Reviews in Mineralogy & Geochemistry Vol. 75 pp. 323-354, 2013 11 Copyright © Mineralogical Society of America Deep Carbon Emissions from Volcanoes Michael R. Burton Istituto Nazionale di Geofisica e Vulcanologia Via della Faggiola, 32 56123 Pisa, Italy
[email protected] Georgina M. Sawyer Laboratoire Magmas et Volcans, Université Blaise Pascal 5 rue Kessler, 63038 Clermont Ferrand, France and Istituto Nazionale di Geofisica e Vulcanologia Via della Faggiola, 32 56123 Pisa, Italy Domenico Granieri Istituto Nazionale di Geofisica e Vulcanologia Via della Faggiola, 32 56123 Pisa, Italy INTRODUCTION: VOLCANIC CO2 EMISSIONS IN THE GEOLOGICAL CARBON CYCLE Over long periods of time (~Ma), we may consider the oceans, atmosphere and biosphere as a single exospheric reservoir for CO2. The geological carbon cycle describes the inputs to this exosphere from mantle degassing, metamorphism of subducted carbonates and outputs from weathering of aluminosilicate rocks (Walker et al. 1981). A feedback mechanism relates the weathering rate with the amount of CO2 in the atmosphere via the greenhouse effect (e.g., Wang et al. 1976). An increase in atmospheric CO2 concentrations induces higher temperatures, leading to higher rates of weathering, which draw down atmospheric CO2 concentrations (Ber- ner 1991). Atmospheric CO2 concentrations are therefore stabilized over long timescales by this feedback mechanism (Zeebe and Caldeira 2008). This process may have played a role (Feulner et al. 2012) in stabilizing temperatures on Earth while solar radiation steadily increased due to stellar evolution (Bahcall et al. 2001). In this context the role of CO2 degassing from the Earth is clearly fundamental to the stability of the climate, and therefore to life on Earth.