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112lect38 - GY 112 Lecture Notes D Haywick(2006 1 GY 112...

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GY 112 Lecture Notes D. Haywick (2006) 1 GY 112 Lecture Notes Cenozoic Climate and Sea level Changes Today's Lecture Outline A) Cenozoic temperature and sea level shifts B) Plio-Pleistocene Glaciations (Milankovitch Orbital Variations) C) Sea level changes in our backyard Textbook reference: Levin 7 th edition (2003) Chapter 13; Levin 8 th edition (2006), Chapter 15 A) Cenozoic temperature and sea level shifts Before we jump into the Cenozoic, it would be helpful to reflect on what the climate was like during the latter part of the Mesozoic. If you recall, in the late Jurassic and throughout the Cretaceous. it was a very warm time. We know this for several reasons: 1) Sea level was very high (the Western Interior Seaway had flooded the central part of North America), indicating that all of the polar ice had melted. 2) Fossils (animal and plants) all confirm that Antarctica was essentially ice-free during this time. Tropical and sub tropical plants were doing quite well where there is now ice. 3) The deep ocean currents (which are essentially temperature driven) where seemingly absent during parts of the Mesozoic (especially the Cretaceous) suggesting a more uniform temperature distribution. I think it is important to remind you of a couple of terms and concepts at this point in the lecture that we have previously discussed in GY 112 (e.g., during the Proetrozoic glaciations lecture). At times in the Earth's past when there was apparently no polar ice (i.e., Antarctica and Greenland were ice free), the Earth is said to have been in a Greenhouse state . Greenhouse Earth s (another way to refer to warm times) were relatively common in the past as indicated by the following diagram: Source: http://seis.natsci.csulb.edu/rbehl/300.htm
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GY 112 Lecture Notes D. Haywick (2006) 2 You are probably aware that there is a lot of discussion about the buildup of greenhouse gases (CO 2 and CH 4 ) in today's atmosphere. Some people are concerned that the buildup, which is largely human induced, is causing the next major glaciation. Others say why the concern? The Earth has been a lot warmer in the past, so why stress over a "normal" temperature shift. I say we will just have to wait and see what happens. As you should know by now, the processes that operate on the Earth are slow. Humans are a bit too impatient when it comes to interpreting Her (i.e., the Earth) and the processes that shape her. But here is something that we can safely consider. If Greenhouse Earths are periods when the polar regions were ice free, what do you call the times when polar ice was around? The answer dear reader is Icehouse Earth . We are currently in an Icehouse Earth today. The thing to note about icehouse stages is that they are two components. At times like today when there is some glacial ice at the poles, but not an extreme amount, we say the Earth is in an interglacial stage. When ice coverage is much more widespread, and there were times when it covered much of Canada 1 , we are said to be in a glacial stage . So there you go. The Earth has regularly shifted from Greenhouse to Icehouse conditions.
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