Figure 5. Values of 34S vs. concentration of residual sulfate of all measured pore waters from Site 161 and a schematic diagram showing how different processes may influence the composition of dissolved sulfate. Arrows are theoretical trends starting with Mediterranean seawater (star = surface seawater at Site 973) for (1) authigenic precipitation of gypsum, (2) microbial sulfate reduction, (3) dissolution of Messinian gypsum, and (4) reoxidation of dissolved sulfide. Note that the direction of the gypsum dissolution arrow may change when other initial values for the solution are considered. Arrow sizes indicate the estimated overall importance for the Leg 161 pore waters.