East-Asian monsoon variability between 15 000 and 2000 cal. yr BP recorded in varved sediments of Lake Sihailongwan (northeastern China, Long Gang volcanic field)

摘要

A palaeohydrological reconstruction on decadal scale for the period 15 000-2000 cal. yr BP based on calculated net accumulation rates for biogenic silica (F-bSiO_2) and additional proxies (sedimentological data, geochemical sediment characteristics and pollen) is derived from varved sediments of Lake Sihailongwan (SHL). In Lake SHL, F-bSiO_2 is positively correlated with the inflow of nutrient-rich groundwater. Since groundwater inflow is mainly fed by seepage of summer monsoon rainfall, F-bSiO_2 documents changes in summer monsoon strength. Summer monsoon rainfall was enhanced in the early Holocene around 9800 and 7800 cal. yr BP. Groundwater inflow during these periods did not reach the high level of the Lateglacial warm period (c. 14 300-12 500 cal. yr BP) when the vicinity of the lake was less densely covered with woody vegetation than in the Holocene. Aeolian influx of silt-sized debris was relatively higher during an overall drier period between 9500 and 8000 cal. yr BP. A mid-Holocene sedimentation interval with distinct century-scale variability in summer monsoon rainfall documents a positive correlation between rainfall and siliciclastic influx that reflects a more efficient removal of mineral aerosols for increased rainfall at an overall high dust concentration over the Asian continent. Summer monsoon rainfall reached minima around 6400, 4900, 3700 and 2200 cal. yr BP. Remarkably, aeolian siliciclastic influx peaked at the beginning and at the end of a dry interval between 4100 and 3600 cal. yr BP. Around 3600 cal. yr BP Lake SHL received substantial aeolian influx of different geochemical provenance.