miracles in the Qur'an 1 - oceanography

My Muslim convert friend (whom we shall henceforth refer to as "Kevin") suggested I look at verses on oceanography, such as 25:53 on the separation of sweet and salty water, and 24:40 on the oceanic structure. These verses are not meant as an academic lesson apparently, but they do allude to history and science in a way that can be subjected to verification. I thus attempted to do just that...

"In answer to your suggestion that verse 25:53 alludes to a scientific phenomenon previously unkown/unknowable, it seems the idea was widespread since Aristotle:"The drinkable, sweet water, then, is light and is all of it drawn up: the salt water is heavy and remains behind, but not in its natural place.