ocean living book (geography perspective)

I am looking for a book (for a grade 5 student, but would be happy for anything in a grade 3-6 range) that is about the ocean in a more geography standpoint rather than about sea life.  About currents, coasts, temperature etc…

Most of what  I find when I look is about sea creatures, which is fascinating and a good compliment, but I’m having difficulty finding something that is more specifically geography related.

I’d love any ideas you have!