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

[摘要] Growing evidence points to the dynamic role that kerogen is playing on Earth's surface in controlling atmospheric chemistry over geologictime. Although quantitative constraints on the weathering of kerogen remain loose, its changing weathering behavior modulated by the activity ofglaciers suggests that this largest pool of reduced carbon on Earth may have played a key part in atmospheric CO 2 variability acrossrecent 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 chemicalweathering 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 ofkerogen reburial, and modeling results. The author hypothesizes that the deglaciation of kerogen-rich lithologies in western Canada contributed tothe characteristic deglacial increase in atmospheric CO 2 , which reached an inflection point ≤  300 years after the Laurentide IceSheet retreated into the kerogen-poor Canadian Shield. To reconcile the release of isotopically light carbon via kerogen oxidation with Earthsurface carbon pool constraints, major oceanic degassing and biospheric regrowth must have acted in concert across glacial–interglacialtransitions. Additionally, a process such as a strong shift in the ratio of C 3 to C 4 -derived organic matter must be invoked to maintainisotope mass balance, a point key for reconciling the hypothesis with the carbon isotope record of marine dissolved inorganic carbon. In order totest this hypothesis, quantitative constraints on the contribution of kerogen oxidation to CO 2 rise at glacial terminations are neededthrough systematic studies on (1)  CO 2 fluxes emanating from the weathering of different lithologies, (2) oxidation kinetics of kerogenalong glacial chronosequences, and (3) high-resolution temporal changes in the aerial extent of glacially exposed lithological units and glacialflour.

[学科分类] 大气科学