EARTHSS 21 Lecture 22: Lecture 22
23 Jul 2016
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Lecture 22: glacial world and impact of ice on humans in the past: we are only interested in oxygen-16 and oxygen-18. Easier to evaporate water with oxygen-16 (it"s lighter: oxygen-18: heavier, condenses more easily. Ice has less oxygen-18 than seawater (it has more oxygen-16) Ways we can measure past oxygen isotope ratios: Cooler more ice (a lot of o-16 trapped on land) decreased amount of o-16 in ocean: o-18 (divided by) smaller amount. Greenland correlates with the shut down and restart of the thermohaline circulation. Colder less water vapor more dust. Every 100,000 years: more direct sunlight easier to melt an ice sheet. To melt ice sheet, we need warm summers. Glacial world 20,000 years ago: northern hemisphere has changed the most: where we can grow big ice sheets. Positive feedbacks: albedo (get colder), less carbon less of a greenhouse effect, oceans get colder absorb more co2.
