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.
The alternative would be a food race in which the United States and the Soviet Union tried to outdo each other stockpiling in preparation for a nuclear winter, a race that would threaten to leave the rest of the world, literally and figuratively, out in the cold.