
a whole lot of babbling noise
but no verifiable scientific facts or peer-reviewed data to back up your ravings

since you insanely claim so much more knowledge in oceanic & climate sciences?

please present the findings from data you have collected
& no, your expected hypocritical plagiarizing of other peoples work?
misused in your primitive ignorance?
used out of context or deliberately falsified?

does not count

can you use a thermometer? barometer, depth gauge?
the tools of geodesy?

read a topographic map?
analyze collected charts & satellite images?

nope? didn't think so...

tell you what,
are you capable of holding a yardstick right-side up?

take it down to your nearest beach
find a pier
then measure every low & high tide
over, say, oh, ten years?

old_coot, then you will have actual data to support
your mass delusions

or not

don't worry, no one here
expects you to be accurate

or honest
in stating your conclusion

Oct 10, 2019
no change in sea level rise

https://www.cnsne...HJAwjtt4

Oct 11, 2019
no change in sea level rise

https://www.cnsne...fect-man


That isn't what the papers that the news article cites say. Heck, even the news article says that there is an observable sea level effect:
"Since 1993, sea level variations have been measured precisely by satellite altimetry. They indicated a faster sea level rise of 3.3 mm/yr over 1993-2015. " - Palanisamy


"superimposed on any anthropogenic trend there are also considerable decadal to centennial signals linked to intrinsic natural variability in the climate system… This result is consistent with recent findings that [b]beside the anthropogenic signature[/b], a non-negligible fraction of the observed 20th century sea level rise still represents a response to pre-industrial natural climate variations such as the Little Ice Age" - Danglendorf (emphasis added)


Thanks for providing citations that show sl rise!

Oct 12, 2019
However, we found that a possible candidate for such anthropogenic development, i.e. the large sea-level rise after 1970, is completely contained by the found small residuals, long-term oscillators, and general trend. Thus, we found that there is (yet) no observable sea-level effect of anthropogenic global warming in the world's best recorded region."

add, most tide data is linear [ until it gets '' adjusted'' ]

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