Mercury fluxes from volcanic and geothermal sources: an update

Abstract

We review the state of knowledge on global volcanogenic Hg emissions to the atmosphere and present new data from seven active volcanoes (Poás, Rincón de la Vieja, Turrialba, Aso, Mutnovsky, Gorely and Etna) and two geothermal fields (Las Pailas and Las Hornillas). The variability of Hg contents (c. 4–125 ng m−3) measured in gaseous emissions reflects the dynamic nature of volcanic plumes, where the abundances of volatiles are determined by the physical nature of degassing and variable air dilution. Based on our dataset and previous work, we propose that an average Hg/SO2 plume mass ratio of c. 7.8×10−6 (±1.5×10−6; 1 SE, n=13) is best representative of open-conduit quiescent degassing. Taking into account the uncertainty in global SO2 emissions, we infer a global volcanic Hg flux from persistent degassing of c. 76±30 t a−1. Our data are derived from active volcanoes during non-eruptive periods and we do not have any direct constraint on the Hg flux during periods of elevated SO2 flux associated with large-scale effusive or explosive eruptions. This suggests that the time-averaged Hg flux from these volcanoes is even larger if the eruptive contribution is considered. Conversely, closed-conduit degassing and geothermal emissions contribute modest amounts of Hg

Historical (1850–2010) mercury stable isotope inventory from anthropogenic sources to the atmosphere

“…The Hg flux from passively degassing volcanic activity is relatively well constrained at 76 ± 31 Mg y -1 (Bagnato et al, 2014). No Hg flux measurements exist for explosive volcanism.…”

“…Transfer of Hg from Earth's lithosphere to the atmosphere and other surface environments is continuous by natural processes, and has been accelerated by human activities dating back to antiquity (Goldwater, 1972;Nriagu, 1979). Natural atmospheric Hg emissions from volcanoes, crustal weathering and hydrothermal activity are thought to be 1-2 orders of magnitude smaller than modern anthropogenic Hg emissions (Amos et al, 2015;Bagnato et al, 2014;UNEP, 2013). Prior to the 1850s, anthropogenic Hg releases mainly came from primary Hg mining and use of Hg as amalgamation agent for silver extraction in the Spanish colonial Americas (Camargo, 2002;Hagan et al, 2011;Robins and Hagan, 2012).…”

Uncertainties in Atmospheric Mercury Modeling for Policy Evaluation

“…Hg emissions from volcanoes are often derived from Hg/SO 2 ratios and SO 2 emission inventories due to the difficulty of obtaining Hg measurements from these sources. A compilation of Hg/SO 2 ratios from volcanic gases has shown an order of two magnitude difference depending on the volcano types [78]. Similar ratio-based methods and inventory of CO emissions are used to estimate Hg emissions from biomass burning.…”

Volatiles in subduction zone magmatism

“…At Merapi volcano, Indonesia, metals and sulphur outgas in the same proportions as found in sulphide minerals contained in minerals as inclusions, suggesting that entrainment of sulphide and its subsequent dissolution is the source for outgassing metals (Nadeau et al 2010). In this volume, Bagnato et al (2014) show that volcanoes are also significant sources of mercury released into the atmosphere, perhaps accounting for up to one-quarter of natural atmospheric emissions.…”