How does the sulphate from exhaust gas cleaning systems affect seawater composition?
Sulphate is a naturally occurring constituent of seawater. It is soluble and has a long “residence time”, as it is unaffected by the natural pH, temperatures and pressures found in the oceans. It is therefore said to be “conservative” in that regardless of the total salinity it occurs mixed throughout the oceans in the same ratio to the other conservative constituents such as sodium . The large amount of sulphate in seawater is derived from volcanic activities and degassing at the seafloor. Further, sulphates reach the oceans via river flows, but the concentration in open seawater remains constant at around 2.65 g/l  or about 20kg of sulphur per tonne of seawater.
Studies  and in field testing  confirm that the sulphate increase from exhaust gas scrubbing will be insignificant when compared with the quantity already in the oceans.
An analogy that has been used is if all the sulphur in the world’s oceans were to be removed, it would form a layer around the earth about 1.7M thick. All the sulphur in all the known oil reserves would add only another 10 micron to this layer .