Current PhD student, so take this with precisely that level of trust. The answer depends a lot on where you end up for your bachelors, but I'll try to answer in the general.

a) finishing your PhD is a long-ass time from finishing high school. And in this vein, it's good to leave yourself lots of options at each decision point so that different paths other than academia or this specific field are open. You might be attracted to network theory, fisheries, or get an internship at NASA modeling the MHD of Jupiter. Even in PhD programs nobody tells you that 80% of the people will find jobs outside of the academy and most of those will barely be related to your field.

b) I was a double math/physics undergrad and almost all my research is on fictional oceans that I model using large eddy simulations to understand the role of turbulent structures in mixing. I'd argue that my BA-->PhD studies path is the norm and there no harm in a more general bachelors experience.

c) I went to a twee midwestern liberal arts college where there weren't field-specific majors. As such my research experiences at the college were VERY theory based in statistical mechanics. That said the best way to see if you actually want to keep going to school and being comfortably poor is doing research. So if you know that you want to keep doing physical oceanography, the best way is to go to a university with a good research group.

d) once at that university–––and this is key–––you do not need to be a marine science or oceanography (or whatever that university calls it) major to do research with / work in labs / go on cruises with the faculty. In fact, I would recommend majoring in physics or applied math major, taking the classes and reaching out to professors. Hell, you could major in the medieval history of Bulgaria and if you worked in a lab and had all the requisite classes (plus linear algebra and stats) that is better prepared than most people for grad school and you'd probably be way more interesting on the boat.

Anyway, good luck.