EPS 102 lecture 20 - E PS 102 lecture 20 T uesday April 7,...

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EPS 102 lecture 20 Tuesday April 7, 2009 p The Earth has seen very different climates over it's lifetime. Record of Oxygen isotopes in benthic critters ; we use benthic organisms because they live on the bottom and they aren't subject to short term temperature fluctuations at the surface. Oxygen isotopic compositions of shells which is the ratio of heavy: light and this ratio changes according to the temperature at which the organism made it's shell. These fluctuate more wildly than the deep. Over recent time periods of glacial cycles, we realize that the variations that are possible are larger than anything we can imagine. Methane is a super greenhouse gas; it lasts about 10 years before it is oxidized but it raises the temperatures. We look at benthic organisms and by the time these organisms sensed it, it was all oxidized. People not only look at oxygen isotopes but also at the carbon isotopes in the same way. Cores have been looked at in different oceans; changes in isotopes of Carbon have been looked at C-12 and C-13. The variations in those 2 carbon pools will affect the composition of the shell. If the environment is rich in C-12, then the plankton will make a lighter shell but if the C isotopic composition of the atmosphere is heavier, we will make heavier shells. Analyzing methane in ice is very light; if you know the isotopic composition of methane and how much carbon is in your pool in the atmosphere and oceans, how much methane would you have to burp out to change the isotopic composition of the environment? 2000 Gigatons. Maybe this isn't so. .. The carbon cycle has been distorted by this event. CO2 concentration goes up in the atmosphere causes shells to dissolve in oceans due to increased acidity. The acidity of the water was so great that all the CaCO3 completely dissolved. The normal composition of sediments is mostly shells on the seafloor. Essentially, water is becoming more acidic. How much C do we have to dump into the atmosphere to do this? 5000 Giga tons. There are not enough methane clathrates to create 5000 Gigatons though. There seems to be a trend in periods of time where deep waters are colder than average and then warmer than average. The time scales for these observations is on the order of several hundred million years. Not only do temperatures seem to change, but we have changes in sea level over geologic times. The Indiana Limestones was deposited around 340 million years ago; at this point in time Indiana was under a shallow ocean. We can see sedimentary rocks that are signature to moraines , etc. .. that suggest that the time these rocks were formed must have been glaciers present. A lot of the ice sheets in Antarctica accumulate a lot of debris on their bottom. As they slide over bedrock they drag out striations; when all this debris reaches the ocean, the debris falls out of the melting iceberg onto the seafloor and we see gigantic stones in the middle of marine sediments far from land. When our oxygen isotopes tell us the temperature was cold, we can find
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EPS 102 lecture 20 - E PS 102 lecture 20 T uesday April 7,...

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