Which geophysical outcome primarily disrupts global anchovy populations from South American upwelling regions during an El Niño event?

💡 Explanation

During El Niño, reduced trade winds cause the thermocline depth (boundary between warm surface water & cold deep water) to increase, decreasing the upwelling of nutrient-rich waters because of diminished vertical temperature gradients. Therefore populations are affected, rather than wind changes, sediment discharge, or seabed nutrients which don't directly affect food availability.

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