流域生物、化学风化对小冰期气候变化的响应

A rapid response of chemical weathering and biocommunity to the Little Ice Age climate oscillation in the Daihai Lake watershed, northern China

岱海近500年沉积物的孢粉、介形类和地球化学记录表现了流域生物、化学风化对全球性小冰期气候波动明显而快速的响应。孢粉量的下降、化学风化强度的减弱(高Rb/Sr比值)以及意外湖花介(Limnocythereinopinata)的繁盛反映了小冰期最盛期岱海地区以干旱为特征的气候环境及其造成的高矿化度湖水。其中,介形类丰度及种类对环境变化的反应最迅速,植被生长的调节则要缓慢一些。内陆湖泊流域植被的衰弱与干旱环境下化学风化强度的减弱以及风尘作用的加强是相辅相成的。

A high resolution record from a 78 cm long lake sediment core from northern China on the basis of 210Pb and AMS 14C dating is presented. The hydrological closed Daihai Lake is located in a transitional zone of semi arid and semi humid which is sensitive to environmental change around the watershed. The pollen assemblages, calcareous shell of ostrocodes and geochemical record since the last 500 years indicate a rapid response of chemical weathering and biocommunity to the Little Ice Age climate oscillation. Our results show decrease of both pollen and chemical weathering intensity (higher Rb/Sr ratios in the lake sediments), and prosperous Limnocythere inopinata recorded in lake sediments during the Little Ice Age. These phenomena suggest the Little Ice Age is characterized by arid and cold, resulting in a lake water with a higher degree of mineralization (4 245 mg/L) of lake water. Under arid and cold environment, decline of vegetation results in weaker chemical weathering and stronger dust storm around the watershed. The respond of variations of ostrocodes abundance and species to environmental change is the most rapid, whereas plant growth regulation to it is relatively slow. This cold event recorded in the lake sediments appears to be contemporaneous with the events identified in the decrease of lake level in the African lakes, and in other independent signals from the glacier advance in the Qinghai Xizang Plateau and South Norway, and in the sea surface temperature decrease of North Atlantic, further suggesting that these cold fluctuations should be resulted from a larger regionally atmospheric circulation change during the Little Ice Age.