Why are ocean surface waters generally warmer near the equator than near the poles?

Ocean surface temperatures are generally warmer near the equator than near the poles primarily due to the latitudinal distribution of solar radiation.1

The intensity of solar energy received at the Earth's surface depends on the solar elevation angle, which varies systematically with latitude. Near the equator, the Sun reaches a high elevation angle, concentrating solar energy over a smaller area. Conversely, at higher latitudes, the Sun’s rays strike the surface at more oblique angles, spreading the same amount of energy over a larger area and resulting in less intense heating. Additionally, the duration of daylight hours and the tilt of the Earth's axis contribute to a significant radiation surplus at low latitudes and a radiation deficit at high latitudes.21

This uneven heating is further influenced by the fact that the ocean acts as a heat engine, with ocean currents and atmospheric circulation—such as the Hadley cell—transporting heat from the tropics toward the poles. Consequently, while tropical surface waters remain warm year-round, polar surface temperatures remain near the freezing point of seawater.341