Characteristics of late Quaternary monsoonal glaciation on the Tibetan Plateau and in East Asia

Abstract Glaciers fed by monsoonal precipitation are mainly located on the Tibetan Plateau and easternmost Asia. These are characterized by simultaneous accumulation and ablation in summer season. The southeast part of the Tibetan Plateau experiences monsoonal precipitation in excess of 1000 mm/yr resulting in maritime temperate glaciers. In contrast, precipitation in the middle and northwest part of the Tibet Plateau decreases from 1000 to 200 mm/yr, resulting in the formation of continental cold glaciers. During the last glacial, the regions of heavy monsoonal precipitation were restricted to the southeast corner of the Plateau. The westerly weak precipitation zone shifted southward, and occupied the major northwest part of the Plateau, where the extreme continental type glaciers greatly expanded. In the eastern margin of Asia including Taiwan, Central Japan, Hokkaido and probably Mount Changbai, maritime type glaciers were more extensive because of higher monsoonal precipitation, especially heavy snowfall in northwest Japan owing to the rich moisture content of the winter monsoon over the Japan Sea. The millennial scale monsoon intensity and glacial cycle in the Tibetan Plateau are strongly affected by the precession cycle and the orbit-inclination cycle which dominate the solar irradiance variation in low latitudes, as the high radiation and strong monsoon caused the warmer and wetter climate during 40–30 ka. The low radiation produced a weak monsoon and large depression of temperature and precipitation around 21 ka. This climatic pattern differs from that in the high latitudes where the eccentricity cycle is prominent. The temperature during the last glacial maximum (LGM) was 6–9°C lower than today on the Tibetan Plateau and the equilibrium line altitude was depressed by about 1000 m in the southeast part, and in the east, south and west margins of the Plateau where precipitation was high. The equilibrium line depression was 500–300 m in the inner and especially the west part of the Plateau. This variation in equilibrium lines might be caused by the combined effect of the decrease in precipitation, the expansion of extreme continental glaciers and the active uplift of glaciated mountains. The estimation of a glaciated area of about 350,000 km2 in the Tibetan Plateau and roughly 500,000 km2 in High Asia based on observations of prominent features of LGM glacier extension, may be the direct evidence that shows there was no Quaternary unified ice sheet developed in the Tibetan Plateau.