Environmental magnetic record of a ~ 3000-years subalpine peat core from the western Nanling Mountains, South China

Abstract

A 95-cm subalpine peat core from the Daping Swamp, located in the transition zone between the middle and southern subtropical regions of China, provides an environmental mineral magnetism record over the past ~ 3000 years. Magnetic concentration-dependent parameters [i.e. magnetic susceptibility (χlf), anhysteretic susceptibility (χARM), and saturation isothermal remanent magnetization (SIRM)] and grain size-dependent parameters [i.e. percentage frequency-dependent susceptibility (χfd%), SIRM/χlf, and χARM/χlf] of core and catchment sediments were measured to characterize provenance and catchment processes. Multi-magnetic parameters revealed that the primary magnetic minerals in the peat samples were mainly detrital magnetic minerals, which originated from catchment surface soil erosion. Changes in vegetation coverage as well as pedogenesis induced by rainfall variation play an important role in controlling the input of magnetic materials. Therefore, we infer that variations of magnetic features in the core bear potential to elucidate the history of environmental changes in the past ~ 3000 years, which are closely related to Asian summer monsoon evolution. Multiple parameters revealed that in three periods (i.e. 2700–2500, 1600–1000, and 500–300 cal year BP), decreased pedogenesis intensity and increased erosion induced by decline in vegetation coverage under dry conditions led to increased input of magnetic minerals, especially the coarser minerals in peat samples. However, in the two periods (i.e. 2500–1600, and 1000–500 cal year BP), multi-magnetic proxies indicate increased pedogenesis and decreased input of magnetic minerals dominated by fine-grained magnetic minerals caused by increased vegetation coverage under relatively wet and warm conditions. These climatic periods are of broad regional consistence across the world. The general trend of the late Holocene climate revealed by magnetic parameters confirms the sensitivity of environmental magnetism in this peat succession from the subalpine western Nanling Mountains to the climatic/environmental variability in the Asian summer monsoon region.