In the last decades, the environmental hazards of mercury (Hg) have been widely publicized, and particular emphasis has been addressed to the study of Hg from Earth degassing, in light of its high toxicity, long-range atmospheric transport and its tendency to bio-accumulate in aquatic ecosystems through methylation processes. In the specific, knowledge of the contribution of volcanic degassing systems and geothermal fields to the global budgets of Hg in the Earth's atmosphere is essential to evaluate the role that the volcanoes play on the reservoir cycling of this element and the potential fates it could represent once it reaches the ecosystems. All of these features have motivated intensive research on volcanogenic Hg within the framework of a pollutant of global concern. As a result, continued field research has been performed in geothermal and volcanic areas, by evaluating the Hg/SO2 and Hg/CO2 ratios in the emitted gases needed in estimating Hg fluxes in the atmosphere, and concentrations of gaseous Hg elevated above background levels were observed on most occasions. Based on our dataset, we propose that an average Hg/SO2 plume mass ratio of about 7.8×10-6 (±1.5×10-6; nvolcanoes= 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 about 76±30 t yr-1. These data suggest that open-conduit volcanoes in a state of passive degassing represent an important contribution to the global volcanic Hg emissions into the atmosphere. It is therefore likely that volcanic contributions to the global atmospheric Hg budget will be even more important during large eruptive events. With these new measurements, we shall critically revisit the status of the global volcanic Hg emissions budget, and its uncertainties. On the other hand, based on our dataset and previous works, we propose that an average GEM/CO2 molar ratio of ~2×10-8 is best representative of hydrothermal degassing. Taking into account the uncertainty in global hydrothermal CO2 emissions from sub-aerial environments (~1012 Mol yr-1; Seward & Kerrick, 1996), we infer a global volcanic Hg flux from hydrothermal environments of ~ about 8.5 t yr-1, resulting less important if compared to persistently degassing open-vent volcanoes, which dominate the global volcanic Hg budget. Finally, recent evidences have indicated the influence of submarine geothermal activity in controlling the dispersion of Hg as well. While Hg contribution from sub-aerial volcanism is now more or less constrained, the research on submarine hydrothermal activity could represent the most challenging and significant scientific advances of the 21th century in terms of Hg research as a global pollutant.
Advances on the role of Earth degassing in controlling atmospheric mercury budget
Bagnato E;Sprovieri M;Barra M;
2015
Abstract
In the last decades, the environmental hazards of mercury (Hg) have been widely publicized, and particular emphasis has been addressed to the study of Hg from Earth degassing, in light of its high toxicity, long-range atmospheric transport and its tendency to bio-accumulate in aquatic ecosystems through methylation processes. In the specific, knowledge of the contribution of volcanic degassing systems and geothermal fields to the global budgets of Hg in the Earth's atmosphere is essential to evaluate the role that the volcanoes play on the reservoir cycling of this element and the potential fates it could represent once it reaches the ecosystems. All of these features have motivated intensive research on volcanogenic Hg within the framework of a pollutant of global concern. As a result, continued field research has been performed in geothermal and volcanic areas, by evaluating the Hg/SO2 and Hg/CO2 ratios in the emitted gases needed in estimating Hg fluxes in the atmosphere, and concentrations of gaseous Hg elevated above background levels were observed on most occasions. Based on our dataset, we propose that an average Hg/SO2 plume mass ratio of about 7.8×10-6 (±1.5×10-6; nvolcanoes= 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 about 76±30 t yr-1. These data suggest that open-conduit volcanoes in a state of passive degassing represent an important contribution to the global volcanic Hg emissions into the atmosphere. It is therefore likely that volcanic contributions to the global atmospheric Hg budget will be even more important during large eruptive events. With these new measurements, we shall critically revisit the status of the global volcanic Hg emissions budget, and its uncertainties. On the other hand, based on our dataset and previous works, we propose that an average GEM/CO2 molar ratio of ~2×10-8 is best representative of hydrothermal degassing. Taking into account the uncertainty in global hydrothermal CO2 emissions from sub-aerial environments (~1012 Mol yr-1; Seward & Kerrick, 1996), we infer a global volcanic Hg flux from hydrothermal environments of ~ about 8.5 t yr-1, resulting less important if compared to persistently degassing open-vent volcanoes, which dominate the global volcanic Hg budget. Finally, recent evidences have indicated the influence of submarine geothermal activity in controlling the dispersion of Hg as well. While Hg contribution from sub-aerial volcanism is now more or less constrained, the research on submarine hydrothermal activity could represent the most challenging and significant scientific advances of the 21th century in terms of Hg research as a global pollutant.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
