12/10/2023 0 Comments Age of water masses![]() The third major source of deep water is called Antarctic Intermediate Water or AIW. Some of the water mass spills over into the eastern part of the South Atlantic, while the remainder travels into the equatorial channel between South America and Africa. ![]() AABW travels northward along the western side of the South Atlantic underneath NADW. This water is relatively fresh (average 34.6 ppt). With this source, AABW is amongst the coldest water in the ocean with a temperature of -0.4oC. Moreover, brine exclusion intensifies the cooling by wind.Ĭredit: Hannes Grobe, Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, Germany, Creative Commons CC-BY-SA-2.5Īntarctic Bottom Water or AABW is produced by evaporative cooling off the coast of Antarctica and under the Ross ice shelf. Pockets of salty water around the margins of the ice sink as a result of their higher density. In certain locations, the formation of sea ice also causes an increase in salinity as the freezing removes fresh water, leaving the salt behind in a process known as brine exclusion. Falling temperature and increasing salinity render these surface water masses denser, allowing them to downwell. This evaporation targets just the water molecules, resulting in an increase in the salinity of the water. Wind moving over the water both cools it and causes an increase in evaporation. The production of deep-water masses via downwelling occurs in high-latitude regions of the northern and southern hemispheres, where the surface ocean is cooled by winds. Downwelling water travels along lines of equal density known as isopycnals and spreads out horizontally at the level where it is equal in density to the surrounding water mass. Generally, downwelling occurs where the surface ocean is cool, or, rarely, unusually saline. ![]() Deep-water masses are produced at the surface of the ocean and transported to depth via downwelling. The thermocline is the sharp temperature decrease that lies at the base of the surface mixed layer, where waters are generally uniform in temperature as a result of convection. Credit: AE Nieblas, CSIRO ( deep ocean is generally considered to include the ocean below a transition known as the thermocline. ![]()
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