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Holocene vegetation variation in the Daihai Lake region of north-central China: a direct indication of the Asian monsoon climatic history

2004; Elsevier BV; Volume: 23; Issue: 14-15 Linguagem: Inglês

10.1016/j.quascirev.2004.01.005

1873-457X

Jule Xiao, Qinghai Xu, Toshio Nakamura, Xiaolan Yang, Wendong Liang, Yoshio Inouchi,

Archaeology and ancient environmental studies

DH99a sediment core recovered at the center of Daihai Lake in north-central China was analyzed at 4-cm intervals for pollen assemblage and concentration. The pollen record spanning the last ca 10,000yr revealed a detailed history of vegetation and climate changes over the Daihai Lake region during the Holocene. From ca 10,250 to 7900calyr BP, arid herbs and shrubs dominated the lake basin in company with patches of mixed pine and broadleaved forests, indicating a mild and dry climatic condition. Over this period, the woody plants displayed an increasing trend, which may suggest a gradual increase in warmth and humidity. The period between ca 7900 and 4450calyr BP exhibits large-scale covers of mixed coniferous and broadleaved forests, marking a warm and humid climate. Changes in the composition of the forests indicate that both temperature and precipitation displayed obvious fluctuations during this period, i.e., cool and humid ca 7900–7250calyr BP, warm and slightly humid ca 7250–6050calyr BP, warm and humid between ca 6050 and 5100calyr BP, mild and slightly humid ca 5100–4800calyr BP, and mild and humid ca 4800–4450calyr BP. The period can be viewed as the Holocene optimum (characterized by a warm and moist climate) of north-central China, with the maximum (dominated both by warmest temperatures and by richest precipitations) occurring from ca 6050 to 5100calyr BP. During the period of ca 4450–2900calyr BP, the woody plants declined, and the climate generally became cooler and drier than the preceding period. This period is characterized by a cold, dry episode from ca 4450 to 3950calyr BP, a warm, slightly humid interval between ca 3950 and 3500calyr BP and a mild, slightly dry episode from ca 3500 to 2900calyr BP, and appears to be a transition from warm and humid to cold and dry climatic conditions. Since ca 2900calyr ago, the forests disappeared and the vegetation density decreased, reflecting a cool and dry climate. However, a relative recovery of the woody plants occurring between ca 1700 and 1350calyr BP may denote an increase both in temperature and in precipitation. Fluctuations in the climatic condition of the Daihai Lake region were not only related to changes in the seasonal distribution of solar insolation and in the axis and intensity of the ocean current in the western North Pacific but were also closely linked to variations in the position and strength of polar high-pressure systems and in the pattern and intensity of the Westerly winds.