The different oceans don’t actually mix.
It seems as though here is just one ocean but this is not the case. There are clear borders as though there is an invisible wall.
Why does this happen? The Atlantic and Pacific ocean have different density and chemical makeup. You can see simply by their colour that they are different. Their differences (physical and biological) are called ocean clines. Haloclines are borders between waters with different salinity. This is what we see when the different oceans meet. They appear when the water in one ocean is at least 5 times saltier than in the other.
Why is the border horizontal and not vertical? The difference in density is not large enough for one to rise and for the other to fall below. Although, the difference is enough for there to be a ‘border’.
Another reason is inertia. One of the initial forces known as coriolis force influences objects when they are moving in the system of axes. This works because earth is always spinning on its axis. This is why the coriolis force only works in long periods, because the Earth takes one day to spin on its axis. This is why the direction of flows in the different oceans are different.
In addition, the strength of molecules connection. This strength means that molecules don’t break apart from each other, it also means that they don’t mix. They also get carried away by the current so do not have the chance to mix.
It is not only the Atlantic and Pacific oceans that don’t mix. There are examples of this all over the world. We know that thermoclines are borders between waters of different temperatures.
There are also chemoclines which are borders with water having different microclimate and chemical make-up. The Sargasso Sea is the most well known chemocline. It is a sea in the Atlantic ocean, with no shores, yet it is impossible to miss.
Some examples of water not mixing are: the Mediterranean sea and Atlantic ocean, the Caribbean sea and the Atlantic ocean, the North and Baltic Seas and the Surinam River and the Atlantic ocean.