Vegetation history, climatic changes and Indian summer monsoon evolution during the Last Glaciation (36,400–13,400 cal yr BP) documented by sediments from Xingyun Lake, Yunnan, China

摘要

We obtained a 9.74-m-long sediment core (XY08A) from Xingyun Lake in central Yunnan Province, southwest China, and used AMS radiocarbon dating of terrestrial plant macrofossils to provide a chronology. Here we present the results of pollen and grain size analyses of the interval ~36,400–13,400 cal yr BP and discuss the vegetation history, and record of climate change associated with the evolution of the Indian summer monsoon (ISM). Three stages of regional vegetation change are documented: (i) During the late Marine Isotope Stage 3 (36,400–29,200 cal yr BP), the study regionwas occupied by mixed coniferous and evergreen broad-leaved forest dominated by Pinus and evergreen Quercus, with Tsuga, Abies/Picea growing on the surrounding mountains. (ii) During the Last Glacial Maximum (LGM, 29,200–17,600 cal yr BP), cold-temperate coniferous forest dominated by species of Abies/Picea expanded and reached amaximumextent; and at the same time, the extent of evergreen broadleaved forest increased. (iii) From17,600 to 13,400 cal yr BP the hemlock forest and Abies/Picea forest began to decline until they disappeared completely in the early phase of the Last Deglaciation, while pine forest and evergreen broadleaved forest dominated the surrounding areas. The vegetation history indicates a generally drying climate from 36,400 to 13,400 cal yr BP, suggesting a gradual weakening of the ISM with the weakest ISM influence occurring during the early part of the Last Deglaciation, when the climate was the driest. The regional temperature first decreased intermittently and then increased gradually, being mild and wet during the late MIS3 stage followed by the coldest but not the driest climate during the LGM when the temperature was at least 3 °C lower than at present.