Study On Late Holocene Environmental Evolution Recorded By Dalianhai Lake

Tibet plateau, as a sensitive area of the global climate, is significant for the study of changing paleoclimate. Dalianhai lake belonging to Gonghe basin which is located in the northeast of Tibet plateau is situated in the intersection of monsoons. The lake sediments have advantage on recording the information of the global environment evolution in continuity, sensibility and high resolution. This place is a good area to study for knowing and predicting the future global climate change. This paper choose 4 meters profile sediments in the center of Dalianhai lake for study. The age of the profile’s bottom is about 3800 a B.P. measured by the AMS 14 C method. The environment proxies of grain-size characteristics and pollen indicates that since 3800 a B.P., the power of water experienced four stages: from weak, strong, weak to strong. The level of the lake surface experienced four stages :high, wide; low, narrow; high,wide and dry up. The pollen data show that grassland and desert grassland appears in turn. About 3800~2900a B.P, the climate was cool and humid, the landscape was grassland, there was a few trees growing and during this time there was a process of arid; About 2900~1500 a B.P., the fluctuant climate and wind-sand activity were obvious. In generally, the climate is cold and arid. The landscape was desert grassland. About 1500~400a B.P., the climate became better, the temperature was higher and the precipitation was increasing. Trees were a few and the landscape is grassland. There was also wind-sand activity during this time. About 400 ~0 a B.P., the climate became drier. The lake surface was shallow and there were lots of wind-sand activities. The landscape was desert grassland.At the age of 3.0ka B.P.、2.7ka B.P.,1.6ka B.P. and 0.8ka B.P., the silt and sand increased obviously. At the same time the pollen percent decreased. It is possible to have cold and dry event in these times.The grain-size Dalianhai Lake sediments in Gonghe Basin has a relationship with the vegetation form. Increasing of coarse grain-size corresponds to the increasing of herb. Another is the increasing of fine corresponds to the increasing of trees.During the 2900 a B.P~1500 a B.P, the grain-size of sediments and the vegetation form change vary obviously. It indicates that the climate fluctuation not only shows in large scale but also in small scale.