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A testable model addressing the issue of East Antartica ice sheet stability?

  1. Oct 12, 2009 #1
    A considerable portion of E. Antarctica ice (average of 1.6 km height) rests on bedrock of 2000+ ft above sea level. https://www.physicsforums.com/showthread.php?t=344123" Would such a core suffice to cover enough glacial and inter-glacial periods; giving an adequate sample? Would any evidence of oceanic sediment, current flows, foraminifora etc. be consistent with breaching of such isthmus; hence consistent with significant sea level elevation, consistent with E. Antarctica dissolution? Would there be any other possible causes of significant sea level elevation? Might we thus have a historical record of whether or not E. Antarctica is stable; using the Isthmus of Panama as our proxy?
     
    Last edited by a moderator: Apr 24, 2017
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  3. Oct 13, 2009 #2

    Xnn

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    There was a recent news release about the discovery of another link between declining CO2 levels and formation of the Antarctic Ice Cap 34 million years ago. They found the tipping point to be around 760 ppm. Of course, when the ice cap formed it was at lower elevation, so it will probably require higher levels of CO2 for the ice cap to become unstable.

    My understanding regarding the Isthmus of Panama is that it gradually formed over millions of years and was essentially intact by about 3 million years ago. It's formation changed the flow of ocean currents, forcing warm water towards the polar regions, in particular Europe. This in turn has allowed the periodic formation and melting of large ice caps in step with orbital and greenhouse gas forcings. That is the Earth has a bi-stable climate.

    Don't believe there has been a significant breaching of the Isthmus during the last 3 million years. However, the Antarctic ice cap formed before the formation of the Isthmus. So, it's future is dictated by long term greenhouse gas levels and not by the Isthmus. For example, the antarctic continent was located near the south pole during the creataceous period (65 to 145 million year ago) and yet there was no isthmus or ice cap since CO2 levels around 1500 ppm.


    http://www.physorg.com/news172072921.html


    Here's a link to a paper in Nature, which also illustrates that the antarctic climate cooling was forced by falling CO2 levels as opposed to tectonic shifts.

    http://www.nature.com/nature/journal/v421/n6920/abs/nature01290.html

     
  4. Oct 13, 2009 #3
    If the Isthmus of Panama were opened by significant rising sea level, then Gulf of Mexico waters might egress to Pacific. This would then seem to disrupt the Gulf Stream. Hence one could also obtain sea bed cores from south more proximal aspect of Stream to see if there has been disruption of flow. This could be compared to Panama Isthmus findings, and also could serve as a proxy for significant sea level increase from East Antarctica dissolution.
     
  5. Oct 13, 2009 #4

    mheslep

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    The Isthmus is not old enough in place (~10 million years) to have seen the Eocene/Oligocene boundary and the onset of the Antarctic ice sheet. See e.g. http://www.springerlink.com/content/wr28854hr7n1535t/
     
  6. Oct 14, 2009 #5
    Additional background articles:

    Links between climate and sea levels for the past three million years

    Kurt Lambeck, Tezer M. Esat, Emma-Kate Potter

    Nature 419, 199-206 12 September 2002. Insight Review http://www.nature.com/nature/journal/v419/n6903/abs/nature01089.html"

    Effect of the formation of the Isthmus of Panama on Atlantic Ocean thermohaline circulation

    Gerald H. Haug, Ralf Tiedemann

    Nature 393, 673-676 18 June 1998. http://www.nature.com/nature/journal/v393/n6686/abs/393673a0.html
     
    Last edited by a moderator: Apr 24, 2017
  7. Oct 16, 2009 #6
    Re: A testable model addressing the issue of East Antarctica ice sheet stability?

    As above: If the Isthmus of Panama were opened by significant rising sea level, then Gulf of Mexico waters might egress to Pacific. This would then seem to disrupt the Gulf Stream. Hence one could also obtain sea bed cores from south more proximal aspect of Stream to see if there has been disruption of flow. This could be compared to Panama Isthmus findings, and also could serve as a proxy for significant sea level increase from East Antarctica dissolution.

    For record of foraminifera for < 3 million years, one has oscillations of glaciation cycles. This approximately corresponds to geological closing of Isthmus of Panama at ~3 M yrs. http://www.nature.com/nature/journal...ture01089.html" Thus a history of cycles of N. ice sheets would seem consistent with persistence of Gulf Stream; and hence consistent with persistence of closure of Isthmus of Panama. Such persistence of Isthmus of Panama (84 ft elevation) would seem consistent with no sea surface elevation of ~180 ft. Hence cycles of glaciation, persistence of Gulf Stream, would seem consistent with no complete melting or dissolution of East Antarctica. Thus via indirect evidence, East Antarctica would seem to be historically stable.
     
    Last edited by a moderator: Apr 24, 2017
  8. Oct 17, 2009 #7

    Xnn

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    The Antarctic ice sheet began to form 34 million years ago when CO2 in the atmosphere reached a tipping point of around 760 parts per million.

    So, as long as CO2 levels remain below that level, the Ice Sheet should be stable.
     
  9. Oct 17, 2009 #8
    There were also assumed to be no ice sheets in the Paleocene when fossil leaf stomata indicated similar CO2 levels with nowadays Royer 2001.
     
  10. Oct 17, 2009 #9
    The Paleocene covers 350 million years. [edit] My mistake I am looking at the Paleozoic. [/edit]

    During the Carboniferous, so named for the enormous amount of carbon sequestered, CO2 levels did drop to those of the present day, and global temperatures were ~12C on average.

    http://www.geocraft.com/WVFossils/Carboniferous_climate.html
     
    Last edited: Oct 17, 2009
  11. Oct 17, 2009 #10
    Royer 2001 conclusion.

    Here is a paper that outlines one possible factor.

    http://www.nature.com/nature/journal/v439/n7072/full/nature04386.html

     
    Last edited by a moderator: May 4, 2017
  12. Oct 18, 2009 #11

    Xnn

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    That's interesting.

    So, if we start to witness changes in deep-ocean circulation, then we may be in for a whole lot more changes than anticipitated.
     
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