The Pacific and Atlantic oceans do mix to some extent, but there are natural barriers that prevent them from fully mixing. These barriers include differences in water temperature, salinity, and density, as well as the Earth’s rotation and the location of ocean currents.
The Pacific Ocean is generally warmer and less salty than the Atlantic Ocean, due to the fact that it receives more direct sunlight and is more affected by the trade winds. The Atlantic Ocean, on the other hand, is colder and saltier, because it is affected by the Gulf Stream, which carries warm, salty water from the tropics to the North Atlantic.
Another factor that affects the mixing of the oceans is their respective densities. The Atlantic Ocean is denser than the Pacific Ocean, due to its higher salt content, which makes it more difficult for the two bodies of water to mix.
Finally, the rotation of the Earth and the location of ocean currents also play a role in preventing the oceans from fully mixing. The Coriolis effect, which is caused by the rotation of the Earth, causes ocean currents to move in circular patterns. This, in turn, causes the waters of the Pacific and Atlantic oceans to flow in different directions, which makes it more difficult for them to mix.
So while the Pacific and Atlantic oceans do mix to some extent, the natural barriers described above make it difficult for them to fully mix.