Chapter 11, Pleistocene Glaciations (1.8 m.y. ago to 10 k.y. ago)

Geologic evidence of Pleistocene Glaciation

Terrestrial     Glacial deposits: glacial striations, moraines, till
Marine The oxygen isotope record: higher ¹⁸O/¹⁶O in calcium carbonate means colder temperature.
              Fig 11-4 100,000 year cycle of glacials
              Glacials: 10 ^oC, 200 ppm CO₂; intergalcials: 15 ^oC, 280 ppm CO₂.
              Periods: 100,000 years (700,000 years ago till now), 40,000 years (before 700,000 years ago)

Milankovitch cycles

Eccentricity: perihelion (closest) aphelion (farthest); e = 0.00–0.06, 0.017 now; 100,000 years and 400,000 years, affects insolation.

Obliquity: Earth’s spin axis tilt 22.5^o–24.5^o; 41,000 years, does not affect insolation.

Precession: the axis wobbles around; 25,700 years (23,000 and 19,000), does not affect insolation.

Optimal conditions for glaciation: low obliquity, high eccentricity, a precession angle that places the Northern Hemisphere summers at aphelion. (i.e. low seasonal contrast, low insolation)

Glacial climate feedbacks

Ice–Albedo feedback: ice ––– albedo ––– temperature; positive.
CO₂ feedbacks: temperature –––CO₂ –––biological pump; positive.

                            Shelf nutrient hypothesis; positive.

                            Iron fertilization hypothesis; positive.

                            Coral reef hypothesis; positive.

                            terrestrial biomass ––– CO₂ ––– temperature; negative.

Cloud––Albedo feedback: algae–––MSA–––cloud–––albedo–––temperature; positive.

Homework:

Review questions 1, 2, 3, 5, 7 in the text book. Type your answers, please.

Useful websites

National Snow and Ice Data Center

http://www-nsidc.colorado.edu/

The National Snow and Ice Data Center is a data and information resource for those studying snow and ice, and their importance to the Earth system. It is maintained by the NSIDC at the University of Colorado, Boulder.

NOAA Paleoclimatology Program

http://www.ngdc.noaa.gov/paleo/paleo.html

A central location for paleoclimate data, research, and education. NOAA's Paleoclimatology program shares scientific data related to climate system variability and predictability. It is maintained by the National Oceanic and Atmospheric Administration.

Earth and Ocean Sciences Image Collections

http://www.science.ubc.ca/~eoswr/cgi-bin/db_gallery/searchframe.html

This extensive photo gallery contains photographs of various glacier features together with a brief description. It is maintained by the University of British Columbia.

Bylot Island

http://sts.gsc.nrcan.gc.ca/page1/landf/ne/baffin/bylot.htm

This site contains maps, graphics, and information regarding the effects of glaciers on Bylot Island. It is maintained by the Geological Survey of Canada.

The Creation of Yosemite

http://www.americanparknetwork.com/parkinfo/yo/geology/index.html

Here is a timeline of Yosemite's history, which includes brief explanations of roche mountonne, glaciers, and dikes. It is maintained by the American Park Network.

Glacial Geology Photo Gallery

http://www.state.me.us/doc/nrimc/pubedinf/photogal/surfical/surfphot.htm

This site offers a photo gallery of surface features created by glacial activity. It is maintained by the Maine Department of Conservation.

Milankovitch Theory

http://www.earthobservatory.nasa.gov/Library/Giants/Milankovitch/milankovitch_2.html

This site, maintained by NASA, explains with nice animations the orbital variations responsible for the Milankovitch climate cycles.

The Pacemaker of the Ice Ages: Milankovich Cycles in Climate

http://ethomas.web.wesleyan.edu/ees123/milank.htm

Glaciers

http://academic.brooklyn.cuny.edu/geology/leveson/core/graphics/nyc_mins2/glac2_rollover.html