Ocean Circulation Summary

Module Overview

  • Module 10: Ocean Circulation
    • Topic 3: Winds can cause vertical movement of the ocean
    • Topic 4: El Niño and La Niña are exceptions to normal wind and current flow
    • Topic 5: Thermohaline circulation affects all the ocean’s water

Key Concepts

Upwelling
  • Upward movement of cold, nutrient-rich water from deep ocean to surface
  • Stimulated by wind; Ekman transport moves surface water offshore.
  • Enhances biological productivity.
Downwelling
  • Downward movement of surface water; supplies deeper ocean with oxygen
  • Occurs when wind pushes surface water toward the shore.
Ekman Transport
  • Movement of surface water at an angle to wind due to Coriolis effect:
    • Northern Hemisphere: 90° to the right.
    • Southern Hemisphere: 90° to the left.
Regional Differences in Pycnocline
  • High latitudes allow easier nutrient mixing; equatorial zones experience upwelling.
  • Pycnocline affects nutrient availability and mixing, contributing to marine productivity.
El Niño and La Niña
  • El Niño: Warms surface waters; weakens trade winds, reduces upwelling, and impacts climate globally.
  • La Niña: Strengthens trade winds, enhances upwelling, and can lead to cooler ocean conditions.
Thermohaline Circulation
  • Global system of ocean currents driven by temperature and salinity differences.
  • Forms cold, dense water in polar regions that sinks and undergoes a long-term circulation.

Tides Overview

  • Tides: Longest ocean waves, influenced by gravitational pull of Moon and Sun.
  • Two main types:
    • Diurnal: One high and one low tide daily.
    • Semidiurnal: Two high and two low tides (regular).
  • Spring Tides: Occur during full/new moon, largest range.
  • Neap Tides: Occur during first/third quarter moon, smallest range.

Waves Summary

Wave Types
  • Deep-Water Waves: Occur when depth > L/2 (not affected by sea floor).
  • Shallow-Water Waves: Occur when depth < L/20 (affected by sea floor).
  • Tsunamis: Long-wavelength, shallow-water waves caused by seismic activity.
Wave Creation
  • Wind transfers energy to ocean surface; fetch and wind duration influence wave size.

Marine Life and Biological Interaction

  • Plankton: Drifters in the ocean. Two main groups:
    • Phytoplankton: Autotrophic, primary producers.
    • Zooplankton: Heterotrophic, consumers of other organisms.
  • Energy flows through marine food webs detracting at each trophic level (10% energy transfer).

Coastal Features

  • Erosional Coasts: High energy environments, featuring sea cliffs, caves, stacks, and platforms caused by wave action.
  • Depositional Coasts: Low energy, characterized by sediment accumulation (e.g., beaches, spits).