Ocean Currents and Climate

About this topic

Ocean currents are large flows of seawater driven by wind, Earth's rotation, differences in temperature and salinity, and continents' shapes. Surface currents form gyres. Warm currents like the Gulf Stream carry heat toward the poles, making northwest Europe milder than other places at the same latitude.

Deep thermohaline circulation (the "conveyor belt") links the oceans over centuries. El Niño disrupts normal patterns, causing global weather changes. Climate change may alter currents.

Consider the Gulf Stream: it carries about 150 times the flow of all the world's rivers combined, bringing warm water from the Caribbean toward Europe. Because of it, Britain (latitude 51 N) has a far milder climate than Labrador in Canada at the same latitude. In contrast, the California Current is cold and brings fog and cool summers to San Francisco. Upwelling along coasts such as Peru brings nutrient-rich cold water to the surface and supports huge fisheries.

In an El Nino year, trade winds weaken, warm water spreads east across the Pacific and Peruvian fisheries collapse, while Australia and Indonesia often face drought and the Americas get heavy rain. La Nina is the opposite. Thermohaline circulation begins when cold salty water sinks near Greenland and Antarctica, and a full cycle may take about 1,000 years. Scientists worry that freshwater from melting ice might slow it. Ships, fishing fleets and shipping routes make use of currents, and floating plastic gathers in gyres such as the Great Pacific Garbage Patch. A misconception is that currents are just surface water; deep currents are huge and driven by density.