EXPLORING SOIL CARBON BURIAL OVER THE PALEOCENE EOCENE THERMAL MAXIMUM: A CASE STUDY OF SOIL CARBON RESPONSE TO RAPID WARMING

Currently, the land carbon sink sequesters about a third of human CO₂ emissions each year, but predictions of the response of this carbon sink to rapid global warming is relatively unknown. Even without human influence, there are many complex controls on land carbon balance including: respiration rate influences on soil organic matter, soil inorganic carbon storage response to increasing evapotranspiration rates, and increases in CO₂ and temperature changing plant communities. The Paleocene-Eocene Thermal Maximum (PETM) was the largest carbon cycle perturbation of the Cenozoic and thus could give us insight into terrestrial carbon dynamics over periods of CO₂-driven rapid warming. Paleosol deposits have very low organic carbon preserved compared to modern soils, but still have the potential to reconstruct relative soil organic carbon storage. Furthermore, paleosol carbonates are a CO₂ sink because the carbon in them is mainly derived from a mix of atmospheric and respired CO₂. Paleosol carbonates are also resistant to diagenesis and can therefore faithfully reconstruct soil inorganic carbon storage. While volumetric estimates of paleosol carbonates are easily quantified in continental cores, they can be difficult to quantify in-outcrop. New techniques quantifying pedogenic carbonate amounts in-outcrop were tested on the Flagstaff Formation of Axhandle Basin, UT, USA. These data, along with total organic carbon (TOC) data, were compared to pedogenic carbonate amounts and TOC data from the Bighorn Basin, WY, USA continental core to quantify carbon storage in paleosols over the PETM. These basins are both fluvial dominated but have significantly different sedimentary systems. Due to this difference, they record differences in carbon burial rates, with implications for the future of carbon storage in different ecosystems and soil types. Overall, terrestrial carbon burial is changes significantly over the PETM; however, these changes are difficult to apply to modern timescales because the rate of change is dependent on the fluctuating deposition rate of paleosols, which can vary greatly within paleosol sequences.