Mercury gas emissions from La Soufrière Volcano, Guadeloupe Island (Lesser Antilles)

Quantifying mercury (Hg) emissions from active volcanoes is of particular interest for better constraining the global cycle and environmental impact of this highly toxic element. Here we report on the abundance of total gaseous (TGM = Hg⁰_(g) + Hg^II_(g)) and particulate (Hg_(p)) mercury in the summit gas emissions of La Soufrière andesitic volcano (Guadeloupe island, Lesser Antilles), where enhanced degassing of mixed hydrothermal-magmatic volatiles has been occurring since 1992 from the Southern summit crater. We demonstrate that Hg in volcanic plume occurs predominantly as gaseous mercury, with a mean TGM/Hg_(p) mass ratio of ~ 63. Combining the mean TGM/H₂S mass ratio of the volcanic plume (~ 3.2 × 10^− 6), measured close to the source vent, with the H₂S plume flux (~ 0.7 t d^− 1), determined simultaneously, allows us to estimate a gaseous mercury emission rate of 0.8 kg yr^− 1 from La Soufrière summit dome. Somewhat lower TGM/S_tot mass ratio in fumarolic gases from the source vent (4.4 × 10^− 7) suggests that plume chemical composition is not well represented by the emission source (fumaroles) due to chemical processes prior to (or upon) discharge. Current mercury emission from La Soufrìere volcano represents a very small contribution to the estimated global volcanic budget for this element.