What drives global thermohaline (conveyor belt) circulation?

Hi the answer to your question would be, Theremohaline circulation is mostly driven by global density gradients created by surface heat. So, deep ocean currents are caused by the water's density, which is controlled by the temperature (greek word thermo) and salinity (haline). This is thermohaline circulation described. Now once the sea water gets more saltier and then ice forms some salt is left behind and then density increases & starts to sink. Now surface water comes in to replace the sinking water & the temperature drops and then it becomes cold & salty enough to sink. This initiates the deep ocean currents which drives the global conveyor belt. Let me know if you need me to explain more. Hope this helped :)