With 1.3 109 Tg (teragram = megaton = 1012 g) of sulfur present as sulfate, the oceans represent one of the largest sulfur pools on earth (Vairavamurthy et al. 1995). The main influx of sulfur to the oceans occurs via river water carrying the products of mechanical and chemical weathering of continental rocks. Relative to this fluvial input, the atmospheric transport of sulfur is of minor importance. It mainly consists of recycled oceanic sulfate from seaspray, volcanic sulfur gases, H2S released by sulfate-reducing bacteria, organic Sbearing compounds released into seawater and subsequently into the atmosphere by phytoplankton, and anthropogenic emissions of sulfur dioxide. Due to the oxic conditions that prevail in the world's oceans, the dominant sulfur species in seawater is by far the sulfate ion (SO42-). Sulfate is the second most abundant anion next to chloride and has a concentration of 29 mM (2.71 g/kg) in ocean water. Marine sediments are the main sink for seawater sulfate which demonstrates that the sedimentary sulfur cycle is a major component of the global sulfur cycle. The most important mechanisms for removing sulfate from the oceans to the sediments are (1) the bacterial reduction of sulfate to hydrogen sulfide, which subsequently reacts with iron to form sulfide minerals, particularly pyrite (FeS2), (2) the formation of organic sulfur, i.e. the incorporation of sulfur into sedimentary organic matter during early diagenesis, and (3) the precipitation of calcium sulfate minerals in evaporites (Vairavamurthy et al. 1995). With respect to the relative importance of each pathway, Vairavamurthy et al. (1995) point out that although marine evaporites were important sinks for sulfate from the Late Precambrian to the late Tertiary, their rate of formation in today's oceans, over the last few million years, is quantitatively insignificant. Thus, they conclude that the burial of sulfide minerals and, to a less extent, of organic sulfur represents the major sink for oceanic sulfur in the modern ocean.