Glacier - Interglacial cycles Flashcards
What was Ice Age Earth?
The presence of ice sheets on Earth
An unusual feature of Earth’s history
Over last billion years
- Global warming - “greenhouse”, ice-free
- Global cooling - “Icehouse”, ice-sheets
What are we in now?
The Cenozoic ice age
What happened 2.5mya in the Northern Hemisphere?
Ice sheets began
What has happened over the Quaternary period?
Glacials and inter-glacials
Ice advance and retreat
Glacials have varied in intensity
Global impact
What evidence do we use?
Terrestrial evidence
Marine sediment evidence
Ice-sheet core evidence
What can Marine Sediment cores offer?
Organic origin containing mineral deposits
Slow by continuous accumulation of sediment of deep open ocean floors
Immune to major episodes of erosion
Can provide record of climate change throughout the Quaternary
What do Ice-sheet cores do?
Show layers of snow fall
Compressing into successive layers of ice
What does the ice consist of?
Water, air bubbles, dust, volcanic ash, sea salt
Providing clues about climate at the time they were deposited
What does the water show?
Oxygen isotopes preserving the temperature
What can air bubbles show?
Preserve past atmosphere
What does dust, ash, and sea salt show?
Index of strength of atmospheric circulation (how windy)
Can date known volcanic eruptions
Indicate how surrounding areas have changes
What are some causes of climate change over 100s thousands years?
- Orbital forcing
- Changing Earth’s orbit -> changing spatial + temporal distribution of solar energy
- Changes favour/hinder ice-sheet growth
First discussed by Croll (1860s)
What do the combined cycles show?
A continuous variable but predictable pattern of solar energy receipts
What do Oxygen isotope fluctuations have cyclic periods of ?
41,000 years
19-24,000 years
100,000 years
What are the limitations of Milankovitch cycles?
- 100,000-year glacial cycle has the strongest amplitude but the 100,000-year orbital cycle is relatively weak
- Need an amplification of climate response
> ie positive feedback (ocean circulation)
Was there a British and Irish Ice Sheet?
Yes, vast amounts of geomorphic evidence
- On land
- And below sea
What did the glaciations of N. America involve?
Two major ice masses
- Formed over rocky mnts
- Fed by moist westerlies from pacific
What did the Laurentide Ice Sheet cover?
Covered most of the rest of Canada and northern USA
What happened to the North American ice sheets during the Last Glacial Maximum?
They joined with Greenland Ice Sheet
- Lots of geomorphological evidence
What is less well-known about the North American Ice Sheet?
The elevation
How can the North American Ice Sheet’s elevation be estimated?
Isostatic uplift
How can you reconstruct the ice sheet?
Using numerical ice sheet modelling
- Use an understanding of glaciological processes
- Ice core records of climate change
What are the issues with reconstructing the North America Ice Sheet?
Difficult to do using waxing and waning of sheet through time
Needs to be attempted to determine ice sheet volumes
