However, because this thermohaline upwelling is so widespread and diffuse, its speeds are very slow even compared to the movement of the bottom water masses. Saltier water is denser than fresher water because the dissolved salts fill interstices between water molecules, resulting in more mass per unit volume. [ thermo- + Greek halinos, of salt (from hals, hal-, salt; see halo- ).] The blend of North Atlantic Deep Water, with a total formation rate of 15 to 20 million cubic metres (530 to 706 million cubic feet) per second, quickly ventilates the Atlantic Ocean, resulting in a residence time of less than 200 years. A number of scientists have tried to use these tracers to infer where the upwelling occurs. Additional deep water is formed in the Labrador Sea. By signing up for this email, you are agreeing to news, offers, and information from Encyclopaedia Britannica. Vertical velocities as high as 10 cm per second have been observed within these convective features. The thermohaline circulation is mainly triggered by the formation of deep water masses in the North Atlantic and the Southern Ocean caused by differences in temperature and salinity of the water. Blue paths represent deep-water currents, while red paths represent surface currents. Evaporation removes only water molecules, resulting in an increase in the salinity of the seawater left behind, and thus an increase in the density of the water mass. The movements of ocean waters are influenced by numerous factors, including the rotation of the Earth (which is responsible for the Coriolis effect), atmospheric circulation patterns that influence surface waters, and temperature and salinity gradients between the tropics and the polar regions (thermohaline…, Waves usually approach the coast at some acute angle rather than exactly parallel to it. AABW formed in the Weddell Sea will mainly fill the Atlantic and Indian Basins, whereas the AABW formed in the Ross Sea will flow towards the Pacific Ocean. Antarctic Bottom Water, formed at a rate of 30 million cubic metres per second, slips below the Antarctic Circumpolar Current and spreads to regions well north of the Equator. The deep water masses that participate in the MOC have chemical, temperature and isotopic ratio signatures and can be traced, their flow rate calculated, and their age determined. The Gulf Stream is also a significant potential source of renewable power generation.[12][13]. Benjamin Franklin’s map of the Gulf Stream, The Gulf Stream, together with its northern extension towards Europe, the North Atlantic Drift, is a powerful, warm, and swift Atlantic ocean current that originates at the tip of Florida, and follows the eastern coastlines of the United States and Newfoundland before crossing the Atlantic Ocean.

The continual diffuse upwelling of deep water maintains the existence of the permanent thermocline found everywhere at low and mid-latitudes. In the ocean, the thermocline divides the upper mixed layer from the calm deep water below. It is part of the North Atlantic Gyre. The brine progressively melts the ice just beneath it, eventually dripping out of the ice matrix and sinking. The resulting Antarctic Bottom Water (AABW) sinks and flows north and east, but is so dense it actually underflows the NADW. Measuring seawater temperature and salinity distribution is the chief method of studying the deep-flow patterns. It is estimated that the overturning rate of water south of the Antarctic Circumpolar Current amounts to 35 to 45 million cubic metres (1.2 to 1.6 billion cubic feet) per second, most of which becomes Antarctic Bottom Water. Meanwhile, sea ice starts reforming, so the surface waters also get saltier, hence very dense. Get kids back-to-school ready with Expedition: Learn! Winds drive ocean currents in the upper 100 meters of the ocean’s surface. They position themselves one above or below each other according to their density, which depends on both temperature and salinity. This is also known as ‘haline forcing’ (net high latitude freshwater gain and low latitude evaporation). The sinking of North Atlantic Deep Water is compensated for by the slow upwelling of deep water, mainly in the Southern Ocean, to replenish the upper stratum of water that has descended as North Atlantic Deep Water. The latter is formed in the northwestern Pacific Ocean. Thermohaline circulation also drives warmer surface waters poleward from the subtropics, which moderates the climate of Iceland and other coastal areas of Europe. [16] However, the underlying assumptions of this particular analysis have likewise been challenged. “The concept of the thermohaline circulation”, http://oceanservice.noaa.gov/facts/conveyor.html, “Satellites Record Weakening North Atlantic Current Impact”, Gulf Stream’s Tidal Energy Could Provide Up to a Third of Florida’s Power, 10.1175/1520-0442(2001)014<3433:EOMAAO>2.0.CO;2. There is often confusion over the components of the circulation that are wind and density driven. It continually replaces seawater at depth with water from the surface and slowly replaces surface water elsewhere with water rising from deeper depths. Although this process is relatively slow, tremendous volumes of water are moved, which transport heat, nutrients, solids, and other materials vast distances. [15] Changes in the thermohaline circulation are thought to have significant impacts on the Earth’s radiation budget. The thermohaline circulation plays an important role in supplying heat to the polar regions, and thus in regulating the amount of sea ice in these regions, although poleward heat transport outside the tropics is considerably larger in the atmosphere than in the ocean. Thus the deep ocean — devoid of wind — was assumed to be perfectly static by early oceanographers.

The primary site of Antarctic Bottom Water formation is within the continental margins of the Weddell Sea, though some is produced in other coastal regions, such as the Ross Sea. In contrast, thermohaline circulation is much slower, with a typical speed of 1 centimetre (0.4 inch) per second, but this flow extends to the seafloor and forms circulation patterns that envelop the global ocean. The basic dynamics of the Antarctic Circumpolar Current lift dense deep water occurring north of the current to the ocean surface south of it. In some areas of the ocean, generally during the winter season, cooling or net evaporation causes surface water to become dense enough to sink. North Atlantic Deep Water is primarily formed in the Greenland and Norwegian seas, where cooling of the salty water introduced by the Norwegian Current induces sinking. : involving or dependent upon the conjoint effect of temperature and salinity thermohaline circulation in the Pacific. Thermohaline circulation ( THC) is a part of the large-scale ocean circulation that is driven by global density gradients created by surface heat and freshwater fluxes. North Atlantic Deep Water exported to the other oceans must be balanced by the inflow of upper-layer water into the Atlantic. Measuring seawater temperature and salinity distribution is the chief method of studying the deep-flow patterns. For full treatment, see Ocean current: Two types of ocean currents: Thermohaline circulation. The thermohaline circulation reaches down to the seafloor and is often referred to as the deep, or abyssal, ocean circulation. The basic thermohaline circulation is one of sinking of cold water in the polar regions, chiefly in the northern North Atlantic and near Antarctica. Thermohaline circulation (THC) is a part of the large-scale ocean circulation that is driven by global density gradients created by surface heat and freshwater fluxes. The Gulf Stream influences the climate of the east coast of North America from Florida to Newfoundland, and the west coast of Europe. The dense water masses formed by these processes flow downhill at the bottom of the ocean, like a stream within the surrounding less dense fluid, and fill up the basins of the polar seas.

The thermohaline circulation reaches down to the seafloor and is often referred to as the deep, or abyssal, ocean circulation. Cold winds blowing over the oceans chill the waters beneath them. It then spreads slowly into the rest of the ocean. It then spreads slowly into the rest of the ocean. A variety of water types contribute to the so-called North Atlantic Deep Water. The movement of surface currents pushed by the wind is fairly intuitive. Coincidentally, scientists at Woods Hole had been measuring the freshening of the North Atlantic as Earth becomes warmer. [4] Extensive mixing therefore takes place between the ocean basins, reducing differences between them and making the Earth’s oceans a global system. In the process it transports heat, which influences regional climate patterns. Thermohaline circulation transports and mixes the water of the oceans. While the bulk of it upwells in the Southern Ocean, the oldest waters (with a transit time of around 1000 years)[3] upwell in the North Pacific. The outflow of the Mediterranean plays a significant role in boosting the salinity of North Atlantic Deep Water. The thermohaline circulation, often referred to as the ocean's "conveyor belt", links major surface and deep water currents in the Atlantic, Indian, Pacific, and Southern Oceans. Convection penetrates to a level where the density of the sinking water matches that of the surrounding water. The surrounding seawater gets saltier, increases in density and sinks.

Multiple mechanisms conspire to increase the density of surface waters at high latitudes. Remnants of North Atlantic Deep Water mix with Southern Ocean water to spread along the seafloor into the North Pacific Ocean. The process of western intensification causes the Gulf Stream to be a northward accelerating current off the east coast of North America. This high latitude cooling and the low latitude heating drives the movement of the deep water in a polar southward flow. Because of the immenseness of the North Pacific and the extremely long residence time (more than 500 years) of the water, enormous quantities of North Pacific Deep Water can be produced by vertical mixing. This belt establishes the Antarctic Circumpolar Current, which isolates Antarctica from the warm surface waters of the subtropics.

While it is often stated that the thermohaline circulation is the primary reason that Western Europe is so temperate, it has been suggested that this is largely incorrect, and that Europe is warm mostly because it lies downwind of an ocean basin, and because of the effect of atmospheric waves bringing warm air north from the subtropics. The Antarctic Circumpolar Current does not completely sever contact with the lower latitudes. These, however, are superimposed on the much more sluggish circulation driven by horizontal differences in temperature and salinity—namely, the thermohaline circulation.

Other water must replace the surface water that sinks. Recent papers by Lynne Talley at the Scripps Institution of Oceanography and Bernadette Sloyan and Stephen Rintoul in Australia suggest that a significant amount of dense deep water must be transformed to light water somewhere north of the Southern Ocean. It is known as overturning. Hence, a recent and popular name for the thermohaline circulation, emphasizing the vertical nature and pole-to-pole character of this kind of ocean circulation, is the meridional overturning circulation. In the Northern Hemisphere the primary region of deep water formation is the North Atlantic; minor amounts of deep water are formed in the Red Sea and Persian Gulf.