Andrea's point is probably the answer you're looking for, however, you should keep in mind that many (most?) environmental laws are driven more by politics than by the available data. Scientists do research on any number of topics (environmental or not) that have implications for our society. We (scientists) like to think that policy makers take our data and results into consideration when drafting legislation, but I would say that in my experience this rarely happens. For one, there have rarely been any federal legislators who understand science. Even the few physicians who've gone into politics seem largely to fail to understand very basic tenets of science, or at least they don't often demonstrate it with their political actions. Leaving environmental issues, for example, if politicians took science into account, there would be no discussion in any school district in the country about whether or not evolution should be taught in schools, as there are simply *NO* scientists who are qualified to have an opinion who would suggest it shouldn't. Environmental issues are not really any different.
Answer - The Arctic Ocean has the lowest average salinity, especially due to low evaporation (caused by reduced temperature), but also by heavy freshwater inflow from rivers and
