共和盆地末次冰消期以来的植被和环境演变

Palaeovegetational and Palaeoenvironmental Changes in Gonghe Basin since Last Deglaciation

在青藏高原共和盆地中的内陆湖泊——达连海获取40.92m长的湖泊岩芯(DLH钻孔),选用植物残体作为测年材料,利用AMS14C测年技术建立可靠的地层年代序列,对岩芯进行孢粉分析,重建该地末次冰消期以来的古植被和古环境。末次冰消期以来达连海周围山地在14.8～12.9Cal ka BP和9.4～3.9Cal ka BP时段曾发育森林,气候较湿润,达连海附近盆地发育的荒漠草原盖度增加或演化为草原;在15.8～14.8CalkaBP、12.9～9.4Cal ka BP和3.9～1.4Cal ka BP时段该地气候比较干旱,依据干旱的程度周围山地森林退化或消失,盆地内发育盖度较低的荒漠草原或草原化荒漠。1.4Cal ka BP以来湿度有所增加,发育草原植被类型。依据植被的演替历史推断该地气候的变化历程是15.8～14.8Cal ka BP干旱,14.8～12.9CalkaBP湿润,12.9～9.4CalkaBP干旱,9.4～3.9Cal ka BP湿润,3.9～1.4Cal ka BP干旱,1.4～0Cal ka BP湿润。达连海的孢粉记录与附近青海湖的孢粉结果对比,发现两地植被发育基本一致。末次冰消期Blling-Allerd时期,山地森林发育;新仙女木事件发生时森林萎缩;全新世中期两地针叶林发育达到鼎盛,之后逐渐减少至消失。早全新世达连海森林扩张的时间滞后于青海湖,主要与两地森林树种的不同和植被演替的时间差异有关。该区森林发育的全盛时期在中全新世,这与石笋记录到的亚洲季风强盛时期在早全新世不相一致,可能与植被复杂的响应机制有关。

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 14 C 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 B lling-Aller d 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.