[yawpitch]

The ocean can’t have GPS because GPS relies on time of flight calculations for radio waves (aka light) traveling at the speed of light through air. The ocean, to the surprise of many, is not composed of air, and is really, really, exceptionally good at scattering light. What you could have, instead, is an acoustic positioning system that would rely on fixed transponders that would allow time of swim calculations for sound waves traveling through water. This would be phenomenally problematic, as you’d need a near perfect understanding of confounding factors like salinity, temperature, depth, etc to accurately model the incoming reply… you’d also drive the whales and fishes to consider well justified total warfare against the really loud and insensitive terrestrial creatures they vastly outnumber.