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GEOG 205 Lecture Notes - Laurentide Ice Sheet, Forebulge, Sea Level

Course Code
GEOG 205
Gail Chmura

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February 11th, 2013: Changes in the Level of Land and Sea
last glacial maximum 26 000 - 20 000 years ago as thick as 4 km
Laurentide Ice Sheet covered Canada & went south into states
ice sheets covered Scandinavia & Europe & East Asia (greater aridity over N Asia
caused temperatures to not be ideal to create ice sheets)
moisture came from oceans (evaporation & precipitation)
sea levels decreased 80-120 m exposing more land mass including land bridges
eustatic change: change in volume of earth’s oceans due to meltwater & thermal
isostatic change: shifts in land surfaces
forebulge: earth surface bulges up due to weight of ice retreating
weight of ocean water has effect on earth’s crust under the ocean when sea levels
dropped, the continental shelf uplifted this contributed to the decrease in relative
sea level
use C-dating and species who lived at specific sea levels to track changes in sea
rise in eustatic sea level caused submergence of today’s coastlines & created inland
o Montreal used to be submerged under the Champlain sea
transgression: increase in relative sea level
regression: decrease in relative sea level occurred as ice sheets grew
rate of isostatic changes is greater than the rate of isostatic changes, so eustatic
changes are greater than isostatic changes
the Dutch Problem
o before 12th century, Dutch tidal sea (Waadden sea) = freshwater sea, nearly
untouched by the oceans
o expansion of agriculture & draining of wetlands = peats decomposed &
o surface elevations declined
o started building up dykes to stop influx of ocean water into freshwater
Canada has dykes in the Maritimes Bay of Fundy
prediction of future sea levels complicated & difficult must predict future
temperatures & how much today’s glaciers will melt
as ocean temperatures increase, densities will decrease so volume will increase
varies with salinity of sea water
regression still happening in some regions
o James Bay is still rebounding from the last glaciers cause the Cree to move
their settlements
Dating Techniques: Carbon-14 Dating and Dendrochronology
carbon-14 has 2 extra neutrons
o C-12 = 6 p+ and 6N 98.89%, stable
o C-13 = 6 p+ and 7N 1.11%, stable
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