ocean circulation ocean circulation: surface...

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• 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


1. Gyres

-Subtropical

-Subpolar


2. Equatorial counter 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


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4. Geostrophic flow

• Ekman transport piles up water

within subtropical gyres


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: 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


Average flow rate (Sv)


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South Atlantic Subtropical Gyre1. South Equatorial Current

2. Brazil Current

3. Antarctic Circumpolar Current

4. Benguela Current


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

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• El Niño-Southern Oscillation (ENSO)

• Warm phase: El Niño

• Cold phase: La Niña


El Niño

Normal

La Niña

Normal

Normal

El Niño


• 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

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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



Depth

Variable

Water temperature, salinity, density profiles Water temperature & density profiles

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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

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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





CPW: Circumpolar Water

PDW: Pacific Deep Water


No deep water formation in the Pacific Ocean

Source: M. Tomczak

AIW: Artic Intermediate Water





PDW: Pacific Deep Water

RedSW: Red Sea Water


No deep water formation in the Indian Ocean

Ocean circulation: Deep currents

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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

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• 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

ocean circulation ocean circulation: surface...

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