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What Caused 33.7 Million Year Ago Eocene-Oligocene(E-O) Boundary Event?

  1. Jan 16, 2010 #1
    Zhonghui Liu of the University of Hong Kong has made the most comprehensive deep-sea core research to date Global Cooling During the Eocene-Oligocene Climate Transition. Global SST's fell by an average of 4.5 to 6 degrees F at the E-O boundary, with temps near the South Pole and North Pole dropping 9 to 11 degrees. An atmospheric CO2 drop is the most likely culprit for such widespread cooling, Lui says. But what caused the theoretical greenhouse-gas plunge remains to be shown. Amazingly, Antartica would have been free of ice and populated by primitive dinosaurs before the E-O boundary event incidentally.
     
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  3. Jan 16, 2010 #2
    http://en.wikipedia.org/wiki/La_Garita_Caldera" [Broken]
     
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  4. Jan 16, 2010 #3
    Could be..thanks for the link to La Garita Caldera:
    A 1/50 of the size of Chicxulub impact, speculated to be the most energetic incident since then. Why would the volcanic explosions cause such an extreme temperature decrease though?
     
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  5. Jan 16, 2010 #4

    Xnn

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    Here's another fairly recent paper on the subject.

    http://www.nature.com/nature/journal/v445/n7128/abs/nature05551.html

     
  6. Jan 16, 2010 #5

    Xnn

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    errr, that San Juan volcano was huge, but it occurred a few million years after the transition.
     
  7. Jan 16, 2010 #6
    CO2 (probably) did not fall until a few million years after the glaciation event which occured between 33.6 million to 33.5 million years ago.

    There is not a lot of CO2 estimates overlapping the period - the Zachos 2001 and Royer compilations show CO2 did not decline until between 32.2 million to 30.6 million years ago (high at 32.2 million, lower by 30.6 million but no estimates in between) - and a recent paper by Pearson 2009 has a dip about at the right time but it went up soon after and the glaciers survived.

    Continental Drift needs to be taken into account to explain the event. Antarctica was connected to South America and Australia about 40 million years ago and the ocean currents mixed with mid-latitude and tropical ocean waters (keeping Antarctica warm enough in the summer so that large glaciers did not develop).

    You can see an animation of the continental drift from the University of Texas plates project here (Power Point animation).

    http://www.ig.utexas.edu/research/projects/plates/movies/akog.ppt [Broken]

    By 33.6 million years ago, enough separation occured between Antarctica and the two other continents so that the Antarctic Circumpolar Current developed and Antarctica became isolated in a polar climate at the south pole. It rapidly glaciated over as this occured.

    Here is a reconstruction of the ocean currents at 35 million years ago by Bijl et al 2009

    Early Palaeogene temperature evolution of the southwest Pacific Ocean
    Nature 461, 776-779 (8 October 2009) | doi:10.1038/nature08399;

    http://www.es.ucsc.edu/~jzachos/pubs/Bijl_etal_09.pdf


    http://img35.imageshack.us/img35/8862/antoceancurrents35m.jpg [Broken]

    Between 27 million to 14 million years ago, the glaciers on Antarctica receded substantially as there was some jostling of the small cratons between South America and Antarctica and the Circumpolar Current was disrupted again. The glaciers didn't match today's proportions again until about 2.5 million years ago.
     
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  8. Jan 16, 2010 #7

    Xnn

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    Recommend extreme caution before assuming CO2 measurements of such a long time ago are accurate. Ice cores are the only direct paleo record of atmospheric CO2. However, they only go back about 800,000 years and have only been confirmed to about 450,000 years.

    So, to measure CO2 levels beyond a million years or so, one is left with only in-direct measurements. These include:

    - C12:C13 ratios in alkenones from plants
    - B11:Ca ratios in shells from CO2s influence on ocean acidity
    - Leaf Stomata size since plants adopt to higher/lower levels

    If abstracts or better yet links to complete papers can be found then it'd would probably be okay to discuss them here. But I'd still urge caution in their interpretation since the cause of differences between the various techniques are still being ironed out.

    Also, there is a huge difference between glaciers at high elevation and at sea level.
    Antarctica is a large continent and East Antarctica has extensive highlands.
    So, we need to be careful to not jump to premature conclusions about the timing and significance of glacial advances.
     
  9. Jan 18, 2010 #8
    Thanks for the input guys; I can see the creation of the Circumpolar Current being very significant, and causing a temp decrease of the southern polar region. This agrees with the OP paper abstract of Lui:

    Great links and diagrams btw. I'm now more interested in the fauna of pre-glacial Antarctica, were there any refugia for example? Did any fauna manage to migrate to either South America or Australia during the big freeze? (the origin of New World proto-monkeys even?)
     
    Last edited: Jan 18, 2010
  10. Jan 18, 2010 #9
    This 2009 paper http://www.nature.com/nature/journal/v459/n7249/full/nature08069.html reveals the -5 degree drop in the Northen Hemisphere:

     
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  11. Jan 18, 2010 #10

    Xnn

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    As I understand it, East Antarctica used to be connected to Australia before it broke off.
    The Antarctic Peninsula on the other hand was connected to South America.
    The last piece of land to actually break free was New Guinea.

    At one time, East Antarctica was located in the Northern Hemisphere and there are fossils of some Dinosaurs. There were probably also Marsupials similar to ancient Australia.
     
  12. Jan 19, 2010 #11
    I think that the unique location of Antarctica could have spawned advanced species of the avian variety. Half the year is in Summer, which currently averages 20 degrees whislt the long dark Winter is -30 degrees. Is doesn't take a genius to work out that the ability to migrate from one half of the continent to the other would have been highly advantageous! (A fossil of the oldest mammal treeglider at 125 million years old could have evolved to make this migration for example, V. Antiquum). Here's a BBC article on the fossil fiind and it's significance on how early mammals lived amongst dinosaurs Flying Mammals 150mya
     

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  13. Jan 20, 2010 #12
    I think there has to be an additional 'something' to explain the magnitude of the event. The creation of the circumpolar current may mean that there is a colder Antarctica relative to the Arctic, but there still has to be a mechanism for global temperature decreases, doesn't there?
     
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  14. Jan 20, 2010 #13
    The Albedo of the Earth (the amount of solar irradiance reflected) will increase with the glaciation event.
    Take the small circle (60S) surrounding Antarctica in the graphic above and increase its Albedo from an average 0.41 to about 0.60. If you run all the numbers you would get -2C change using the Stefan Boltzmann equations and if one used the global warming theory sensitivity value of 0.75C/watt/m^2 change in forcing, the temperature change would be -5C.
     
  15. Jan 21, 2010 #14
    Ah, of course! Thanks for data Bill, it does seem rather convincing. The nature of Antarctica being a landmass over the pole compared to an ocean at the North pole would mean that snow would accumulate more readily and be less likely to melt during the summer I guess.

    Why does the author of the paper not agree with you though? Why does Lui speculate on a loss of CO2 greenhouse gas? Also, I've just noticed that the South Pole droppped by around 10 degrees, so where's the extra 5 degree drop come from? (North Pole glaciation and increased albedo?)
     
  16. Jan 22, 2010 #15

    Evo

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    Staff: Mentor

    Asperger's your article is about a find in China. Since Antarctica, India, Australia, Africa & South America were connected during the Jurassic period, wouldn't it make more sense to look at the flying species known in those areas during that time? Also, this should have been a different thread, as it is a completely different period that what is in your thread title.

    Here is a map of the Jurassic from http://science.nationalgeographic.com/science/prehistoric-world/jurassic.html
     

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  17. May 2, 2011 #16
    Hmmm... the timing of the CO2 drawdown os broadly coincident with the evolusiton of c4 photosynthesis in grasses. The spread of grasses likely would represent a step-change in the surface area that is given over to photosynthesis. Increased vegetation would be associated with increased carbon burial, hence CO2 drawdown.

    This paper http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2486.2008.01688.x/abstract puts the origin of c4 at around 32ma which is good timing for it to be causal; but this paper http://paleobiol.geoscienceworld.org/cgi/content/abstract/37/1/50 puts the wide spread of grasslands into the Miocene-Pliocene (8-2ma), so working against the idea that c4 is causal.

    If you look at the broad sweep of planetary climate through geological time, many of the major climate shifts have been associated with plant innovation. The early evolution of photosynthesis in the Archaen (http://www.nature.com/ngeo/journal/v3/n9/full/ngeo942.html) resulting in the first slushball Earth, The late precambrian greening of Earth (http://www.nature.com/nature/journal/v460/n7256/full/nature08213.html) resulting in slushball Earth #2 (aka "snowball Earth"), The Ordovician evolution of woody tissue resulting in CO2 drawdown and glaciation (Gensel, P; The Earliest Land Plants, Annual Review of Ecology, Evolution, and Systematics v39 2008 and also http://sp.lyellcollection.org/content/339/1/37.abstract), The invention of trees in the Devonian, and the spread of Carboniferous coal forests resulting in a big uptick in atmospheric O2 (http://www.pnas.org/content/107/42/17911.full) possibly being associated with the End Devonian Extinctions and Carboniferous glaciations. Then the angiosperm revolution seems tentatively correlated with the general cooling trend of the late Cretaceous. The c4 revolution in grasses would make a neat explanation for Co2 drawdown from the Eocene onwards, with albedo and global current changes playing their role too. It seems that the oceant current changes affect heat distrubution but not directly CO2 levels. Albedo comes into play once you have ice, but does not direcly affect CO2 drawdown. Other theories involving increased ocean fertility are also good explanations of the CO2 drawdown (http://geology.gsapubs.org/content/39/4/383.abstract).

    Thoughts?
     
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