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

Friday, 19 December 2014
Mariko Harada1, Kazumi Ozaki2, Eiichi Tajika1 and Yasuhito Sekine1, (1)The University of Tokyo, Kashiwa, Japan, (2)Atmosphere and Ocean Research Institute University of Tokyo, Kashiwa, Japan
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.