LATE PLEISTOCENE AND HOLOCENE GLACIAL FLUCTUATIONS: IMPLICATIONS FOR THE CAUSE OF ABRUPT GLOBAL CLIMATE CHANGES

Two late Pleistocene glacial advances are commonly recognized in many regions, one about 21–23 ka and another about 17–19 ka. The earlier advance is often referred to as the Late Glacial Maximum (LGM), but in some cases, the later advance was more extensive. The 17–19 ka advance was synchronous throughout much of North America (e.g., The Puget Lowland, Wallowa Mts., OR, Sawtooth Range, ID, Wind River Mts., WY, Yellowstone, WY, Rocky Mts., CO, San Bernadino Mts., CA, and others) and in the Southern Hemisphere (e.g., Southern Alps, New Zealand, Andes Mts., Chile and Argentina). Retreat from the maximum extent began about 17 ka and multiple nested moraines were built as glaciers backwasted and stabilized repeatedly over a period of several thousand years. The youngest recessional moraines of successive stillstands typically range from 14.0–14.5 ka. The strikingly similar pattern and chronology of glacial advance and retreat in both hemispheres suggests that global climates oscillated synchronously and raises the question of the cause of such short term climate changes.

Similar abrupt climate oscillations occurred during the Younger Dryas in the Puget Lowland, Mt. Baker, WA, Icicle Creek, WA, Mt. Rainier, WA, Wallowa Mts., OR, San Bernadino Mts., CA, Sawtooth Range, ID, Wind River Mts., WY, Nova Scotia, Canada, Scandinavia, Swiss Alps, Greenland ice cores, and elsewhere in the Northern Hemisphere. In the Southern Hemisphere, The Younger Dryas has been recognized and dated at several places in the Southern Alps, New Zealand and in the Antarctic ice cores.

Synchronous Little Ice Age moraines have been recognized in the European Alps, throughout much of the western US, the Southern Alps of New Zealand, and many other parts of the world.

These synchronous, interhemispheric climatic oscillations cannot be explained by Milankovitch/Croll orbital forcing, North Atlantic thermohaline switches, or Laurentide ice-sheet surges. The world's glaciers clearly fluctuated in response to globally synchronous climate changes whose source was atmospheric.