working on my 3rd ambient record right now, and there is an āocean 3ā on it, so I completely agree, hah. I think water is so inspiring in terms of ambient stuff, especially gigantic bodies of water like the ocean, because they can be visually limitless (both horizon-wise and depth wise), but can also have so much complexity in them (ripples, sea life, etc.). They also have extremely slow cyclic/tidal movement which I feel like can be interesting to try to invoke in a longer form piece.
EDIT: released this before the comp on my last record, but here is one of my long-form slow moving takes on the ocean if anyone is interested: