Ocean currents are the great rivers of the sea, redistributing heat around the planet and shaping regional climates. The Gulf Stream is one of the most influential: it originates in the Gulf of Mexico, flows northeast along the U.S. East Coast, and crosses the Atlantic toward Europe, where it plays a major role in warming the climate of Western Europe. In the North Pacific, the Kuroshio Current — also called the Japan Current — plays a similar role, carrying warm tropical water northeast past Japan. The Antarctic Circumpolar Current is the largest ocean current by volume, flowing eastward around Antarctica and linking the Atlantic, Pacific, and Indian Oceans in a single continuous flow.
Cold currents are just as important as warm ones. The Humboldt Current flows northward along the west coast of South America, cooling coastal Peru and Chile and fueling some of the richest marine ecosystems — and fisheries — on Earth. The Benguela Current does the same along the southwestern coast of Africa, supporting major fisheries off Namibia and South Africa. Together, these boundary currents help regulate temperatures and nutrients across vast stretches of coastline.
Winds and the Coriolis effect combine to form large circular current systems called ocean gyres, of which there are five major ones in the North and South Atlantic, the North and South Pacific, and the Indian Ocean. Unfortunately, these gyres also accumulate marine debris: the Great Pacific Garbage Patch, located in the North Pacific Subtropical Gyre, holds an estimated 1.6 million km² of mostly plastic waste. Below the surface, deep circulation is driven by differences in water temperature and salinity — a global conveyor belt called thermohaline circulation. Cold, salty surface water sinking in the Greenland and Labrador Seas forms the North Atlantic Deep Water, which then flows southward and helps drive this worldwide system.
Tides are governed primarily by the gravitational pull of the Moon and, to a lesser extent, the Sun on Earth's oceans. When the Sun, Moon, and Earth align — during new and full moons — spring tides produce the highest tidal ranges, while during the quarter moons, neap tides produce the lowest ranges. Most coastal locations experience two high tides and two low tides per day in what is known as a semidiurnal pattern, with each cycle taking roughly 12 hours and 25 minutes. The highest tidal range in the world occurs in the Bay of Fundy in Canada, where the difference between high and low tide can reach 16 meters (53 feet).