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The role of volcanism and mantle dynamics in the long-term evolution of Venus' atmosphere: outgassing and volatile sink.

Cedric Gillmann 1, Gregor Golabek2, Paul Tackley1

  • Affiliations: 1Department of Earth And Planetary Sciences, ETH, Zürich, Switzerland; 2Bavarian Research Institute of Experimental Geochemistry & Geophysics, Bayreuth Universität, Bayreuth, Germany

  • Presentation type: Poster

  • Presentation time: Tuesday 16:30 - 18:30, Room Poster Hall

  • Poster Board Number: 243

  • Programme No: 1.4.7

  • Theme 1 > Session 4

Abstract

Despite similarities between the two planets, Venus' hostile surface conditions are strikingly different from Earth's, and a direct consequence of its thick CO2-N2 atmosphere. A non-negligible portion of the greenhouse effect leading to high surface temperatures is caused by the tiny relative amount of atmospheric water it contains (about 20 ppmv, while free oxygen is practically absent). We investigate the origins of the present-day atmosphere of Venus by focusing of the sources and sinks of various gas species, with a specific eye for the role of volcanism. In this work, long-term evolution, interior evolution and atmosphere bulk composition are tracked using StagYY mantle dynamics models to calculate volcanic melt production and interaction with the atmosphere. Important volatile-exchange mechanisms include atmosphere escape mechanisms, volcanic outgassing, and gas--surface chemical reactions through oxidation of fresh lava. We estimate volatiles fluxes necessary to obtain the observed Venus conditions at present-day. Low outgassing fluxes of water are required, while that of CO2 and N2 remain poorly constrained. From present-day measurements, non-thermal mechanisms can account for the loss of 4 mbar to a few bar of oxygen, over 4 Gyr. The trapping of oxygen on the surface by oxidation of newly emplaced volcanic material depends on lava composition, lava flow geometry and the oxidation efficiency. While oxidation is fast, it appears limited to a thin layer of material, which limits the overall oxygen sink, for a total loss of O that is similar to that from non-thermal escape.