TOPIC 13: SHORTERM CLIMATE CHANGE
The Once and Future Glacial World (The world ofthe Wisconsin Glacial 12-71,000 years before present)
Ice?
continental glaciers extended over most of Canada, Alska, Greenland, Fennoscandia, and Northern Siberia
permanent ocean ice packs extended farther out to sea around Antarctica and in the North Atlantic Ocean (reaching southern Greenland and Scotland)
Sea Level
sea level was about 150 mlower than today
Baltic and North Seas were dry or covered by glaciers
very little continental shelf environment
Ocean Circulation
stronger thermal gradient between Equator and polar regions
ocean gyres were compressed toward equator by ice packs
stronger circulation
Ocean Chemistry
lower concentrations of greenhouse gases
excess carbon was stored in oceans (colder, can absorb more)
The Once and Future Greenhouse World - The world of the Cretaceous (60-120 million years ago; Age of Dinosaurs)
Ice?
there is no evidence of ice anywhere on the planet
proxy evidence of plant fossils suggest a temperate climate even within the Arctic Circle
even dinosaur fossils have been found north of the Arctic Circle
remember - Arctic Circle of Createous would have had several months of darkness
Sea Level:
sea level was about 150 m higher than today.
there was a major shallow sea in central North america
there were extensive continental shelf environments
Ocean Circulation
much milder climate and lower thermal gradients between equatorial and polar regions
ocean gyres extended much further northward due to plate configuration
circulation may have been weak due to lower thermal gradient
Atmosphere/Ocean Chemistry
much higher concentrations of greenhouse gases (2-10 times today)
excess carbon may have come from volcanism and less absorption in warmer ocean
K/T Boundary Extinction
major biological crisis occurred at end of Cretaceous
all large carnivores on land and in oceans died out
many other organisms died out at same time
Why? - best guess is bolide impact creating 'nuclear winter' conditions