Methanesulfonate (MSA) and non-sea-salt (nss) sulfate concentrations were measured in bulk aerosol samples collected during January 1996 to December 1999 at two stations along the Turkish and Cretan coastline of the eastern Mediterranean. The data set enabled the origin and variability of biogenically derived sulfate concentrations in the eastern Mediterranean atmosphere to be defined. Although similar seasonal patterns of MSA and nss-sulfate concentrations for both stations were detected, the mean concentrations at Erdemli (Turkey) over the sampling period (42 +/- 52 ng m(-3) MSA, and 6.8 +/- 5.2 mug m(-3) nss sulfate) were found to be almost twice that of those measured at Finokalia, Crete (25.8 +/- 14.9 ng m(-3) MSAand 3.9 +/- 1.7 mug m(-3) nss sulfate). Analysis of the air mass back trajectory and the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) data suggests that the majority of the biogenic contribution at Erdemli is originated from summer coccolithophorid Emiliania huxleyi blooms developed in the Black Sea. The data further points to a significant relationship between Saharan dust transport events and local oceanic production of MSA through occasional fertilization of the eastern Mediterranean during wet deposition events. This process accounts for episodic, strong weekly changes in MSA concentrations during the spring months. Considering that Erdemli and Finokalia are approximately 1000 km apart from each other geographically, large differences in their MSA and nss-sulfate concentrations indicates a considerable role of regional mesoscale atmospheric transport processes on the spatial structure of biogenically produced atmospheric sulfur aerosols.