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Ocean currents are horizontal layers of seawater that move. There are three types of currents: coastal, surface layer, and deepwater. Coastal currents occur immediately adjacent to the shore. Wave action, gravity, and hydrostatic pressure generate such currents. Longshore currents, the ebb and flow of tidal currents, and dangerous rip current are common examples of coastal currents. Freshwater inflow from rivers, friction with the seafloor, and irregular coastlines add to their variability. Surface layer currents and deepwater currents occur farther offshore.

The sinking of cold, salty water in polar regions creates deepwater currents. These currents bring oxygen to marine life at great depths. The sinking of surface water and the upwelling of deepwater makes up a “conveyor belt” that includes both surface layer and deepwater currents. The ...

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