The oceans of the world slowly mix and are really one ocean because of thermohaline circulation and other currents.
Thermohaline circulation describes deep water currents which accounts for 90% of the ocean and their movement is due to gravity and density-driven forces. It is also influenced by the horizontal difference in salinity and temperature.
The movement of these water current is very slow; the water transports nutrients, heat, solids, and other material a great distance. It also drives warmer surface water. Thermohaline circulation occurs at deep ocean basins at the slow rate of 1 cm per second and it is influenced by convective currents which displace the water of different temperatures.
