2023/12/12 by Yang Fu, Zhengtang Guo, Guoan Wang
Earth and Planetary Sciences · Agricultural and Biological Sciences · #Geology and Paleoclimatology Research #Soil Carbon and Nitrogen Dynamics #Paleontology and Stratigraphy of Fossils
paper · doi:10.1017/qua.2023.66
Abstract Carbon isotope analysis of pedogenic carbonate (δ 13 C Carb ) and soil organic matter (δ 13 C TOC ) is widely applied in reconstructions of terrestrial paleovegetation. The δ 13 C of different archives is considered well matched and equally reflects the proportion of C 3 /C 4 plant biomass covering the soil profile. However, modern soil and paleosol sequences provide substantial evidence that δ 13 C Carb and δ 13 C TOC do not always match, raising doubts about the accuracy of quantitative C 4 plant reconstructions. Here we report paired δ 13 C records of pedogenic carbonates and organic matter occluded within carbonate nodules from the Shaozhai section in the central Chinese Loess Plateau (CLP). The δ 13 C Carb record exhibits a positive anomaly and exceeds the theoretical fractionation range with the coexisting δ 13 C TOC record during the expansion of C 4 plants. The possibility of contamination by detrital carbonates and atmospheric CO 2 affecting δ 13 C Carb was ruled out based on the morphological features, mineral fractions, and geochemical composition of carbonate nodules. Our study suggests that the enhanced respiration of C 4 plants during pedogenic carbonate precipitation may have caused positive shifts in δ 13 C Carb records, supporting the hypothesis that the discrepancy in carbon sources explains the δ 13 C Carb positive anomaly. Thus, the δ 13 C Carb could reflect the maximum relative abundance of C 4 plants during their metabolic peaks.