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

• Published in: Biogeosciences
• Main Author: T. M. Blattmann
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2022
• Subjects: Ecology; QH540-549.5; Life; QH501-531; Geology; QE1-996.5; Canada; glacier*; Ice Sheet
• Online Access: https://doi.org/10.5194/bg-19-359-2022; https://doaj.org/article/658e61af5ba94d61bd7058c7ec04578b

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 suggests that this largest pool of reduced carbon on Earth may have played a key part in atmospheric CO 2 variability across recent glacial–interglacial cycles and beyond. This work enunciates the possibility of kerogen oxidation as a major driver of atmospheric CO 2 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 atmospheric CO 2 increase, atmospheric CO 2 isotope composition ( 13 C and 14 C ), kerogen oxidation kinetics, observations of kerogen reburial, and modeling results. The author hypothesizes that the deglaciation of kerogen-rich lithologies in western Canada contributed to the characteristic deglacial increase in atmospheric CO 2 , which reached an inflection point ≤ 300 years after the Laurentide Ice Sheet retreated into the kerogen-poor Canadian Shield. To reconcile the release of isotopically light carbon via kerogen oxidation with Earth surface carbon pool constraints, major oceanic degassing and biospheric regrowth must have acted in concert across glacial–interglacial transitions. Additionally, a process such as a strong shift in the ratio of C 3 to C 4 -derived organic matter must be invoked to maintain isotope mass balance, a point key for reconciling the hypothesis with the carbon isotope record of marine dissolved inorganic carbon. In order to test this hypothesis, quantitative constraints on the contribution of kerogen oxidation to CO 2 rise at glacial terminations are needed through systematic studies on (1) CO 2 fluxes emanating from the weathering of different lithologies, (2) oxidation ...