Ocean circulation - Class Notes

surface circulation

• currents are masses that flow from one place to another

• surface currents develop from friction between the ocean and the wind that blows across the surface

  • huge, slowly moving gyres

• deflected by coriolis effect: right in the NH, left in the SH

• currents from low latitudes to higher latitudes transfer heat from warmer to cooler areas

gyres

• large circular, surface ocean current pattern

  • clockwise in NH, counterclockwise in SH

  • mimic overlying subtropical High pressure systems

• Main gyres: North Pacific, South Pacific, North Atlantic, South Atlantic, Indian Ocean

  • four main currents exist within each main gyre

upwelling

rising of cool water from deep areas, brings nutrients - occurs where there is a divergence of water away from the coast

• most characteristic along west coast of continents (Eastern Boundary currents)

• as wind blows paralell to west coast and is deflected by the coriolist effect, surface water is transported to the right, cold water upwells to replace surface water

• other major area is along the equator where waters diverge

ekman spiral

surface water is moved by wind & coriolis effect

• as you go deeper, layers are dragged but coriolis effect deflects further

  • each layer effected more than the one above, creating a spiral

deep-ocean circulation

• a response to density differences

  • temperature - cold water more dense than warm water

  • salinity - density increases with salinity

• begins at high latitudes at the surface

thermohaline circulation (ocean’s conveyor belt)

large-scale system of ocean currents driven by differences in temperature and salinity

Polar Regions:

• water is denser (colder & higher salinity) - it sinks and flows along the ocean floor towards the equator

Tropic Regions:

• water is ligher (warmer & less salinity) - surface waters move from tropics to the poles to replace sinking water

creates global circulation of deep and surface waters around the world

North Atlantic Deep Water (NADW)

cold, salty water sinks in the North Atlantic

• surface water becomes cold and salty due to sea ice formation making water dense enough to sink

  • flows southward

Antarctic Bottom Water

• coldest, densest, water mass in the ocean found in Antarctica

• spreads across deep ocean basins, filling much of the abyssal parts of oceans

• very salty & cold - drives bottom part of global conveyor belt