In order to study the variability of dry versus humid conditions resulting from the East Asian monsoon (EAM) we analyzed hematite and goethite from two high‐resolution Chinese loess sections by diffuse reflectance spectroscopy. The hematite and goethite concentrations are higher in interglacial paleosols than in glacial loess sediments, whereas the hematite/goethite (Hm/Gt) ratios are lower in paleosols than in loess. Such changes are consistent with higher precipitation and temperature and increased pedogenesis during interglaciation and lower precipitation and temperature and decreased pedogenesis during glaciation. The Hm/Gt ratio can be employed as a tool to assess short‐term variations in humidity and aridity of the EAM. The Hm/Gt ratios of the last glacial loess displays millennial‐scale abrupt climate oscillations, revealing a pattern of significantly reduced and enhanced summer monsoon moisture. Our results indicate that the EAM responded to tropical Pacific climate by millennial‐scale changes in precipitation during the last glaciation.

It is well known that carbonates inhibit heavy metals transferring from soil to plants, yet the mechanism is poorly understood. Based on the Yangtze River delta area, we investigated bioaccumulation of Ni and Cd in winter wheat as affected by the presence of carbonates in soil. This study aimed to determine the mechanism through which soil carbonates restrict transport and plant uptake of heavy metals in the wheat cropping system. The results indicate that soil carbonates critically influenced heavy metal transfer from soil to plants and presented a tipping point. Wheat grains harvested from carbonates-depleted (due to severe leaching) soils showed Ni and Cd concentrations 2–3 times higher than those of the wheat grains from carbonates-containing soils. Correspondingly, the incidence of Ni or Cd contamination in the wheat grain samples increased by about three times. With the carbonate concentration >1% in soil, uptake and bioaccumulation of Ni and Cd by winter wheat was independent with the soil pH and carbonate content. The findings suggest that soil carbonates play a critical role in heavy metal transfer from soil to plants, implying that monitoring soil carbonate may be necessary in addition to soil pH for the evaluating soil quality and food safety.

The possibility of using dolomite as a source tracer for Asian dust was assessed. Samples of potential dust sources were systematically collected from the arid‐semiarid areas in north China. Dolomite, of detrital origin, was detected only in samples taken from the regions on the north margin of Tibetan Plateau (NMTP). Thus the NMTP‐originated dust can be detected by the presence of detrital dolomite, and applications are performed for the modern dust in Beijing and the ancient dust deposits of loess in north China. Contribution of the NMTP‐originated particles to the spring dust in Beijing and the loess in Chinese Loess Plateau and eastern Tibetan Plateau are suggested. However, dolomite cannot be detected in the studied dust‐storm dust and the loess in northeast China, indicating their sources other than the NMTP regions.

Dolomite of detrital origin in carbonate‐rich soil can help indicate the intensity of carbonate dissolution and leaching processes. Using Fourier transform infrared spectroscopy, we generated a high‐resolution record of dolomite and calcite contents from eight sections on the Chinese Loess Plateau spanning the last 130 kyr. Based on the relative abundance of calcite and dolomite, four dissolution phases of carbonate minerals related to summer monsoon (SM) variations are identified as follows: (1) coexistence of dolomite and calcite indicating a very weak SM with a mean annual precipitation (MAP) < 610 mm; (2) calcite without dolomite indicating a weak SM, 610 < MAP < 690 mm; (3) both dolomite and calcite are absent, but there is no downward leaching indicating a strong SM, 690 < MAP < 725 mm; and (4) both dolomite and calcite are absent, and downward leaching of the underlying loess layer suggesting a very strong SM with MAP > 725 mm.