Real-time measurements of δ13C, CO2 concentration, and CO2/SO2 in volcanic plume gases at Mount Etna, Italy, over 5 consecutive days

We present new real-time measurements of the CO2 concentration and delta C-13 made from July 16 to 20, 2014 in diluted gases of the active plume emitted by the Central Craters at Mount Etna volcano, Italy. This innovative study involved measuring delta C-13 in plume gases at a very high frequency over 5 days of measurements. The carbon-isotope composition calculated for volcanic CO2 ranged from - 1.3% to + 1.5%, with uncertainties in the repeated single measurements (i.e., made over periods from 4 to 20 min) that were generally <0.7%, and yet surprisingly varied by larger amounts over the 5-day study period. The range of calculated delta C-13 values mostly overlaps with that indicated for the plume of the Central Craters obtained by discrete sampling and using the isotope-ratio mass spectrometry technique (-2.5% < delta C-13 < -0.5%). However, we propose that during particular conditions of volcanic activity, the carbon-isotope composition of CO2 degassed from magma can reach values (up to + 1.5%) that are higher than those reported previously. During this campaign we also made simultaneous measurements of the CO2 and SO2 concentrations using the MultiGAS technique. The volcanic delta C-13 and CO2/SO2 ratios exhibited similar trends over the 5 days of measurements, with the ratios of both tracers peaking on July 16, possibly as a result of the early degassing of CO2 while an eruption was ongoing at Mount Etna. The observed variations and the highest delta C-13 values measured at Mount Etna during this campaign lead to new questions about the variability of this geochemical tracer. The comparisons with the CO2/SO2 ratio also confirm that monitoring delta C-13 in plume gases in real time, coupled to other geochemical tracers, is important for elucidating the magma dynamics at depth. (C) 2015 Elsevier B.V. All rights reserved.