Sulphur isotope geochemistry

Abstract

Sulphur isotope abundances of thirty-nine specimens of seventeen meteorites are reported. The results show again the remarkable constancy of the sulphur isotope ratios for meteorites of all types. However, differences in the S 32/S 34 ratios of 0.4%. would appear to be significant. The S 32/S 34 ratio for meteorites is discussed as a possible base level from which fractionation in the earth's crust began. The value is compared with estimates of average values found for terrestrial samples including some recent results of igneous intrusives. A large suite of sea water samples collected from widely separated points in three oceans at various depths have also been investigated and the S 32/S 34 ratios reported. The results show that the sulphate in the three oceans is exceedingly uniform in isotope ratio, with an enrichment of 20.1%. ± 0.3 in S 34 over that of the meteoritic standard. Sulphur isotope ratios of sulphur in a sea shell, sulphides in shallow ocean sediments, sulphate in rain water and in present-day formation of gypsum evaporites from the sea, have been measured and are compared to the sea water level. The geochemical sulphate cycle is discussed in the light of these results.