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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
