lecture recording on 04 February 2025 at 20.16.20 PM

Water Circulation in the Ocean

• The main forces driving water circulation include upwelling and downwelling.

Upwelling

• Definition: Upwelling is the movement of deep, cold, nutrient-rich water to the surface.

• Creates high productivity areas, especially beneficial for marine life and fishing.

• Deep water brings nutrients that support biological activity, with algae being a significant contributor in these regions.

• Locations: Often occurs along coastlines where winds blow offshore, creating a vacuum that draws deep water upward.

• Example: Equatorial Upwelling is where trade winds diverge and push surface water away, allowing nutrient-rich water to rise.

Downwelling

• Definition: Downwelling is when surface waters converge and sink into deeper waters.

• Involves warmer, nutrient-depleted water moving down; this can negatively affect marine productivity.

• Usually occurs when surface currents combine and push water toward the coastline, causing it to sink due to increased pressure.

Surface and Deep Water Circulation

• Surface Currents: Driven by atmospheric circulation (wind), causing horizontal movement important for heat distribution.

  • Gyres: Large systems of rotating ocean currents. Water accumulates at the center, often leading to pollution accumulation like garbage patches.

  • In the Northern Hemisphere, surface currents deflect to the right; in the Southern Hemisphere, they deflect to the left due to the Coriolis effect.

Vertical Movement

• Water circulates not just horizontally (as in gyres) but also vertically through processes of upwelling and downwelling that are influenced by wind and temperature gradients.

• Ekman Transport: A phenomenon showing the movement of water layers. Surface layer currents, influenced by wind, deflect right in the Northern Hemisphere and left in the Southern Hemisphere, causing a spiraling effect in deeper layers.

• Current speeds decrease with depth, leading to complex patterns in water movement.

Global Ocean Conveyor Belt

• Definition: A system of deep ocean currents driven by differences in water density, temperature, and salinity.

• Cold, salty water sinks in polar regions and flows towards equator, while warmer water rises near the equator, creating a global circulation pattern.

• Importance: Regulates climate, transports nutrients, and impacts marine ecosystems.

The El Niño Southern Oscillation (ENSO)

• El Niño: Strengthens currents that reverse airflow patterns, leading to higher rainfall in the Americas and reduced upwelling, adversely affecting marine life.

  • Leads to warmer water distribution and destabilizes local climates.

• La Niña: The opposite phase that enhances upwelling and brings cooler water to the surface, often resulting in cooler temperatures and stronger trade winds in the Pacific.

Walker Circulation

• A key atmospheric circulation system influencing surface water around the equator.

• During normal conditions, warm, moist air moves east toward the Americas, whereas cooler, drier air flows west toward Asia.

• Changes during ENSO can dramatically impact weather patterns globally, altering precipitation and temperature distributions.

Key Terms to Remember

• Coriolis Effect: The deflection of moving objects caused by Earth’s rotation, impacting ocean and atmospheric currents.

• Gyres: Large-scale ocean currents that can trap debris and plastic, leading to significant environmental issues.

• Ekman Spiral: The theoretical model describing how wind-driven currents decrease in speed and change direction at varying depths.

• Thermohaline Circulation: Driven by differences in water density (affected by temperature and salinity), crucial for global heat distribution and nutrient transport.