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

Quantifying mercury (Hg) emissions from active volcanoes is of peculiar interest for better constraining the global cycle and enviromental impact of this highly toxic element. Here we report on the abundance of total gaseous (TGM = Hg0(g) + HgII(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. TGM was also measured in condensates of fumarolic gases issuing from the South crater for assessing the volcanic Hg source strength in reference to H2S. On average, the TGM/Stot mass ratio in the issuing gases was found to be ~3,5 times lower than in the volcanic plume (6.3×10-7 and 2.2×10-6, respectively), suggesting that there is no fast Hg chemical processing inside fumaroles. From the mean TGM/Stot ratio in the plume and the H2S plume flux, measured for the first time, we evaluate the emission rate of gaseous mercury from La Soufrière summit dome as 0.8 kg yr-1.