Post on 08-Jun-2018
1
• Surface currents
- Wind-driven
- Primarily horizontal motion
• Deep currents
- Driven by differences in density
- Vertical and horizontal motions
Ocean circulation
• Caused by frictional drag between wind and ocean
• Above the pycnocline
• 10% of all ocean water
• Faster than deep ocean circulation
• Also affected by• Distribution of continents
• Gravity
• Friction
• Coriolis effect
Ocean circulation: surface currents
1. Gyres
-Equatorial current
-Western Boundary currents
-Northern or Southern
Boundary currents
-Eastern Boundary currents
Subtropical gyres
Ocean circulation: surface currents
1. Gyres
-Subtropical
-Subpolar
Ocean circulation: surface currents
2. Equatorial counter currents
Ocean circulation: surface currents
3. Ekman spiral
• Surface currents move at angle to wind due to Coriolis
• Each successive layer moves increasingly
• to the right in N hemisphere
• to the left in S hemisphere
Ocean circulation: surface currents
2
4. Geostrophic flow
• Ekman transport piles up water
within subtropical gyres
Ocean circulation: surface currents
4. Geostrophic flow
• Surface water flows
downhill (gravity)
and to the right
(Coriolis effect)
• Balance of downhill
and to the right
causes geostrophic
flow around the
“hill”
Ocean circulation: surface currents
Ocean circulation: Southern Ocean
North Atlantic Subtropical Gyre
1. North Equatorial Current• Antilles Current
• Caribbean Current
• Florida Current
2. Gulf Stream
3. North Atlantic Current
4. Canary Current
Ocean circulation: Atlantic
Gulf Stream• Warm-core rings
• Cold-core rings
• Unique biology
Ocean circulation: Atlantic
Average flow rate (Sv)
Ocean circulation: Atlantic
3
South Atlantic Subtropical Gyre1. South Equatorial Current
2. Brazil Current
3. Antarctic Circumpolar Current
4. Benguela Current
Ocean circulation: Atlantic
Indian OceanSubtropical Gyre1. South Equatorial
Current
2. Agulhas Current
3. Antarctic CircumpolarCurrent
4. West AustralianCurrent
Ocean circulation: Indian
Summer(rain!)
Winter(dry!)
HH
LL
LL
HH
Climate Patterns: Indian
North Pacific
subtropical gyre1. North Equatorial Current
2. Kuroshio Current
3. North Pacific Current
- Alaskan Current
4. California Current
Ocean circulation: Pacific
South Pacificsubtropical gyre
1. South Equatorial Current
2. East Australian Current
3. Antarctic Circumpolar Current
4. Peru Current
Ocean circulation: Pacific
Normal conditions
Climate Patterns: Pacific
4
• El Niño-Southern Oscillation (ENSO)
• Warm phase: El Niño
• Cold phase: La Niña
Climate Patterns: Pacific
El Niño
Normal
La Niña
Normal
Normal
El Niño
Climate Patterns: Pacific
• Surface currents
- Wind-driven
- Primarily horizontal motion
• Deep currents
- Driven by differences in density
- Vertical and horizontal motions
- Below the pycnocline
- 90% of all ocean water
- Slow velocity
Ocean circulation Water Properties: TemperatureAverage kinetic energy of molecules in a substance
5
Water Properties: TemperatureAverage kinetic energy of molecules in a substance
General relationship:! water temp.
" water density
Exception:
When water freezesBig ! water density
Water Properties: SalinityTotal amount of solid ions dissolved in water
General relationship:" water salinity
" water density
Water Properties: SalinityTotal amount of solid ions dissolved in water
Water Properties: SalinityTotal amount of solid ions dissolved in water
Depth
Variable
Water temperature, salinity, density profiles Water temperature & density profiles
6
Water salinity profiles
Deep currents, thermohaline circulation
• Cold, salty, surface water sinks at polarregions and moves equatorward
• Deep water formation
• Antarctic Bottom Water
• Antarctic Intermediate Water
• North Atlantic Deep Water
Ocean circulation: deep currents
Global conveyor belt
Ocean circulation: deep currents Ocean circulation: deep currentsAntarctic Weddell
Sea
Ross
Sea
• Sinking of cold water around ice sheet
Ocean circulation: deep currentsAntarctic Bottom Water
• Convergence at the polar front
Ocean circulation: deep currentsAntarctic Intermediate Water
7
Ocean circulation: deep currentsAntarctic Intermediate Water
• Labrador Sea Water, Denmark Strait Overflow Water,
Greenland Sea Water
Ocean circulation: deep currentsNorth Atlantic Deep Water
Source: M. Tomczak
40S 40N0
AIW: Arctic Intermediate Water
AAIW: Antarctic Intermediate Water
AABW: Antarctic Bottom Water
MedW: Mediterranean Water
NADW: North Atlantic Deep Water
Ocean circulation: deep currentsNorth Atlantic Deep Water
Source: M. Tomczak
40S 40N0
AIW: Arctic Intermediate Water
AAIW: Antarctic Intermediate Water
AABW: Antarctic Bottom Water
MedW: Mediterranean Water
NADW: North Atlantic Deep Water
CPW: Circumpolar Water
PDW: Pacific Deep Water
Ocean circulation: deep currents
No deep water formation in the Pacific Ocean
Source: M. Tomczak
AIW: Artic Intermediate Water
AAIW: Antarctic Intermediate Water
AABW: Antarctic Bottom Water
MedW: Mediterranean Water
NADW: North Atlantic Deep Water
PDW: Pacific Deep Water
RedSW: Red Sea Water
Ocean circulation: deep currents
No deep water formation in the Indian Ocean
Ocean circulation: Deep currents
8
Extra slides
• Downwelling
• Upwelling
Vertical movement of water
• Surface seawater piles up
• Downwelling
• Low biological productivity
• Surface water is nutrient
poor
• Deep water is nutrient rich
Converging surface water
• Surface seawatermoves away
• Upwelling
• High biologicalproductivity
Diverging surface water
Example of diverging surface
water: southeast trade winds blow
across the equator
• Ekman transportcan move surfaceseawater onshoreor offshore
Coastal upwelling
Example of Ekman transport andupwelling
Coastal upwelling
9
• El Niño warm phase about every 2 to 10 years
• Highly irregular
• Phases usually last 12 to 18 months
Climate Patterns: Pacific Climate Patterns: Pacific