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GEO302C-L26 - ^14C dating i LGM 20,000 yrs 5 Deglacial 2...

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GEO 302C 03/26/08 Lecture 26: The Last Deglaciation Guest Lecturer: Jessica Rasmussen Definitions Dates Important People 1. Last Deglaciation a. 21,000-6000 ybp b. 21,000 ybp: large ice sheets, lower CO2 levels c. 10,000 ybp: Higher summer insulation 2. Retreat of Ice Sheets a. Dated by radiocarbon dating of moraines b. N American ice sheets began to retreat 151k^14C yrs ago i. Disappeared by 6k14C yrs ago c. Retreat agrees with the timing from Milankovitch Theory d. Production of ^14C isn’t constant- time spans must be calibrated into ^14C yrs. e. Causes i. Milankovitch Theory: obliquity, precession, eccentricity 3. Best record of Ice Sheet Melting a. Tropical coral reefs like to grow at a certain depth b. During LGM, lower sea level coral reefs above sea level reefs died c. Coral reefs function as a dipstick 4. Deglacial rise in Sea Level
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Unformatted text preview: ^14C dating i. LGM- 20,000 yrs 5. Deglacial 2 Step a. Summer insulation- 60 degrees N b. Melt water pulses c. During deglaciation, organisms delta 18 values were more negative 6. Mid Deglacial Cooling a. Younger-Dryas event b. Dryas- An artic plant appeared in Europe for the first time c. Occurred in only 3-10 years 7. Melting Glacier a. Melt water to the Gulf of Mexico b. Sudden collapse goes in to North Atlantic → stops deep ocean circulation c. However, have not found path of glacial water to North Atlantic d. Should have affected the whole globe, but no evidence 8. Preglacial Lakes moving north a. Bedrock depressed under glaciers b. Rebounds when glacier melts c. When it rebounds, it moves the glacial lakes north d. Lake Agassie, Great Lakes e. Channeled scablands- huge flood from melting glaciers 9. Over the last century, earths temperature increase by .75 degrees C...
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