Water is propelled around the globe in sweeping currents, waves transfer energy across entire ocean basins, and tides reliably flood and ebb every single day. But why does this occur? Ocean movement is created by the governing principles of physics and chemistry.

Blue arrows show cold, relatively fresh water and red arrows show warm, salty water that has entered the system from the North Atlantic. The image also shows the prominent Beaufort gyre which has been an area of great scientific research in the last decade.

Ocean current, stream made up of horizontal and vertical components of the circulation system of ocean waters that is produced by gravity, wind friction, and water density variation in different parts of the ocean.

The Arctic Ocean, the northerly extension of the Atlantic, is almost a maritime cul de sac, but the wide opening that stretches from Greenland to Scandinavia allows huge masses of water to circulate both near the surface and at great depth. Upward and downward currents generate major heat exchanges that are a key to the Northern Hemisphere climate.