Iodine degassing from basaltic volcanic systems

Despite its low abundance in natural magmas, iodine released to the atmosphere by volcanic activity is not well constrained as well as its potential impact on ozone destruction. To better understand and quantify the iodine contribution of volcanic degassing to the atmosphere, we have experimentally monitored iodine degassing from natural basaltic melts in real time at magmatic pressure and temperature for different situations: hydrous systems relevant for subduction zone context and anhydrous systems relevant for rifts and intraplate volcanisms. We show that for anhydrous systems, when CO2 is the major volatile phase, iodine degassing is not significant whereas for hydrous systems, when water is the major volatile phase, iodine degassing is significant. In this last case, the composition of the melt has no real impact on iodine degassing which is water-driven. We show that volcanic iodine degassing is significant at subduction zones during effusive volcanism. A maximal effusive volcanic flux of 1.95 Gg/year iodine is calculated, suggesting that volcanic injection of oxidised iodine species in the atmosphere must be taken into account for the Earth’s catalytic cycle of ozone destruction.