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.