Because salinity (in concert with temperature) affects the density of seawater, it can play a role in its vertical stratification. Essentially, lower salinity water (= lower density) floats on top of higher salinity water (= higher density).
Alternative definition, a choice limited to one of two or more possibilities, as of things, propositions, or courses of action, the selection of which precludes any other possibility: You have the alternative of riding or walking. See more.
Also referred to as one-and two-sided hypotheses, these refer to the alternative hypothesis. The alternative hypothesis, referred to above, is a non-directional alternative hypothesis; it states that there is a difference, with no indication of the direction of change, eg higher or lower, more or less. This is a non-directional (two-tailed) alternative hypothesis.