The Pleistocene

The Early Quaternary, the Pleistocene (1800-11 ky BP), is characterized by successive glaciations and interglaciations. The timescales of their recurrence correspond to the Milankovitch periods. In the Early Pleistocene (older than 700 ky), the dominant period of recurrence was about 40 ky, and it is shifted to about 100 ky lately.

Among the Late Pleistocene glacials/interglacials, a warm period around 120 ky BP (the 'Eemian interglacial'), is very notable. Changes in orbital parameters in comparison to those at present (greater obliquity and eccentricity, and perihelion) have led to greater seasonal temperature variations in the Northern Hemisphere. Sea level is supposed to be about 4-6 m higher than today, with much of this additional liquid water coming from Greenland.

At the end of the Eemian interglacial, temperature dropped rapidly during about 10 ky and then cooled more gradually, leading to the development of the last major glaciation. The peak of this glaciation was at 1822 ky BP, the Last Glacial Maximum (LGM). At this time, huge ice sheets covered Northern Europe, Canada, and the northern half of the West Siberian Plain. In the South America, the Patagonian Ice sheet developed. The flows in the Ob and Yenisei Rivers were stopped due to ice sheets, creating large lakes. Permafrost covered most part of Europe. In warmer regions, LGM climates were dry. Sea level dropped by about 120 m due to the huge amount of water stored in ice sheets with thickness up to 3 km. Global mean temperature is estimated to be about 5° lower than today. The concentration of the carbon dioxide in the atmosphere was about 200 ppmv, and the concentration of methane was about 350ppbv.

In the period 18-11 ky BP, the climate warmed gradually. However, this gradual warming was interrupted, for example, during the Younger Dryas (about 12 ky BP). This cold event is attributed to the large influx of freshwater to the North Atlantics from the melting Laurentide Ice Sheet. Freshening of the North Atlantic surface water may have resulted in the weakening of the thermohaline circulation which transports warm water from the low latitudes to the northern subpolar belt. Lacking this heat transport, the North Atlantics had to cool.

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