what causes ocean currents to be warm or cold?

Answer 1

when water goes to the poles, its temperature decreases and salinity increases, making it more dense. This dense water sinks to the bottom of the oceans and form a current of cool water. When this water reaches the equator it heats up making it less dense and forms a warm current. i hope this answers your question:)

Answer 2

If they come from near the equator, they are warm. If they start or spend a lot of time at the poles, they are cold.