A 40,000 year record of vegetation, environment and climate change from Chongqing, Central China
Palaeogeography, Palaeoclimatology, Palaeoecology
Congping is a wetland at about 2100 m asl in Chongqing Province. It is surrounded by a shrubby grassland which grades into a mixed conifer and deciduous woodland. A record based on pollen, microcharcoal and geochemistry has been used to reconstruct an environmental history covering the last approximately 40 kyr BP. The site was wooded throughout the entire record and there were two relatively warm periods; during Marine Isotope 3 (MIS 3) and for the Holocene from about 9 kyr BP. From 27 to 18 kyr BP a gradual cooling occurred and the coldest part of the record was between 22 and 18 kyr BP when a mixed conifer cool temperate deciduous forest occurred, The warmest part of the record lasted from about 9 to 1.5 kyr BP when mixed evergreen and deciduous forest occurred. The broad pattern of changes is in accord with pollen records from Dajiuhu in Hubei, and demonstrates that this was a regional signal. A moist central China at Last Glacial Maximum (LGM) shows that the East Asian Summer Monsoon was delivering enough moisture on the mainland to sustain forest cover, even at 2120 m asl. The large-scale changes are interpreted as relating to changes in Earth's orbital parameters and sea-level changes in the South China Sea which had an impact on moisture delivery into central China. It is surmised that the westerlies which created dry climates in northeastern China trapped the summer Monsoon influence enough to keep central China moist. The Younger Dryas (YD) is present in the weathering parameters as evident in several changes in elemental abundance delivered to the sediments. The Congping record shows no clear evidence of human impact on its vegetation, and there were no local fires to have caused any vegetation changes. In the last 1.5 kyr BP a slight cooling caused a rise in conifers, a decline in broad-leaved tree taxa and increased weathering rates.
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Chinese Academy of Sciences