IS VOLCANIC CO2 A PLAUSIBLE DRIVER FOR CARBON ISOTOPE EXCURSIONS OF THE PALEOGENE? (Invited Presentation)

Volcanic carbon emissions have been invoked as drivers for both multi-million year Meso-Cenozoic climatic trends and short-lived (<500 kyr) Paleogene ‘hyperthermals’ (negative carbon isotope excursions associated with warming) identified from foraminiferal carbon and oxygen isotope records. Mass balance approaches are a powerful way to assess the plausibility of a volcanic source for various trends or events — namely addressing whether the mass of carbon required to match an observed carbon isotope change using a carbon source with typical mantle isotopic composition is consistent with the magnitude of observed warming. Additional observations may also provide complementary constraints such as changes in the carbonate compensation depth (CCD) or the evolution of ocean pH, both of which relate to the mass of carbon emissions. However, the relationships between mass of carbon emissions and the various climatic and environmental mass balance constraints are variably sensitive to the rate of carbon input to the atmosphere and ocean system. Here we use the Earth system model cGENIE to generate an ensemble of illustrative carbon isotope excursions using an idealized Paleocene model configuration. Assessing carbon isotope excursions with durations that range from geologically brief to million-year long trends, we calculate the required rate of volcanic CO₂ input and identify characteristic changes in climate, ocean chemistry, and the sedimentary record consistent with varying carbon injection rates and masses. Finally, we explore a variety of assumptions regarding the style and intensity of negative feedbacks required to return the ocean-atmosphere system to steady state and demonstrate that weathering alone is insufficient to remove excess volcanic CO₂ over hyperthermal timescales.