Seawater is not acidic. There is no such thing as 'acidification' in the literal sense. The water is simply moving closer to ph neutral.
Take a look here:
http://www.miseagrant.umich.edu/lessons/lessons/by-broad-con...
Take a look here:
http://www.miseagrant.umich.edu/lessons/lessons/by-broad-con...
You don't get to redefine commonly used terms just because they're new to you and you think that they sound scary.
Another definition of a basic salt would be a salt that contains amounts of both hydroxide and other anions. White lead is an example. It is basic lead carbonate, or lead carbonate hydroxide. These salts are insoluble and are obtained through precipitation reactions.
So good luck with that exercise.