Overshoot of atmospheric oxygen caused by the Paleoproterozoic snowball glaciation: constraining its magnitude and duration from biogeochemical cycle modeling

Abstract:

Rise of atmospheric oxygen in the Paleoproterozoic has been long recognized as a unidirectional, stepwise oxidation event. However, recent geochemical studies have reported the occurrences of deep-water oxygenation and sulfate accumulation in the Paleoproterozoic oceans [e.g., 1], suggesting that the oxidation was a dynamic transition associated with an overshoot of oxygen (so called, ‘the Great Oxygen Transition’ or GOT) [2]. During the GOT, the oxygen levels might have achieved 0.1-1 Present Atmospheric Level (PAL) over ~10⁸ years [2]. Such an intense long-term oxygen overshoot appears to require some specific mechanism and strong oxidative forcing as a trigger. In this study, we provide the first numerical model that is capable of explaining the dynamics of the atmospheric oxygen during the GOT. We focus on a climate jump at the end of the Paleoproterozoic snowball glaciation as a trigger, and constrain the magnitude and duration of the snowball-induced oxygenation by using a biogeochemical cycle model.

The results show that super greenhouse condition after the glaciation causes an increase in nutrient input from the continent to the oceans, which lead to a high rate of organic carbon burial in the oceans. This triggers a rapid jump in oxygen levels from low (<10^-5 PAL) to high (~0.01 PAL) steady states within <10⁴ years after deglaciation. The jump in oxygen levels is followed by the massive deposition of carbonate minerals, which corresponds to the “cap-carbonates”. The elevated rate of organic carbon burial is prolonged over ~10⁶ years, which results in an overshoot of atmospheric oxygen by up to ~0.1-1 PAL. The overshoot lasts for ~10⁷-10⁸ years because net consumption of oxygen accumulated in the atmosphere does not proceed efficiently. Such an extensive overshoot causes the oxygenation of the deep-water, and lead to the accumulation of sulfate ions by up to 1-10 mM and the deposition of sulfate minerals in the oceans. These results are in good agreement with the geological and geochemical data in the Paleoproterozoic [2, 3], implying that the Paleoproterozoic snowball glaciation would have been a sufficiently strong forcing to trigger the GOT.

[1] Canfield et al. 2013, Pros. Natl. Acad. Sci. U.S.A., 110, 16736. [2] Lyons et al. 2014, Nature, 506, 307. [3] Schröder et al. 2008, Terra Nova, 20, 108.