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.
Explain, elucidate, expound, interpret imply making the meaning of something clear or understandable. To explain is to make plain, clear, or intelligible something that is not known or understood: to explain a theory or a problem. To elucidate is to throw light on what before was dark and obscure, usually by illustration and commentary and sometimes by elaborate explanation: They asked him to elucidate his statement.