Light noble gases and nitrogen in the crater fluids at Vulcano (Italy): special survey from June to September 1988

Nitrogen, noble gases (He, Ne, Ar) and some of their isotopes (4He, 20Ne, 22Ne, 36Ar, 38Ar, 40Ar) were measured in the fumaroles at the crater of Vulcano (Italy), during a special survey from June to September 1988. Since 1979 the survey has been carried out on two fumaroles (F1 and F5) but it was extended to other medium-temperature fumaroles (F5AT, FO, FA) during the summer of 1988. In 1987 a decrease was recorded in the 40Ar/36Ar, N2/Ar, He/Ne and He/Ar ratios; these are still decreasing towards values close to atmospheric in all the sampled fumaroles. The excess of the radiogenic component (4He, 40Ar), that was clearly detected in the period 1982-1986, is thus masked by the increase of the atmospheric species (in particular Ar). The Ne/Ar and N2/Ar ratios suggest that an inflow of a non-degassed air saturated water in the volcanic system is the likely explanation for the observed variation.