Palaeovegetation Changes In Dalianhai Lake From Last Deglacial To Early Holocene

To understand the regularity and mechanism of past global change is the precondition for exploring future environment change.Gonghe Basin is located on the northeast margin of Tibetan Plateau where is the limit of modern Asian monsoon and the junction of arid and semiarid regions of China,and is very sensitive to the climate changes.Thus,it's an ideal area for the study of regional climate history and its response to global change.A 199.71m long core DLH12A was obtained from dry lake bed of the terminal lake of the Shazhuyu River in the Gonghe Basin.The reliable chronology of core DLH12A was established by AMS 14C dating from 11 plant remains and 14 bulk organic matter samples.Then the chronology of the top 51.63m of the core was built from last glacial.43,21-23.2m of the core was selected and divided into 101 pollen samples,which sliced every 20cm.All samples were analyzed to reconstruct the palaeovegetation and palaeoenvironment of Gonghe Basin from last deglacial to early Holocene.The result shows that there are 3 pollen assemblage zones can be partitioned in the whole diagram and each zone is mainly characterized with the growth and decline of arbor,herbaceous and shrub pollen percentage.On the basis of the characteristics of each zone,the evolutionary history of palaeovegetation and palaeoenvironment of Gonghe Basin during last deglacial and early Holocene was reconstructed.Zone I 14.7-13.4Cal ka BP(43.21-35.61m),the herbaceous and shrub pollen dominant pollen assemblage mainly including Chenopodiaceae,Artemisia and Poaceae,the arbor pollen are dominated by Picea.During this period,the coniferous Picea forest was grown on the mountains around the Dalianhai Lake.The basin was covered with desert mainly including Chenopodiaceae,Artemisia,Poaceae and Elaeagna.During this period,the climate was cool and wet in general,roughly equivalent to the B(?)lling-Aller(?)d period.Zone ?13.4-11.6Cal ka BP(35.61-24.6),the pollen concentration increase and fluctuate within the zone.While the percentage of arbor pollen decrease.The herbaceous and shrub pollen become significant predominance mainly including Artemisia,Chenopodiaceae,Poaceae and Elaeagna.After 13.4Cal ka BP,the forest in sounding mountains shrank.There were desert steppe and desert within the basin.The regional environment became colder than before,and cold and dry in general.Zone ? 11.6-10.7Cal ka BP(24.6-23.2m),the percentage of herbaceous pollen was relatively high,marked by an increase of Poaceae and a decrease of Artemisia pollen,as well the A/C.Arbor pollen displays its highest value,with the increase of Picea,Pinus and Betula pollen,which indicate that coniferous forest and mixed coniferous broad leaved forest expanded in the surrounding mountains.The environment was cool and wet.Moisture loving herb Poaceae grown,Poaceae and Chenopodiaceae as the main herb,the basin was covered with desert steppe and dry steppe.The Holocene began at 11.6Cal ka BP.The pollen based palaeoclimate history during last deglacial and early Holocene in Dalianhai Lake consistent well with the climate records in Tibetan Plateau and northern part of China as well as northern hemisphere ice core and high-resolution speleothem stalagmite,which indicated that the vegetation in Gonghe Basin can sensitively reflect the global climate changes.The pollen records of Dalianhai Lake tracked well with the northern hemisphere insolation and the Asian monsoon.So the climate change during last deglacial to early Holocene in Gonghe Basin is considered to be driven by the insolation-driven Asian monsoon.