Ocean currents shape our planet's climate and marine ecosystems. Wind, density differences, and Earth's rotation drive these massive flows of water. Surface currents, like the Gulf Stream, are wind-driven, while deep currents are density-driven.

Thermohaline circulation forms a global conveyor belt, moving heat and nutrients around the world. This system moderates climate and supports marine life. Climate change could disrupt this delicate balance, with far-reaching consequences for our planet's ecosystems and weather patterns.

Ocean Currents

Drivers of ocean currents

• Wind stress creates friction between wind and ocean surface driving surface currents
  • Trade winds, westerlies, and polar easterlies contribute to major wind-driven currents (Gulf Stream, Kuroshio Current)
• Density differences from variations in temperature and salinity create density gradients
  • Denser water sinks while less dense water rises driving thermohaline circulation
• Coriolis effect deflects moving objects including ocean currents due to Earth's rotation
  • Deflection is to the right in the Northern Hemisphere and to the left in the Southern Hemisphere
  • Contributes to the formation of large-scale ocean gyres (North Atlantic Gyre, North Pacific Gyre)

Surface vs deep ocean currents

• Surface currents occur in the upper 400 meters of the ocean primarily driven by wind stress
  • Examples include the Gulf Stream, Kuroshio Current, and Antarctic Circumpolar Current
• Deep ocean currents occur below 400 meters primarily driven by density differences (thermohaline circulation)
  • Slower and more stable than surface currents
  • Examples include the North Atlantic Deep Water and Antarctic Bottom Water

Thermohaline Circulation

Thermohaline circulation and distribution

• Thermohaline circulation (THC) is large-scale ocean circulation driven by density differences from variations in temperature (thermo) and salinity (haline)
• Formation of deep water masses occurs when cold, salty water in high latitudes becomes dense and sinks
  • North Atlantic Deep Water (NADW) forms in the North Atlantic
  • Antarctic Bottom Water (AABW) forms in the Southern Ocean
• THC transports warm surface water from the equator to the poles releasing heat to the atmosphere in high latitudes, moderating climate
• Upwelling of deep, nutrient-rich water in certain regions (equatorial Pacific) supports primary productivity and marine ecosystems

Ocean conveyor belt in climate

• Global ocean conveyor belt (Great Ocean Conveyor) is a large-scale, interconnected system of ocean currents driven by thermohaline circulation
  • Connects the world's oceans and redistributes heat, salt, and nutrients
• Transports heat from the equator to the poles, reducing temperature gradients helping maintain a more balanced global climate
  • Influences regional climates such as the mild climate of Western Europe
• Absorbs atmospheric carbon dioxide in cold, high-latitude regions transporting carbon to the deep ocean where it can be stored for long periods
• Potential impacts of climate change:
  1. Melting of ice sheets and glaciers can disrupt the conveyor belt by altering salinity and density gradients
  2. Slowdown or shutdown of the conveyor belt could have significant consequences for global climate and ecosystems