1. Ocean Circulation
Page 42 in Notebook

2. Ocean Layers
- Ocean is stratified based on its temperature, density, and salinity
- Well-mixed surface layer of approximately 100 m (330 ft)
- Layers of increasing density and salinity and decreasing temperature to a depth of about 1000 m (3300 ft)
- Pycnocline – between 100m and 1000m, where density increases rapidly
- Thermocline – between 100m and 1000m, where temperature decrease rapidly
- Halocline – between 100m and 1000m, where salinity increases rapidly.

3. Water Exchange
- Processes that increase the water’s density at the surface cause density-driven vertical circulation.
- Typically, the salinity and temperature change at the surface, so this process is most often called thermohaline circulation
- Downwelling – areas of thermohaline circulation where water converges and sinks
- Upwelling - areas of thermohaline circulation where water diverges and rises

4. Downwelling - Brings oxygen-rich surface water to the depth
- Occurs in areas where surface waters are driven together by the wind or against a coast
- Can be affected by seasons – for example, downwelling occurs along west coast of U.S. during winter as winds blow from south to north and upwelling occurs along the west coast of U.S. during summer as winds blow from north to south

5. Upwelling
- Returns low oxygen-content water with dissolved, decay-produced nutrients to surface
- Deep sea nutrients act as fertilizers to promote photosynthesis and the production of more oxygen in sunlit surface waters
- Occurs when the wind blows surface waters away from an area or coast.

6. Internal Mixing of Water
- Surface mixing occurs during turbulence caused by wind-driven waves and surface currents at the surface.
- Deeper water mixes due to tides at depth.

7. Surface Currents
- Surface currents are caused by atmospheric circulation in the form of wind.
As wind blows over the water, the greater mass of the water is pushed forward. This mass continues moving due to its inertia.
- While currents generally always flow the same way, they will shift slightly due to seasonal changes with the wind.
- Currents are also modified by the action of other currents and areas of convergence (downwelling) and divergence (upwelling).

8. Direction of Currents
- The Coriolis Effect describes the deflection of moving water to one direction or the other based on the Earth’s rotation.
- In the Northern Hemisphere, surface currents are deflected to the right of the driving wind force (clockwise).
- In the Southern Hemisphere, surface currents are deflected to the left of the driving wind force (counterclockwise).
- Surface water also moves at an angle of 45 degrees to the wind direction.

9. Gyres - Gyres are large, circular-motion wind-driven current systems.
- These gyres exist in every major ocean basin, circulating water towards the poles and back again to the equator.
- In the Northern Hemisphere, they spin clockwise.
- In the Southern Hemisphere, they spin counterclockwise.
- Currents flowing on the western side of each ocean tend to be much stronger and deeper. This is known as western intensification.