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Topic: Currents and Ocean Circulation

Theme: Energy

Key Concepts:

Wind-driven Currents

  • When winds blow across the ocean surface, kinetic energy is transferred from the wind to surface water as a result of the friction between the wind and the ocean surface. The kinetic energy transferred to the ocean surface sets the surface layer of water in motion and generates both waves and currents.
  • Sunlight shining on the oceans adds thermal energy to the surface layer. Currents carry the thermal energy to other regions
  • The process of energy transfer from winds to waves and currents is complex and depends on many factors, including wind speed, air-sea temperture difference, and roughness of the surface (whether or not waves are already present and how high they are). Therefore the percentage of the wind's energy that is converted into kinetic energy of ocean currents is variable.
  • Wind-generated currents transport large volumes of water and thermal energy across the oceans.
  • Winds are the primary energy source for currents that flow horizontally in the ocean surface layers (less than 1 km deep).
  • Surface currents are often called "wind-driven currents" or "wind drift currents."

Density-driven Currents

  • Density-driven ocean currents, generated by variations in water density, lead to a convective flow or movement.

Heat Transport by Currents

  • Ocean circulation transfers heat from the tropics toward the poles, moderating mid- and high-latitude climates.
  • Heat transported by currents moderates the climates of regions into which they flow. For example, heat is transported north across the Atlantic first by the Gulf Stream and then east across the Atlantic by the North Atlantic Drift. This transported heat moderates Western Europe's climate.
  • Both wind-driven and density-driven currents are important structures in the heat-transport system.

Boundary Currents

Boundary currents flow parallel to the coast. Two types of boundary currents are important:

  • Western boundary currents on the western edge of the oceans are fast, narrow jets.
    • Gulf Stream
    • Brazil Current
    • Kuroshio Current
    • East Australian Current
    • Agulhas Current
  • Eastern boundary currents on the eastern edge of the oceans are generally weaker than western boundary currents.
    • California Current
    • Peru Current
    • Canary Current
    • Benguela Current