What causes water currents?

Answer 1

Surface ocean currents are mainly wind-driven and occur in all of the world's oceans. Examples of large surface currents that move across vast expanses of ocean are the Gulf Stream, the North Atlantic Current, the California Current, the Atlantic South Equatorial Current, and the Westwind Drift. Associated with surface currents are counter-surface and underlying currents. Surface ocean currents are deflected to the right in the Northern Hemisphere and to the left in the Southern Hemisphere due to the Coriolis effect. The Coriolis effect holds that because the Earth is spinning, surface waters move in a clockwise direction in the Northern Hemisphere and in a counterclockwise direction in the Southern Hemisphere. The currents eventually come into contact with the continents which deflect them, creating giant oceanic current circles known as gyres. Vertical and ocean-bottom currents are mainly driven by density differences caused by changes in temperature and salinity. Originating in polar regions, cold, salty waters sink to the ocean bottom and move toward the opposite poles where they again surface. Vertical upwelling currents can also be caused by winds "blowing off" a coastline. The displaced waters are then replaced by underlying bottom waters. Currents are important to marine life as they help to move food and nutrients, making them available for photosynthesis, metabolic requirements and/or consumption.