High atmospheric CO2 levels in the early Mesoproterozoic estimated from paired carbon isotopic records from carbonates from North China

•High atmospheric pCO2 levels, constrained by the paired C-isotopic compositions of carbonate and organic carbon from ∼1.6 Ga Gaoyuzhuang Formation, could have played an important role in compensating for the low solar luminosity and maintaining the temperature of the Mesoproterozoic Earth's surface. It is hypothesized that the Mesoproterozoic was characterized by a prevailing warm climate and a high atmospheric pCO2 level. However, quantitative constraints on Mesoproterozoic atmospheric pCO2 are scarce. Here, we report high-resolution organic and inorganic carbon isotope records from sediment samples aged ∼1.6 Ga, collected from Hebei Province in North China. The δ13Corg values of these Mesoproterozoic samples vary from −28.4‰ to −34.3‰, and the δ13Ccarbonate values range from −2.1‰ to 0.4‰. The paired carbonate and organic carbon isotope records can be used as a proxy to quantify the atmospheric CO2 concentration during the Mesoproterozoic. According to the calibration between the photosynthetic isotopic effect and atmospheric CO2, atmospheric CO2 concentrations are estimated to be within the range of 910–18,800 ppmv, ∼2–50 times greater than the present atmospheric level. The results support the previous hypothesis which suggests that high levels of atmospheric CO2 prevailed in the Early Mesoproterozoic. High atmospheric pCO2 levels could have played an important role in compensating for the possible lower solar luminosity and maintaining the temperature of the Mesoproterozoic Earth's surface.