Wallace Broecker's 'Conveyor Belt' theory is described as thermohaline circulation, which means driven primarily by heat (therme) and salt (hals). It spreads solar heat from the tropics to the high latitudes and transports salt out of it. As it switches states it changes the amount of heat it transports to the North Atlantic.
It is a broad band of deep water sweeping down the center of the Atlantic to the Antarctic, spreading into the Indian and Pacific, welling up to the surface there, and returning as an equally broad and unwavering band to the North Atlantic. (This is a very crude simplification of the complicated flow of water.)