The Surface Currents

Chapter 9

Surface Currents Wind driven

Coriolis effect

45º

Surface CurrentsEkman Spiral

V. Walfrid Ekman~100-150 m

Ekman Transport90

Surface Currents

Ocean Gyres

Surface CurrentsGeostrophic Flow

Pacific Ocean CurrentsNorth EquatorialNorth Pacific CaliforniaKuroshioOyashioAlaska

Pacific Ocean Currents South Equatorial West Wind Drift Peru (Humbolt) East Australia Equatorial Countercurrent Cromwell

Atlantic Ocean Currents North Atlantic North Equatorial Gulf Stream Canary Florida Labrador East Greenland Norwegian

Atlantic Ocean Currents West Wind Drift South Equatorial Brazil Benguela

Indian Ocean Currents West Wind Drift South Equatorial West Australia Agulhas North Equatorial Equatorial Countercurrent

Arctic Ocean Currents Clockwise gyre

Not centered on North Pole

Current Flow Current Speed

0.01 times average wind speed0.1 – 0.5 m/sec

Narrow straitsIncrease of speedFlorida current

VolumeSverdrups1 Sverdrup = 1 million m3/sec

Current FlowWestern Intensification

Western Boundary Current Eastern Boundary Current

Eddies Meanders Surface or at depth Vary in size

10–100’s km in diameter

Can alter surface flow pattern Retain properties

Eddies Gulf Stream

Rotational speed0.51 m/sec (1 knot)

Diameter325 km (200 mi)

Reach bottomAbyssal storms

Convergence & Divergence

Convergence & Divergence

Langmuir Cells

Seasonal Zones

Seasonal Zones

Global Currents

Global Currents

Milankovitch cycles1. Shape of Earth’s orbit

100,000 years

Global Currents

Milankovitch cycles2. Tilt of Earth’s axis of rotation

41,000 years

Global Currents Milankovitch cycles

3. Circular revolution23,000

Recent History of Climate Change

Minimum solar radiation23,000 years ago

Maximum land ice & minimum water temps

17,000 years ago

Return to high solar radiation12,000 years ago

Recent History of Climate Change

Younger Dryas event

Recent History of Climate Change

North Pacific Oscillations

PDOPacific Decadal Oscillation

Yellow = Warm & dryRed = Cold & wet

North Atlantic Oscillations

NAOPools of warm & cool surface water4 to 10 years

Measuring the Currents

Highly sophisticated equipment:

Measuring the Currents

Measuring the Currents Current Meters

Measuring the Currents

Doppler current meter

Emits sound of known frequency Measures frequency of returning echoes