SOURCES OF SULFUR IN RAINWATER AS INDICATED BY ISOTOPIC DELTA-34S DATA AND CHEMICAL-COMPOSITION, ISRAEL

Seventeen rainwater samples from 11 different locations in Israel have been analyzed for their chemical composition and deltaS-34 values. The deltaS-34 range between 0.0 and 15.3 parts per thousand and fall within the deltaS-34 variations in rainwater in nature (-2.5-19.4 parts per thousand). This range is characteristic for the last 40-50 years over various parts in the world. Higher deltaS-34 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 deltaS-34 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 parts per thousand, 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 deltaS-34 value is in disaccord with the wide deltaS-34 range of anthropogenic sulfur, and can be explained by efficient mixing of anthropogenic sulfates resulting in a homogeneous ''hemispherical'' reservoir.