North American glaciation

North American glaciation
Name	North American glaciation
Caption	Maximum extent of major ice sheets during the Last Glacial Maximum
Type	Continental glaciation
Location	Laurentide Ice Sheet, Cordilleran Ice Sheet, Innuitian Ice Sheet
Epoch	Pleistocene

Contents

North American glaciation describes the repeated advance and retreat of continental and alpine ice across North America during the Pleistocene and into the Holocene. The complex history involves interactions among the Laurentide Ice Sheet, Cordilleran Ice Sheet, and Innuitian Ice Sheet and produced landscapes across the Canadian Shield, Great Lakes, New England, Midwest, and Pacific Northwest. Reconstruction integrates evidence from radiocarbon dating, luminescence dating, marine isotope stages, and stratigraphic correlation with sites such as Beringia, Alberta, Ontario, Mackenzie River, and Hudson Bay.

Overview and Chronology

Glacial episodes in North America correlate with global MIS 2, MIS 4, MIS 6, and earlier Quaternary cycles identified at locations like Vancouver Island, Newfoundland and Labrador, Nova Scotia, Quebec, and Greenland Ice Sheet cores. Major phases include the Wisconsin glaciation (Late Pleistocene), the Illinoian glaciation (middle Pleistocene), the Sangamonian interglacial, and earlier events recorded near Lake Agassiz, Lake McConnell, Lake Manitoba, Great Slave Lake, and Lake Athabasca. Chronologies derive from work at Camp Century, GISP2, Vostok, and from field campaigns by institutions such as the United States Geological Survey, Geological Survey of Canada, Smithsonian Institution, and university teams at University of Minnesota, McGill University, University of British Columbia, and Yale University.

The Laurentide Ice Sheet centered on the Keewatin Region, Baffin Island, and Hudson Bay expanded to cover much of New England, New York, Ohio, Michigan, Wisconsin, Illinois, Minnesota, Iowa, Saskatchewan, Manitoba, and Alberta. The Cordilleran Ice Sheet grounded on Coast Mountains, Columbia Icefield, and British Columbia valleys, while the Innuitian Ice Sheet affected northern archipelagos near Ellesmere Island and Baffin Island. Peripheral mountain glaciers in the Rocky Mountains, Appalachian Mountains, Sierra Nevada, Cascade Range, and Alaska Range produced local cirque and valley glaciation evident in places such as Mount Rainier, Mount St. Helens, Denali, Mount Baker, and Sierra Nevada. Ice-marginal features include moraines at drumlins, Oak Ridges Moraine, Niagara Escarpment, and deposits feeding the Mississippi River and St. Lawrence River drainage reorganizations.

Ice dynamics such as basal sliding, subglacial deformation, and surging shaped features documented at sites like Mackenzie Delta, James Bay, St. Lawrence Lowlands, and Prairie Provinces. Glaciofluvial systems produced outwash plains at Saskatchewan River Delta, Red River Valley, and Chukchi Sea-proximal deltas during meltwater pulses like those from Lake Agassiz and Lake Ojibway. Catastrophic drainage events carved channels such as the Missoula Floods analogues in eastern basins and reworked bedrock scours near Niagara Falls, Grand Canyon tributaries, and Finger Lakes. Periglacial processes left patterned ground, ice-wedge casts, and thermokarst features across the Yukon, Nunavut, Manitoba, and Alberta plains, while glacial erratics and striations appear from Ontario to Montana and Newfoundland and Labrador.

Orbital forcing described by Milankovitch cycles modulated insolation linked to glacial-interglacial transitions recorded in Greenland ice cores, Antarctic ice cores, and North Atlantic Deep Water proxies near Baffin Bay and Labrador Sea. Atmospheric greenhouse gas concentrations from ice cores at GISP2, Dome C, and EPICA correlate with temperature proxies used by researchers at Columbia University, Lamont–Doherty Earth Observatory, University of Colorado Boulder, and NOAA. Ocean circulation shifts including changes in Atlantic Meridional Overturning Circulation and freshwater pulses from Lake Agassiz outbursts influenced regional climates recorded in marine sediments off Nova Scotia, Newfoundland, Gulf of Mexico, and Bering Strait. Paleobotanical records from Packrat middens, pollen analysis in prairie and boreal forest sequences, and fossil assemblages catalogued by institutions such as the Royal Ontario Museum and Smithsonian Institution document vegetational responses.

Glaciation drove range contractions and expansions for megafauna including Woolly Mammoth, American Mastodon, Steppe Bison, Giant Short-faced Bear, Saber-toothed Cat, and avifauna recorded at sites like La Brea Tar Pits analogues and fossil localities in Alberta and Saskatchewan. Postglacial colonization routes utilized refugia in the Appalachian Mountains, Pacific Northwest, Beringia, and unglaciated corridors such as the Missouri River basin and coastal corridors near Vancouver Island, producing modern distributions of taxa studied by Royal Botanic Gardens, Kew collaborators and biogeographers at University of Michigan and University of Toronto. Soil development, peat accumulation in Hudson Bay Lowlands, and wetland evolution in the Great Lakes Basin altered carbon storage important for carbon budget studies by IPCC-affiliated researchers.

Human presence in formerly glaciated regions is traced through sites such as Bluefish Caves, Meadowcroft Rockshelter, Monte Verde-related debates, Clovis culture assemblages in New Mexico, Florida, Texas, and South Carolina, and pre-Clovis evidence at Gault Site and Page-Ladson. Migration across Beringia and coastal routes influenced peopling models evaluated by archaeologists at Smithsonian Institution, University of Alaska Fairbanks, American Museum of Natural History, and Canadian Museum of History. Glacial refugia, isostatic rebound recorded at Hudson Bay, and meltwater floods impacted settlement patterns, lithic raw material transport from regions like Superior Province and Keewatin and preservation of organic artifacts in peatlands and submerged landscapes now studied by marine archaeologists using techniques developed at Woods Hole Oceanographic Institution.