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The ice age and the ice volume problem

  1. Jan 12, 2009 #1
    Multiple evidence suggest that the Pleistocene epoch (2.56 Million years - 11.6 thousand years) was about waxing and waning Ice sheets with the pace of the milankovitch wobbles superimposed on the earth orbit.

    One intriguing element showing this is a multiple multi-millenium cycle in variation of isotope ratios in foraminifera remains in the ocean sediments, which all show the same pattern, which is also matched in the ice cores of Antarctica.

    This cyclic variation in isotopes is thought to be basin effect in pace with the waxing and waning of the ice sheets. Evaporation favors light isotopes, escaping much more easily from the liquid condition into gas. Hence if the ice sheets are growing with more light isotopes, the concentration of heavy isotopes in the ocean is increasing. And it is thought that this is reflected in the isotope ratio in the biota sediments. This is considered to be easily quantifiable and hence the isotope ratios in the ocean cores are considered to be a proxy for ice volume.

    Bintanja et al 2002 model those quantities for the last glacial maximum as function of contribution to sea level rise and propose:

    Now let’s focus on that 65 meters stored in the Eurasian continent. Bintanja shows the essence of the publication on his webside

    [​IMG]
     
    Last edited: Jan 12, 2009
  2. jcsd
  3. Jan 12, 2009 #2
    Note that Bintanja et al merely propose an outcome of a model run at state:

    There is the key, "if properly validated"; has this ever been properly validated against field data?

    Take for instance the ice sheet height, the domes on Russia seem to exceed 4000 meter height. That's of Antarctic proportion and the oldest ice in the EPICA dome C cores is at least 800,000 years old. The 3000 meters of Greenland, a much faster accumulating ice sheet is estimated to be 130 - 200,000 years old

    So how does that compare to the accumulation time of that Eurasian ice sheet?

    [​IMG]

    So that means that the hypothetical Eurasian ice grew to one and a half time the Greenland ice sheet height in about half the time, in an area with a logically continental arid climate; and the higher, the more arid. How does that compare to reality?
     
    Last edited: Jan 12, 2009
  4. Jan 12, 2009 #3

    Xnn

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    Can a free copy of this paper be make available.
     
  5. Jan 12, 2009 #4
    Perhaps indeed
     
  6. Jan 12, 2009 #5

    Xnn

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    According to their website, it is a crude model:

    So, there were no seasons in the model; just 4 year averages.

    Albedo changes are much more complicated than that. Remember melt ponds!

    Everyone should realize that mile high ice sheets impact circulation patterns big time.

    and in conclusion.

     
  7. Jan 13, 2009 #6
    Anyway, the proof is in the pudding.

    Svendsen et al 2004, also here

    from the abstract:

    Looks a bit neutral or even the opposite when comparing to the predicted ice sheet volume:

    [​IMG]
    starting off small and growing bigger.

    Also the readvances would have had not too much time to attain the heights as predicted by Bintanja et al. Instead, there were mammoths walking, where they predicted the ice sheets.

    In a word, not looking good, but Xnn already suspected that in his post.

    Yes but calculating ice volume does not require a model, just an empiric basic function with isotope value as main variable, the model is more a simulation to see where the ice would grow

    Note that Bintanja et al basically did nothing wrong here. They just took an hypothesis and formulated a prediction from that. Only the last step was missing, testing against reality, alas, another beautiful theory destroyed by an ugly fact.
     
    Last edited: Jan 13, 2009
  8. Jan 13, 2009 #7
    Here is a rough projection of the field results plot of the LGM of Svendsen et al in red aganst the computations of Bintanja et al

    [​IMG]

    Considired that also the dome of Svendsen et all is around 2500 meters versus 4000 meters for Bintanja, it is clear that a lot of ice volume is missing, seriously challenging one of the fundamentals of paleo climatology, that maritieme isotopes are a proxy for ice volume.
     
  9. Jan 13, 2009 #8

    Xnn

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    I think it is more likely their simplifying assumption that atmospheric circulation is not altered by huge ice sheets is obviously wrong. In addition, they did not have a climate model included. To do so, takes lots of time and money.
     
  10. Jan 14, 2009 #9
    Certainly, but that's not the point. The essence is that it is a checksum problem. No matter where ice sheets would or would not be accumulating and how that would happen; everybody would require so many cubic kilometers ice in total to fit in the total sum of isotopes/sea level/ice volume formulas, regardless of the sophistocation of their models. But there were mammoths no ice. For instance the most easterly part of the red outlined LGM area according to Svendsen et al is known as the Taimyr peninsula.
    [​IMG]

    Check what happened there just before the Last Glacial Maximum. For instance, Mol et al 2006 also outlined here.

    Trees on places presently well north of the present treeline on a place where others expect the ice accumulating. Seems that something is wrong here.
     
    Last edited: Jan 14, 2009
  11. Jan 14, 2009 #10
    Addendum,

    It may be interesting to see how the hypothesis was develloped about the deep sea isotopes being a proxy for total ice sheet volume. It was thought out by Late Nick Shackleton but it has always been plagued by complications like this. The attempt of Bintanja et al for linking assumed sea levels to ice volume is one of the latest I know about. However as the fieldwork shows, there wasn't enough ice volume to suit the assumptions.

    It could be that the isotope signal reflected in the carbonate shells of the foraminifera is not only a function of the isotopes in the sea water but also functions of unknown changing conditions and we know that the oceans did unexpected things during the last Glacial transition for instance Marchitto et al 2007
     
  12. Jan 14, 2009 #11

    Xnn

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    No; my read from the website, is that they assumed current atmospheric circulation pattens and then varied temperature in proportion to the Antartic ice record. And they did it in 4 year steps! No days, no nights, no seasons, just 4 year averages and without any variation in circulation. And they have already realized the serious shortcomings of their model.

    Also, they don't discuss it, but I can also see that they made huge simplyfying assumptions about albedo.

    So, they have a lot of work to do. Eventually, I'm sure if they get the funding, there will be future attempts to improve their model and compare it against independant data. At this point in time, it is obviously very crude, and I wouldn't be surprised if somebody else has a better model.
     
  13. Jan 14, 2009 #12
    But what is on that webside is irrelevant, they could have everything as right as possible with the most modern means and yet they still would have to put rougly 3-4 times more ice on the Eurasian continent to get the checksum matching the hypothesis.
     
  14. Jan 15, 2009 #13

    Xnn

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    Andre;

    That paper by Williams is 28 years old!

    There has to be something more recent than that.
     
  15. Jan 17, 2009 #14

    The idea was to give some illustration of the problems around the isotopes - ice volume hypothesis.
     
  16. Jan 20, 2009 #15
    The idea of a stronger Gulf Stream reaching the Arctic Basin can explain this scenario.

    I agree.
     
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