Oceanic Circulation

1
Oceanic Circulation

• Current a moving mass of water

2
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

3
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

4
Fig. 8-1, p. 172
5
Fig. 8-4, p. 173
6
Figure 7.4
7
Figure 7.7 Ekman Transport
8
Figure 7.8
9
Geostrophic Gyres

• Gyres in a balance between the pressure gradient
  (due to gravity) and the Coriolis Effect

10
Figure 7.5
11
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

12
Fig. 8-3, p. 173
13
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

14
Figure 7.8
15
Fig. 8-13b, p. 180
16
Flow within Gyres

• Eastern Boundary Currents (ex Canary Current)
• broad, slow, shallow currents that carry cold
  water toward equator

17
Table 7.2
18
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

19
Flow within Gyres

• Currents affect climate
• North Atlantic current warms England
• California current cools San Francisco in the
  summer

20
Figure 7.5
21
Figure 7.9
Sea Surface Temp in August And in February
22
Vertical Circulation

• Upwelling
• upward movement of water
• Downwelling
• downward movement of water

23
Figure 7.12a
24
Vertical Circulation

• Coastal Upwelling
• cold, deeper water upwells to replace the surface
  water
• leads to increased nutrients productivity and
  cooler climates

25
Figure 7.10
26
Vertical Circulation

• Equatorial Upwelling
• westward flowing equatorial currents are
  deflected poleward
• deeper water comes up to replace the surface
  water

27
Figure 7.13- Causes of upwelling
28
Vertical Circulation

• Downwelling
• water driven toward the coast will be forced down
• Brings down dissolved gases

29
Figure 7.11
30
Deep CirculationThermohaline Circulation

• Driven by density differences
• water masses do not mix easily but flow above or
  beneath each other

31
Some Water Masses in the Deep Atlantic

• Antarctic Bottom Water
• North Atlantic Deep water
• Mediterranean Intermediate Water
• Antarctic Intermediate Water

32
Figure 7.27
33
Thermohaline Circulation

• Sinking of water masses is offset by slow,
  gradual rising across warmer temperate and
  tropical zones

34
Fig. 8-26, p. 192
35
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

36
Figure 7.28- The Ocean Conveyor Belt Model