North Atlantic Deep Water (NADW) is a deep water mass formed in the North Atlantic Ocean. Thermohaline circulation of the world's oceans involves the flow of warm surface waters from the southern hemisphere into the North Atlantic. Water flowing northward becomes modified through evaporation and mixing with other water masses, leading to increased salinity. When this water reaches the North Atlantic it cools and sinks through convection, due to its decreased temperature and increased salinity resulting in increased density. NADW is the outflow of this thick deep layer, which can be detected by its high salinity, high oxygen content, nutrient minima, high 14C/12C, and chlorofluorocarbons (CFCs).
Salinity is the saltiness or amount of salt dissolved in a body of water, called saline water. It is usually measured in g/L or g/kg.
The Drake Passage is the body of water between South America's Cape Horn, Chile and the South Shetland Islands of Antarctica. It connects the southwestern part of the Atlantic Ocean with the southeastern part of the Pacific Ocean and extends into the Southern Ocean.
Physical oceanography is the study of physical conditions and physical processes within the ocean, especially the motions and physical properties of ocean waters.
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 adjective thermohaline derives from thermo- referring to temperature and -haline referring to salt content, factors which together determine the density of sea water. Wind-driven surface currents travel polewards from the equatorial Atlantic Ocean, cooling en route, and eventually sinking at high latitudes. This dense water then flows into the ocean basins. While the bulk of it upwells in the Southern Ocean, the oldest waters upwell in the North Pacific. Extensive mixing therefore takes place between the ocean basins, reducing differences between them and making the Earth's oceans a global system. The water in these circuits transport both energy and mass around the globe. As such, the state of the circulation has a large impact on the climate of the Earth.
The Strait of Sicily is the strait between Sicily and Tunisia. The strait is about 145 kilometres (90 mi) wide and divides the Tyrrhenian Sea and the western Mediterranean Sea, from the eastern Mediterranean Sea. The maximum depth is 316 meters (1,037 ft).
The Florida Current is a thermal ocean current that flows from the Straits of Florida around the Florida Peninsula and along the southeastern coast of the United States before joining the Gulf Stream Current near Cape Hatteras. Its contributing currents are the Loop Current and the Antilles Current. The current was discovered by Spanish explorer Juan Ponce de León in 1513.
The Norwegian Current is one of two dominant arctic inflows of water. It can be traced from near Shetland, north of Scotland, otherwise from the eastern North Sea at depths of up to 100 metres. It finally passes the Opening into the Barents Sea, a large outcrop of the Arctic Ocean. Compared to its partial source the North Atlantic Current it is colder and less salty; the other sources are the less saline North and Baltic seas and the Norwegian fjords and rivers. It is considerably warmer and saltier than the Arctic Ocean, which is freshened by precipitation and ice in and around it. Winter temperatures in the flow are typically between 2 and 5 °C — the co-parent North Atlantic flow, a heat remnant of its Gulf Stream chief contributor, exceeds 6 °C.
Henry Melson Stommel was a major contributor to the field of physical oceanography. Beginning in the 1940s, he advanced theories about global ocean circulation patterns and the behavior of the Gulf Stream that form the basis of physical oceanography today. Widely recognized as one of the most influential and productive oceanographers of his time, Stommel was both a groundbreaking theoretician and an astute, seagoing observer.
The oceanic or limnological mixed layer is a layer in which active turbulence has homogenized some range of depths. The surface mixed layer is a layer where this turbulence is generated by winds, surface heat fluxes, or processes such as evaporation or sea ice formation which result in an increase in salinity. The atmospheric mixed layer is a zone having nearly constant potential temperature and specific humidity with height. The depth of the atmospheric mixed layer is known as the mixing height. Turbulence typically plays a role in the formation of fluid mixed layers.
Salt fingering is a mixing process, example of double diffusive instability, that occurs when relatively warm, salty water overlies relatively colder, fresher water. It is driven by the fact that heated water diffuses more readily than salty water. A small parcel of warm, salty water sinking downwards into a colder, fresher region will lose its heat before losing its salt, making the parcel of water increasingly denser than the water around it and sinking further. Likewise, a small parcel of colder, fresher water will be displaced upwards and gain heat by diffusion from surrounding water, which will then make it lighter than the surrounding waters, and cause it to rise further. Paradoxically, the fact that salinity diffuses less readily than temperature means that salinity mixes more efficiently than temperature due to the turbulence caused by salt fingers.
A subsurface current is an oceanic current that runs beneath surface currents. Examples include the Equatorial Undercurrents of the Pacific, Atlantic, and Indian Oceans, the California Undercurrent, and the Agulhas Undercurrent, the deep thermohaline circulation in the Atlantic, and bottom gravity currents near Antarctica. The forcing mechanisms vary for these different types of subsurface currents.
Internal tides are generated as the surface tides move stratified water up and down sloping topography, which produces a wave in the ocean interior. So internal tides are internal waves at a tidal frequency. The other major source of internal waves is the wind which produces internal waves near the inertial frequency. When a small water parcel is displaced from its equilibrium position, it will return either downwards due to gravity or upwards due to buoyancy. The water parcel will overshoot its original equilibrium position and this disturbance will set off an internal gravity wave. Munk (1981) notes, "Gravity waves in the ocean's interior are as common as waves at the sea surface-perhaps even more so, for no one has ever reported an interior calm."
The West Spitsbergen Current (WSC) is a warm, salty current that runs poleward just west of Spitsbergen,, in the Arctic Ocean. The WSC branches off the Norwegian Atlantic Current in the Norwegian Sea. The WSC is of importance because it drives warm and salty Atlantic Water into the interior Arctic. The warm and salty WSC flows north through the eastern side of Fram Strait, while the East Greenland Current (EGC) flows south through the western side of Fram Strait. The EGC is characterized by being very cold and low in salinity, but above all else it is a major exporter of Arctic sea ice. Thus, the EGC combined with the warm WSC makes the Fram Strait the northernmost ocean area having ice-free conditions throughout the year in all of the global ocean.
Mode water is defined as a particular type of water mass, which is nearly vertically homogeneous. Its vertical homogeneity is caused by the deep vertical convection in winter. The first term to describe this phenomenon is 18° water, which was used by Valentine Worthington to describe the isothermal layer in the northern Sargasso Sea cool to a temperature of about 18 °C each winter. Then Masuzawa introduced the subtropical mode water concept to describe the thick layer of temperature 16–18 °C in the northwestern North Pacific subtropical gyre, on the southern side of the Kuroshio Extension. The terminology mode water was extended to the thick near-surface layer north of the Subantarctic Front by McCartney, who identified and mapped the properties of the Subantarctic mode water (SAMW). After that, McCartney and Talley then applied the term subpolar mode water (SPMW) to the thick near-surface mixed layers in the North Atlantic’s subpolar gyre.
Karen Joy Heywood is a British Antarctic oceanographer and Professor of Physical Oceanography at the University of East Anglia (UEA). She is best known for her work developing autonomous measurements of the Southern Ocean.
Trevor John McDougallFAGU is a physical oceanographer specialising in ocean mixing and the thermodynamics of seawater. He is Scientia Professor of Ocean Physics in the School of Mathematics and Statistics at the University of New South Wales, Sydney, Australia. He is President of the International Association for the Physical Sciences of the Oceans (IAPSO) of the International Union of Geodesy and Geophysics.
The Mediterranean Outflow is a current flowing from the Mediterranean Sea towards the Atlantic Ocean through the Strait of Gibraltar. Once it has reached the western side of the Strait of Gibraltar, it divides into two branches, one flowing westward following the Iberian continental slope, and another returning to the Strait of Gibraltar circulating cyclonically. In the Strait of Gibraltar and in the Gulf of Cádiz, the Mediterranean Outflow core has a width of a few tens of km. Through its nonlinear interactions with tides and topography, as it flows out of the Mediterranean basin it undergoes such strong mixing that the water masses composing this current become indistinguishable upon reaching the western side of the strait.
Open ocean convection is a process in which the mesoscale ocean circulation and large, strong winds mix layers of water at different depths. Fresher water lying over the saltier or warmer over the colder leads to the stratification of water, or its separation into layers. Strong winds cause evaporation, so the ocean surface cools, weakening the stratification. As a result, the surface waters are overturned and sink while the "warmer" waters rise to the surface, starting the process of convection. This process has a crucial role in the formation of both bottom and intermediate water and in the large-scale thermohaline circulation, which largely determines global climate. It is also an important phenomena that controls the intensity of the Atlantic Meridional Overturning Circulation (AMOC).
The Haline contraction coefficient, abbreviated as β, is a coefficient that describes the change in density in the ocean due to the salinity change, while the potential temperature and the pressure are kept constant. It is a parameter in the Equation Of State (EOS) of the ocean. In literature, β is also described as the saline contraction coefficient and is measured in [kg]/[g] in the equation of seawater (EOS) that describes the ocean. An example is the TEOS-10. This is the thermodynamic equation of state.
