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.
Our explanations can give a matter-of-fact account of what happened. Our goal with an explanation is to advise or update the other person about a particular action, event, or situation. On the other hand, the motivation behind an excuse is to convince someone that we are justified in our action or lack of action. Excuses provide the back story for why something happened. While providing an excuse, we often defend our position. We may apologize for not meeting expectations or commitments. Sometimes we plead for forgiveness so that we can resume the relationship without guilt.