system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 How it is determined where one ocean starts and another one ends?
gpt
It is largely arbitrary. The oceans are designated to aid navigation and geography. Of course there are general temperature differences and salinity differences, but it is just one big mass of water, which freely flows together. Of course the oceans don’t know they are separate, and whales swim between them heedless of what we call them.