Because the Gulf Stream carries warm water up from the Gulf of Mexico, what effect does it have

All bodies of water experience thermal stratification. This is when the ocean, for example, forms different layers of water that differ by temperature. It is a result of equilibrium. Since warm water is much heavier than cold, then the thermal stratification starts from the coldest layer as the topmost, and the warmest layers at the very bottom. So, when a stream moves in to a body of water, for a example from gulf to gulf, there will be convection of currents. The stratification gets disturb for a moment causing mixing. After a certain time when it reaches equilibrium, it will achieve thermal stratification again.