A layer of water in which the density changes rapidly with changes in depth.

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pycnocline

Circulation pattern in which surface water moves vertically downward.

​​downwelling

​Circulation pattern in which deep, cold, usually nutrient-rich water moves vertically upward.

​​upwelling

​Change in atmospheric pressures and wind directions in the South Pacific Ocean.

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El Nino Southern Oscillation (ENSO)

​Due to the southern oscillation, upwelling of cool, nutrient-rich water stops and downwelling occurs off the coasts of Peru and Chile.

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El Nino

​Due to the southern oscillation, normal conditions return stronger than usual.

La Nina