Problems of the magnetic susceptibility signature as the proxy of the summer monsoon intensity in the Chinese Loess Plateau

The magnetic susceptibility in the Chinese loess is considered to have recorded the history of pedogenesis or land-surface stability, and has thus been used as an acute proxy of the summer monsoon intensity. With regard to pedogenesis, most authors failed to appreciate the complexity of weathering processes. Specifically, not acknowledged are local redox conditions, carbonate concentration and leaching. Pre-depositional pedogenesis may be another factor undermining the legitimacy of using the susceptibility as an acute proxy of the summer monsoon intensity. These factors may not necessarily reflect the degree of pedogenesis although they have definitely affected the susceptibility signature. Some contributors to the susceptibility are demonstrated to be inorganic iron and other organically complexed iron. The organic iron associated with decomposed plant litter is proven to be the most important contributor to the susceptibility in modern loess. But, magnetotactic bacteria are believed to be the major generators of the ultrafine ferromagnetic particles responsible for the susceptibility signature in the Quaternary loess and paleosols. The factors affecting susceptibility signature may well be site- and time-dependent even within the Chinese Loess Plateau. Therefore, a more comprehensive model and a more comprehensive approach are needed to address the relationship between the paleoclimate and the proxy.