[Eoas-seminar] Tuesday Feb 25th Faculty Candidate for Solid Earth Processes in the Lithosphere (James Eguchi)

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Mon Feb 24 09:13:50 EST 2020

Dear all,

Dr. James Eguchi will be visiting us from Feb. 25th-26th. Dr. Eguchi is a candidate for the faculty search in "Solid Earth Processes in the Lithosphere (Metamorphic Petrology)".

I am attaching the title and abstract of Dr. Eguchi's talk. The talk is scheduled at 3:30 PM on 25th February 2020 (Tuesday) at EOA 1044.

Title: Linking Earth’s surface and interior carbon cycles – Implications for the history of oxygen and carbon isotopes

Abstract: The geologic record suggests that large oxidation events may be associated with large, positive C isotope excursions, with two of the most notable examples occurring at the beginning and end of the Proterozoic. One way to explain the association of O2 accumulation and positive C isotope excursions is an increase in the fraction of carbon buried as organic carbon relative to inorganic carbonate (forg).
However, studies have suggested that the Great Oxidation event may have preceded its associated carbon isotope excursion (Lomagundi event) by tens of millions of years, making it difficult to explain both events by increased forg. For this reason, some researchers have proposed mechanisms which decrease oxygen sinks as the ultimate driver of O2 accumulation in Earth’s atmosphere, but it is unclear how
decreased oxygen sinks would also result in a positive δ13C excursion. Here, I will present a new model which considers how the cycling of carbonates and graphitized organic carbon in the mantle affects the evolution of atmospheric oxygen and the carbon isotope record of marine carbonates. The model assumes that increased volcanic CO2 emissions drive increased burial and subduction of carbonates and organic C. When this process is coupled with preferential release of subducted carbonates at arc volcanoes and deep recycling of graphitized organic carbon to ocean island volcanoes it can explain the association and enigmatic timing of the GOE and Lomagundi Event. Notably, this model does not rely on any changes to forg to change δ13Ccarb. The model’s initial response to increased C subduction fluxes is increased CO2
emissions at arcs (carbonate-enriched, high δ13C), shifting δ13C of atmospheric volcanic CO2 inputs to higher values. δ13Ccarb continues to increase until the increased flux of subducted organic C is released at
intra-plate ocean islands, returning global CO2 emissions at different volcanic settings to their steady-state ratios, ending the δ13C excursion. Increased CO2 emissions in the model can be caused by major
tectonic transitions such as a transition from stagnant/sluggish lid to plate tectonics.  This contribution provides a link between Earth’s evolving tectonics, atmospheric evolution, and the C isotope record.

Thank you
Mainak Mookherjee
Associate Professor
Earth, Ocean and Atmospheric Sciences
Florida State University
Tallahassee, Fl, 32310, USA

Phone:(850) 644-1536 (Office)
Email: mmookherjee at fsu.edu<mailto:mmookherjee at fsu.edu>
Email: mainak.mookherjee at gmail.com<mailto:mainak.mookherjee at gmail.com>

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