Abstract
BackgroundThe loess-paleosol sequence on the Loess Plateau has been considered an important paleoclimatic archive to study global climatic and environmental changes in the Quaternary. So far, little attention has been paid to the characteristics of soil organic carbon fractions in loess-paleosol sequences, which may provide valuable information for exploring the evolution of climate and environment in the Quaternary on the Loess Plateau.MethodsIn order to explore the significance of mineral-associated organic carbon to total organic carbon (MOC/TOC) ratios in the loess-paleosol sequence for reconstructing paleoenvironmental and paleoclimatic evolution in the Quaternary on the Loess Plateau, we selected a typical loess-paleosol profile in Chunhua county, Xianyang city, Shaanxi province, as the research object. The content of total organic carbon (TOC) and MOC/TOC ratio in each loess and paleosol layers of the Chunhua loess-paleosol profile were analyzed, together with the paleoclimatic proxies, such as soil grain size, CaCO3 content and their correlations with organic carbon parameters.ResultsThe main results were as follows: (1) the total content of soil organic carbon and MOC/TOC ratios were generally higher in paleosol layers than in the underlying loess layers of the Chunhua loess-paleosol profile. Compared to total organic carbon content, MOC/TOC ratios changed more obviously in soil layers below a paleosol layer S8; (2) soil clay content and median grain size (Md (ϕ)) were higher in paleosol than in the underlying loess, while CaCO3 content showed an opposite tendency. In the Chunhua profile, the distribution characteristics of the three paleoclimatic proxies showed good indications of paleoclimate changes in the Quaternary; (3) in the Chunhua loess-paleosol profile, MOC/TOC ratios were positively correlated with clay content and median grain size (ϕ), while negatively correlated with CaCO3 content, and the correlations were more significant in soil layers below S8.DiscussionOur results indicated that MOC/TOC ratios in the Chunhua loess-paleosol profile correlated with the cold dry-warm wet paleoclimatic cycle in the Quaternary. The high MOC/TOC ratios in the loess-paleosol profile might reflect warm and humid climate, while lower ratios indicated relatively cold and dry climate. That is because when the climate changed from warm-humid to cold-dry, the vegetation coverage and pedogenesis intensity decreased, which increased soil CaCO3 content and decreased soil clay content and Md (ϕ), leading to decreased MOC/TOC ratios. Compared to TOC, MOC/TOC ratios had greater significance in indicating paleoenvironmental evolution in the Quaternary on the Loess Plateau. Therefore, investigating MOC/TOC ratios in loess-paleosol profile can offer new evidence to reconstructing paleoenvironmental changes, and also provide a basis for predicting responses of soil organic carbon pools to vegetation and climate changes in the future.
Highlights
As the best accessible paleoclimatic archives in terrestrial environments, the loess-paleosol stratigraphic sequences have been proven to preserve continuous paleoenvironment and paleoclimate records during the Quaternary, which are helpful for the reconstruction of regional and global paleoclimate evolution, and provide vital references for the assessment of environmental and climatic changes in the future (An, 2000; Fitzsimmons, 2012; Fischer, 2012; Lehmkuhl et al, 2016)
In all paleosol layers of the Chunhua profile, total organic carbon content ranged from 0.11% to 0.54%, with the average value of 0.18%, while it was within the range of 0.10% to 0.21% in loess layers, with the average value of 0.14%
Total organic carbon contents decreased with the increase of soil depth, while they were higher in paleosol layers than in the underlying loess layers (Fig. 3)
Summary
As the best accessible paleoclimatic archives in terrestrial environments, the loess-paleosol stratigraphic sequences have been proven to preserve continuous paleoenvironment and paleoclimate records during the Quaternary, which are helpful for the reconstruction of regional and global paleoclimate evolution, and provide vital references for the assessment of environmental and climatic changes in the future (An, 2000; Fitzsimmons, 2012; Fischer, 2012; Lehmkuhl et al, 2016). The content of total organic carbon (TOC) and MOC/TOC ratio in each loess and paleosol layers of the Chunhua loess-paleosol profile were analyzed, together with the paleoclimatic proxies, such as soil grain size, CaCO3 content and their correlations with organic carbon parameters. The main results were as follows: (1) the total content of soil organic carbon and MOC/TOC ratios were generally higher in paleosol layers than in the underlying loess layers of the Chunhua loess-paleosol profile. In the Chunhua profile, the distribution characteristics of the three paleoclimatic proxies showed good indications of paleoclimate changes in the Quaternary; (3) in the Chunhua loess-paleosol profile, MOC/TOC ratios were positively correlated with clay content and median grain size (φ), while negatively correlated with CaCO3 content, and the correlations were more significant in soil layers below S8. The high MOC/TOC ratios in the loess-paleosol profile might reflect warm and humid
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
