Long-term variations in terrestrial carbon cycles and atmospheric CO2 levels: Exploring impacts on global ecosystem and climate in the aftermath of end-cretaceous mass extinction

The short-term climate and environmental consequences (<~1.0–10 Kyr) immediately following the end-Cretaceous extinction have been attributed to transient effects originating from Deccan volcanism and the Chicxulub impact. These two events have received significant attention for their role in precipitating extreme climate conditions. In contrast, the long-term (> ~100 Kyr) climate and environmental changes of the post-extinction have been extensively studied in the marine systems, yet their ramifications within terrestrial ecosystems are less well-characterized and require further elucidation. This study presents a carbon isotope analysis of pedogenic carbonates from matured calcisols in the Nanxiong Basin, South China, to reconstruct carbon cycles and atmospheric CO2 concentrations (pCO2) spanning from 76.0 Ma to 62.0 Ma, aiming to decipher the long-term terrestrial environmental and climatic conditions. Results show that δ13C values range from −12.4‰ to −5.0‰ (mean − 9.0‰) and pCO2 varies between ~250 ppmV and ~ 2200 ppmV (mean 920 ppmV). When combined with δ13C data from Songliao Basin, NE China, the carbon cycle variation exhibits a 13C collapse and smooth towards subsequent rebound, indicating a process of ~600 Kyr deterioration, ~600 Kyr stabilization and ~ 400 Kyr recovery in the terrestrial ecosystem. The fluctuation of estimated pCO2 aligns with the change pattern of sea surface temperatures, attesting to the strong perturbation of climate and environment at the same pace as the carbon cycle variations. It is proposed that ecosystems and environments in both terrestrial and surface ocean experienced a more unstable, difficult and erratic recovery process and were much more sensitive to climatic changes than in deep ocean for ~1.5 million years in the aftermath of the end-Cretaceous mass extinction. In addition, the divergence of proxy variations from expected effects implies the Deccan eruption and Chicxulub impact could not have played a long-term role in governing the climatic and environmental perturbations following the Cretaceous-Paleogene Boundary.