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GEOG 205 Lecture Notes - Holocene Climatic Optimum, Tibetan Plateau, Taphonomy

Course Code
GEOG 205
Gail Chmura

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March 18th, 2013: Slow Climate Change: the “Climatic Optimum” of Hypsithermal
this topic is gradual climate change, as opposed to drastic climate change like the
Younger Dryas
this occurred 9000 years ago
climatic optimum… optimum for who?
changes associated with the Hypsithermal
o intensified monsoons (period of heavy, summer rains that occur in tropical
o human settlement on the Tibetan Plateau, at 5200 metres, where no people
live today
o subtropical & tropical forests of SE China expanded northward
o coral reefs developed north of their present growth limit
o prairie expansion in NA
o lakes in the Sahara desert
we will be focusing on prairie expansion & lakes in the Sahara
prairie expansion in NA
o some of the best evidence for this comes from NA Kirchner Marsh,
any change in climate is likely to be expressed in a change in
vegetation since Boreal Forest & Prairie are both at the edge here
o the same thing happened in Alpine Swamp oak replaced with Spruce
o there was both a warming and a cooling at Kirchner expansion of the
o this relates to those assumptions of the principle of uniformitarianism in a
previous reading
modern analogues exist
origin (taphonomy) of a fossil assemblage can be established
o what is missing today in cold biomes that wasn’t during the Pleistocene?
megafaunal if we had mammoths, we would have different biomes today
o there was a readvance of the forest/retreat of the prairies westward
o these changes would have occurred over thousands of years
o there was a 5000 year period that has forest to prairie and then back to
Sahara environmental change
o very different than that occurred in NA
o Sahara desert holds old lake beds & rock paintings of aquatic animals
dating to the Hypsithermal
o back at Kirchner marsh… decrease in precipitation but increase in
evaporation & transpiration, so increase in evapotranspiration
o variability in earth-sun geometry conditions today
N Hemisphere in the summer, earth is most distant from the sun
N Hemisphere in the winter, earth is closer to the sun (perihelion)
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