No abstract

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.

Quantifying ancient atmospheric pCO2 provides valuable insights into the interplay between greenhouse gases and global climate. Beyond the 800-ky history uncovered by ice cores, discrepancies in both the trend and magnitude of pCO2 changes remain among different proxy-derived results. The traditional paleosol pCO2 paleobarometer suffers from largely unconstrained soil-respired CO2 concentration (S(z)). Using finely disseminated carbonates precipitated in paleosols from the Chinese Loess Plateau, here we identified that their S(z) can be quantitatively constrained by soil magnetic susceptibility. Based on this approach, we reconstructed pCO2 during 2.6–0.9 Ma, which documents overall low pCO2 levels (<300 ppm) comparable with ice core records, indicating that the Earth system has operated under late Pleistocene pCO2 levels for an extended period. The pCO2 levels do not show statistically significant differences across the mid-Pleistocene Transition (ca. 1.2–0.8 Ma), suggesting that CO2 is probably not the driver of this important climate change event.

It is generally agreed that the aeolian loess on the Chinese Loess Plateau (CLP) is derived from adjacent upwind arid areas, mainly including the Qaidam Desert, Alxa arid area, and Ordos Desert. However, the mineralogical and geochemical compositions of aeolian materials show several inconsistencies between these adjacent source areas and the CLP. Here, we compare the distribution of carbonate minerals in bulk samples and the <63‐μm fraction from upwind deserts to six loess sections from the CLP. The results show that the detrital dolomite and total carbonate, which are abundant in the loess of the CLP, are concentrated in the Taklimakan Desert rather than adjacent source areas. This finding suggests that the distant Taklimakan Desert is an important source of aeolian deposits on the CLP, reconciling the mineralogical and geochemical inconsistencies between CLP and adjacent areas.