Red palaeosols development in response to the enhanced east asia summer monsoon since the mid-pleistocene in South China: Evidence derived from magnetic properties and molecular fossil records

Abstract

Although Pleistocene red paleosols are widely distributed in South China, paleoenvironmental interpretation has proved difficult because of intense weathering. Here we combine data from molecular fossil and magnetic properties to reconstruct a record of changes in pedogenic intensity for red paleosols in Southeast China. Depth distribution pattern of magnetic properties indicates that lower (higher) χ but higher (lower) values of HIRM (hard isothermal remanent magnetization) and SIRM (saturation isothermal remanent magnetization)/χ has tight relationship with the intensity of pedogenesis, especially the occurrence of well-developed net-like veins, which is absolutely responsible for the presence of anti-ferromagnetic minerals at the cost of fine-grained SP (superparamagnetic)/SD (single domain) ferrimagnetic minerals. The carbon distribution pattern of n-alkanes, n-alkanols, and n-alkanoic acids reflects the predominant contributions of microorganisms to the organic matter during pedogenesis, which provide direct evidence for strong microbial activities in response to the extremely hot-humid condition while white coarse net-like veins occurrence. Our results demonstrate that the presence of the enhanced East Asia summer monsoon has played a key role in the oxide-dominated weathering regime, and pedogenesis, and microbial activities. Changes in molecular ratios and magnetic properties are used to show that red paleosols have undergone three stages of soil formation in striking response to the evolution of the East Asia summer monsoon: (1) the most effective since the Middle Pleistocene; (2) moderately effective since 270 ka or so; (3) least effective since the last glacial. Our research provides important evidence to understand how red paleosols espond to global change since the Middle Pleistocene.