Ocean Currents and Their Impact on Global Climate

Introduction

• Ocean currents play a significant role in global heat transport.
• 30% of global heat transport is accomplished by ocean currents.
• Understanding ocean currents is vital for studying global climate.

Causes and Mechanisms

Relationship Between Winds and Currents

• Surface ocean currents are driven by surface winds.
• Winds drag the top layer of the ocean, creating major ocean currents.

Gyre Circulation

• Northern Hemisphere: Circulation moves clockwise.
• Southern Hemisphere: Circulation moves counterclockwise.
• Equatorial currents move east to west and vice versa.

Important Ocean Currents

• California Current: West coast of the U.S., moving north to south.
• Alaska Current: Moves north toward Alaska.
• Gulf Stream: East coast of the U.S., moving from Gulf of Mexico to northern Atlantic.
• North Atlantic Current/Drift: Extends toward Norway and Western Europe.
• Antarctic Circumpolar Current: Moves around Antarctica without a break.

Formation of Ocean Currents

• Wind Stress: Winds blowing across water create large-scale currents.
  • Similar to atmospheric pressure gradient force.
• Coriolis Effect: Deflects water to the right in the Northern Hemisphere, to the left in the Southern Hemisphere.

Ekman Transport and Ekman Layer

• Surface current moves at a 45-degree angle to the right of wind in the Northern Hemisphere.
• As depth increases, currents deflect further to the right and diminish due to friction.
• Ekman Transport: Overall movement of water, 90 degrees to the right (N. Hemisphere) or left (S. Hemisphere) of wind direction.

Divergence and Convergence

• Divergence: Surface waters move away, causing upwelling (deeper waters rise).
• Convergence: Waters accumulate, leading to downwelling (water moves downward).

Example: Upwelling along California Coast

• Northerly winds cause upwelling on the west coast, bringing cold water from the ocean depths to the surface, affecting local sea temperatures.

Oceanic Gyres and Garbage Patches

• Convergence in gyres leads to accumulation of debris.
• Great Pacific Garbage Patch: Collection of marine debris in ocean gyres.
• Tiny plastics, often mistaken as food by marine life, significantly outnumber plankton.

Characteristics of Major Currents

Boundary Currents

• Western Boundary Currents (e.g., Gulf Stream): Narrow, fast.
• Eastern Boundary Currents (e.g., Canary Current): Wide, slow.

Important Definitions

• Gulf Stream: Western boundary current, fast and narrow.
• California Current: Eastern boundary current, wide and slow.

Conclusion

• Understanding surface currents is crucial for comprehending global climate systems and marine ecosystems.
• Practice and application of knowledge about wind direction and ocean currents reveal the dynamic interactions within oceanic systems.