Extra-terrestrial noble gases in deep sea sediments

Abstract

Magnetic fractions separated from four deep sea sediments from the Pacific Ocean were analysed for elemental abundances and isotopic ratios of noble gases by stepwise heating. A 3He 4He ratio of (1.8 ± 0.4) × 10 −4 was observed in most samples in the high temperature fractions. In all the samples 20Ne 22Ne ratios are constant (11.6 ± 0.6) in most temperature fractions. These ratios are different from He-A, Ne-A and He-B, Ne-B and appear to come from a unique component. The 40Ar 36Ar ratios in high temperature fractions are lower than the atmospheric ratio, indicating the existence of extra-terrestrial Ar, while the 38Ar 36Ar ratios are indistinguishable from atmospheric, planetary, and solar Ar, indicating negligible spallogenic Ar. The isotopic ratios of Kr and Xe are indistinguishable from atmospheric ratios. From the 20Ne 22Ne ratios and from thermal release patterns of He, we conclude that the extra-terrestrial noble gases are implanted solar flare particles. The energy range of the solar flares is estimated from the relation between the grain size of IDPs (Interplanetary Dust Particles) and the penetration depth of particles impinging on to a grain, which gives less than 1 MeV/n. The uniformity of isotopic ratios of He and Ne can be explained by a grain size sieving effect of IDPs during atmospheric entry and by the subsequent diffusion loss of shallowly implanted solar wind noble gases.