Paleozoic carbon cycle dynamics: Insights from stable carbon isotopes in marine carbonates and C₃ land plants

C₃ land plants dominated the Paleozoic landscape since the Devonian and played an essential role in enhancing continental chemical weathering. Vast amount of organic carbon isotope data exist from Paleozoic-aged sediments deposited in fluvial, lacustrine, and floodplain environments. These carbon isotope data are measured from well-preserved plant fossils, paleosols, coals, charcoals, and bulk organic matter within the sediments. They are often used for age correlations with contemporaneous marine sections as a stratigraphic correlation tool, and are interpreted as indicators of the global carbon cycle. Here, we review the stable carbon isotope records of C₃ land plants (δ¹³C_plant) in various forms in Paleozoic sediments (mostly Devonian, Carboniferous, and Permian), as well as marine carbonate carbon isotopes (δ¹³C_carb), and interpret them in the context of global carbon cycle. The increasing trend of δ¹³C in both marine carbonates and terrestrial organic matter suggests an increase in organic carbon burial in the form of coal or petroleum, which is controlled by sea level, nutrient availability, and innovation of life. This compilation allows for the reconstruction of a new high-resolution atmospheric pCO₂ from 423 to 252 Ma. We noted that the pCO₂ was ~2000 ppmv in the Devonian, then lowered to ~850 ppmv in the Carboniferous, and peaked at ~7600 ppmv during the Late Permian. This trend is broadly consistent with pCO₂ reconstructed from other proxies, including pedogenic carbonate proxy, stomatal proxy, and phytane proxy, with the exception of the Late Devonian when our reconstructed pCO₂ is significantly higher than the other proxy records. Proxy-based paleotemperature records suggest higher pCO₂ in the Late Devonian is more consistent with the elevated paleotemperatures.