Ocean Circulation and Thermohaline Circulation

Key Concepts

• Ocean circulation plays a crucial role in transporting solar energy from the equator towards the poles.
• This circulation is influenced by:
  • Uneven heating
  • The Coriolis effect

Differences Between Ocean and Atmospheric Circulation

• Oceans are warmed from the top down, unlike the atmosphere.
• Heat-driven convection is insufficient for ocean circulation.
• Wind can move surface water, but vertical mixing requires density differences.

Factors Influencing Water Density

• Temperature and salinity are critical in determining seawater density.
• Salinity varies due to evaporation and precipitation patterns:
  • Lower salinity near the equator due to higher precipitation.
  • Increased salinity in mid-latitudes due to evaporation.
  • Decreased salinity towards the poles because of increased precipitation.

Stratification in the Oceans

• Due to warming, temperature stratifies water at low latitudes.
• The thermocline is the transition region between warm surface water and cooler, denser water below.
• Near the poles, the thermocline breaks down, allowing for mixing from top to bottom.

Density-Driven Circulation

• Dense water sinks near the poles and flows equatorward under less dense water.
• Ice formation plays a significant role in increasing salinity and density.
• Ice crystals exclude salt, increasing salinity in water that remains, allowing it to sink.

Locations of Dense Water Formation

• Significant ice formation occurs in:
  • North Atlantic (two locations)
  • Southern Ocean (one location)
• The dense water formed is:
  • North Atlantic Bottom Water: Spreads southward, creating cold dense bottom water.
  • Antarctic Bottom Water: Densest water in the oceans, less abundant than North Atlantic Bottom Water.

Ocean Circulation Process

• North Atlantic Bottom Water and Antarctic Bottom Water mix with other water masses.
• This deep water eventually reaches the surface through upwelling and mixing.
• Once at the surface, it warms and returns to the deep sea, completing the cycle.
• Cycle Duration: Takes upwards of 1,000 years to complete.

Thermohaline Circulation

• The process is also known as the ocean conveyor belt.
• It drives the movement of warm surface water toward the poles, transporting heat in the process.