Workshop Delivers New Estimate of Global Carbon Degassing
Twenty-eight DCO members came together from 29 April – 4 May, 2018 at the Carnegie Institution for Science in Washington, DC to calculate a new estimate of global carbon dioxide (CO2) degassing from large volcanic emitters, small volcanic sources and diffuse degassing from volcanic regions. The synthesis of massive amounts of data was successfully tackled through a hands-on approach. Science talks were interspersed with breakout sessions, followed by more of the same. “It was the most productive workshop I have ever attended,” said Terry Plank, DCO Executive Committee member and Reservoirs and Fluxes Science Community member (Columbia University, USA), “and should serve as a model for others to come.”
The DECADE synthesis workshop group attendees came prepared with a wealth of available volcanic emissions data they used to create a new global estimate. Their work was exhaustive, with some of the highlights provided below.
The attendees evaluated emissions from subaerial volcanoes with active gas plumes to produce an updated and improved estimate of global SO2 flux. This quantity was then combined with their best present knowledge of C/S ratios in the plumes of those volcanoes to derive a corresponding emission of volcanogenic carbon.
They accounted for different types of emitters, including passively degassing volcanoes, explosive eruptions, and effusive eruptions and distinguished between arc and non-arc volcanic sources. They compiled data covering 11 years from 2005 to 2015, and used information from long-term monitoring from space (mostly OMI satellite) and ground (mostly NOVAC network), as well as short-term campaign data and reports from the literature. The group also identified the need for further comparisons between satellite- and ground-based flux observations and the lack of C/S data, in particular for large eruptions.
To improve estimates from small volcanic sources, they assembled a new compilation of worldwide data from more than 40 volcanoes that emit small CO2 plumes and carefully selected appropriate volcanoes to include in the extrapolation. The group then individually reviewed more than 750 volcanoes from across the globe that could potentially host small plumes and categorized their emissions as ‘magmatic’, ‘hydrothermal’, or ‘none’. Said Tobias Fischer (University of New Mexico, USA), one of the initial workshop organizers, “When complete, this analysis will be the most rigorous and transparent estimate of global CO2 emissions from small volcanic sources yet determined.”
Attendees also delivered the first estimate of global carbon dioxide (CO2) degassing from diffuse degassing sources of volcanoes based on the published data reported in MaGa, a recent catalogue of diffuse gas emissions around the world, while also addressing uncertainties of the data. Other attendees analyzed subduction data that are providing insights into volatile cycling on both regional and global scales, while others considered what could be learned from the rock record.
Overall, the results from this workshop will provide new and more rigorously constrained global deep carbon emission estimates, new insights into the fate of subducted carbon and new methods for estimating volcanic CO2 fluxes through time using petrologic parameters. The workshop also highlighted the need for continued multi-disciplinary efforts in the area of volcanic and tectonic degassing to advance understanding of the transfer of volatiles between Earth’s reservoirs.