Ideas and perspectives: Emerging contours of a dynamic exogenous kerogen cycle

Abstract. Growing evidence points to the dynamic role that kerogen is playing on Earth's surface in controlling atmospheric chemistry over geologic time. Although quantitative constraints on the weathering of kerogen remain loose, its changing weathering behavior modulated by the activity of glaciers suggest that this largest pool of reduced carbon on Earth may have played a key part in atmospheric CO2 variability across recent glacial-interglacial times and beyond. This work enunciates the possibility of kerogen oxidation as a major driver of atmospheric CO2 increase in the wake of glacial episodes. This hypothesis of centennial and millennial-timescale-relevance for this chemical weathering pathway is substantiated by several lines of independent evidence synthesized in this contribution including the timing of CO2 increase, CO2 isotopic composition (13C and 14C), seawater osmium record, kerogen oxidation kinetics, observations of kerogen reburial, and modeling results. The author hypothesizes that the deglaciation of kerogen-rich lithologies in western Canada contributed majorly to the characteristic deglacial increase in atmospheric CO2, which reached an inflection point ≤ 300 years after the Laurentide Ice Sheet retreated into the kerogen-poor Canadian Shield. To quantitatively constrain the contribution of kerogen oxidation to CO2 rise at glacial terminations, systematic studies on CO2 fluxes emanating from the weathering of different lithologies, oxidation kinetics of kerogen along glacial chronosequences, and high-resolution temporal changes in the aerial extent of glacially exposed lithological units are needed.