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Geology and Physics, the 100,000 cycle of the ice age.

  1. Jan 2, 2005 #1
    ..... asked what to study if he wanted to investigate creationism versus evolution. I advised continuing physics and chemistry and avoid having to learn flawed theories as paradigms. So, predictably, I was challenged to expose some of them. I choose for the problems in the 100,000 "ice age" cycle and continue that here.

    So there we go.

    The ice ages are usually explained as a result of difference in solar radiation due to Milankovitch cycles in the Earths orbit.

    We think we see those cycles back in sea sediment cores like the compiled benthic stack, the reaction of miniscule ocean bottom dwelling "benthic foraminifera" on climate on the surface.

    However this graph are indicates some problems with that idea, explained by Richard Muller here and more scientifically here..

    In short, we have work to do.
  2. jcsd
  3. Jan 2, 2005 #2


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    isn't this the mission of all science?
  4. Jan 2, 2005 #3
    Absolutely, but sometimes wrong wrenches are used to punch in a wrong screw. Anyway I'd also recommend this thread for some basic philosophies.

    Back tomorrow.
  5. Jan 2, 2005 #4


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    The article you give on Milankovitch Cycles seems like a mistake -- it suggests that the perihelion becomes as much as 30% more distant than the apohelion, but I couldn't find anything on Wikipedia to confirm.
  6. Jan 3, 2005 #5
    Good catch and I see that many other sites have the same mistake. So a copy - paste problem. Obviously when the eccentricity varies between about 0% and 5% (presently about 3%) the max difference in insolation between extremes via the inverse square is about 9,4%. Of course, the obliquity varies between 22,1 and 24,5 degrees, causing a summer max insolation differences of about 3,7% at 65 degrees lattitude (delta cos(lattitude-obliquity)). So when all the cycles reinforce each other, there is a max insolation difference of about 13%, not 30%. But this happens only once every few 1,000,000 years, not every 100,000 years, due to several complications, like the cycle of max eccentricity change of 413,000 years. Evidently this cycle should be more important than the 95,000 years cycle, however the 413,000 years cycle is not visible in the "proxies" at all, like the benthic stack, the registration of the past.

    When familiar with physics about signal analysis (Fourrier) it will be evident that the explanation of the mechanism in the last link seems to be far fetched:
    edit to insert this part:
    Things get even more complicated when we see here that more than a million years ago, the oceanic "proxies" dove tailed nicely with the Milankovitch cycles but some million years ago the dominant 100,000 year cycle kicked in out of nowhere, which was not compatible with the Milankovitch cycles, suggesting that something had happened that changed the world.

    So, quoting Richard Muller:
    In short, there may be a crisis and this calls for a paradigm shift.

    Next time, oceanic foraminifera isotopes.
    Last edited: Jan 3, 2005
  7. Jan 3, 2005 #6
    Just a small intermezzo. I try not to copy all the common places and scholar paradigms about the ice age. So if not familiar, you should have a look at the links for that otherwise this thread would not make sense.

    Since my usual rambling monologue seems to have struck again, I'm very curious if the thread makes sense, if it's understandable, if I move too fast or to slow, if you're curious to the outcome, if you like to play with ideas yourself, etc.

    When I was deliberating this and that and we were toying with ideas, all of a sudden a friend said to me that the ultimate consequence of my use of the available evidence of the ice age for something else was, that you cannot use the same evidence twice, consequently the ice age could not have existed as such. I was flabbergasted. Had I killed the ice age? Incredible. But in fact he was right. The ultimate consequence of:

    I hope this will trigger the dialogue a bit.
  8. Jan 4, 2005 #7
    Okay, So I lost everybody?

    One more ramble then, before I quit. Rich Muller's quote that actually calls for a paradigm change, is only calling for a partial one. that 100,000 years cycle visible in the heavy oxygen ratio (d18O) of the tiny foraminifera shells in sea bottom sediments is still considered a climate signal:

    I would say, we must look at the data again, as if for the first time and form ideas about why those data signals change. Is it climate or something else?

    So lets look to the isotope fractination processes of the tiny foraminifera creatures in the oceans. Can't find a link to a suitable page explaining the basics so I use my own words.

    Oxygen comes mainly in two isotopes normal light 16O and rare heavy 18O. Approximate ratio 500:1. Although chemically both are identical. Physically they react different, simply because heavy 18O is less agile than it's lighter counterpart. Therefore, during a chemical or physical process, the reaction speed is different. For buiding their calcite shells, foraminifera can grab heavy oxygen atoms more easily than the lighter ones, hence the ratio of heavy 18O (or d18O) in the shells of the creatures is slightly higher than the surrounding sea water and CO3 ions. This process depeds on several factors, most notably temperature. Higher temperature means less fractination and apparantly the difference in ratio can be used as a paleo thermometer.

    However this idea was abandoned immediately when it was recognised that the temperature at the bottom of the oceans is a constant 4 degrees C, where water is the most dense. Temperature changes at the surface of the ocean does not penetrate deeper than some 1000 meters, at 4000 meters, temperature is always 4 degrees, yet the (benthic) foraminifera, dwelling over there do show about the same variation in d18O as the surface dwelling (planctonic) foraminifera.

    The solution for this seemed to be another effect, the ice age cycle. During cold eras ice accumulates at the poles. Since light 16O evaporate much more easily than the heavy 18O, the ice is rather strongly depleted of 18O, consequently if more water evaporates than returns, the remaining water in the ocean gets enriched in 18O. This enrichment seems to be reflected in the d18O of the benthic foraminifera. So, the Benthic stack seems to show us volume of ice sheets versus sea level change or obviously ice age climate and its yoyo-ing. Note the very strong 100,000 years signal.
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