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The Rise of Oxygen in the Atmosphere and the Carbon Subduction Cycle

The net flux of carbon between the Earth’s interior and exterior, which is critical for redox evolution and planetary habitability, relies heavily on the extent of carbon subduction. While the fate of carbonates during subduction has been studied, little is known how organic carbon is quantitatively transferred from the Earth’s surface to the interior, although organic carbon sequestration is related to sources of oxygen in the surface environment. Here we conducted high pressure-temperature experiments to determine the carbon carrying capacity of rhyolitic melts under graphite-saturated slab conditions to constrain subduction efficiency of organic carbon, the remnants of life, through time. Based on experimental data and developed thermodynamic model of CO2 dissolution in slab melts, we quantified organic carbon mobility as a function of slab parameters. Our data and model suggest that the subduction of graphitized organic (reduced) carbon, and the graphite/diamond formed by reduction of carbonates with depth, remained efficient even in ancient, hotter subduction zones where oxidized carbon subduction likely remained limited. We suggest that immobilization of organic carbon in subduction zones and deep sequestration in the mantle facilitated the rise and maintenance of atmospheric oxygen since the Paleoproterozoic and is causally linked to the Great Oxidation Event (GOE). Our modeling shows that episodic recycling of organic carbon pre-GOE may also explain occasional whiffs of atmospheric oxygen observed in the Archean.

By: Megan Duncan, Postdoctoral Associate, Carnegie Geophysical Laboratory

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Host: Matt Weller, UTIG

When: Fri Apr 14, 2017 11:30am – 12:30pm Central Time