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February 18th

2 Pages

Course Code
GEOG 205
Gail Chmura

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February 18 , 2013: Rapid Climate Change, the Younger Dryas  not all climate change is gradual & slow  Younger Dryas: short duration cold event (stadial) first recognized from evidence in NW Europe  after last glacial maximum, ice sheets begun to retreat & climate warming  pollen in cores from lakes/bogs in Europe provide evidence of changes in vegetation that reflect warming in climate 18 000 years ago  but, found pollen from Dryas octopetela 11 000 years ago from the tundra that pointed to abrupt cooling in western Europe  1975 Bob Mott reported similar abrupt cooling in New Brunswick & Nova Scotia  evidence shown through lake sediments on glacial tills covered by peat/soil that were thin & covered by second till with little organic matter  C-14 dating confirmed cooling on both sides of Atlantic occurred same time but restricted to lands bordering North Atlantic  simple explanation: as temperatures warmed, large ice sheet began to break up & sent icebergs into the N Atlantic which cooled temperatures in the region  BUT  Alpine Swamp, NJ showed no evidence of younger dryas o C-14 dating shows very small amounts (single seed, a needle) o palynology used: study of pollen & spores  pollen from before 11 000 BP indicated temperate forest, but pollen after 11 000 BP indicated boreal forest  signaled abrupt climate reversal  new consensus = younger dryas not restricted to Maritimes of Canada & NW Europe  paleoecology o make assumptions based on principle of uniformitarianism o fossils can be identified to a meaningful level of taxonomic resolution  palynology: study of pollen & spores  pollen: male gamete produced by flowering plant; no pollen = no new plant  spores: produced by plants without flower; asexual  pollen & spores made of organic compounds that are resistant to decomposition so easily preserved in sediment record  SO taxonomic resolution = variable but us
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