LECTURE NOTES: Ice Age of Pleistocene

Many times in the geologic past, mass extinction has been linked to drastic changes in climate. Global ice ages for example are characterized as periods of extensive cooling and advance of continental ice sheets and alpine glaciers. The last global scale event happened during the late Pleistocene epoch.

 

Late Pleistocene Glaciation in Ohio 21,000-10,000 ybp

Evidence of Pleistocene Glaciation:

Moraine: poorly-sorted sediment deposited by a glacier.  Note: Deep lakes formed during this time left behind extensive beach deposits and other forms of sediments.  See Photos at the bottom of the page.

Grooves in Silurian Limestone on Kelley’s Island

Glacial sediments found in Ohio

How might an Ice Age begin?

  • Plate Tectonics:
    • Opening and closing of ocean basins changes ocean circulation patterns.
    • Mountain building and atmospheric circulation
  • Decreased Greenhouse gasses in the atmosphere.
  • Short term changes due to changes in Earth’s orbit reducing the amount of solar radiation at the surface

How do Scientists study Ice Age Climate?

All of these systems record extreme changes in climate over Geologic Time.

  • Marine Sediment cores - marine skeletal remain containing carbonate minerals
  • Lake sediment cores - trapped pollen
  • Tree Rings - thickness related to amount of rain
  • Ice Cores - O18/O16 of ice changes during glacials - interglacial; bubbles contain CO2& Methane; changes in dust and volcanic ash.  See Below

Continental Ice Sheet and Valley Glacier Ice Cores

Stable Isotopes

Lighter O16 evaporates with ocean water and accumulates in snow and ice. During times of glaciation, ocean water becomes enriched in O18. Therefore, marine organism will show a high O18/O16 ratio and the ice sheet will have a lower ratio.

This process is temperature dependent and therefore is used as a "paleothermometer"

Computer Models:Atmospheric Circulation at 18ka

Computer Models Large with Grid Size

Our Local Climate Model better represents topography

Models tested using Geologic Evidence for Past Large Lake Systems in the Great Basin, USA.

 

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