Characterizing magnetic mineral assemblages of surface sediments from major Asian dust sources and implications for the Chinese loess magnetism

Abstract

Eolian dust plays an important role in the Earth's climate system. Environmental magnetism has been widely used to trace dust variations at different spatial and temporal scales. However, the magnetic properties of sediments from key dust sources have not been well determined. In this study, surface samples from potential dust sources in inner Eastern Asia were systematically investigated. Our results indicate that ferrimagnetic and antiferromagnetic minerals are both present in surface sediments and that they have broad grain size distributions. Ferrimagnetic components are dominated by partially oxidized coarse-grained (pseudo-single domain and multi-domain) lithogenic magnetite particles with minor contributions from pedogenic fine-grained (single domain and superparamagnetic) particles. Antiferromagnetic hematite can be classified into three groups in terms of diffuse reflectance spectroscopy (DRS) band positions (P 560 nm, P 545 nm, and P 535 nm, where numbers indicate the DRS band wavelength for hematite). The first group (P 560 nm) is the coarse-grained hematite of lithogenic origin and is mostly confined to western China. The P 535 nm group is of pedogenic origin. The P 545 nm group is an intermediate phase that is present both in surface samples from the source regions and in loess. Therefore, the P 545 nm and P 535nm groups are related to eolian inputs to the Chinese Loess Plateau and pedogenic processes, respectively. In addition, significant differences exist between the magnetic properties of eolian material from sources and depositional regions due to gravitational sorting. These insights provide strong constraints on interpretation of dust signals recorded by the Chinese loess and marine sediments from the North Pacific Ocean.