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

Abstract C3 land plants dominated the Paleozoic landscape since the Devonian and played essential role in enhancing continental chemical weathering. Vast amounts 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 leaf cuticles, pollen grains, kerogen (non-soluble organic component to organic solvent), charcoal, individual organic compounds (e.g., lignin, cellulose, n-alkane, and cellulose),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 (δ13Cplant) in various forms in Paleozoic sediments (mostly Devonian, Carboniferous, and Permian), as well as marine carbonate carbon isotopes (δ13Ccarb), and interpret them in the context of global carbon cycle. The increasing trend of δ13C in both archives, bulk marine carbonates and terrestrial organic matters, suggest the variation on the burial of organic matter in the form of coal or petroleum controlled by sea level, nutrient availability, and innovation of life. This compilation allows for the reconstruction of a new high-resolution atmospheric pCO2 from 420 to 251 Ma. We noted that the pCO2 was ~2000 ppmv in the Devonian, then lowered to ~850 ppmv in the Carboniferous, and peaked at ~2200 ppmv during the end-Permian. This trend is broadly consistent with pCO2 from other proxies, including paleosol carbonate, stomatal index, and phytane, with the exception of the Late Devonian when our reconstructed pCO2 is significantly higher than the other proxy records. A higher pCO2 in the Late Devonian is more consistent with the elevated paleotemperature records.