What causes currents? (surface and deep ocean)?

Question

What causes currents? (surface and deep ocean)?

Answer 1

The main causes of currents are: solar heating, winds and gravity.

Surface ocean currents, which make up about 10% of all the water in the ocean and are restricted to approximately the upper 400 meters of the ocean, are generally wind driven and develop their typical clockwise spirals in the northern hemisphere and counter-clockwise rotation in the southern hemisphere because of the imposed wind stresses.

Deep ocean currents are driven by density and temperature gradients. Thermohaline circulation, also known as the ocean's conveyor belt, refers to the deep ocean density-driven ocean basin currents. Upwelling and downwelling areas in the oceans are areas where significant vertical movement of ocean water is observed.

The movement of deep water in the ocean basins is by density driven forces and gravity. The density difference is a function of different temperatures and salinity. Deep waters sink into the deep ocean basins at high latitudes where the temperatures are cold enough to cause the density to increase.