Lecture_21_Ice_Age_World - 1 Glacial Cycles Higher 18 O/ 16...

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Unformatted text preview: 1 Glacial Cycles Higher 18 O/ 16 O, more ice Last Ice Age 20,000 yrs bp 2 Evidence for lower temperature on land • Mountain glaciers at low latitudes descend 1 km, indicating 5-7°C cooling • Noble gasses in groundwater indicate 5-7°C cooling in tropical and temperate regions • Vegetation ranges shifted toward equator as recorded in pollen from lake sediments 3 4 Lapse rate = 6.5°C/km 5 Lapse rate = 6.5 °C per km 1 km lower snowline = 6.5° cooling at surface 6 7 • Gases are soluble in liquid • Gases are continually moving across the gas-liquid interface • At equilibrium (no net flux of gas across the interface), the concentration of the gas in solution is proportional to the pressure of the gas in the overlying space e.g. [O 2 ] = K x pO 2 Where the solubility constant K is specific for each gas and generally increases with decreasing temperature 8 Noble gases in Groundwater Water that has equilibrated with the atmosphere at cold T contains more gas 9 Old water equilibrated with atmosphere at LGM temperatures recent water recent water equilibrated with atmosphere at modern temperatures 10 Present - Ice Age temperatures from noble gases in aquifers 11 Water that left the earth’s surface 20,000 years ago has more Xe than surface water today because 1. Gas solubility increases at cold temperatures 2. Xe accumulates in the water over time 3. Xe is heavier than Ne 12 What can cause lower surface temperature globally? 1. Decrease in amount of sunlight? NO—while seasonal distribution changes, total solar energy averaged over the year does not vary....
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This note was uploaded on 02/08/2011 for the course EAS 1601 taught by Professor Lynch during the Spring '08 term at Georgia Institute of Technology.

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Lecture_21_Ice_Age_World - 1 Glacial Cycles Higher 18 O/ 16...

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