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<div class="">On Feb 24, 2020, at 9:13 AM, eoas-seminar--- via Eoas-seminar <<a href="mailto:eoas-seminar@lists.fsu.edu" class="">eoas-seminar@lists.fsu.edu</a>> wrote:</div>
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<div class="" style="word-wrap:break-word"><font face="Georgia" class="">Dear all,</font>
<div class=""><font face="Georgia" class=""><br class="">
</font></div>
<div class=""><font face="Georgia" class="">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)".</font></div>
<div class=""><font face="Georgia" class=""><br class="">
</font></div>
<div class="">
<div class=""><font face="Georgia" class="">I am attaching the title and abstract of Dr. Eguchi's talk. The talk is scheduled at <b class="">3:30 PM </b><span class="">on</span><b class=""> 25th February 2020</b> (Tuesday) at</font><span class=""> </span><b class="">EOA
1044</b><span class="">.</span></div>
<div class=""><font face="Georgia" class=""><br class="">
</font></div>
<div class=""><font face="Georgia" class=""><span class=""><b class="">Title:</b></span><b class=""> </b></font><span class="" style="text-align:justify">Linking Earth’s surface and interior carbon cycles – Implications for the history of oxygen and carbon
isotopes</span></div>
<div class=""><font face="Georgia" class=""><br class="">
</font></div>
<div class=""><font face="Georgia" class=""><b class="">Abstract:</b> </font><font face="Georgia" class=""><span lang="EN-GB" class="" style="text-align:justify; text-indent:14.2pt">The geologic record suggests that large oxidation events may be associated
with large, positive C isotope excursions, with two of the most </span></font><span class="" style="text-align:justify; text-indent:14.2pt">notable examples occurring at the beginning and end of the Proterozoic. One way to explain the association of O</span><sub class="" style="text-align:justify; text-indent:14.2pt">2</sub><span class="" style="text-align:justify; text-indent:14.2pt"> accumulation
and positive C isotope </span><span class="" style="text-align:justify; text-indent:14.2pt">excursions is an increase in the fraction of carbon buried as organic carbon relative to inorganic carbonate (</span><i class="" style="text-align:justify; text-indent:14.2pt">f</i><sub class="" style="text-align:justify; text-indent:14.2pt">org</sub><span class="" style="text-align:justify; text-indent:14.2pt">).</span></div>
<div class=""><span class="" style="text-align:justify; text-indent:14.2pt">However, studies have suggested that </span><span class="" style="text-align:justify; text-indent:14.2pt">the Great Oxidation event may have preceded its associated carbon isotope excursion
(Lomagundi event) by tens of millions of years, making it difficult </span><span class="" style="text-align:justify; text-indent:14.2pt">to explain both events by increased </span><i class="" style="text-align:justify; text-indent:14.2pt">f</i><sub class="" style="text-align:justify; text-indent:14.2pt">org</sub><span class="" style="text-align:justify; text-indent:14.2pt">.
For this reason, some researchers have proposed mechanisms which decrease oxygen sinks as the ultimate driver </span><span lang="EN-GB" class="" style="text-align:justify; text-indent:14.2pt">of O<sub class="">2</sub> accumulation in Earth’s atmosphere, but
it is unclear how</span></div>
<div class=""><span lang="EN-GB" class="" style="text-align:justify; text-indent:14.2pt">decreased oxygen sinks would also result in a positive </span><span lang="EN-GB" class="" style="text-align:justify; text-indent:14.2pt">δ</span><sup class="" style="text-align:justify; text-indent:14.2pt"><span lang="EN-GB" class="">13</span></sup><span lang="EN-GB" class="" style="text-align:justify; text-indent:14.2pt">C
excursion. </span><span class="" style="text-align:justify; text-indent:14.2pt">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 </span><span class="" style="text-align:justify; text-indent:14.2pt">atmospheric
oxygen and the carbon isotope record of marine carbonates. The model assumes that increased volcanic CO</span><sub class="" style="text-align:justify; text-indent:14.2pt">2</sub><span class="" style="text-align:justify; text-indent:14.2pt"> emissions drive
increased </span><span lang="EN-GB" class="" style="text-align:justify; text-indent:14.2pt">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 <i class="">f</i><sub class="">org</sub> to change </span><span lang="EN-GB" class="" style="text-align:justify; text-indent:14.2pt">δ</span><sup class="" style="text-align:justify; text-indent:14.2pt"><span lang="EN-GB" class="">13</span></sup><span lang="EN-GB" class="" style="text-align:justify; text-indent:14.2pt">C</span><sub class="" style="text-align:justify; text-indent:14.2pt"><span lang="EN-GB" class="">carb. </span></sub><span lang="EN-GB" class="" style="text-align:justify; text-indent:14.2pt">The
model’s initial response to increased C subduction fluxes is</span><span lang="EN-GB" class="" style="text-align:justify; text-indent:14.2pt"> increased CO<sub class="">2</sub></span></div>
<div class=""><span lang="EN-GB" class="" style="text-align:justify; text-indent:14.2pt">emissions at arcs (carbonate-enriched, high </span><span lang="EN-GB" class="" style="text-align:justify; text-indent:14.2pt">δ</span><sup class="" style="text-align:justify; text-indent:14.2pt"><span lang="EN-GB" class="">13</span></sup><span lang="EN-GB" class="" style="text-align:justify; text-indent:14.2pt">C),
shifting </span><span lang="EN-GB" class="" style="text-align:justify; text-indent:14.2pt">δ</span><sup class="" style="text-align:justify; text-indent:14.2pt"><span lang="EN-GB" class="">13</span></sup><span lang="EN-GB" class="" style="text-align:justify; text-indent:14.2pt">C
of atmospheric volcanic CO<sub class="">2</sub> inputs to higher values. </span><span lang="EN-GB" class="" style="text-align:justify; text-indent:14.2pt">δ</span><sup class="" style="text-align:justify; text-indent:14.2pt"><span lang="EN-GB" class="">13</span></sup><span lang="EN-GB" class="" style="text-align:justify; text-indent:14.2pt">C<sub class="">carb</sub> continues
to increase until the increased flux of subducted organic C is released at</span></div>
<div class=""><span lang="EN-GB" class="" style="text-align:justify; text-indent:14.2pt">intra-plate ocean islands, returning global CO<sub class="">2</sub> emissions at different volcanic settings to their steady-state ratios, ending the </span><span lang="EN-GB" class="" style="text-align:justify; text-indent:14.2pt">δ</span><sup class="" style="text-align:justify; text-indent:14.2pt"><span lang="EN-GB" class="">13</span></sup><span lang="EN-GB" class="" style="text-align:justify; text-indent:14.2pt">C
excursion. Increased CO<sub class="">2</sub> emissions in the model can be caused by major</span></div>
<div class=""><span lang="EN-GB" class="" style="text-align:justify; text-indent:14.2pt">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.</span></div>
<div class=""><font face="Georgia" class=""><br class="">
</font></div>
<div class="">Thank you</div>
<div class=""><font face="Georgia" class="">Mainak</font></div>
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----------------------------------------------------------------------------<br class="">
Mainak Mookherjee<br class="">
Associate Professor<br class="">
Earth, Ocean and Atmospheric Sciences<br class="">
Florida State University<br class="">
Tallahassee, Fl, 32310, USA<br class="">
<br class="">
Phone:(850) 644-1536 (Office)<br class="">
Email: <a href="mailto:mmookherjee@fsu.edu" class="">mmookherjee@fsu.edu</a><br class="">
Email: <a href="mailto:mainak.mookherjee@gmail.com" class="">mainak.mookherjee@gmail.com</a><br class="">
URL:http://<a href="http://myweb.fsu.edu/mmookherjee" class="">myweb.fsu.edu/mmookherjee</a><br class="">
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