system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How can we tell the oceans apart?

I know this seems really strange, but basically since they all eventually touch, like the Atlantic touching the Pacific, the Atlantic touching the Indian Ocean, the Atlantic touching the Arctic Ocean, the Indian Ocean touching the Pacific... what makes them individual bodies of water instead of one mega-ocean? 

I know they have a variance of temperatures, under water ecosystems/animals, but is this the only thing stopping them from being a mega-ocean?
gpt
They ARE a single mega-ocean. You have to remember: humans only name and classify things in order to make things convenient for ourselves. There's literally no such thing as "the Atlantic Ocean," as a discrete, specific body of water. It's all in our heads.

It helps us to have names for things, so we can refer to them...but the ocean doesn't care, because it's just a bunch of water. You ask "what makes them individual bodies of water instead of one mega-ocean?" The answer is: we do. Nothing else. It's just humans being human. The parameters might be specific or vague, but they're really just arbitrary, human conventions.