Oceanic Circulation Current = a moving mass of water
Oceanic Circulation Surface Currents –horizontally flowing water in the uppermost 400m of the ocean –driven by wind Thermohaline Circulation –slower, deeper circulation –due to the action of gravity on water masses of different densities
Surface Currents Wind –primary force responsible for surface currents Friction drags water along Coriolis effect Continents prevent continuous flow and deflect water… Gyre –the circular flow around the periphery of an ocean basin
Fig. 8-1, p. 172
Fig. 8-4, p. 173
Figure 7.4
Figure 7.7 Ekman Transport
Figure 7.8
Geostrophic Gyres Gyres in a balance between the pressure gradient (due to gravity) and the Coriolis Effect
Figure 7.5
Six great surface current North Atlantic Gyre South Atlantic Gyre North Pacific Gyre South Pacific Gyre Indian Ocean Gyre West Wind drift or Antarctic Circumpolar Current
Fig. 8-3, p. 173
Flow within Gyres Western Boundary Currents (ex: Gulf Stream) –westward intensification - more concentrated due to water piling up due to eastward rotation of earth and the Coriolis Effect –narrow, fast ( 3-10 km per hour or 2-6 miles per hour), deep currents that carry warm water toward poles
Figure 7.8
Fig. 8-13b, p. 180
Flow within Gyres Eastern Boundary Currents (ex: Canary Current) –broad, slow, shallow currents that carry cold water toward equator
Table 7.2
Flow within Gyres Transverse Currents –Northern or Southern Border currents (ex: North Atlantic Current) –Equatorial currents (ex: North Equatorial current) –currents that flow from east to west or west to east
Flow within Gyres Currents affect climate: –North Atlantic current warms England –California current cools San Francisco in the summer
Figure 7.5
Figure 7.9 Sea Surface Temp in August And in February
Vertical Circulation Upwelling –upward movement of water Downwelling –downward movement of water
Figure 7.12a
Vertical Circulation Coastal Upwelling –cold, deeper water upwells to replace the surface water –leads to increased nutrients & productivity and cooler climates
Figure 7.10
Vertical Circulation Equatorial Upwelling –westward flowing equatorial currents are deflected poleward –deeper water comes up to replace the surface water
Figure Causes of upwelling
Vertical Circulation Downwelling –water driven toward the coast will be forced down –Brings down dissolved gases
Figure 7.11
Deep Circulation Thermohaline Circulation Driven by density differences water masses do not mix easily but flow above or beneath each other
Some Water Masses in the Deep Atlantic Antarctic Bottom Water North Atlantic Deep water Mediterranean Intermediate Water Antarctic Intermediate Water
Figure 7.27
Thermohaline Circulation Sinking of water masses is offset by slow, gradual rising across warmer temperate and tropical zones
Fig. 8-26, p. 192
Thermohaline Circulation Much slower than surface circulation –10-20 km per year or 6-12 miles per year –Would take water a year to move as far as surface water would move in an hour
Figure The Ocean Conveyor Belt Model