Ocean currents can be divided into two types of flow based on the forces that drive them. Most currents in the upper kilometer of the ocean are driven by the wind. Deeper currents are driven by mixing which brings very cold dense water up to the surface. The dense water is replaced by cold dense water that sinks to the bottom near Greenland, Norway and Antarctica. Deeper water is affected by long variability of climate.
Climate controls salinity and temperature of the water which has everything to do with density .
The arrows in the image represent the currents directions. The length of the arrows represents the currents speed.