EART 2 Lecture 20: Ancient Climates

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21 Dec 2016
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The most important climate proxy - oxygen isotopes. 18o - heavy (& rare) oxygen - 2 extra neutrons. Global water has some 18o16o ratio, but varies from place to place. Leave h2o with 18o (heavy) evaporate h2o with 16o (light) 18o = 18o/16o - standard in parts per thousand. Drill down into sediments accumulate the ocean floor over time. Bring back sediment core, and use a mass spectrometer to measure oxygen isotope ratio (18o/16o) from older sediments to younger sediment (vertically in the core) Oxygen ratio fluctuates as function of time. Chemistry of ocean changes over time because of changes in sea level and ice melting. You find the same record in ocean sediments globally. Seawater isotopic ( 18o) composition reflects the size of continental polar ice sheets (rich in 16o). Variation in amount of ice causes isotope ratio to vary. Glacial period 18o 0 to -1 (heavy) Thus, we can infer global ice volume through time!

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