Thermohaline circulation and El Niño

Ocean water is layered by density: a warm, well-mixed surface layer sits above the thermocline, where temperature drops quickly with depth, and cold, dense water fills most of the deep ocean below. Density depends on temperature and salinity: colder and saltier water is denser. Surface currents are driven mainly by winds, deflected by the Coriolis effect, and shaped by the continents into large circular gyres, such as the one that carries the warm Gulf Stream north along the U.S. East Coast. Deep ocean circulation is driven by density differences, which is why it is called thermohaline (heat plus salt) circulation. In the North Atlantic and around Antarctica, surface water becomes cold and salty, partly because forming sea ice leaves salt behind, so it sinks and spreads through the deep ocean before rising again elsewhere. This global conveyor moves heat, oxygen, and nutrients around the planet, and water can take roughly a thousand years to complete the loop. Fresh water from melting ice sheets and glaciers makes surface water less dense, which can weaken the sinking, and climate models project that the Atlantic part of this circulation will weaken this century. Changes in surface ocean conditions also shift weather worldwide. In an El Niño, the trade winds weaken and warm water spreads east across the tropical Pacific, bringing heavy rain to Peru and often the southern United States and drought to Indonesia and Australia; in La Niña, the opposite phase, the trade winds strengthen and the eastern Pacific cools. This cycle is called the El Niño-Southern Oscillation, or ENSO.

This explanation is AI-generated and can occasionally be wrong. 🚩 Report