Deposit Record Of Climatic And Environmental Changes Of Taihu Lake Since 10,000a

As the information database of climatic and environmental changes, Lakesediment provides high-resolution climatic change information which at the scale of century or even decade. For the special location of ocean-land transitional area in Yangtze Delta, Taihu Lake can reflect environmental change sensitively. The deposit records of Taihu Lake help us discover the evolution of paleoclimate and paleoenvironment of this area and also have a practical signification on the forecast of environment evolvement in the future.This work was carried out on the basis of former researchers. The pole (97C) is drilled on the buried fluvial valley, south bank of Taihu Lake. Through the systematical measure of mineral magnetism, grain-size, organics and content of Fe ,we get about 20,000 pieces of data. By the statistical analysis of these data, we found out the deposit characteristic and the law of climatic change during the Holocene period, as well as strong proofs of confirming the occurrence of short-term abrupt climatic change in Taihu area.The best feature of this paper is the clear description of paleoenvironment evolution and climate change during 10,000 years in Taihu Lake with sufficient data and comparison analysis. We can divide the evolvement history in Holocene into seven stages.The first stage is from the beginning of Holocene about 9,400aBP to 8,800aBP. During this period,the temperature rose rapidly.As a result,it became warm and humid. At the period, seawater began to intrude into Taihu area through river channel from Hangzhou Bay, which led to the expansion of water area and the form of gulf and lagoon, Taihu Lake formed primarily.After that, with the descending of temperature, the transgression stagnated and the environment started to deteriorate. Such condition last about 500 years. From 8,300 aBP to 7,800 aBP, the climate turned warm and humid again, but the environment was not as good as the first period.In the next stage, from 7,800 aBP to 5,800 aBP, the temperature dropped significantly and seawater retreated from the Taihu area. As a result, the whole Taihu area was in a semi-saltwater condition. From 5,800 aBP -3,500 aBP, the water level ofTaihu Lake was the lowest. Taihu Lake even became drying up, which led to the interruption of lake sediment. At about 5,000aBP, with channels being filled up, Taihu area began to enclose, which made the control of precipitation to the lake level stonger.After 3,500 aBP, temperature began ascending slowly, however, seawater had not affect Taihu Lake. And during this period,Taihu Lake gradually turned from a semi-saltwater lake to a freshwater lake. Contemporaneity Taihu Lake was formed in this period.From l,100aBP, the climate became stable, and the whole environment was comparatively pleasant and comfortable. Especially after 600aBP, the bank was silted into land and the shape of contemporaneity Taihu Lake was finalized.Whether or not the transgression occurring in Taihu Lake in the Holocene is the focus of contention in academe. This research has confirmed the exist of transgression and even step with the rising of temperature. At forepart of Holocene, transgression started to invade Taihu Lake through channels which connected with Qiantang River. Between 8,800-8,300aBP,temperature fell abruptly. As a result, the range of transgression dwindled rapidly. After that, seawater entered into interior of Taihu Lake again. About 7,800aBP, temperature and transgression got to the peak, Taihu Lake began to under the conditon of lagoon. Subsequent temperature dropped down persistently and the rang of transgression decreased gradually. Sediment inbreaks in Taihu Lake about 4,500aBP, Taihu Lake entirely turned into freshwater one with the end of Holocene transgression.This research work gives a relatively integrated explanation of the form process and evolvement laws of Taihu Lake. The conclusions are in accorded with the results of other research. And moreover, it adds fresh content to the environmental evolvement research and territorial response of global...