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Understanding Surface Currents and Gyres

Oct 1, 2024

Surface Currents and Ocean Gyres

Introduction to Surface Currents

  • Surface currents occur within and above the peak decline at the surface, up to 1 km depth.
  • Affect only about 10% of the ocean's volume.
  • Formed by wind blowing across the water surface.
    • Friction from air molecules creates waves, leading to surface currents.
    • Only about 2% of wind energy is transferred to water.
    • Example: 50 knot wind creates a 1 knot surface current.

Understanding "Knots"

  • Knot: unit of speed equal to 1 nautical mile per hour.
  • 1 nautical mile = 1.85 kilometers or 1.15 miles.

Factors Influencing Surface Currents

  • Wind belts: Major influence on current direction.
  • Continents: Alter current paths.
  • Other factors: Friction, gravity, Coriolis effect.
  • Coriolis effect: Major role in defining surface currents.

Wind Belts and Current Formation

  • Trade winds (light green): Blow west.
  • Prevailing westerlies (dark green): Blow east.
  • Surface currents (light blue): Form circular tracks called gyres.

Ocean Gyres

  • Large, circular or oval patterns of ocean currents.
  • Types of gyres:
    • Subtropical gyres
    • Equatorial currents
    • Subpolar gyres

Subtropical Gyres

  • Five main gyres: North Atlantic, South Atlantic, North Pacific, South Pacific, Indian Ocean.
  • Located at 30 degrees latitude north or south.
  • Rotate clockwise in the northern hemisphere, counterclockwise in the southern hemisphere.

Components of a Subtropical Gyre

  1. Equatorial Currents:

    • Driven by trade winds (east to west)
    • Named northern/southern equatorial current based on hemisphere.
  2. Western Boundary Currents:

    • Occur when equatorial currents meet landmasses on western ocean basins.
    • Deflect due to Coriolis effect (right in northern hemisphere, left in southern).
    • Carry warm water to higher latitudes.
  3. Northern/Southern Boundary Currents:

    • Named based on hemisphere.
    • Driven east by prevailing westerlies.
  4. Eastern Boundary Currents:

    • Deflect toward equator upon meeting landmasses.
    • Carry cooler water from high latitudes to the equator.

Equatorial Countercurrent

  • Flows opposite to equatorial currents.
  • Formed by water piling up on western ocean basin side.
  • Flows downhill toward the east due to gravity.
  • Most pronounced in the Pacific Ocean.

Subpolar Gyres

  • Smaller, fewer than subtropical gyres.
  • Rotate opposite to subtropical gyres in the same hemisphere.
  • Locations:
    • Atlantic Ocean (between Europe and Greenland)
    • South of Alaska in the Pacific
    • Off Antarctica

Conclusion

  • Understanding of ocean currents influenced by multiple factors.
  • Importance of recognizing different currents and their effects on global climate and ocean dynamics.