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.
It means: to form a question based on something that interests you (example: why did my CD player stop working?);a hypotheses is a statement (using the words if, then, and because) based on your prediction or predictions (example: If i plugged in my CD player, then it will work again because CD players need electricity to work).