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2010 Spike in Greenland Ice Loss Lifted Bedrock, Implying “We’ll Experience Pulses of Extra Sea Level Rise”

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"2010 Spike in Greenland Ice Loss Lifted Bedrock, Implying “We’ll Experience Pulses of Extra Sea Level Rise”"

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Ohio State News Release

http://www.sciencedaily.com/images/2011/12/111209123214.jpg

The 2010 Uplift Anomaly (green arrows), superimposed on a map showing the 2010 Melting Day Anomaly (shaded in red). Click to Enlarge.

An unusually hot melting season in 2010 accelerated ice loss in southern Greenland by 100 billion tons – and large portions of the island’s bedrock rose an additional quarter of an inch in response.

That’s the finding from a network of nearly 50 GPS stations planted along the Greenland coast to measure the bedrock’s natural response to the ever-diminishing weight of ice above it.

Every year as the Greenland Ice Sheet melts, the rocky coast rises, explained Michael Bevis, Ohio Eminent Scholar in Geodynamics and professor in the School of Earth Sciences at Ohio State University.  Some GPS stations around Greenland routinely detect uplift of 15 mm (0.59 inches) or more, year after year. But a temperature spike in 2010 lifted the bedrock a detectably higher amount over a short five-month period – as high as 20 mm (0.79 inches) in some locations.

In a presentation Friday at the American Geophysical Union meeting in San Francisco, Bevis described the study’s implications for climate change.

Pulses of extra melting and uplift imply that we’ll experience pulses of extra sea level rise,” he said. “The process is not really a steady process.”

Because the solid earth is elastic, Bevis and his team can use the natural flexure of the Greenland bedrock to measure the weight of the ice sheet, just like the compression of a spring in a bathroom scale measures the weight of the person standing on it.

Bevis is the principal investigator for the Greenland GPS Network (GNET), and he’s confident that the anomalous 2010 uplift that GNET detected is due to anomalous ice loss during 2010: “Really, there is no other explanation. The uplift anomaly correlates with maps of the 2010 melting day anomaly. In locations where there were many extra days of melting in 2010, the uplift anomaly is highest.”

In scientific parlance, a melting day “anomaly” refers to the number of extra melting days – that is, days that were warm enough to melt ice – relative to the average number of melting days per year over several decades.

In 2010, the southern half of Greenland lost an extra 100 billion tons of ice under conditions that scientists would consider anomalously warm.

GNET measurements indicate that as that ice melted away, the bedrock beneath it rose. The amount of uplift differed from station to station, depending on how close the station was to regions where ice loss was greatest.

Southern Greenland stations that were very close to zones of heavy ice loss rose as much as 20 mm (about 0.79 inches) over the five months. Even stations that were located far away typically rose at least 5 mm (0.2 inches) during the course of the 2010 melting season. But stations in the North of Greenland barely moved at all.

From 2007 to 2009, GNET installed GPS stations in the bedrock that lay exposed around the ice sheet margins along the Greenland coast. The research team is using the earth’s natural elasticity of to “weigh” the ice. As previous Ohio State studies of Antarctica revealed, ice weighs down bedrock, and when the ice melts away, the bedrock rises measurably in response.

GNET and similar GPS networks around the world could thus allow scientists to continue to measure ice loss after the Gravity Recovery and Climate Experiment (GRACE) satellites are retired in 2015. (GRACE is a joint project of NASA and the German Aerospace Center.)

– Ohio State News Release.  The image “was produced by R. Simmon of the NASA Earth Observatory using data provided by M. Tedesco. (Credit: Courtesy of Ohio State University.)” h/t ScienceDaily

Related Post:

The Greenland and Antarctic ice sheets are losing mass at an accelerating pace, according to a new NASA-funded satellite study. The findings of the study — the longest to date of changes in polar ice sheet mass — suggest these ice sheets are overtaking ice loss from Earth’s mountain glaciers and ice caps to become the dominant contributor to global sea level rise, much sooner than model forecasts have predicted.

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26 Responses to 2010 Spike in Greenland Ice Loss Lifted Bedrock, Implying “We’ll Experience Pulses of Extra Sea Level Rise”

  1. Leif says:

    ““Pulses of extra melting and uplift imply that we’ll experience pulses of extra sea level rise,” he said. “The process is not really a steady process.””

    I must assume that because the earth is elastic, the rising bedrock does not end at the sea shore, as might be implied, but extend some distance out to sea. Thus raising the very bottom of the ocean and displacing that sea water hither and yon as well. Ultimately adding yet more sea level rise to the melt water total.

    • Buzz Belleville says:

      Great Q Leif, as I’m trying to get my head around the correlation myself. I must admit I am way beyond my expertise here, but wouldn’t a rising land mass actually cause sea levels to drop? If I have a rock in a glass of water, and I lift the rock half way out, the water level is going to drop. I must missing something here, so if anyone can shed light I’d appreciate it.

      • PeakVT says:

        In your example, the water can move around the rock. Instead, when Greenland (or anywhere else) rises, it displaces water sideways. Effectively, it makes the space between Greenland and everywhere else slightly smaller, so the same volume of water takes up more space vertically.

        • Buzz Belleville says:

          Thanks Peak. That makes sense if what Leif says is accurate, that the rise in Greenland actually lifts the whole ocean floor, and that the land mass is impermeable. That is, if land mass on the planet creates some finite bowl and we’re just pulling up one of the sides. I can grasp that I guess …

          • Leif says:

            That would be my understanding. I would add one point though, the sea floor is not “impermeable” as you state Buzz, but it is saturated having been the sea floor for quite some time. The volume beneath the sea floor rise is just filled with the “fluid” of the melted mantel beneath attempting to reach its own equilibrium having been displaced in the first place by the ice load above. I am quite sure that any measurements of the possible extent of the sub-sea lifting is unknown because of the difficulty of finding suitable bench marks, and data collection, for the instruments. (Although some numbers might be estimated from land observations else where.) As I write this it occurs to me that the rise might be countered by subsiding else where. Clearly I am out over my head as well.

      • I think you’re partially right, Buzz. As the weight of ice is reduced on Greenland, that melted ice has to go somewhere. Most of it is going into the ocean. It makes sense that the oceans will increase in mass about equal to the reduction over Greenland, causing a small depression of the ocean bottom. You also have the effect of more rain water over other land masses, which works the other way. End result is that if all the ice on Greenland melted, sea level would rise about 7 meters.

    • Joan Savage says:

      Earthquakes along the coast of Greenland have been attributed to post-glacial rebound.

      “The observed normal faulting of this earthquake can be interpreted as a rupture due to an extensional stress field at the forebulge outside of the ice sheet because of deglaciation flexure in the region.”

      The Greenland earthquake of 11 July 1987 and postglacial fault reactivation along a passive margin. Wai-Ying Chung and Hong Gao

      http://bssa.geoscienceworld.org/content/87/4/1058.abstract

  2. Stanley Vehl says:

    Granted that the land under the edges of the ice sheet is rising, what about what’s happening in the center of the sheet?

  3. Phil Ridge says:

    If a huge land mass lifts a quarter of an inch, what is the effect on the ocean? Does the ocean rise an inch or two?
    cheers

  4. Bryan S says:

    Stanley: The middle of the ice sheet is thickening as precipitation increases there due to warming. It was one of the reasons that the IPCC report on sea level rise actually forecasted that Greenland and Antarctica will actually have net ice sheet growth in the next century with global sea level rise almost all due to thermal expansion and the melting of non-Greenland/Antarctic glaciers. Other studies have contradicted this, but the IPCC position is that the Greenlandic and Antarctic ice caps will grow overall, not shrink.

    • Leif says:

      I do not believe that observation is in agreement with it data that is currently being collected with the GRACE gravety observations Bryan. It must also be noted that the Arctic and the Antarctic are two completely different systems and as such behave in completely different manor. Antarctic being land surrounded by ice. The Arctic being ice surrounded by land.

  5. Ananth says:

    Hi,

    If the bed rocks are lifting, dow this mean that some other place the plates are going to submerge to compensate the increase in height. It is posible that the weight of ise has maintained presure on the techtonic plates, if this presure is removed and distributed as an even load by form of water, then , the plates some where else must submerge. correct me if I am wrong.

  6. Maurice Tetrault says:

    Taking weight off land causes it to rise, adding that same weight to the ocean would cause the land mass under the ocean to depress, therefore no rise in sea level.

    • Colorado Bob says:

      MT -
      Except for the nature of water as liquid vs a solid. The ice sits on the island as a focused weight over the island, once it melts and enters the ocean it’s weight is diffused over the whole ocean. The water doesn’t flow out, and concentrate it’s weight over a single spot in the ocean.

  7. Rabid Doomsayer says:

    Imagine a balloon with a hand pressing on it. Take off the hand and that part of the balloon comes up, the rest of the balloon goes down.

    The hand is the ice on Greenland. Take away the ice and Greenland goes up, everywhere else goes down. Isostatic rebound adds to the Sea Level Rise.

    Roughly one for four. Take off 4 meters of ice, land underneath comes up 1 meter. Everywhere else goes down, but the process takes thousands of years to complete.

    However the process is quickest immediatly following the ice loss.

    It is also worth noting that the paleo evidence agrees with the authors conclusion of sea level rise in pulses.

  8. Merrelyn Emery says:

    I don’t think it’s just about sea level rise. I seem to remember some old physics about changes in temperature and pressure that would imply that we are in for a rash of geologic changes as magma chambers rise or fall. Heaven only knows what is going on down there, ME

  9. Raul M. says:

    Given that cities harbor greater amounts of metal and metal is magnetic, the areas where the metal was mined has less magnet pull down of the crust and the areas where the metal is put has more magnet pull down.
    Such a thing would have subtle effects?

  10. Raul M. says:

    If the hard rock of Greenland is continuous then Greenland at present tilts with the present rise to the southern end? But some adjustment to the new normal allows stretch to the hard rock below?

  11. Raul M. says:

    And if the hard rock is continuous through the island then the northern edge gets a twist where the continuity ends?

  12. Colorado Bob says:

    Speaking of ice sheets …..
    Plunge in CO2 put the freeze on Antarctica

    But when the vastly different ancient Southern Ocean currents and temperatures of that period were factored in, it quickly became apparent that Antarctica’s big freeze followed a fall in CO2 levels.

    The paper, “The Role of Carbon Dioxide During the Onset of Antarctic Glaciation”, reinforces carbon dioxide’s place as a primary driver for global temperatures. It was lead authored by Mark Pagani, of Yale University, and co-authored by University of NSW Climate Change Research Centre researcher Dr Willem Sijp.

    “Our research recognised that the flows of deep ocean currents at the end of the Eocene were dramatically different from those of today because of the altered position and shape of continental masses,” said Dr Sijp.

    “Previous research relied on different temperature estimates and had also not taken these different currents into account. This led to significant upward biases in calculated CO2 which made it appear that carbon dioxide was actually increasing around the Southern Ocean as the Antarctic ice sheet formed. We can now see the reverse was true.

    http://www.spacedaily.com/reports/Plunge_in_CO2_put_the_freeze_on_Antarctica_999.html

  13. Colorado Bob says:

    What I find the most interesting, is the 1/4 inch rise in 5 months.
    Hard to get the speed of this in perspective, but it increased the mean rise by around 50%.
    That’s a lot of rocks going very fast.

  14. Ray Huebner says:

    The total weight of the H2O doesn’t change, regardless of whether it is ice or water. It is always pulled down by the force of gravity. And there is “solid rock” under it all.

  15. Robert In New Orleans says:

    I wonder when the other shoe of unseen unknowns will drop and where will it land?

    Maybe a major eruption of Icelandic volcanoes as the weight of the ice cap is removed over the magma chambers?

    Maybe more powerful earthquakes along tectonic stress zones?

    • Merrelyn Emery says:

      Robert, of course it will land – the question is where, and when.

      The answer is that nobody knows because the Earth has not been studied as a system but just as isolated bits which cannot lead us to to an answer about the future of the whole.

      I think reality is going to force a change in thinking and conceptualizing. Forget Durban, the future is now running the show, ME