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Peatlands provide a widespread terrestrial archive for Holocene study. However, little is known about the grain-size characteristics of peaty sediments and their environmental significance. In order to study these phenomena in detail, two sections from the Hani and Gushantun peatlands in the Changbai Mountain Area were cored and sub-sampled. Based on reliable calibrated AMS 14 C ages, we established grain size variations in the peat cores since 15.6 ka cal. BP. Our results showed that the peaty sediments in the Changbai Mountains are mainly composed of silt. Moreover, the grain size component, which is related to paleoclimate variables, can be classified into three groups based on the “Grain size class vs. standard deviation” method. These sensitive grain size components are <37.0 μm (Component 1 or C1), 37.0–497.8 μm (Component 2 or C2) and >497.8 μm (Component 3 or C3). C1 comprises the finest silt in the peaty sediment and is mainly conveyed by the East Asian winter monsoon (EAWM), whereas C2 is transported into the peatland by surface runoff related to the enhancement of the East Asian summer monsoon (EASM). C3 is conveyed in saltation and bed-load mode by strong surface runoff linked to high-energy flow caused by a strong EASM, and perhaps is an indicator of extreme rainfall events in the Changbai Mountains. Our results suggest that the study region was dominated by a cold/dry environment during the late-glacial period under a strong EAWM. However, there was a marked climatic shift from an EAWM-dominated cold/dry climate to an EASM-dominated more mesic environment during the early Holocene. Increased percentage of C2 in peat cores during the Holocene Optimum (9.0–4.5 ka) indicates abundant rainfall in the study region (even with extreme rainfall events) as a result of a significant enhancement of the EASM. Weak monsoon events occurred at 10.5 ka, 9.2 ka, 8.2 ka, 7.2 ka, 6.2ka, 5.5 ka and 4.2 ka shown by sharp decreases in C2, agreeing with the stalagmite δ 18 O records in China. The results obtained from environmentally sensitive grain-size component records are largely consistent with other palaeoenvironmental records in the East Asian monsoon area, substantiating the regional climate patterns and monsoon evolution since late-glacial time. Because intensity of the East Asian monsoon is likely responsible for the grain-size change in the peat samples, the grain size components in peat samples may be used for reconstructions of past environmental conditions and of variability in the East Asian monsoon. [ABSTRACT FROM AUTHOR]

Phytoliths as a climate proxy are one of the most important and effective tools for reconstruction of paleoenvironment. In this paper, twelve Gramineae species of the subfamilies Panicoideae, Pooideae and Arundinoideae from the Changbai Mountains were selected, and 3698 phytoliths were counted. We measured six parameters of dumbell, elongate, lanceolate, crenate, saddle and silicified stomata. The seven shape factors of different types of phytoliths were deduced by the six parameters measured above and analyzed by nonparametric testing and discriminant analysis. The nonparametric testing indicated that the average value of the shape factor SF 4 among the three subfamilies was obviously different. Discriminant analysis for the three subfamilies, also revealed that the discriminant accuracy was high (89.81%). Total discriminant accuracy using shape factors of dumbell phytoliths of Panicoideae was 73.12%. Discriminant accuracies using shape factors of elongate, lanceolate and crenate phytoliths of Pooideae were respectively 60.87, 59.21 and 87.07%. The discriminant accuracies using shape factors of saddle phytoliths and silicified stomata of Arundinoideae were 59.06 and 71.77%. At the same time, the shape factors of phytoliths from Setaria viridis and Leymus chinensis were used to test whether the discriminant functions established at the subfamily level were effective or not. Results showed discriminant functions precisely classify them, thus verified discriminant functions were useful. In conclusion, using the seven shape factors of phytoliths not only may improve the accuracy of classifying Gramineae, but also provides basis reference data for better understanding the presence and function of Gramineae plants at archaeological sites. [ABSTRACT FROM AUTHOR]