Sources of sulfur in rainwater as indicated by isotopic δ34S data and chemical composition, Israel

Seventeen rainwater samples from 11 different locations in Israel have been analyzed for their chemical composition and δ34S values. The δ34S range between 0.0 and 15.3% and fall within the δ34S variations in rainwater in nature (− 2.5–19.4%). This range is characteristic for the last 40–50 years over various parts in the world. Higher δ34S values were found in Mediterranean coast samples with relatively high Cl/SO4 ratios, while lower values were recorded inland, especially in the Negev desert and along the Dead Sea Rift Valley. The Na/Cl ratios demonstrate a clear marine origin for these ions in the rainwater, while for other solutes, especially for SO4, a strong non-seaspray (NSS) contribution is observed. In 11 out of 17 samples (i.e. 65%), seaspray sulfate constitutes a minor fraction (< 0.5). A mixing model was formulated to apply the composition of rainwater (Cl and SO4) and its isotopic δ34S values for the estimation of the SO4 sources. Four major end-members were considered: (a) seaspray, (b) marine gypsum and anhydrite, (c) marine dimethylsulfide (DMS) and (d) anthropogenic sources. The uniform isotopic composition, around 0%, of the NSS sulfate indicate minor contribution of end-member (b) and (c), and support on end-member (d) as the major non-seaspray donor. This constant δ34S value is in disaccord with the wide δ34S range of anthropogenic sulfur, and can be explained by efficient mixing of anthropogenic sulfates resulting in a homogeneous “hemispherical” reservoir.