The Pleistocene epoch, spanning 2.58 million to 11,700 years ago, saw dramatic climate swings. These glacial-interglacial cycles reshaped Earth's surface, with ice sheets covering vast areas and sea levels fluctuating by up to 120 meters.

Milankovitch cycles drove these climate shifts, altering Earth's orbit and axial tilt. These changes triggered feedback loops involving ice sheet growth, atmospheric CO2 levels, and ocean circulation patterns, amplifying the initial orbital forcing.

Pleistocene Epoch and Glacial Cycles

Pleistocene epoch and global glaciations

• Pleistocene epoch spanned 2.58 million to 11,700 years ago marked significant global climate fluctuations
• Quaternary Period subdivision witnessed repeated glacial-interglacial cycles shaped Earth's surface
• Extensive ice sheet coverage during glacial periods dramatically altered landscapes (North America, Europe)
• Sea level fluctuations up to 120 meters due to ice volume changes reshaped coastlines
• Modern landscapes sculpted by glacial erosion and deposition (fjords, Great Lakes)
• Species distribution and evolution influenced by changing habitats (woolly mammoths, saber-toothed cats)
• Global climate patterns affected long-term atmospheric and oceanic circulation

Causes of glacial-interglacial cycles

• Milankovitch cycles primary driver of glacial-interglacial cycles
  • Eccentricity alters Earth's orbital shape over ~100,000 years affects total solar energy received
  • Obliquity varies Earth's axial tilt over ~41,000 years impacts seasonal contrasts
  • Precession wobbles Earth's rotational axis over ~26,000 years shifts seasons relative to orbit
• Solar radiation distribution changes trigger climate feedbacks
  • Affects seasonal and latitudinal insolation patterns influence ice sheet growth/decay
• Feedback mechanisms amplify initial orbital forcing
  • Albedo changes due to ice sheet expansion/contraction reflect more/less solar radiation
  • Atmospheric CO2 concentration variations affect greenhouse effect
• Ocean circulation changes redistribute heat globally
  • Thermohaline circulation alterations impact heat and nutrient transport
  • North Atlantic Deep Water formation varies affects global climate

Ice Sheets and Evidence of Glaciations

Ice sheets during Last Glacial Maximum

• North American ice sheets covered vast areas ~21,000 years ago
  • Laurentide Ice Sheet blanketed most of Canada and northern United States (Great Lakes region)
  • Cordilleran Ice Sheet covered western North America (Rocky Mountains)
• Eurasian ice sheets reshaped northern landscapes
  • Fennoscandian Ice Sheet spread across northern Europe and western Russia (Scandinavia)
  • British-Irish Ice Sheet covered British Isles and North Sea
• Antarctic Ice Sheet expanded onto continental shelf increased global ice volume
• Greenland Ice Sheet covered most of Greenland contributed to sea level lowering

Evidence for Pleistocene glaciations

• Glacial deposits provide direct evidence of ice presence
  • Till unsorted sediment deposited directly by glaciers indicates ice extent
  • Erratics large boulders transported by ice reveal ice flow directions
  • Glacial striations scratches on bedrock caused by moving ice show ice movement patterns
• Glacial landforms sculpted by ice movement
  • U-shaped valleys carved by glacial erosion (Yosemite Valley)
  • Cirques bowl-shaped depressions at glacier origins indicate past glacier formation sites
  • Moraines ridges of glacial debris mark former ice margins
  • Drumlins elongated hills shaped by ice movement reveal ice flow direction
• Ice core data provides detailed climate records
  • Oxygen isotope ratios serve as temperature proxies reveal past climate fluctuations
  • Trapped air bubbles allow atmospheric composition analysis shows past CO2 levels
  • Dust and pollen enable environmental reconstruction indicates past vegetation patterns
• Marine sediment cores offer oceanic climate information
  • Foraminifera assemblages estimate past ocean temperatures
  • Ice-rafted debris indicates iceberg presence and extent of sea ice

Glaciations vs long-term climate change

• Global temperature fluctuations averaged 5-7℃ between glacial and interglacial periods
• Sea level changes of up to 120 meters occurred between glacial and interglacial periods
• Atmospheric CO2 concentrations fluctuated between ~180 ppm (glacial) and ~280 ppm (interglacial)
• Biosphere responses included shifts in vegetation patterns (tundra expansion during glacials)
• Ocean circulation changes altered deep water formation sites affected global heat distribution
• Feedback mechanisms amplified initial climate forcings
  • Ice-albedo feedback increased cooling/warming trends
  • Carbon cycle feedbacks affected atmospheric CO2 levels
• Long-term climate trends showed overall cooling throughout the Pleistocene
• Increasing amplitude of glacial-interglacial cycles observed in later Pleistocene (Mid-Pleistocene Transition)