What causes surface currents to reverse in the southern Pacific Ocean during an El Niño event?

💡 Explanation

During an El Niño event, the Walker circulation weakens, leading to a reduction in the strength of the easterly trade winds. Because these trade winds normally drive westward surface currents, their weakening causes the currents to slow and even reverse; therefore, the weakening trade winds explain the current reversal, rather than other factors like glacial melt or thermohaline changes.

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