Precipitation thresholds for iron oxides dissolution and the enhanced Eurasian aridity across the Mid-Pleistocene Transition: Evidence from loess deposits in subtropical China

The extensive loess deposits in southern China (‘Xiashu’ loess) are a valuable paleoclimatic archive in the subtropical monsoon region. We carried out a combined study of iron oxide mineralogy, pedostratigraphy, and magnetostratigraphy of three new loess sections in subtropical China. A detailed comparison of the iron oxides content of the Xiashu loess and the loess of the Chinese Loess Plateau reveals that the iron oxides of paleosol units in the Xiashu loess are partially dissolved. The estimated minimum mean annual precipitation levels required for the dissolution of maghemite, hematite, and goethite and the 95% confidence bounds are ~793 mm (679–907 mm), 728 mm (683–772 mm), and 941 mm (834–1048 mm) respectively. A regional comparison of the stratigraphy and magnetic susceptibility of the loess deposits in subtropical China reveals a general lack of correlation. The relatively low continuity of dust deposition combined with iron oxide dissolution is the main cause of the spatial inconsistency of the stratigraphy and magnetic properties. Magnetostratigraphic analysis reveals a basal age of 1.1 Ma for the loess deposits in subtropical China, which demonstrates that the intensification of aridification of the subtropical regions and a strengthened East Asian winter monsoon began by at least 1.1 Ma. Thus, the loess deposits in subtropical China provide terrestrial evidence from mid−low latitudes for global cooling and enhanced aridity across the Mid-Pleistocene Transition.