Due to the connection between geological records and instrument-recorded materials, the environmental changes during the past 2000 years has been already an important time window in the global changes, in which short span and high resolution records are especially significant because they are the base for comparison of environmental changes. Among the multiple methods for detecting past global changes, lake deposits and their environmental significance are still not substitutable. In particular, as there are rigorous natural condition, poor population and wide areas, shortage of climatic changes derived from historical records and tree-rings as well as less disturbance of human beings on the Tibetan Plateau, lakes and their environmental significance are apparently important.

South Hongshan Lake is situated at 35°10'N 80°04'E which is in the Tianshuihai area of west Kunlun Mountains, northwestern Tibetan Plateau. With the average elevation of 4800-5100 m asl, it is very cold-dry in this area. The annual mean precipitation is 23.8 mm, the annual mean temperature is -7.7°C while that in July is only 6.0°C. The lake is a 3.35 km² close lake and mainly supplied by snow and ice thawy water. It is intensively retreated in recent years and the average salinity reaches 9.4g/l. With the more than 5 meters of average water depth and rich sullage in the lake bottom, this lake provided better materials for the study of its modern sedimentary environment and reconstruction of past environmental changes.

Past environmental records are mainly inferred by the study of core SHC-2. It is a 1.07 m long lake core which was taken on the aquatic platform by piston sampler in 1998. The sample site is 5 m deep of the water depth and 100 m far to the lake bank. The average sedimentary rate is 0.72 mm/yr determined by radioactive isotope ²¹⁰PB, and the attenuation of ¹³⁷Cs also tested the veracity of this data. Thus, a 150-yr continuous sedimentary sequence was obtained. For capturing the effective environmental proxy indexes to detect past environmental changes, grain-size, total organic carbon (TOC), total nitrogen (TN) CaCO₃ and part of trace elements were analyzed.

TOC represent the lake biomass in some degree, and reflect the cold and warm condition of the lake. Grain-size distribution is the result of water dynamical changes, it indicates the water depth and thus reflects the lake water quantity. Due to the dry condition of the depositing of CaCO₃, its contents may reflect the dry and humid condition in the lake drainage basin. In trace elements, Fe³⁺ is transformed from Fe² during oxidation circumstance which is generally caused by the increasing of water content and temperature under the natural condition. The increasing of its contents may indicate the enhancement of hot and wet degree. TN generally reflect the nutritional degree of the lake.

The contents variation of TOC, grain-size, CaCO₃ and Fe³⁺ showed that the lake experienced alternate changes of water dynamical and cold-warm conditions during the past 150 years. Though the contents of TOC is not high (less than 3%) under the rigorous natural condition, the tendency of its variation obviously appeared the low value in the later half of 19th century, the end of 1920s, 1950s and 1980s, the high values are in the beginning of 20th century, the end of 1930s and the beginning of 1970s. They represent the corresponding cold period and warm period respectively. Corresponded to the high values of the TOC content, the mean grain-size diameters were significantly fine and indicated the increasing of lake water quantity except those in the end of 1930s. The content variation of Fe³⁺ was well corresponded to that of TOC and represented the changes of water-heat condition during the sedimentary period. However, the vibration amplitude is not very clear due to the complexity of lake deposits. With the over 50% in the total content of deposits, the content of CaCO₃ appeared clear changes in the former half of 20th century. It was increased corresponded to the low value of TOC in 1920s while decreased corresponded to the high value in the end of 1930s. However, these changes were not clear in the other time section. The content of TN was very low (less than 0.25%) and had not notable fluctuation in the total lake core. This may indicate the poor nutrition of the lake and reflect the rigorous ecological environment in this area.

The environmental records in SHC-2 core is well coincided with that of Guliya ice records in the same area. There is better corresponding relation between TOC in SHC-2 core and Q¹⁸O in Guliya ice core before 1960s. The similar variations also appeared in the grain-size distribution and Fe³ profiles, they all showed the cold period in the later half of 19th century, the end of 1920s and 1950s, and the warm period in the beginning of 19th century and the end of 1930s. In spite of the same variation tendency between them, the changing amplitude is very different after 1960s. It may be caused by the increasing of human activities in this area. The environmental sequence of SHC-2 core also showed the relativity to the snow accumulation of Guliya glacier, but the later lagged about 20 years behind the former in the time scale. Although the changes of snow accumulation lagged 50 years behind that of temperature in Guliya by obtained results, it is not such in the sequence of this lake. Because it is mainly supplied by ice and snow thawy water, the largest quantities of water and the most humid period of the lake rested on the thawing rate during the increasing period of temperature, and is not synchronal to the peak of snow accumulation. This may be the cause of the different sluggish time of the most humid period between that from the ice core and that from the lake core. However, temperature is the main dominant factor and have well synchronization to those reflected from the ice core and the lake core.