A new approach for reconstruction of the Holocene climate in the Mongolian Altai: The high-resolution δ~(13)C records of TOC and pollen complexes in Hoton-Nur Lake sediments

摘要

δ~(13)C of total organic carbon (TOC) and pollen grain, TOC, C/N ratio, and δ~(15)N of total organic nitrogen (TON) in a 2.57-m long core from Hoton-Nur Lake in Mongolian Altai have been measured for reconstruction of the Holocene climates. The δ~(13)C values of TOC and pollen carbon have similar average values but different ranges. Pollen δ~(13)C has negative correlation with %AP (arboreal taxa pollen) and positive correlation with %NAP (herbaceous pollen and spores) that are connected with conditions of humidity in the area. Taiga-biome has lighter δ~(13)C than steppe-biome. Hence, pollen δ~(13)C composition is more sensitive to changes of humidity in the analogous spectra than palynotaxonomical structure and δ~(13)C of TOC. Based on our results, the Holocene climates in Mongolian Altai are: (1) dry conditions prior to 11.5 kyr BP; (2) wet conditions between 11.5 and 6.0 kyr BP; (3) a relatively dry/cool episode during 6-4 kyr BP; (4) stable cool and semiarid conditions with moderately effective moisture during the past 4000 years. Two abrupt climatic changes occurred at ～7.45 kyr BP and ～11.5 kyr BP might be related to glacial activities. The Holocene climatic trend in Mongolian Altai which is controlled by the Westerlies is similar to the trend of monsoonal climate shown by the Chinese speleothem records as well as the lake/sand dune evidence in the deserts of NW China. The contact of the two climatic systems and shift of the monsoonal boundary during the past need to be further studied.