Variations in erosion intensity and soil maturity as revealed by mineral magnetism of sediments from an alpine lake in monsoon-dominated central east China and their implications for environmental changes over the past 5500 years

Measurements of mineral magnetism were performed on a sediment sequence recovered from Foye Chi, an alpine lake (3410 m a.s.l.) on the southern slope of the Taibai Mountain (3767 m a.s.l.), the highest mountain in east mainland China (east of 105 degrees E) influenced by East Asian summer monsoon (EASM) and East Asian winter monsoon (EAWM). Mineral magnetism were also measured for surface sediments from the lake, rock debris, surface soils and a soil profile from its catchment and surface soils at the elevations of 600-3767 m a.s.l. of the southern slope of the Mountain. AMS(14)C dating, analyses of pollen, particle size, TOC, TN and delta N-13(org) were conducted for the sediment sequence while pollen analysis was also made for the surface-sediment sample. Variations in chi(lf), chi(ARM), IRM300mT and SIRM of the sediment sequence were attributed to changes in erosion intensity, while those in IRM20mT/ARM and particularly chi(ARM)/SIRM to changes in soil maturity. With aid of the other data, the magnetic data of the sediment sequence revealed environmental changes over the past similar to 5520 years. The weighted chi(ARM)/SIRM values of the sediment sequence in comparison with chi(ARM)/SIRM of the surface soils distributed on different elevations allowed estimating the altitudes where the present environments are similar to the past ones for different periods of the past similar to 5520 years. The reconstructed environmental changes are generally in agreement with the centennial-scale variability of EASM indicated by a stalagmite O-18 record and with that of EAWM indicated by an O-18 record of planktonic foraminiferal.