SIO40lecture14

SIO40lecture14 - SIO 40 Life and Climate on Earth Oct 29,...

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SIO 40 – Life and Climate on Earth Oct 29, 2010 Lecture 14 – Pleistocene Glaciations Ice cores like the one shown here are valuable archives of past climate.
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Outline -Proxies for studying glacial cycles -Milankovitch cycles as a forcing function -Glacial climate feedbacks
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Quaternary period - includes two epochs: The Pleistocene (~ 2 million years ago to 10,000 years ago) and the Holocene (10,000 years ago to today). This time has in general been characterized by regular cycles of growth and decay of Northern Hemisphere ice sheets. Although Antarctica has been covered with ice sheets for tens of millions of years, only during the past 2.5 million years or so have ice sheets extended from the Arctic into the northern and mid-latitudes. Where are we in time and temperature?
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Methods of determining climate change vary depending on the timescale being considered. For climate change during the Quaternary Period, there are a variety of proxies to take advantage of. We will focus first on ocean sediment cores.
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Foraminefera are tiny marine organisms that secrete a shell made out of CaCO 3 . They can be found in ocean surface waters, and in benthic environments on the sea floor. Scientists can use the shells of forams deposited in ocean sediment cores to tell things about ancient climate. The ratio of the stable isotopes 18 O and 16 O in the CaCO 3 skeletons of forams (ie. the δ 18 O) depends on the 18 O/ 16 O ratio of the seawater that the organisms grew in. The δ 18 O of seawater is itself affected by the growth and decline of continental ice sheets over glacial/interglacial cycles. Thus, glacial/interglacial cycles are readily apparent in the δ 18 O record of foram shells from deep sea sediment cores. Forams in deep-sea sediment cores record ocean chemistry
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Glacial mass balance in the global water cycle Throughout Earth's history, changes in the relative sea level have occurred over glacial/interglacial cycles because of the mass balance of water between the oceans and glaciers. Changes in sea level can be identified in the geologic record by variations in the oxygen isotope composition ( 18 O/ 16 O) of seawater (see above). During glacial times, seawater becomes enriched in 18 O due to the growth of the glacial ice sheets, which are preferentially enriched in
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SIO40lecture14 - SIO 40 Life and Climate on Earth Oct 29,...

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