Quantifying the carbon source of pedogenic calcite veins in weathered limestone: implications for the terrestrial carbon cycle

作     者：Lin Zou Lin Dong Meng Ning Kangjun Huang Yongbo Peng Shujian Qin Honglin Yuan Bing Shen 

作者机构：Key Laboratory of Orogenic Belts and Crustal EvolutionMOE and School of Earth and Space SciencePeking UniversityBeijingPeople's Republic of China Shaanxi Key Laboratory of Early Life and EnvironmentsDepartment of GeologyNorthwest UniversityXi'anPeople's Republic of China Department of Geology and GeophysicsLouisiana State UniversityBaton RougeLA 70803USA 

出 版 物：《Acta Geochimica》 (地球化学学报（英文）)

年 卷 期：2019年第38卷第4期

页      面：481-496页

核心收录：

学科分类：0709[理学-地质学] 0819[工学-矿业工程] 07[理学] 0708[理学-地球物理学] 

基　　金：funded by the National Key Technology Program during the 13th Five-Year Plan Period (Grant No. 2016ZX05034001-007) National Natural Science Foundation of China (Grant No. 41772359) 

主　　题：Mg isotope Calcite veins Pedogenic carbonate Silicate weathering Carbonate weathering 

摘      要：The continent is the second largest carbon sink on Earth’s surface.With the diversification of vascular land plants in the late Paleozoic,terrestrial organic carbon burial is represented by massive coal formation,while the development of soil profiles would account for both organic and inorganic carbon burial.As compared with soil organic carbon,inorganic carbon burial,collectively known as the soil carbonate,would have a greater impact on the long-term carbon cycle.Soil carbonate would have multiple carbon sources,including dissolution of host calcareous rocks,dissolved inorganic carbon from freshwater,and oxidation of organic matter,but the host calcareous rock dissolution would not cause atmospheric CO2drawdown.Thus,to evaluate the potential effect of soil carbonate formation on the atmospheric p CO2level,different carbon sources of soil carbonate should be quantitatively differentiated.In this study,we analyzed the carbon and magnesium isotopes of pedogenic calcite veins developed in a heavily weathered outcrop,consisting of limestone of the early Paleogene Guanzhuang Group in North China.Based on the C and Mg isotope data,we developed a numerical model to quantify the carbon source of calcite veins.The modeling results indicate that4–37 wt%of carbon in these calcite veins was derived from atmospheric CO2.The low contribution from atmospheric CO2might be attributed to the host limestone that might have diluted the atmospheric CO2sink.Nevertheless,taking this value into consideration,it is estimated that soil carbonate formation would lower 1 ppm atmospheric CO2within 2000 years,i.e.,soil carbonate alone would sequester all atmospheric CO2within 1 million years.Finally,our study suggests the C–Mg isotope system might be a better tool in quantifying the carbon source of soil carbonate.