| 1. Surface Currents and Gyres: |
| Learning Objectives: |
- Appreciation of the role of the Coriolis force in controling current
directions
- Understanding how currents form and how the water moves
- Recognition of the characteristics of surface ocean circulation in
the oceans
|
| Influence of Ekman spiral and Ekman Transport: |
- Coriolis effect acts on surface water
- deflects it from the wind direction
- Transfer of wind with depth to about 100 -150m
- deflected by Earth's rotation
- right in N. hemisphere
- left in S. hemisphere
- speed decreases
- Net result:
- water movement at 90° to wind direction
- dependent on wind persistence.
|
| Geostrophic Flow: |
- Convergence of surface water thickens surface layer
- divergence of surface water thins surface layer
- water flows away from domes created by convergence
- moves down under gravity
- deflected by Coriolis effect
- result: circular motion
- Dynamic topography mapping by satellite, related to standard height
|
| Gyres: |
- Circular current systems
- eastward flowing water (weak) at higher latitudes
- boundary currents parallel to continental margins.
|
| Characteristics of Individual Oceans: |
- Pacific Ocean:
- North and South Equatorial currents, westward flowing
- separated by eastward flowing Equatorial Countercurrent (doldrums)
- northeast Pacific: California current
- northwest Pacific: Kuroshio
- smaller gyres within subpolar/polar regions
- south Pacific: West Wind Drift, Peru (Humbolt) Current
- southwest Pacific: East Australia Current.
- Atlantic Ocean:
- equatorial currents like the Pacific
- northeast Atlantic: Canary
- northwest Atlantic: Gulf Stream
- smaller gyres within subpolar/polar regions:
- Labrador, E. Greenland, Norwegian Currents.
- south Atlantic: Brazil and Benguela Currents.
- Indian Ocean:
- equatorial currents, Agulhas and W. Australian Currents.
- Arctic Ocean:
- cockwise gyre creating ice drifting.
|
| Characteristics of Ocean Currents: |
- Speed of ocean currents
- wind-driven currents
- range of speeds (e.g. 0.1 - 0.5m/s) faster through narrow gaps.
- move large volumes of water: Gulf Stream 55 x 10
6 m3/s.
- Western intensification of currents:
- gyres displaced to W. by Earth's rotation
- deeper pycnocline in west
- Earth's rotation strengthens currents as they flow to higher latitude:
Boundary currents
- western, Gulf Stream and Kuroshio
- narrow, fast moving bands of water, separated by fronts
- eastern
- weaker, slow moving, more diffuse.
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