Mantle Volatiles and Global Carbon Flux and Budget

Abstract:

The global volcanic carbon flux to the surface of Earth is a fundamental parameter in understanding the global carbon cycle that includes deep carbon as well as the degassing history of the mantle. The flux has been estimated before (e.g., Marty and Tolstikhin, 1998). Recent progress has significantly revised some of the parameters used in the estimation, e.g., the oceanic ³He flux has been re-evaluated (Bianchi et al., 2010) to be only about half of the earlier widely-used estimate, and numerous subaerial volcanic degassing data are now available. In this report, a new attempt is made to assess the global carbon flux and budget.

Rather than dividing the carbon flux by categories of MORB, Plumes and Arcs, we estimate the global carbon flux by considering oceanic and subaerial volcanism. The oceanic ³He flux is 527±102 mol/yr (Bianchi et al., 2010). Most of the flux is from spreading ridges with only minor contributions from submarine oceanic hotspots or arc volcanism. Hence, the mean CO₂/³He ratio in MORB is applied to estimate oceanic flux of CO₂. The subaerial CO₂ flux is based on evaluation of different arc segments and is messier to compute. Literature estimates use estimated SO₂ flux in the last tens of years combined with estimated CO₂/SO₂ degassing ratios (Hilton et al., 2002; Fischer, 2008). Assuming that the last tens of years are representative of recent geological times in terms of volcanic degassing, the estimated global CO₂ flux still depends critically on a couple of arcs that are main contributors of the subaerial volcanic CO₂ flux, and those seem to have been rather loosely constrained before. Using recently available data (although there are still holes), we derive a new global subaerial volcanic CO₂ flux. By combining with oceanic volcanic CO₂ flux, we obtain at a new global flux. The significance of the new estimate to the global volatile budget will be discussed.