Which effect most immediately reduces primary productivity during El Niño events where upwelling of the Humboldt Current weakens?

💡 Explanation

When upwelling weakens during El Niño, nutrient transport from deep ocean layers to the surface decreases because the upwelling currents are diminished, curtailing nutrient delivery. Therefore, reduced surface nutrients is the immediate outcome, suppressing productivity, unlike other effects which impact this process indirectly.

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