Holocene vegetation and climate of the Alashan Plateau, NW China, reconstructed from pollen data

摘要

A set of 55 recent pollen spectra from the Alashan Plateau and the Qilian Mountains (Qilianshan), northwestern China has been analyzed. The established relationships between the pollen spectra and modern vegetation and precipitation patterns of the studied area have been applied to 65 fossil pollen spectra from a 825 cm long sediment record collected in the topographic depression formerly occupied by Eastern Juyan palaeolake (41.89°N; 101.85°E; 892 m a.s.l.). Several qualitative approaches (e.g. indicator plant species; Artemisia/Chenopodiaceae and Ephedra fragilis-type s.l./Ephedra distachya-type pollen ratios) and quantitative methods of vegetation and climate reconstruction have been tested with the surface pollen and then applied to the Eastern Juyan pollen record. Fossil pollen data reveal pronounced environmental changes in the studied area of the Alashan Plateau between ca. 10,700 and 1700 cal. yr B.P. Desert taxa, as Chenopodiaceae, Nitraria, Calligonum, Reaumuria were abundant in the vegetation cover around the study site through the whole record. Pollen spectra dated to ca. 10,700–5400 cal. yr B.P. are characterised by highest values of Chenopodiaceae, E. fragilis-type and other desert indicating taxa, suggesting rather dry climate. Most favourable conditions are reconstructed between 5400 and 3900 cal. year B.P. on the basis of relative increase in abundance of Artemisia pollen. A return to dry conditions occurred at about 3900 cal. yr B.P. The lake finally desiccated after 1700 cal. yr B.P. Reconstructed dry climate oscillations between 5900 and 5400 and 3100 cal. yr B.P. correlate well with similar events found in the published records from northern and western China and central Mongolia. However, Eastern Juyan record does not show the early Holocene humidity maximum, as suggested by the sedimentary data from monsoon-influenced areas of China.