Climatic changes documented by stable isotopes of sedimentary carbonate in Lake Sugan, northeastern Tibetan Plateau of China, since 2 kaBP

摘要

Stable isotopes of carbonate in Lake Sugan better recorded the climatic changes. The oxygen isotope indicates the effective moisture in the region, and the carbon isotope indicates the freeze-up duration of the lake and further reveals the air temperature variations in winter half year. The climatic changes in the study area have experienced five stages since 2 kaBP: 0--190 AD, warm-dry climate; 190-580 AD, cold-dry climate; 580-1200 AD, warm-dry climate, corresponding to the Medieval Warm Period; 1200--1880 AD, cold-wet climate, corresponding to the Little Ice Age; 1880 - 1950 AD, cold-dry climate; and from 1950s onwards, climate warming, which is consistent with the observation data. The climatic changes history recorded by stable isotopes of Lake Sugan since 2 kaBP, especially the climatic cooling and warming variations revealed by carbon isotope, not only has better comparability with other records, but also coincides with the temperature variations recorded by historical literatures of China. It can be seen that the climatic changes recorded by stable isotopes since 2 kaBP are of universal significance, and it means that the research of palaoeclimatic changes in the lake still has a great potential. However, further research is needed. The accurate ages of the lake sediments need to be further determined and an attempt is being made to determine the ages of authigenic carbonate in the sediment using the thermal ionization mass spectrometric technique (TIMS) so as to check and correct the reservoir effect of the lake. In addition, the carbonate mineral composition of the lake and the fractionation mechanism of carbon isotope in the atmospheric COa-lake water-carbonate system also need to be further understood.