@Amphibious54- A few different types of currents circle the oceans. I cannot say this for sure, but your assumption about ocean trenches having an effect on the currents is probably right. The deepest parts of the ocean would have an effect on the deep ocean currents that exist due to density changes.
From what I can remember from geology, the thermohaline currents follow the ocean trenches because they are the deepest point where the cold, dense water accumulates. This is also the reason that the ocean trenches are the coldest place on earth.
If my memory serves me correctly, the sun heats the surface water, which sits on the top. As the water reaches the poles, it cools and begins to sink. This cold water then gets pushed along the trenches until it warms in the Pacific and Indian oceans, losing density and rising to the surface, the cycle then repeats itself in perpetuity.