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.
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!