Finding: Antarctica’s Ross Ice Shelf has collapsed before

The front of the Ross Ice Shelf floats in the Ross Sea, as seen from the cockpit of an LC130 aircraft flown by the New York Air National Guard. Photo by Matt Siegfried

Retracing Antarctica’s Glacial Past

LSU geologist uncovers new data to inform future sea level rise

BATON ROUGE – More than 26,000 years ago, sea level was much lower than it is today partly because the ice sheets that jut out from the continent of Antarctica were enormous and covered by grounded ice — ice that was fully attached to the seafloor.

The ice sheets were as large as they could get and at the time, sea level was much lower because a lot of ice was sequestered on the continent. As the planet warmed, the ice sheets melted and contracted, and sea level began to rise. LSU Department of Geology & Geophysics Associate Professor Phil Bart and his students have discovered new information that illuminates how and when this global phenomenon occurred. Their research recently published in Nature’s Scientific Reports may change today’s sea level rise predictions as Earth and its icy continent continues to warm.

Bart and his students conducted one of the largest geological surveys of the Antarctic continental shelf to-date. His team of undergraduate and graduate students spent 28 days at sea aboard the U.S. Antarctic Programs’ research ship, the Nathaniel B. Palmer RVIB, to scan the topography of the seafloor in the Ross Sea. They scanned and mapped a roughly 2,500-square-kilometer, or 965-square-mile, area to create a three-dimensional picture of the ocean floor. The scientists retraced the past movements of the West Antarctic Ice Sheet and its adjacent floating ice shelf as global climate warmed.

The ice shelf is a critical part of the climate system, because it slows down the breaking up and melting of grounded ice, which results in sea level rise. The scientists confirmed that the West Antarctic Ice Sheet had begun contracting and a relatively small ice shelf existed by 14,000 years ago. The ancient Ross Sea Ice Shelf then collapsed and calved into the ocean about 12,300 years ago.

More recently in 2002, in the northern part of Antarctica called the Antarctic Peninsula, the Larsen Ice Shelf collapsed. The collapse of this ice shelf quickly led to inland glaciers buttressed by the Larsen Ice Shelf to break up and melt. Scientists have thought that a similar process could have occurred when the Ross Ice Shelf collapsed thousands of years ago in the West Antarctic Ice Sheet.

However, Bart and colleagues from the University of South Florida, Auburn University and the Polish Academy of Sciences found that there was a centuries-long delay from when the Ross Ice Shelf collapsed and the grounded ice began to contract. In the Ross Sea, the delay was between 200 to 1,400 years later. This new information adds a layer of complexity for sea level rise computer simulations and predictions.

LSU Geology & Geophysics Professor Phil Bart led a team of scientists to 3D map the sea floor to find out how and when the West Antarctic Ice Sheet (outlined in white) moved and changed over the past 14,000 years. Photo Credit: Phil Bart, LSU.

The researchers made this discovery by combing through the imagery from their virtual map to find where sediment was being deposited while the ice was last in contact with the seafloor. At those locations, they collected sediment cores, which they analyzed and looked for evidence of fossilized life near the bottom of the ocean. In the sediment cores, they found fossilized shells of single cell organisms called foraminifera.

LSU researchers excavated and analyzed ancient fossilized organisms from the bottom of the ocean in Antarctica and discovered new information about an ice shelf that will inform future sea level rise predictions. Photo Credit: Phil Bart, LSU

These fossils provide a timestamped footprint that give the researchers an estimate of when the ice was last there through radiocarbon dating. The fossils retrieved from where the ice shelf collapsed are about 200 to 1,400 years older than the fossils found in the grounding line trough.

“We know that the West Antarctic Ice Sheet retreated more than 200 kilometers after the paleo-ice shelf collapsed. The radiocarbon dating of this past event is important because it shows that ongoing changes to ice shelves may trigger dynamics whose consequences are realized only after a significant delay,” Bart said.


The paper: A centuries-long delay between a paleo-ice-shelf collapse and grounding-line retreat in the Whales Deep Basin, eastern Ross Sea, Antarctica, Scientific Reports:
https://www.nature.com/articles/s41598-018-29911-8

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36 thoughts on “Finding: Antarctica’s Ross Ice Shelf has collapsed before

  1. Why is the fact that healthy, advancing glaciers naturally calve ice, as well as thinning, retreating ones, never mentioned? When the mass of ice grows so much that it breaks off into the sea, it doesn’t mean that the cause was melting

  2. “The ice shelf is a critical part of the climate system, because it slows down the breaking up and melting of grounded ice, which results in sea level rise.”

    I have often seen this claim. However, I have yet to see a rigorous defense of the claim. I’m sure that the friction between ice and the bedrock is orders of magnitude larger than the friction between ice and water. The presence of tension cracks in the floating ice suggests that it is not under compressive load from the advancing glaciers. The sea ice is probably just going along for the ride on a virtually frictionless water-bearing. Inertia may play a role, but once the shelf ice is moving at the same speed as the glacier, Newton’s First Law states that a body in motion tends to remain in motion unless acted on by an external force.

    • Other forces such as ocean circulation, tide cycles, surface wind direction & speed, etc. would add to the dynamics of the ice shelf. I’m sure it’s been studied.

    • Clyde, I agree. Also ice doesn’t preserve stress. If you truly blocked its path like the nonengineer geoengineerists dreamt up in a paper a week or so ago, it would thicken at the tongue (and/or widen if not constrained laterally) and ride over the barrier (if it didnt actually just remove the barrier altogether which is what is most likely) as long as the “head on the glacier was significantly higher than the barrier. The stuff deforms plastically. Grounded ice too would thicken and continue moving, perhaps the volume moving out to sea essentially unchanged. Their intuition leads then to think: Gee, ice is hard. When it grounds, the plate of ice holds back the whole glacier. The fact ice flows at all is all the thought experiment you need to understand this.

      Even the North American continental ice sheet of the glacial max flowed soutward simply because it was thicker to the N and moved by “flattening” and spreading as more ice accreted on top. There is a lubricating factor of liquid water in planes in flowing ice and the action of crystal liquifaction in high pressure locales and recrystallization in lower pressure zones as part of its motion. They are all very wet on the bottom. Hey how much more grounded can you get than with the N.Am. ice sheets that ground the hardest granites. They transported diamonds from the Arctic circle to Wisconsin!

      Much of the flood of hundreds of thousands of papers from our post normal ordinary minds in climate science depend on a priori reasoning ( the kind used by smart adolescents in arguments with their parents because the lack real experience).

      • The bloated forams are of the genus globigerina. If one goes to the trouble of collecting these fossils for determing age, surely you would mention what genus they are. I’m perhaps showing my age in this complaint because 50 -60 yrs ago you would be considered an illiterate clod to have pictures illustrating your samples without this identification 8n your caption and text.

        BTW, globigerina has been in existence pretty much unchanged since the hot Jurassic – Age of Dinosaurs, and here they are in the icy vault of Antarctic waters. Global Warming -Globigerinal Shmorming to you!

  3. ‘More than 26,000 years ago, sea level was much lower than it is today partly because the ice sheets that jut out from the continent of Antarctica were enormous and covered by grounded ice’

    Perhaps the Ice sheets over North America had something to do with it as well…

  4. No problem, Arctic and Greenland ice are increasing, nature is doing its things. Another sign of the impending cooling: a Beluga whale has moved all the way from the Arctic to the river Thames few miles downstream from London.
    “Belugas are commonly found in coastal waters of the Arctic Ocean, but are also at home in large rivers. They can move between salt and fresh water. They are common to Alaska, Russia, Canada, and Greenland.”
    https://ichef.bbci.co.uk/news/520/cpsprodpb/127ED/production/_103575757_beluga_whale_v4_640-nc.png
    We are all doomed by the global warming’s mysterious ways of doing things.

    • Don’t worry, fella, the BBC have already slipped AGW into that one about the whale, experts from all over the place spending their tuppence-hap’ney worth of “expertise” on the matter! 😉

  5. Excerpted from above commentary, to wit:

    The ice shelf is a critical part of the climate system, because it slows down the breaking up and melting of grounded ice

    The above is a true statement if one ignores the “noted” part.

    Ice shelves are destined to form where glacial ice comes in contact with sea water ……. and those same ice shelves are destined to fracture and/or break “free” from the grounded ice of the glacier, in part or in whole, and float away as sea ice or icebergs. And there is no pre-defined “time-line” for the aforenoted to occur. It might happen next month, 100 years from now, or 1000 years in the future.

    The collapse of an ice shelf (Ross Sea Ice Shelf, Larsen Ice Shelf, etc.) has nothing whatsoever to do with the near-surface temperatures or the ocean water temperature, …… but everything to do with the force of gravity …. and the force of physical pressure directed at said ice shelf resulting from glacier movement, wind driven wave action and daily tidal action,

    And, of course, the collapse of an ice shelf will oftentimes quickly led to the demise of the grounded ice ……. and/or the leading edge of the glacier where it buttressed the now defunct ice shelf …… simply because it is now subject to erosion by the turbulent ocean water.

    • “Ice shelves are destined to form where glacial ice comes in contact with sea water ”

      Actually no. In most cases ice shelves don’t form. There is none in the Northern Hemisphere for example. It only happens under extreme arctic climates, like in parts of Antarctica, and further requires rather special topographic conditions that “pin” and stabilize the shelf.

      • @ tty – September 25, 2018 at 1:58 pm
        There is none in the Northern Hemisphere for example.

        tty, I thank you for your response to my post …. and I will research your above “statement of fact”.

        Ice Shelves

        An ice shelf is a thick, floating slab of ice that forms where a glacier or ice flows down a coastline. Ice shelves are found only in Antarctica, Greenland, and Canada. Thicknesses of floating ice shelves range from 100-1,000 meters.

        Ice shelves are formed by forces of gravity from ice along the shore. Gravity constantly pressures the movement of ice from the land to the shelf. Ice shelves lose mass when chunks break off and slide into the ocean water. Shelves gain mass by snow accumulation on the upper surface.

        Read more @ http://ete.cet.edu/gcc/?/icecaps_icesheets

        • Could you please tell where these supposed ice shelves around Greenland and Canada are to be found? Because they don’t show up on any maps.

          There are a few small “shelves” on the north coast of Ellesmere land, but they aren’t true shelf ice because they don’t “form where a glacier or ice flows down a coastline”. They are just very old fast sea ice. For more detail read:

          http://davidmlawrence.com/Woods_Hole/References/Bradley_2008_YoungerDryas_SeaOfAncientIce.pdf

          The site you link to is junk.

          • tty, …… GETTA clue, …… my posted comment was in response to the published commentary that specifically defined the study results that was conducted in Antarctica, … and specifically pertaining to Antarctica’s Ross Ice Shelf, …….. not the Arctic, ….. not Greenland, …. not Australia,…. not Mars, ….. not Pluto, ….. not Japan …… and not Miami, Florida.

            So, tty, … iffen that’s what ”turns-your-crank”, ….. you have my permission to claim that …. “ice shelves are NOT destined to form anytime within the next 7 years in places such as: Arctic, ….. Greenland, …. Australia,…. Mars, ….. Pluto, ….. Japan …. and/or Miami, Florida” …… and I am sure you would be 100% correct.

            But now all bets are off concerning “ice shelves in the NH” …… iffen the current “solar minimum” continues resulting in another LIA.

            Cheers

        • There are very, very few sq kilometers of ice shelves in the northern hemisphere.
          Not zero, but very, very few. Especially when compared to the 14 Million sq kilometers of the Arctic sea ice.
          Even the Bering Sea or Sea of Okhotsk have more sea ice at minimum (200 – 600 sq kilometers) than the total NH ice shelves.

          The NH ice shelves do make good press releases though.

  6. The headline is misleading. It wasn’t the Ross shelf that collapsed. It was small shelf several hundred kilometers to the seaward of the Ross shelf, which was not a shelf but rather a grounded glacier at the time.

    As a matter of fact the Ross shelf seems remarkably stable, probably because it is pinned by Ross Island and Roosevelt Island. The Andrill-1B core suggests that it has never retreated much behind its current position during any interglacial since the “Super Interglacial” MIS 31/33 for 1.1 million years ago.

      • Since any carbon in the glaciers is going to be older than the carbon in sea water, if there is an increase in the amount of melt water, it could temporarily make things that grow in the older have an older radio carbon date.

  7. Kind of like announcing that leaves fell in the forest before. ‘but I do know that these points keep needing to be made anyway.

  8. “The ancient Ross Sea Ice Shelf then collapsed and calved into the ocean about 12,300 years ago.”

    Younger Dryas anyone?

  9. Sorry, but nothing the LSU Geology Department will ever do will rival the importance of registering an Earthquake at Tiger Stadium in 1988 when LSU scored the go-ahead touchdown against Auburn.

  10. I’m surprised nobody has noted that the Larsen ice shelf has NOT collapsed. Portions of it have broken away and melted, but much of the ice sheet remains in place.

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