Quantitative reconstruction of atmospheric pCO2 sources during Eocene hyperthermal events based on data from the Fushun Basin, Northeast China

Abstract

Eocene hyperthermal events are thought to be closely linked to rapid increases in atmospheric CO2. It is important to better understand the atmospheric triggers of these extreme events; however, reconstruction of pCO2 from sedimentary records remains challenging. Eocene hyperthermal events (Eocene thermal maximum, ETM; Early Eocene Climatic Optimum, EECO; Mid-Eocene Climatic Optimum, MECO) are well documented in the Fushun Basin of northeast China, but the source of organic matter (OM) used as a pCO2 archive in previous studies includes land plants, algae, mixed land and aquatic organisms in the Ypresian, Lutetian and Bartonian intervals, respectively. In this paper, we calculate pCO2 concentrations using δ13CTOC and δ13C27–31 and discuss the factors influencing discrepancies based on various calculations. Results show that both δ13CTOC and δ13C27–31 from single OM sources are reliable proxies for pCO2. During the ETM2, ETM3, EECO and MECO intervals, pCO2 was 638–2277 ppm, and palaeotemperature was approximately 2.6–8.9 °C higher than present. The background and peak values of pCO2 during hyperthermal events were compared with those related to methane hydrate, OM oxidation and volcanic sources of pCO2 carbon. The comparison revealed that pCO2 values associated with the ETM2, ETM3, EECO and MECO events were more consistent with those calculated by OM oxidation and locally overlapped with volcanic sources. These results indicate that these pCO2 estimates of hyperthermal events are predominantly derived from terrestrial OM oxidation and were influenced by volcanism.