Seriously, nothing separates them

Isn't it more of a territorial type of thing

Some borders of some of the oceans meet but don't mix.

What separates most countries? An invisible line.

In history we were discussing geography and oceans. My teacher said that in a different class period a kid asked why the oceans have different names if they're all one ocean. She told him that they're not one ocean and they have glass walls separating the oceans. Another kid piped up and said "yeah so if a shark tries to cross into a different ocean it'd just hit the glass." He believed it.