Concentrations and isotope ratios of helium and other noble gases in the Earth's atmosphere during 1978–2011

Abstract

The evolution of the atmospheric noble gas composition during the past few decades has hardly been studied because, in contrast to many other atmospheric gases, systematic time-series measurements have not been available. Based on theoretical considerations, the atmospheric noble gas isotope composition is assumed to be stable on time scales of up to about 10 6 years, with the potential exception of anthropogenic changes predicted for the He concentration and the 3 He/ 4 He ratio.However, experimental assessments of the predicted changes in the atmospheric He isotope composition are controversial. To empirically test these assumptions and predictions, we analysed the noble gas isotope composition in samples of the * Corresponding author Cape Grim Air Archive, a well-defined archive of marine boundary layer air in the southern hemisphere. The resulting time series of the 20 Ne, 40 Ar, 86 Kr and 136 Xe concentrations and 20 Ne/ 22 Ne and 40 Ar/ 36 Ar ratios during 1978-2011 demonstrate the stability of the atmospheric Ne, Ar, Kr and Xe composition during this time interval. The He isotope data provide strong evidence for a decrease in the 3 He/ 4 He during the same time interval at a mean rate of 0.23-0.30 per year. This result is consistent with most model predictions of the rate of decrease in the atmospheric 3 He/ 4 He ratio associated with mining and burning of fossil fuels.

No evidence for change of the atmospheric helium isotope composition since 1978 from re-analysis of the Cape Grim Air Archive

“…The He isotope residence time in the atmosphere is of the order of 10 4 -10 6 yr (Torgersen, 1989;Kockarts, 1973), much longer than the atmospheric mixing time of 10 yr. Thus, the 3 He/ 4 He ratio of modern air (1.34-1.40 × 10 −6 , Mamyrin et al, 1970;Clarke et al, 1976;Davidson and Emerson, 1990;Hoffman and Nier, 1993;Sano and Wakita, 1988) should be constant on a decadal timescale. However, it has been suggested that this may no longer be the case (Sano et al, 1989;Pierson-Wickmann et al, 2001;Brennwald et al, 2013;Lupton and Evans, 2013).…”

“…Thereby, variation of the atmospheric helium isotope ratio ( 3 He/ 4 He) has been proposed as a possible new atmospheric tracer of industrial activity. However, the magnitude of such change is debated, with possible values ranging from 0 to about 2h/yr (Sano et al, 1989;Hoffman and Nier, 1993;Pierson-Wickmann et al, 2001;Brennwald et al, 2013;Lupton and Evans, 2013). A new analytical facility for high precision (2h, 2σ ) analysis of the 3 He/ 4 He ratio of air has been developed at CRPG Nancy (France) capable of investigating permil level…”

Insight into chemical, biological, and physical processes in coastal waters from dissolved oxygen and inert gas tracers

“…The Lott and Jenkins is solubility ∼2 % higher than published data from Weiss (1971). The He solubility is for bulk He and we calculate the 3 He solubility using an atmosperic mole ratio ( ( Mamyrin et al, 1970;Porcelli et al, 2002), although some more recent results indicate the current ratio may be slightly lower, ≃1.390 x 10 −6 (Brennwald et al, 2013b). We use the He equilibrium isotopic fractionation as described in Benson and Krause (1980b).…”

Atmospheric helium isotopic ratio from 1910 to 2016 recorded in stainless steel containers

“…According to Oliver et al (1984), the exploitation of natural gases (NG) could have increased the global atmospheric helium content by 1 to 6 ‰ between 1939 and 1981. Because NG are rich in radiogenic 4 He generated in the continental crust, the R AIR could have decreased by ≤3 ‰/yr (Brennwald et al, 2013 and references therein; see also Fig. S-1).…”