Ocean Circulation

Currents

Currents

• Horizontally

• Vertically

The Forces That Drive Currents

• Primary forces– Starts water movement and determine its velocity

• Stress of wind

• Secondary forces– Influence the direction and nature of flow

• Coriolis effect

• gravity

• friction

• shape of ocean basins

Surface currents

• Wind

• Surface currents– rapid with well defined boundaries– slow and diffuse– horizontal or vertical

• Gyre

Bottom Currents

• Driven by the force of gravity - dense water sinks and less dense water rises

Flow within a Gyre

• North Atlantic gyre– Four inter connected currents

• Eckman spiral

• Eckman transport

Geostrophic Gyres

• Geostrophic Gyre– 5 Geostrophic gyre

• North Atlantic gyre

• South Atlantic gyre

• North Pacific gyre

• South Pacific gyre

• Indian Ocean gyre

– Geostrophic gyres independent of each other in each hemisphere

• Geostrophic currents• 6 current circuits in the world ocean

– 2 in Northern hemisphere 4 in southern hemisphere

Currents within Gyres

• Western boundary Currents

• Eastern Boundary Currents

• Transverse currents

Western Boundary Currents

• Fastest and deepest• Found at the western boundaries of the Ocean

basins• Narrow• Move warm water poleward in each gyre

Western boundary currents

• Five western boundary currents– Gulf stream

– Japan or Kuroshio current

– Brazil current

– Agulhas current

– East Australian current

• Sverdrup

• Eddies– Cold core eddies

– Warm core eddies

Eastern Boundary Currents

• The Canary Current

• The Benguela Current

• California Current

• West Australian Current

• The Peru or Humboldt Current

Eastern Boundary Currents

• Carry cold water equatorward

• Shallow and broad

• Boundaries not well defined

• Eddies tend not to form

Westward Intensification

• The converging flow of the trade winds on either side of equator

• The rotation of the earth

Transverse Currents

• Currents that flow from east to west– Linking the eastern and western boundary

currents

• Counter Currents

• Under Currents

Exceptional Surface Currents

• Monsoon Currents

• High Latitude Currents

Effects of Surface Currents on Climate

• Distribute tropical heat

• Influences climate and weather

Wind-Induced Vertical Circulation

• Upwelling– Equatorial upwelling– Coastal upwelling

• Downwelling

Langmuir Circulation (page 222 fig 9.16)

• Langmuir Circulation

El Nino

Thermohaline Circulation

• Density driven

Water Masses

• Five common water masses– Surface water– Central water– Intermediate water– Deep water– Bottom water

Formation and downwelling of Deep water

• Antarctic bottom water

• North Atlantic deep water

Thermohaline Circulation Patterns

• Low and mid latitudes

• Caballing

• Contour currents

Studying Currents

• Float method

• Flow method

• Acoustical Tomography