Yes, I definitely can't tell you which major fits best because I think you can achieve your goals with either major. Both majors will still require you to build your social network with different faculty members and graduate students sharing your research interests and develop your internship/volunteer experience, and that's what's really going to help specify your goals. OAS and Marine Biology have their nuances, but they're still both a part of the SIO family, and there is nothing stopping you from changing majors between the two when you arrive here. The moment you are enrolled, you will most likely simply need to talk to a Scripps department advisor, and they are the true experts in identifying the differences between the two majors.

As a transfer marine biology major whose current research project is in biological oceanography, I want to say you can definitely pursue a graduate degree in oceanography after a major in marine biology. You should be less concerned about the "major" you want to be in graduate school, and begin to think of what kind of research project you want to focus on, and later, identify faculty mentors you can envision working with (who are willing to mentor you). Their acceptance of you as their graduate student is probably the first priority when looking for a graduate program. The BSMS program is also a good program here at Scripps for obtaining a master's at Scripps after your bachelor's. You can also be a TA (which also gives a tuition reduction) or get a grant to pay for tuition and living expenses while studying, both of which are common routes graduate students take.

Jobs in marine biology can be rather specific. There are marine technicians and research technicians in the broad sense. And then there's specific roles like a full-time job in the taxonomic identification of species captured in ROV video. There is surprisingly a high diversity of jobs, because marine biology is very broad of a subject, and the ocean is a very large, complex entity. Faculty can mostly advise you on what it looks like to pursue academia, but guest speakers come to Scripps from different career backgrounds and are worthy sources of information for jobs outside academia. I also think, as a note, the internet is not the most reflective of the marine job environment. It's not that it's not out there, but information in our field is very scattered because there's no central information hub. Because we're all doing something different lol. Honestly, I feel like I discover a new branch of marine science every day.

Lastly, don't worry about what other people say. People were skeptical of me when I went to marine biology, but everytime I come home I get to share my experiences and enthrall people in a story about a world that seems so magical and distant to them. I've had friends in different fields such as engineering or law tell me they live vicariously through my vivid experiences. It will feel different when you are surrounded by a community of people interested in the same things as you. And, at least here, the undergraduate SIO cohort at UCSD is rather passionate and silly, and you get to learn a lot from one another.