The water in the ocean is constantly on the move. These movements, called ocean currents, usually involve large water masses and may flow at the surface or far below it.
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Surface Current: an ocean current that generally flows in the upper 1000 m of the ocean
-Caused mainly by the wind. Also by Earth’s rotation and the presence of continents
Warm and Cold Currents
–Warm Currents: flow away from the equator on the western side of ocean basins
–Cold Currents: flow toward the equator on the eastern side of ocean basins
*The temperature from these ocean currents is transferred to the atmosphere, thus affecting the climate of the areas around them!
Countercurrents: flow in the opposite direction of the wind-related currents
-Due to the displacement of water caused by the wind-related currents
Density Current: current in the deep ocean, driven by gravity and differences in density (NOT wind!)
-Move slowly compared to surface currents
-Only source of oxygen for deep sea life
-Densest water comes from polar regions
*Due to intense cooling and freezing
*Increase in compactness and salinity causes this water to sink toward the bottom of ocean and circulate in the deep ocean.
-In hot, dry climates evaporation changes density (by increasing salinity).
Upwelling: when cold, deep water comes to the surface to replace the surface water that is pushed away by the winds
-Contains large amounts of nutrients that phytoplankton need to grow!
-Very important to life in the ocean!