1. Current Variations Not all currents are driven by the wind

2. El Niño-Southern Oscillation (ENSO) El Niño = warm surface current in equatorial eastern Pacific that occurs periodically around Christmastime Southern Oscillation = change in atmospheric pressure over Pacific Ocean accompanying El Niño ENSO describes a combined oceanic- atmospheric disturbance

3. Normal conditions in the Pacific Ocean Figure 7-18a

4. El Niño conditions (ENSO warm phase) Figure 7-18b

5. La Niña conditions (ENSO cool phase; opposite of El Niño) Figure 7-18c

6. The 1997-98 El Niño Sea surface temperature anomaly map shows warming during severe 1997-98 El Niño Internet site for El Niño visualizations Current state of the tropical Pacific Figure 7-19a

7. El Niño recurrence interval Typical recurrence interval for El Niños = 2-12 years Pacific has alternated between El Niño and La Niña events since 1950 Figure 7-20

8. Effects of severe El Niños Figure 7-21

10. Surface salinity variation High latitudes have low surface salinity High precipitation and runoff Low evaporation Tropics have high surface salinity High evaporation Low precipitation Equator has a dip in surface salinity High precipitation partially offsets high evaporation

11. Salinity changes with depth Salinity variation with depth Curves for high and low latitudes begin at different surface salinities Halocline = layer of rapidly changing salinity At depth, salinity is uniform

12. Seawater density Factors affecting seawater density: Temperature, Density (inverse relationship) Salinity, Density Pressure, Density Temperature has the greatest influence on surface seawater density