Palaeovegetational and Palaeoenvironmental Changes in Gonghe Basin since Last Deglaciation
Received date: 2010-01-20
Revised date: 2010-08-05
Online published: 2010-11-20
Supported by
111 Program of Ministry of Science and Technology of China, No.B06026; National Natural Science Foundation of China, No.40721061; No.90502008; No.40871093
This paper presents a high-resolution pollen record from a 40.92-m-long sediment core taken from Dalianhai Lake, a terminal lake situated in the Gonghe Basin, northeast Tibetan Plateau, in order to reconstruct the vegetation and climate history in the period from the last deglaciation through the Holocene. The 158000-yr chronology of the sediment core was controlled by ten AMS 14C dates on plant remains. The result of pollen analysis shows that six pollen zones can be partitioned in the whole pollen assemblages, and each zone is mainly characterized by the growth and decline of tree or herb pollen percentage. During the periods of 14.8-12.9 Cal ka BP and 9.4-3.9 Cal ka BP, the arboreal pollen increased, indicating that the subalpine forest developed in the surrounding mountains, and the basin was characterized by the increased coverage of desert steppe or typical steppe, reflecting a moister climate. During the periods of 15.8-14.8 Cal ka BP, 12.9-9.4 Cal ka BP and 3.9-1.4 Cal ka BP, the forest shrank or disappeared due to different degrees of aridity, and the desert steppe degraded to a more arid steppe desert in the basin, showing a dry climate. After 1.4 Cal ka BP, vegetation type around the Dalianhai Lake was mainly dominated by steppe suggested by the increased Artemisia. Our results suggest the climate in this region was dry from 15.8 to 14.8 Cal ka BP, humid from 14.8 to 12.9 Cal ka BP and dry from 12.9 to 9.4 Cal ka BP, and then the climate was humid during 9.4-3.9 Cal ka BP, followed by dry conditions during 3.9-1.4 Cal ka BP and humid conditions in the last 1.4 Cal ka BP. The change of pollen percentage and the evolution of palaeovegetation in the Dalianhai Lake since the Last Deglaciation were similar to those in the Qinghai Lake. The forest expanded in the mountains around the Dalianhai Lake during the Bølling-Allerød period, and it shrank during Young Dryas and early Holocene. Then it developed and reached its maximum in mid-Holocene, after that it began to shrink till disappearance. However, the timing of forest expansion in the Holocene lagged behind that of the Qinghai Lake, and this spatial heterogeneity was probably caused by different forest species composition between these two places. The maximum of forest development was asynchronous with the period of stronger summer monsoon in the early Holocene indicated by stalagmite records, which might be related to the complexity of vegetation in response to long-term climatic change.
Key words： Dalianhai Lake; Last Deglaciation; Holocene; pollen record; palaeovegetation
CHENG Bo, CHEN Fahu, ZHANG Jiawu . Palaeovegetational and Palaeoenvironmental Changes in Gonghe Basin since Last Deglaciation[J]. Acta Geographica Sinica, 2010 , 65(11) : 1336 -1344 . DOI: 10.11821/xb201011003
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