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The investigation of two profiles (DYS1 and DYS5) from the Daiyun Mountains in southeastern China sheds new light on the history of regional climate changes and the variability of the intensity of the East Asian Summer Monsoon (EASM) over the past 10350 years based on the degree of peat humification, loss on ignition (LOI), magnetic susceptibility (MS) and geochemical (Rb, Zr and Zr/Rb) data. The records indicate that three main climatic regimes have occurred over the past 10350 years: 1. relatively warm and wet conditions from ~10350 to 8800 cal BP; 2. a warmer and wetter climate from 8800 to 3000 cal BP that was interrupted by four cold episodes at 7500, 6400, 5400, and 4400 cal BP; and 3. a dry and cool climate after ~3000 cal BP. These climatic changes were probably associated with a weak EASM, which was related to the latitudinal movement of the Intertropical Convergence Zone (ITCZ). Other important influences include solar radiation, etc. [ABSTRACT FROM AUTHOR]

Quantitative reconstruction of past precipitation for the monsoonal region in east-central China is of necessity in understanding East Asian Summer Monsoon (EASM) evolution. In this study, pollen-based quantitative reconstructions of the precipitation for Dajiuhu area since the late glacial period were produced by two appropriate approaches: Weighted Averaged Partial Least Squares (WAPLS) and Locally-Weighted Weighted-Averaging (LWWA). After numerical analysis, a modern pollen training set with a radius of 1000 km around the Dajiuhu Lake was established and two precipitation variables were selected for reconstruction. Mean Annual Precipitation (MAP) and Mean Summer Precipitation (MSP) reconstructed based on the two approaches had relatively high consistency (though the reconstructed value of LWWA is lower than that of WAPLS): (1) in the period of 16.0 ipitation was 10% lower than the mean value for the Holocene; (2) in the period of 10.0 cal ka BP - 7.0 cal ka BP, the precipitation reached an optima of the Holocene; (3) in the period of 7.0 cal ka BP - 4.0 cal ka BP, the precipitation was considerably lower than the mean of the Holocene; (4) in the period of 4.0 cal ka BP - present day, the precipitation fluctuated relatively drastically around the average line of the Holocene. The results indicated that the maximum intensity of the EASM in the data-covering period of the past ∼16,000 years occurred in the early and middle Holocene, specifically from ∼10.0 cal ka BP to ∼7.0 cal ka BP. On the whole, our quantitative reconstruction results were highly coincident with the other proxy-based reconstructions of the changes in the East Asian monsoon. In the early and middle Holocene period when the monsoon was the strongest, synchronous changes in precipitation promoted regional expansion of mixed coniferous forests and broad-leaved forests. We preliminarily conclude that the periodic seasonal variation of longitudinal solar radiation gradient in summer at the low latitudes of the northern and southern hemispheres was the main controlling factor for precipitation in this region. [ABSTRACT FROM AUTHOR]