Where do all cold and warm ocean currents originate?

Are the major ocean currents the ones that are closer to the surface?

• Which ocean currents and Prevailing winds be similar and which would be different? If there were any reasons in why they are different, would that be because of their depth? Example, deep ocean currents are not greatly influenced by air masses, right? Also, the ones that are similar are the ones closer to the surface, right?

• Answer:

  Very good question, Jude! Fluids and gases are affected by the Coriolis force that is the result of the earth spinning on itself. It works only for very large systems moving slowly. That the water drains from your sink in one or the other way is an urban legend; it doesn't at that scale. But air masses and oceanic water does. In the northern hemisphere, for example, the Coriolis force makes moving water and air to turn to the right. For example, in the northern Atlantic, the air moves in a general direction that is clockwise around a center that is the Azores islands. At its north; the prevailing westerlies and at its south, the Trade winds. With time, that has also moved the surface water of the ocean in a similar pattern. But water is more complex; it reacts to salinity and temperature. Salty water sinks and so does cold water. In fact, water is heaviest at 4 degrees Celsius and that is the temperature at the bottom of all oceans. That complex system results in what is known as the thermohaline circulation that is also known as the oceanic conveyor belt. It takes the water from all oceans in a pattern that takes thousand years to loop. For example, the warm water from the Mexican Gulf moves north east toward Europe and Norway; where it sinks as it gets colder, under the north pole, to reappear as a deep oceanic current moving, this time, southward, to the southern Atlantic. This is, in fact, the pattern that some are afraid global warming may disturb. If it should happen, the warm water from the Gulfstream will turn south before reaching northern Europe and some predict that Scandinavia and Scotland may be under a huge glacier, as it was during the last ice age. Just to show how much it affects the climate: The Gulfstream water is the reason north Norway, at latitude 71 north (!) is ice free even during the coldest winter.