California State University Long
Beach
GEOL 300i; Earth Systems and Global Change
Lecture 9
Dr. Rick Behl
Oceanic Circulation
Surface currents in the Oceans
- Main surface currents driven by winds
- Surface Water - above thermocline (warm -- less dense)
- Winds move surface water - The Ekman Spiral
- Surface "layer" moves about 45
degrees to right of wind (northern hemisphere)
- Deeper "layers" move to right of
shallower layers (down to a depth of approximately 150 m)
- Net transport of water (sum of all movement) is 90 degrees to right of wind (N.
Hemisphere)
- Gyres of surface currents
- Sub-tropical and sub-polar gyres
- Centers shifted to western side of ocean basin
- Consequence: intensification of western boundary current
- Western boundary currents (eg. Gulf Stream, Brazil Current, etc.)
Vertical movement of water
- Local vertical movement
of water caused by winds
- Coastal upwelling/downwelling
- Surface waters move offshore and are replaced by deeper
waters (colder with more nutrients)
- Areas of major upwelling along eastern boundary currents, such as the California Current
- Downwelling = "reverse" of
upwelling
- Equatorial upwelling
- Change in direction of Coriolis at the equator
to right in NH -- to left in SH
- Divergence of surface water away from equator
Deep Ocean Circulation
- Currents resulting from density differences in SW
- Temperature: colder seawater = more dense
- Salinity: higher salinity = more dense
- Density of seawater controlled by both factors
- thermohaline circulation
- = ocean circulation driven by temperature
& salinity
Sources of deep water flow
- Atlantic Ocean:
- Antarctic (Weddell Sea) - AABW (Antarctic
Bottom Water)
- North Atlantic (Norwegian Sea) - NADW (North
Atlantic Deep Water)
- Intermediate Water - mixtures and other sources
- Mediterranean Water - (warm, salty)
- Pacific Ocean:
- Pacific Common Water (mixture of AABW and NADW)
- Surface Water - same as before
Together, these water masses and their formation
- Give the vertical structure of the oceans
- Propel deep water circulation
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Phone: 562-985-4928
written by R. Behl.
Last changes: 01 Oct 1997