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Why does the Equatorial Countercurrent flow eastward?

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World map showing major ocean current systems, with arrows indicating the direction and speed of warm and cold currents in the Atlantic, Pacific, Indian, Southern, and Arctic Oceans. Warm currents are marked in red and cold currents in blue, with currents labeled by name and symbols denoting those that reverse direction seasonally. A legend explains current speed categories and color codes. — ocean current Major ocean current systems of the world.

The Equatorial Countercurrent flows eastward primarily due to the influence of the trade winds. These winds blow constantly across the Atlantic, Pacific, and Indian oceans, pushing vast volumes of water westward and creating the North and South Equatorial currents.12

This westward movement of water causes the sea level to rise in the western regions of these ocean basins. The Equatorial Countercurrent, which is located within the doldrums—a region characterized by the absence of strong, constant winds—acts as a return flow. Because the sea level is higher in the west, the water naturally flows downslope toward the east to achieve equilibrium.2