Contributions of Atmospheric Deposition to Pb Concentration and Isotopic Composition in Seawater and Particulate Matters in the Gulf of Aqaba, Red Sea.

Abstract

Lead concentrations [Pb] and isotope ratios (206Pb/207Pb, 208Pb/207Pb) have been measured in samples of total suspended particulate (TSP) aerosols, seawater, and suspended and sinking particles in the Gulf of Aqaba (GOA), Red Sea. Isotope ratios of Pb in seawater and in the soluble fraction of Pb in atmospheric TSP were similar suggesting that TSP is an important source of Pb in this area. Pb concentrations in seawater measured in this study (max 76.8 pmol kg-1) were much lower than those recorded at the same location in 2003-2004 (up to 1000 pmol kg-1). Changes in Pb isotope ratios in TSP depositions in these years indicate that leaded gasoline was responsible for the high dissolved Pb in GOA more than a decade ago and that recent regulation reduced Pb contamination. The similarity in Pb isotope ratios in suspended and sinking particles implies close interactions between these two size fractions. This study demonstrates the effect of the phasing out of leaded gasoline on TSP and seawater Pb chemistry in the Northern GOA; the rate of change in dissolved Pb concentrations in the GOA is faster than that reported for the open ocean possibly due to higher particle scavenging and the relatively short residence time of deep water in the Basin.