Which mechanism primarily diminishes near-surface chlorophyll concentrations across equatorial Pacific during El Niño events?

💡 Explanation

During El Niño, weakening trade winds cause a reduction in the equatorial undercurrent and upwelling because suppression of normal flow disrupts the transfer of nutrient-rich deep waters towards the surface. Therefore, diminished upwelling lowers nutrient availability and decreases chlorophyll, rather than increased sunlight, more grazing, or phytoplankton booms, which may occur in other contexts and conditions.

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