[1] Bromine monoxide (BrO) and sulphur dioxide (SO 2 ) abundances as a function of the distance from the source were measured by ground-based scattered light Multiaxis Differential Optical Absorption Spectroscopy (MAX-DOAS) in the volcanic plumes of Mt. Etna on Sicily, Italy, in August-October 2004 and May 2005 and Villarica in Chile in November 2004. BrO and SO 2 spatial distributions in a cross section of Mt. Etna's plume were also determined by Imaging DOAS. We observed an increase in the BrO/SO 2 ratio in the plume from below the detection limit near the vent to about 4.5 Â 10 À4 at 19 km (Mt. Etna) and to about 1.3 Â 10 À4 at 3 km (Villarica) distance, respectively. Additional attempts were undertaken to evaluate the compositions of individual vents on Mt. Etna. Furthermore, we detected the halogen species ClO and OClO. This is the first time that OClO could be detected in a volcanic plume. Using calculated thermodynamic equilibrium compositions as input data for a one-dimensional photochemical model, we could reproduce the observed BrO and SO 2 vertical columns in the plume and their ratio as function of distance from the volcano as well as vertical BrO and SO 2 profiles across the plume with current knowledge of multiphase halogen chemistry, but only when we assumed the existence of an ''effective source region,'' where volcanic volatiles and ambient air are mixed at about 600°C (in the proportions of 60% and 40%, respectively).

[1] Constraining fluxes of volcanic bromine and iodine to the atmosphere is important given the significant role these species play in ozone depletion. However, very few such measurements have been made hitherto, such that global volcanic fluxes are poorly constrained. Here we extend the data set of volcanic Br and I degassing by reporting the first measurements of bromine and iodine emissions from Mount Etna. These data were obtained using filter packs and contemporaneous ultraviolet spectroscopic SO 2 flux measurements, resulting in time-averaged emission rates of 0.7 kt yr À1 and 0.01 kt yr À1 for Br and I, respectively, from April to October 2004, from which we estimate global Br and I fluxes of order 13 (range, 3-40) and 0.11 (range, 0.04-6.6) kt yr À1 . Observed changes in plume composition highlight the coherent geochemical behavior of HCl, HF, HBr, and HI during magmatic degassing, and strong fractionation of these species with respect to SO 2 .

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The hydrothermal system at Vulcano, Aeolian Islands (Italy), is home to a wide variety of thermophilic, chemolithoautotrophic archaea and bacteria. As observed in laboratory growth studies, these organisms may use an array of terminal electron acceptors (TEAs), including O2, , Fe(III), , elemental sulphur and CO2; electron donors include H2, , Fe2+, H2S and CH4. Concentrations of inorganic aqueous species and gases were measured in 10 hydrothermal fluids from seeps, wells and vents on Vulcano. These data were combined with standard Gibbs free energies () to calculate overall Gibbs free energies (ΔGr) of 90 redox reactions that involve 16 inorganic N‐, S‐, C‐, Fe‐, H‐ and O‐bearing compounds. It is shown that oxidation reactions with O2 as the TEA release significantly more energy (normalized per electron transferred) than most anaerobic oxidation reactions, but the energy yield is comparable or even higher for several reactions in which , or Fe(III) serves as the TEA. For example, the oxidation of CH4 to CO2 coupled to the reduction of Fe(III) in magnetite to Fe2+ releases between 94 and 123 kJ/mol e−, depending on the site. By comparison, the aerobic oxidation of H2 or reduced inorganic N‐, S‐, C‐ and Fe‐bearing compounds generally yields between 70 and 100 kJ/mol e−. It is further shown that the energy yield from the reduction of elemental sulphur to H2S is relatively low (8–19 kJ/mol e−) despite being a very common metabolism among thermophiles. In addition, for many of the 90 reactions evaluated at each of the 10 sites, values of ΔGr tend to cluster with differences < 20 kJ/mol e−. However, large differences in ΔGr (up to ∼ 60 kJ/mol e−) are observed in Fe redox reactions, due largely to considerable variations in Fe2+, H+ and H2 concentrations. In fact, at the sites investigated, most variations in ΔGr arise from differences in composition and not in temperature.

[1] Marked increases of CO 2 , H 2 and He dissolved in thermal waters and changes in the dissolved carbon isotopic composition, were observed at Stromboli before the 28 December 2002 eruption and before a violent explosive paroxysm occurred on 5 April 2003. High anomalous CO 2 flux values were recorded at the crater rim since a week before the eruption onset. The first anomalies in the thermal waters (dissolved CO 2 amount) appeared some months before the eruption, when magma column rose at a very high level in the conduit. High peaks of dissolved H 2 and He were recorded a few days before the paroxysm. Carbon isotopic composition indicates a magmatic origin of the dissolved CO 2 whose increase, together with those of H 2 and He, is attributed to an increasing output of deep gases likely produced by depressurization of a rising batch of a deep gas-rich magma, whose fragments have been emitted during the explosion.