Reconstruction of atmospheric CO2 concentration during the late Changhsingian based on fossil conifers from the Dalong Formation in South China

A single species of fossil conifer with well-preserved cuticles from multiple layers of the Dalong Formation in two sections in Duanshan Town, Guizhou Province, Southwest China has been used to reconstruct palaeo-atmospheric pCO(2). The age of these layers can be dated back to the late Changhsingian (latest Permian), corresponding to the Clarkina changxingensis and Clarkina yini conodont Zones. Two calibration approaches were employed in this study. Using the stomatal ratio method, the pCO(2) curves of the two sections showed matching trends, with levels decreasing in the middle of the profiles, and similar ranges at ca. 340-510 ppm and ca. 300-440 ppm. Similar values (ca. 360-520 ppm), yet with wider error ranges, were obtained when the mechanistic model proposed by Franks et al. in 2014 was applied to one of the sections. Our values are lower than the mean pCO(2) values from coeval palaeosols, but partly overlap with them when error ranges are taken into consideration, thus more independent studies are needed to evaluate the discrepancies between the two proxy methods. The low atmospheric CO2 concentrations in this study suggest a cool climate rather than extensive glaciation for the brief period of late Changhsingian, which is supported by the oxygen isotope record of conodont apatite and a major restructuring of Late Permian flora and fauna.