Holocene vegetation and climate in Northeast China revealed from Jingbo Lake sediment

摘要

Vegetation and climate changes in Northeast China during the Late Quaternary are poorly known. Pollen analyses were undertaken on a 890-cm-long lacustrine sediment core recovered from Jingbo Lake, located in Southeastern Heilongjiang Province, China. Based on ~(14)C dating, the pollen record provides a basis for the reconstruction of vegetation and climatic changes since 9600 cal. BP in NE China. Prior to 6100 cal. BP, broad-leaved deciduous forest of Quercus, Fraxinus, and Betula dominated this area, which indicates that the climate during this period was warm and the Asian summer monsoon was stronger. From 6100 to 5600 cal. BP, the deciduous trees declined and Pinus increased, which suggests a transition of vegetation from broad-leaved deciduous forest to mixed coniferous-deciduous forest. Mixed coniferous-deciduous forest with Pinus, Quercus, and Betula expanded and dominated since 5600 cal. BP, indicating a gradual weakening of the Asian summer monsoon. During 2000-680 cal. BP, trees such as Pinus and Quercus declined and herbs including Artemisia, Labiatae, and Scrophulariaceae increased, indicating an extensive human impact on the vegetation. After 680 cal. BP, the forest regenerated due to changed agricultural activities, although the forest was cleared after the 18th century. The vegetation changes superimposed upon this general trend, especially the abundance of trees demanding warm climate conditions, show eight low temperature events at 9200-9000, 8200, 7000-6900, 6000-5600, 4200-3800, 2200-1800, 800, and 600 cal. BP. These short-lived events can be correlated to the spells of δ~(18)O depletion in the Dongge Cave stalagmite record, which is widely accepted as a summer monsoon record.