A high-resolution Holocene record of the East Asian summer monsoon variability in sediments from Mountain Ganhai Lake, North China

A high-resolution environmental magnetic records from a sediment profile in Mountain Ganhai Lake, has provided new insights into modulation of the East Asian summer monsoon (EASM) on climatic changes in North China from the final period of last deglacial stage to Holocene. Large pseudo-single-domain (PSD) to multi domain (MD) detrital magnetite grains are identified in the lake samples. The upwards decreasing magnetic susceptibility (chi) and anhysteretic remanent magnetic susceptibility (chi(ARM)) are consistent with the dominant vegetation changes: grassland (similar to 13.0-10.5 ka) under dry and cold conditions, shrub-forest-grassland (similar to 10.5-5.8 ka) in a warm and humid climate, and forest where the Pinus trees increase rapidly to be the dominant taxa, indicating the climate changes from warm and humid to cooler but drier between similar to 5.8 ka and similar to 4.0 ka. The lower S-100mT and S-300mT ratios coincide with the higher degree of soil stability and a stable lake stage at similar to 11.8-6.5 ka. Changes in magnetic anisotropy are also linked to environmental and climatic changes, with T parameters showing higher values during warm/interglacial periods. The anisotropy patterns indicate three different stages of the lake evolution: (1) an early stage of the lake, accompanied by a disturbed high-energy flow, a coarse average mineral particle diameter (MPD) distribution (> 16.28 mu m) and scattered sub vertical minimum direction (K-3 at similar to 13M-11.8 ka; (2) a fairly stable lake environment between similar to 11.8 ka and 6.5 ka, indicated by a low-energy flow, finer MPD (similar to 9.69 mu m) and subvertical K-3 axes; (3) an unstable, high-energy flow and coarse MPD (similar to 20.03 mu m) with tilted K-3 axes, thus indicating a transition from lake-center to lakeside (similar to 6.5-4.0 ka). These multi-proxy records reveal a weak EASM activity in the final period of the last deglaciation (similar to 13.0-11.8 ka), a high EASM intensity in the early-mid Holocene (similar to 11.8-4.8 ka), an EASM maxima in the mid-Holocene (similar to 8.0-5.8 ka), which then generally weakens at similar to 4.3-4.2 ka. Overall, this study suggests the anisotropy and climatic changes in the alpine lake are significantly affected by the insolation-driven EASM.