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 minimum tax (AMT) is an extra tax some people have to pay on top of their regular income tax. It has its own set of rates and rules for deductions, which are less generous than the non-AMT rules. The idea behind the AMT tax was to prevent people with very high incomes from using special tax benefits to pay little or no tax. But the AMT kept expanding its reach over a 42-year history and has applied to taxpayers who don't have a very high income or who don't claim lots of special tax benefits.