Lacustrine mineral magnetic record of postglacial environmental changes from Dahu Swamp, southern China

Systematic studies of lacustrine magnetic sediments can provide useful information to decipher the catchment processes of specific environmental changes. To explore the magnetic mineral-paleoenvironment connections, we have conducted a mineral-magnetic investigation on a lacustrine sediment core recovered from a closed-basin lake in the eastern Nanling Mountains of southern China. Our results show that the magnetic minerals in the sediments were mainly catchment-derived, and the post-depositional effects, or biogenic and authigenic growth of secondary ferrimagnetic minerals, were probably insignificant or absent. The catchment soil erosion, pedogenic development, and vegetation coverage are interpreted as the main forcing in controlling the variations in magnetic parameters. During the last deglaciation period (~16,500-11,100 yr BP), the relatively high and significant variations in magnetic parameters of sediments could have corresponded to the rapid climate fluctuations after the cool and dry Last Glacial Maximum. In the Holocene (11,100 yr BP to present), the low magnetic concentrations and increases in finer magnetic particles likely resulted from the stabilization of the watershed and more intense pedogenic processes under the warm and wet climate. Because changes in surface-runoff, vegetation coverage, and soil pedogenic processes are closely related to Asian summer monsoon (ASM) intensity, the sedimentary magnetism of Dahu Swamp can provide another valuable source of information to investigate the development of the ASM in southern China.