Atmospheric CO 2 estimates during the Aptian (Early Cretaceous): New Evidence from Carbon Isotopes of Sediments in Northeast China

The Aptian (Early Cretaceous) is a critical interval for understanding greenhouse climate dynamics, yet high-resolution continental records of atmospheric CO 2 remain poorly understood. Here, we reconstruct Aptian atmospheric CO 2 levels using paired carbon isotopic analyses (δ 13 C org and δ 13 C carb ) from a lacustrine succession of the Jiufotang Formation in Northeast China. Our record reveals pronounced p CO 2 fluctuations, with values ranging from 337 to 1145 ppmv (mean ∼626 ppmv). These variations show higher concentrations in the lower and upper segments of the formation, separated by a mid-interval decline. Spectral analysis further identifies strong ∼165 kyr, ∼260 kyr and ∼405 kyr eccentricity cycles, indicating that orbital forcing played a key role in modulating the carbon cycle. The observed p CO 2 peaks coincide with enhanced of intracontinental volcanism and oceanic anoxic events (OAE1a), suggesting a combined forcing from volcanism, orbital rhythms, and carbon sequestration. This study provides a high-resolution continental perspective on CO 2 dynamics during the Aptian, offering a valuable continental archive to decipher carbon-climate interactions under greenhouse conditions.