| Abstract: | A 107cm piston-core (SHC-2) was drilled at the site with water depth of 5m in South Hongshan Lake, northwest Tibet in 1998. Based upon the 0.72cm/a of modern sedimentary rate that was tested by 210Pb method and also calibrated by 137Cs method as well as the 1cm interval sample cutting level, a lake sedimentary record of 150-yr old and with a resolution of 1.4 yrs was obtained. Ratio of geochemistry contents (TOC, TN, CaCO3) and concentrations of trace elements such as B, Sr, Ba, Ca, Mg, K, Na, Al, Ti, Cu, Zn, Fe, Mn, Ni, Cr, V, Pb, etc were analyzed. The values of TOC, TN, C/N, CaCO3, Sr/Ba and Fe/Mn had clear environmental significance and well reflected the environmental changes. Geochemical multi-proxies of lacustrine sediments from SHC-2 core showed that the environmental changes in this area during the past 150 years could be reconstructed as follows: Stage 1 (1850s-1880s) was a cold period; Stage 2 (1880s-1920s) was a warm period. But the variation of lake water volume was stable in the two periods. Stage 3 (1920s-1950s) was a fluctuant and transitional period in temperature, but there were a short cold period in the 1920s and a warm period in the 1930s. Stage 4 (1950s-) showed a warming tendency, though there existed a cold period from the mid 1970s to the end of the 1980s. In the view of general trend in the past 150 years, South Hongshan Lake was shrinking gradually. It showed that, from the comparison with the Guliya ice core and meteorological records of adjacent weather stations, there is difference in the variations of temperature and precipitation among different regions and altitudes in Tibetan Plateau. It is necessary to search multi-scale and high-resolution records for environmental reconstruction and comparison. |
