Glacial/Interglacial cycles

Glacial/Interglacial cycles

1. Glacials

   • protracted (Extended time) climatic cold periods (ice ages)
     • ice sheets form in mid-latitude lowlands or low-latitude mountain areas, polar caps extend out to sea.
   • global climates were colder and drier than interglacials.
   • Modifies atmospheric and oceanic circulation.
   • Evidence that the world was more arid, subtropical desert margins more extended towards the equator, savannah grasslands more extensive, restricting the extent of tropical rainforests.
   • Increased ice volume in northern hemisphere forced polar front closer to the equator, limiting Gulf stream northern penetration and NADW formation weakening.

2. Interglacials

   • phases of warm climate between glacials where ice has retreated, temperate forests replace tundra veg in northern hem.
   • Current interglacial period = Holocene, 10.000 years.
   • Eamian Interglacial period 125,000 years warmer (marine oxygen isotope stage 5b)
   • Past 2.5 myr (millions on years) 100 glacial/interglacial periods formally indentified.
     • In marine records, assigned numbers (odd=inter) we're in Stage 1, Stage 100 taken as marking the beginning of the Quaternary period when there was a massive buildup of ice in northern hem.
     • oscillations in global climate have continued over a much longer period of time but before 2.5 Ma overall climate warmer, restricting glaciations to polar regions and high-latitude mountains.

3. climates may oscillate between g/I periods calling for further subdivision

   • Stadial short cold phase within an interglacial. Not cold enough to permit full gl conditions local ice advances generally occur.
   • Interstadial - short warm phase within a glacial. Temps not as high as interglacial period. In lowland mid-latitude regions the climax veg was boreal woodland.