A normal part of nature – sea ice retreat in Antarctica

From the UNIVERSITY OF CAMBRIDGE

‘Scars’ left by icebergs record West Antarctic ice retreat ten thousand years ago – occurred under climate conditions that were relatively similar to those of today.

Thousands of marks on the Antarctic seafloor, caused by icebergs which broke free from glaciers more than ten thousand years ago, show how part of the Antarctic Ice Sheet retreated rapidly at the end of the last ice age as it balanced precariously on sloping ground and became unstable. Today, as the global climate continues to warm, rapid and sustained retreat may be close to happening again, and could trigger runaway ice retreat into the interior of the continent, which in turn would cause sea levels to rise even faster than currently projected.

Ice cliffs in Pine Island Bay, taken from the IB Oden. CREDIT Martin Jakobsson

Researchers from the University of Cambridge, the British Antarctic Survey and Stockholm University imaged the seafloor of Pine Island Bay, in West Antarctica. They found that, as seas warmed at the end of the last ice age, Pine Island Glacier retreated to a point where its grounding line – the point where it enters the ocean and starts to float – was perched precariously at the end of a slope.

Break up of a floating ‘ice shelf’ in front of the glacier left tall ice ‘cliffs’ at its edge. The height of these cliffs made them unstable, triggering the release of thousands of icebergs into Pine Island Bay, and causing the glacier to retreat rapidly until its grounding line reached a restabilising point in shallower water.

Today, as warming waters caused by climate change flow underneath the floating ice shelves in Pine Island Bay, the Antarctic Ice Sheet is once again at risk of losing mass from rapidly retreating glaciers. Significantly, if ice retreat is triggered, there are no relatively shallow points in the ice sheet bed along the course of Pine Island and Thwaites glaciers to prevent possible runaway ice retreat into the interior of West Antarctica. The results are published in the journal Nature.

“Today, the Pine Island and Thwaites glaciers are grounded in a very precarious position, and major retreat may already be happening, caused primarily by warm waters melting from below the ice shelves that jut out from each glacier into the sea,” said Matthew Wise of Cambridge’s Scott Polar Research Institute, and the study’s first author. “If we remove these buttressing ice shelves, unstable ice thicknesses would cause the grounded West Antarctic Ice Sheet to retreat rapidly again in the future. Since there are no potential restabilising points further upstream to stop any retreat from extending deep into the West Antarctic hinterland, this could cause sea-levels to rise faster than previously projected.”

Pine Island Glacier and the neighbouring Thwaites Glacier are responsible for nearly a third of total ice loss from the West Antarctic Ice Sheet, and this contribution has increased greatly over the past 25 years. In addition to basal melt, the two glaciers also lose ice by breaking off, or calving, icebergs into Pine Island Bay.

Pine Island Glacier as seen from Google Earth – click to enlarge

Today, the icebergs that break off from Pine Island and Thwaites glaciers are mostly large table-like blocks, which cause characteristic ‘comb-like’ ploughmarks as these large multi-keeled icebergs grind along the sea floor. By contrast, during the last ice age, hundreds of comparatively smaller icebergs broke free of the Antarctic Ice Sheet and drifted into Pine Island Bay. These smaller icebergs had a v-shaped structure like the keel of a ship, and left long and deep single scars in the sea floor.

High-resolution imaging techniques, used to investigate the shape and distribution of ploughmarks on the sea floor in Pine Island Bay, allowed the researchers to determine the relative size and drift direction of icebergs in the past. Their analysis showed that these smaller icebergs were released due to a process called marine ice-cliff instability (MICI). More than 12,000 years ago, Pine Island and Thwaites glaciers were grounded on top of a large wedge of sediment, and were buttressed by a floating ice shelf, making them relatively stable even though they rested below sea level.

Eventually, the floating ice shelf in front of the glaciers ‘broke up’, which caused them to retreat onto land sloping downward from the grounding lines to the interior of the ice sheet. This exposed tall ice ‘cliffs’ at their margin with an unstable height, and resulted in rapid retreat of the glaciers from marine ice cliff instability between 12,000 and 11,000 years ago. This occurred under climate conditions that were relatively similar to those of today.

“Ice-cliff collapse has been debated as a theoretical process that might cause West Antarctic Ice Sheet retreat to accelerate in the future,” said co-author Dr Robert Larter, from the British Antarctic Survey. “Our observations confirm that this process is real and that it occurred about 12,000 years ago, resulting in rapid retreat of the ice sheet into Pine Island Bay.”

Today, the two glaciers are getting ever closer to the point where they may become unstable, resulting once again in rapid ice retreat.

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The research has been funded in part by the UK Natural Environment and Research Council (NERC)

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44 thoughts on “A normal part of nature – sea ice retreat in Antarctica

  1. Sea ice retreat in Antarctica? The Ship of Fools expedition by Professor Turney followed in the footsteps of Mawson’s Antarctic expedition one hundred years earlier, but got trapped by sea ice where Mawson sailed freely.

    • I always have thought of “Nature” as being alive; sort of like my Mother Gaia; Maxwell’s lab assistant.

      So Ice does not strike me as being alive; so how can it be part of Nature ??

      g

      • “Robert Kernodle

        Dry skin cells do not strike me as being alive, yet they are part of my living body.”

        Hair is dead, but still part of your living body.

    • Why no analyais of.effect of heat of decay of garbage & oth.e rrefuse in ” garbage” islands. 100 millions tona of garbage annually are dymped into oceans. Whyconceal this fact?

      • “Why no analyais of.effect of heat of decay of garbage…Whyconceal this fact?”

        It’s not concealed. Probably on scale lost heat from aquatic mammals. Earth’s oceans have a volume of 1.332 billion cubic kilometers, do the math.

      • Does this create the mythical “trash islands”? the ones we hear about, but they don;t actually exist? In fact, why do all of the “telltale” signs of global warming, etc. seem to happen where it’s almost impossible to see, like Antarctica, and the middle of the ocean?

  2. …marine cliff instability…between 12,000 to 11,000 years ago…climate conditions relatively similar to today…! Looks like SUV’s and cow farts are much older than I thought. This is another normal conditions are spun as abnormal and need study story.

  3. I remember surveying literature from the 1960s on this topic. Back then, it was the Ross Ice Shelf, grounded below sea level, unstable, and primed for destruction. Without the ice shelf, huge amounts of Antarctic ice would collapse into the ocean. If that happened, *Disaster*.

    Not too many years ago, an underwater survey revealed that the ice shelf has been in it’s current location for 5,000 years. The only thing we can conclude is that the Ross Ice Shelf is totally unstable and ready to collapse at a moments notice, and has been for the last 5,000 years.

    This alarmist stuff follows a predictable script as closely as a weekly TV show.

  4. Think about if the ice shelfs would not break up or the glaciers not calve icebergs?
    This is naturally and a sign that the ice/snow inlands is in good and stable condition.
    If a glacier do not calves icebergs, we would either have lost the glacier to GW or we would have a new ice time.
    The talk of collapse regarding polar icecaps need a completely new interpretation of the word collapse.
    My interpretation of collapse is something that takes minutes, not thousands of years.

    • Yes, collapse is a very much abused word nowadays.

      It should be the equivalent of the medical condition of dropping suddenly unconscious.

  5. Meanwhile, the East Antarctic Ice Sheet, which has been growing for over 3000 years, continues to do so.

    And Antarctic sea ice set a satellite era record high in 2014 and is now in the normal range, despite last year’s El Nino.

  6. Pitiful attempt to project ‘catastrophe’ onto todays Antarctic conditions with a make-it-up-as-they-go-along theory from 12,000 years ago. These people are shameless.

  7. “Today, as the global climate continues to warm, rapid and sustained retreat may be close to happening again, and could trigger runaway ice retreat into the interior of the continent, which in turn ”
    All of this has happened before and all of it will happen again. It’s a natural cycle, not some disastrous episode that will exterminate something or other. I’m slowly moving toward the “Okay, but I’ve got cookies in the oven” mindset.
    Remember, Greenland (up at the other end of the planet) was called “Green Land” for a reason: when the Vikings moved there to colonize it, there was plenty of arable land exposed and the weather was temperate. Then it changed, the harbors froze, they couldn’t get their boats out to the open ocean to haul in fish, and they couldn’t farm the land any more. In spite of this, the planet did not go into a catastrophic extermination period.
    Antarctica is simply in a freaking cycle that has a beginning and an ending and will continue to do what it’s done in the past until it starts moving north. WE have no control over it, and I know that upsets the Greenbeans and Warmians but they are all about controlling this and that. They must all be Capricorns.
    Thanks for the article.

    • “Remember, Greenland (up at the other end of the planet) was called “Green Land” for a reason: when the Vikings moved there to colonize it, there was plenty of arable land exposed and the weather was temperate.”

      Sara, while it is true a 1000 years ago we were in a cyclical warm period called the Medieval Warm Period that seems to happen every 1000 years, (witness our Modern Warm Period today) and probably somewhat warmer than today for a longer period of time, Greenland was still mainly covered by the icecap. Yes, there was some arable land as there is today, but it wasn’t an oasis in the Arctic as some people say. It was a bit of sales job by the Viking, Erik the Red, who had been banished from Norway for manslaughter and then he moved to Iceland with his family (father of Leif Erikson who discovered Vineland), and wound up discovering and moving to Greenland after he again wound up banished from Iceland for 3 years for manslaughter. He was a bit of a rascal…but wanted people to move to his settlement he founded in Greenland.

      When Erik returned to Iceland after his exile had expired, he is said to have brought with him stories of “Greenland”. Erik deliberately gave the land a more appealing name than “Iceland” in order to lure potential settlers. He explained, “people would be attracted to go there if it had a favorable name”. https://en.wikipedia.org/wiki/Erik_the_Red

      I think it is a mistake to perpetuate this myth that ‘Greenland’ was some arable oasis in the age of the Vikings. While it was as warm today or probably warmer since we find evidence of habitation under retreating ice, albeit maybe LIA ice, it was still no green land, except for a smaller patches on the west coast of Greenland that benefited from the Gulf Stream. It all came to a crashing end at the start of the Little Ice Age about 1350 AD, when temps plummeted, and combined with the arrival of the war like Inuit.

      • Underneath ice we have a settlement. The settlement lasted for nearly 500 years. The land near the coast must have been snow and ice free. Higher land would have been snow covered. Not unlike Iceland, Scandinavia. It would have been harsh, but so is Iceland and Scandinavia. They manged for nearly 500 years before they gave up. That is quite a long period. These are facts.

        I do like how you have deduced that it was a marketing ploy. Somehow warmests know what was going through the minds of these early settlers. I do not believe we have a clue what their thought processes were. You somehow believe you do.

        We are also told it was localised warming, somehow 25% of the northern hemisphere got hotter and the rest of the planet did not. I find that very dubious. You could show me a scientific paper that describes this behaviour.

        The Medieval Warm Period destroys man made global warming. The world has been hotter in the past than it is today. The world has been colder, CO2 was not involved.

      • Both written sources and archaeology shows that barley was grown, though probably only on a small scale, in southern Greenland during the MWP. Try that today and see how far you will get (it is actually done, and the crop is used as green fodder, because it doesn’t ripen).

  8. “Today, as the global climate continues to warm, rapid and sustained retreat may be close to happening again,”

    Only if the ice pack has increased a lot since then, which it has since a river of ice flows out and away from the continent. Otherwise, most of the easily detachable ice has already been set free. Besides, none of this matters for sea levels, as this ice is floating since there isn’t a lot of cantilevering from the solid land further in.

  9. “As the global climate continues to warm….” these ‘researchers do realize that we are at the cold end of the Holocene?

  10. What I got out of this article was a bunch of coulds, ifs, and maybes. I seem to remember a lot of previous coulds, ifs, and maybes from quite a few years ago which we are still waiting on. Will someone please wake me up when we get there?

  11. Where were these ice shelves when sea level was 300 ft lower than now during the last glacial maximum. The current high sea level is the exception over the last million years.

  12. “buttressed by a floating ice shelf”
    I see this claim frequently, but don’t recall ever seeing a justification for it. Grounded ice experiences far more friction with the bedrock than floating ice experiences from the water. Newton’s First Law says that an object in motion will continue in motion unless acted on by some outside force. That is, the ice that was formerly grounded has the same forward velocity as it did previously and therefore the same momentum. How is it going to impede the grounded ice behind it if it has negligible friction? If the floating ice were effectively buttressing the ice, one would expect tension cracks to be closed by the forward movement of the ‘buttressed’ ice. I don’t see that. Instead, when a tension crack forms, it tends to propagate and be the boundary where large shelves calve. This seems to be another example of hand wringing over a claim that has not been rigorously proven.

    • Clyde, I don’t think you’re meant to be using physics and engineering to think about these issues. You’re supposed to be using emotionally charged terminology while shrieking and hair-rending. Some jumping up and down, flinging of your own faeces, gibbering and wild-eyed pointing would go down pretty well too.

  13. The big word … “could”!! That’s what all these alarmists stories consist of … what “could” happen. Sure, its possible … but not very probably.

  14. What about the Antarctic tides? Flood tide lifts the ice shelf, ebb tide leaves it hanging … a sort of icey metal fatigue should be expected breaking off the shelf? how is this related to golbal warming? Oh! and how does a degree or two of global warming impact an ice sheet that is 20-40* below freezing?
    Bahamamike

  15. “Faster than previously predicted” is a pretty broad statement. The warmists of 1965 believed that melting of antarctica and Greenland would cause 10 feet of sea level rise by y2k, and another 1 foot per year after y2k.

    Is that the ‘previous prediction’ they are referring to?

  16. Many of you have probably traveled to Alaska and visited Glacier Bay National Park and have been served hot soup on the deck of a cruise liner watching the John Hopkins glacier caving into the inlet with massive splashes and noise .
    The Glacier Bay was first discovered by French explorers in the 1700s and the glacier was caving on the Pacific Ocean coast.In the 1800s the British found that the glacier had retreated some 50 kilometers up the sound In1912 they found that the glacier had retreated a great deal further .
    In the last 100 years the retreat has been very slow a few kilometers .You can google this for your information .
    This shows that scare stories like this one about glaciers in Antarctica are nonsense and nothing to do with CO2 .
    But then I forgot that the little ice age never happened . sarc

    • I first learned that when I worked in Alaska about 35 years ago. I also monitored deep strings of thermistors where some (minor) temperature increases were from the bottom up. My Glacier Bay experience was in 2006.

  17. Today, as warming waters caused by climate change

    How can GHGs make any measurable difference to ocean temperatures? The heat content of the world’s oceans is far too massive to make the sort of difference described

  18. I’d like to see a temperature profile and flow chart of the currents under the ice shelves and through the glaciers, and a comparison of the effect of gravity to ice jacking. I believe that ice jacking causes most glacial movement, at about 38000 psi.

  19. I think the geology of this is what is interesting. The shape of the gouges by normal ice fluctuations is fascinating to me. Forget the alarmist crap to get published (to say nothing of the money necessary to conduct the research), what they discovered is pretty cool and could translate…the problem is, are the shape and size of the gouges repeatable and can they be said to an “overall” shape in the Earth from massive glaciers? A question not answered and probably not put forth in the summary.

    The overall sadness of articles and studies like this is the constant harp on global warming. It dilutes the science. They discovered what happens to the Earth when the ice sheet goes through it’s normal process. More could be extrapolated…pressures especially from which we can get an idea of shapes around the Earth, utilizing that data to create more studies and discover a better understanding of the Earth’s cycles. But unfortunately the angle was not for looking into the past but to predict the future–unscientific and more mystic than real science.

    Shame. I would have like to see a comparison of other formations of the same size and shape–and a possible suggestion for further study utilizing what they discovered. There are many hypothesis in marine biology that are based upon a very broad geological history. This study could have used to expand those hypothesis or nixed them, but instead it erred on the side of mysticism.

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