Upwelling is very good for supplying nutrients to the shallow waters and creates the greatest fisheries in the World. Likewise, the currents of the oceans are known, but mysterious. The deep ocean waters are controlled by density differences. There is no effect of wind at depth. Saline water is heavier than fresh water.
Cold water is more dense than hot water.
That s it. Everything that happens can be explained in terms of this. The only other variable is the winds on the surface of the Oceans. They drive the shallow currents, which end up in the deep ocean. It runs up to about 35 N. Warm waters, approx.