Study On Environmental Change Of Dalianhai Lake In Gonghe Basin Since The Mid-Holocene

Gonghe Basin located in the transition zone of the westerly,Asian southeastern and southwestern monsoons, and between arid and semi-arid places, Where desertification is very serious. Being Special location,The fragile ecological environment attributed to more sensitive to global climatic changes.Therefore,studying on the paleo-climate and paleo-environment of Gonghe Basin not only help to clarify the environmental drying history of past in Gonghe Basin But also for the accurate assessment of climate change and human activities on desertification in China that may affect further to combat desertification, dust storms reduce hazards, the development of adaptation and mitigation of global climate change to provide a scientific basis.This article choose two shallow profiles from Dalianhai Lake for studying , respectively , Dalianhai profile I is 2.52m , Dalianhai profile II is 2.60m . Based on AMS¹⁴C dating and chronological study, the bottom ages of Dalianhai profile I is about 5600 cal a B. P. Combine with grain-size ,magnetic susceptibility,CaCO₃ content and color of Lacustrine sediments as environmental proxies. the result showing after analysis that Fine sediments reflecting on weak hydrodynamic,while the coare one indicate strong;The magnetic susceptibility is Better Corresponds to the medium grain-size of Lacustrine sediments, when warm ahd wet,. The value of High magnetic susceptibility is high ,contray to Cool and dry environment ; The CaCO₃ content is better sensitive to the regional climate change;The L^* of color,is less Corresponds to CaCO₃ content, but close relationship with organic matter, a^*and b^* of color, Consistent with c environment changes, both are reflecting on climatic changes of warm-wet and cold-dry.The climate and environment changes of Dalianhai Lake In Gonghe Basin since the Mid-Holocene can be divided into the following four stages:â… 5600-5100cal a B.P., the mildest climate conditions with a warm and humid, Richer in organic matter;â…¡5100-2500cal a B.P., lower temperature, a cool but arid stage,the organic matter is rich.â…¢2500-800cal a B.P., warmer than the previous stage ,the precipitation is increase a little, the organic matter is less.â…£800-0cal a B.P., a cold and dry arid stage.The results also indicate of all environmental proxies that 2500 cal a B.P. is the boundary of the Middle and the Late Holocene in Dalianhai lake, there is a colder and drier climatic event about 3700-4100 cal a B.P. in The Mid-Holocene , And the several times obvious cold events in the Late Holocene , Among them the last one corresponds to the Little Ice Age(LIA). About 800- 1200 a A.D The Medieval Warm Period was recorded in Dalianhai Lacustrine sediments which provide the evidence of existence in the western region of China.By analysis modern climate changes of Gonghe Basin,the temperature is Gradual increased began in 60's During the 20th century,.The seasonal changes in temperature and precipitation trends are inconsistent, The southwest monsoon probabily weakening gradually, Now, the warmer and drier environment in Gonghe Basin with low precipitation corresponds to the atmospheric circulation, The solar activity may be the main Driving factors at the short-term temperature changes...