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

Abstract

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°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. AMS14C dating, analyses of pollen, particle size, TOC, TN and δ13Norg were conducted for the sediment sequence while pollen analysis was also made for the surface-sediment sample. Variations in χlf, χARM, IRM300mT and SIRM of the sediment sequence were attributed to changes in erosion intensity, while those in IRM20mT/ARM and particularly χARM/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 ~5520 years. The weighted χARM/SIRM values of the sediment sequence in comparison with χARM/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 ~5520 years. The reconstructed environmental changes are generally in agreement with the centennial-scale variability of EASM indicated by a stalagmite 18O record and with that of EAWM indicated by an 18O record of planktonic foraminiferal.