Current Variations Not all currents are driven by the wind.

Current Variations

Not all currents are driven by the wind

El Niño-Southern Oscillation (ENSO)

El Niño = warm surface current in equatorial eastern Pacific that occurs periodically around ChristmastimeSouthern Oscillation = change in atmospheric pressure over Pacific Ocean accompanying El NiñoENSO describes a combined oceanic-atmospheric disturbance

Normal conditions in the Pacific Ocean

Figure 7-18a

El Niño conditions (ENSO warm phase)

Figure 7-18b

La Niña conditions (ENSO cool phase; opposite of El

Niño)

Figure 7-18c

The 1997-98 El NiñoSea surface temperature anomaly map shows warming during severe 1997-98 El NiñoInternet site for El Niño visualizationsCurrent state of the tropical Pacific

Figure 7-19a

El Niño recurrence intervalTypical recurrence interval for El Niños = 2-12 yearsPacific has alternated between El Niño and La Niña events since 1950

Figure 7-20

Effects of severe El Niños

Figure 7-21

Surface salinity variation High latitudes have low surface salinity

High precipitation and runoffLow evaporation

Tropics have high surface salinityHigh evaporationLow precipitation

Equator has a dip in surface salinityHigh precipitation partially offsets high evaporation

Salinity changes with depth

Salinity variation with depth Curves for high and low latitudes begin at different surface salinitiesHalocline = layer of rapidly changing salinityAt depth, salinity is uniform

Seawater density Factors affecting seawater density:

Temperature ↑, Density ↓ (inverse relationship)Salinity ↑, Density ↑Pressure ↑, Density ↑

Temperature has the greatest influence on surface seawater density