Which outcome occurs when El Niño-Southern Oscillation weakens the Pacific Walker Circulation?

💡 Explanation

When El Niño weakens the Walker Circulation, reduced trade winds decrease equatorial upwelling because diminished surface water divergence reduces vertical water movement, suppressing cool, nutrient-rich water reaching the surface along the South American coast. Therefore upwelling decreases, rather than other options which depend on different oceanographic processes and locations.

• Which mechanism determines the rate of sediment subduction along an accretionary wedge?
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• Which mechanism primarily determines the orientation (aspect) of a cirque on a mountain range?
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• Which mechanism causes island arc formation during subduction of an oceanic plate beneath another oceanic plate?