The primary reason warm ocean currents begin at the equator is that the equator receives more direct and intense sunlight, warming the water. This concentrated solar energy heats the surface of the ocean more at the equator than at higher latitudes.
While volcanic activity and geothermal energy can play a role in local water temperatures, the dominant factor for warm ocean currents is the solar heating at the equator. Heat does not significantly rise from the poles to warm the mid-latitudes in a way that directly influences ocean currents. Instead, ocean currents are governed by a combination of wind patterns, Earth's rotation, and temperature differences, with warm water generally moving from the equatorial regions toward the poles.