I am not so sure that it is necessarily one or the other. I remember from oceanogrphy class so many years ago, that ocean salt water can react as either depending on the substance it contacts. ie it can be an acid to some and base to others.
We have a discount gocery down the street that sells 2 liter bottles of diet store brand soda at 3 for a $1.00. That is basically carbolic acid, yet some folks use it to clean their cases. Depending on the lube I use, the ends of my cases stay bright and shiney were the lube has contacted them, even if they started out somewhat dull and tarnished. (Almost like Tarnex is in the lube.) I remember that vinegar and a few other chemicals were used in the old days to clean black powder fouling from brass.
According to some buffalo hunters, they filled the barrels with fresh urine to clean the barrels, I don't know if that neutralized the powder residue, or was a just a source of liquid in an arid country.