DEVELOPMENT OF A NOVEL EMPIRICAL FRAMEWORK FOR INTERPRETING GEOLOGICAL CARBON ISOTOPE EXCURSIONS, WITH IMPLICATIONS FOR THE RATE OF CARBON INJECTION ACROSS THE PETM

As an episode of rapid global warming associated with the release of massive quantities of carbon to the atmosphere and oceans, the Paleocene-Eocene Thermal Maximum (PETM, ~56 Ma) is considered a potential analog for modern anthropogenic carbon emissions. However, the prevailing order of magnitude uncertainty in the rate of carbon release during the PETM precludes any straightforward comparison between the paleo-record and the modern. Similar barriers exist to the interpretation of many other carbon isotope excursions in the geological record. Here we use the Earth system model cGENIE to quantify the consequences of differing carbon emissions rates on the isotopic record of different carbon reservoirs. We explore the consequences of a range of emissions scenarios – from durations of carbon input of years to millennia and constant versus pulsed emissions rates, and trace how the isotopic signal is imprinted on the different carbon reservoirs. From this, we identify a characteristic relationship between the difference in carbon isotope excursion sizes between atmospheric CO₂ and dissolved inorganic carbon (DIC) and the duration of carbon emissions. Applying this empirical relationship and taking available isotope records spanning the PETM, we show that available data suggest the duration of the component of carbon emissions that dominates the isotopic signal could be less than 2000 years. Our general interpretive framework could be equally applied in assessing rates of carbon emissions for other geological events.