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34-552: The Agulhas Current carries around 70 Sv southward towards 32°S. When the current passes the southern African tip, it changes direction and returns to the Indian Ocean. However, part of it (around 2-15 Sv) leaks into the Southern Atlantic. The leakage is mainly driven by large anticyclonic eddies shedded from the retroflection. The process is also induced by cyclonic eddies formed when the main current detaches from

68-692: A high amount of anthropogenic tracers due its exposure to the atmosphere. AIW's tritium and CFC signature is observed in DSOW at the base of the Greenland continental slope. This also showed that the DSOW flowing 450 km to the south was no older than 2 years. Both the DSOW and ISOW flow around the Irminger Basin and Labrador Sea in a deep boundary current. Leaving the Greenland Sea with 2.5 Sv , its flow increases to 10 Sv south of Greenland. It

102-669: A new unit of water flow, "the inflow through Bering Strait is one sverdrup". At the Arctic Basin Symposium in October 1962, the unit came into general usage. The water transport in the Gulf Stream gradually increases from 30 Sv in the Florida Current to a maximum of 150 Sv south of Newfoundland at 55° W longitude . The Antarctic Circumpolar Current , at approximately 125 Sv ,

136-640: A temperature of 2-4 °C with a salinity of 34.9-35.0 psu found at a depth between 1500 and 4000m. The NADW is a complex of several water masses formed by deep convection and overflow of dense water across the Greenland-Iceland-Scotland Ridge. The upper layers are formed by deep open ocean convection during winter. Labrador Sea Water (LSW), formed in the Labrador Sea , can reach depths of 2000 m as dense water sinks downward. Classical Labrador Sea Water (CLSW) production

170-499: A volume of one million cubic meters may be imagined as a "slice" of ocean with dimensions 1  km × 1 km × 1 m (width × length × thickness). At this scale, these units can be more easily compared in terms of width of the current (several km), depth (hundreds of meters), and current speed (as meters per second ). Thus, a hypothetical current 50 km wide, 500 m (0.5 km) deep, and moving at 2 m/s would be transporting 50 Sv of water. The sverdrup

204-635: Is cold and relatively fresh, flowing below 3500 m in the DWBC and spreading inward the deep Atlantic basins. The southward spread of NADW along the Deep Western Boundary current (DWBC) can be traced by its high oxygen content, high CFCs, and density. ULSW is the major source of upper NADW. ULSW advects southward from the Labrador Sea in small eddies that mix into the DWBC. A CFC maximum associated with ULSW has been observed along 24°N in

238-542: Is dependent on preconditioning of water in the Labrador Sea from the previous year and the strength of the North Atlantic Oscillation (NAO). During a positive NAO phase, conditions exist for strong winter storms to develop. These storms freshen the surface water, and their winds increase cyclonic flow, which allows denser waters to sink. As a result, the temperature, salinity, and density vary yearly. In some years these conditions do not exist and CLSW

272-514: Is distinct from the SI sievert unit or the non-SI svedberg unit. All three use the same symbol, but they are not related. The sverdrup is named in honor of the Norwegian oceanographer, meteorologist and polar explorer Harald Ulrik Sverdrup (1888–1957), who wrote the 1942 volume The Oceans, Their Physics, Chemistry, and General Biology together with Martin W. Johnson and Richard H. Fleming. In

306-453: Is equivalent to the SI derived unit cubic hectometer per second (symbol: hm /s or hm ⋅s ): 1 Sv is equal to 1 hm /s. It is used almost exclusively in oceanography to measure the volumetric rate of transport of ocean currents . It is named after Harald Sverdrup . One sverdrup is about five times what is carried by the world's largest river, the Amazon. In the context of ocean currents ,

340-550: Is less dense than DSOW and lays above it as it flows cyclonically in the Irminger Basin. DSOW is the coldest, densest, and freshest water mass of NADW. DSOW formed behind the ridge flows over the Denmark Strait at a depth of 600m. The most significant water mass contributing to DSOW is Arctic Intermediate Water (AIW). Winter cooling and convection allow AIW to sink and pool behind the Denmark Strait. Upper AIW has

374-480: Is not formed. CLSW has characteristic potential temperature of 3 °C, salinity of 34.88 psu, and density of 34.66. Another component of LSW is the Upper Labrador Sea Water (ULSW). ULSW forms at a density lower than CLSW and has a CFC maximum between 1200 and 1500 m in the subtropical North Atlantic. Eddies of cold less saline ULSW have similar densities of warmer saltier water and flow along

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408-495: Is the largest ocean current. The entire global input of fresh water from rivers to the ocean is approximately 1.2 Sv . North Atlantic Deep Water North Atlantic Deep Water ( NADW ) is a deep water mass formed in the North Atlantic Ocean . Thermohaline circulation (properly described as meridional overturning circulation) of the world's oceans involves the flow of warm surface waters from

442-795: The Norwegian Current , which splits into the Fram Strait and Barents Sea Branch. Water from the Fram Strait recirculates, reaching a density of DSOW, sinks, and flows towards the Denmark Strait. Water flowing into the Barents Sea feeds ISOW. ISOW enters the eastern North Atlantic over the Iceland-Scotland Ridge through the Faeroe Bank Channel at a depth of 850 m, with some water flowing over

476-579: The 1950s and early 1960s both Soviet and North American scientists contemplated the damming of the Bering Strait , thus enabling temperate Atlantic water to heat up the cold Arctic Sea and, the theory went, making Siberia and northern Canada more habitable. As part of the North American team, Canadian oceanographer Maxwell Dunbar found it "very cumbersome" to repeatedly reference millions of cubic meters per second. He casually suggested that as

510-567: The AMOC. The propagation of anticyclonic rings into the Atlantic leads to the density surfaces depression inducing planetary waves formation. This can result in AMOC oscillations on both short and interannual-to-decadal time scales. Sverdrup In oceanography , the sverdrup (symbol: Sv ) is a non- SI metric unit of volumetric flow rate , with 1 Sv equal to 1 million cubic metres per second (264,172,052 US gal/s). It

544-436: The AMOC. There is evidence indicating that anthropogenic climate change causes southward expansion of the Indian Ocean subtropical gyre, which results in a southward shift of the westerlies. Simultaneously, no significant trend in wind curl value is observed. As a result, the latitude of the zero wind curl migrates towards the south and the leakage intensifies. Moreover, there has been an increase in eddy kinetic energy in

578-494: The Agulhas Current, as well as the leakage can be reconstructed based on paleoceanographic data such as the provenance of sediments (presence of planktic foraminiferal species Globorotalia menardii , isotope ratio ( 87Sr/86Sr ) in deep ocean cores, abundance of Agulhas fauna ). Paleoclimate observations allow for a reconstruction of the leakage for up to 1 350 000 years (mid Pleistocene ). It has been shown that

612-515: The CFCs to penetrate further downward to 2000m. These minima could be tracked, and were first observed in the subtropics in the early 1990s. ISOW and DSOW flow around the Irminger Basin and DSOW entering the DWBC. These are the two lower portions of the NADW. Another CFC maximum is seen at 3500 m in the subtropics from the DSOW contribution to NADW. Some of the NADW recirculates with the northern gyre. To

646-522: The DWBC at 1500 m. Some of the upper ULSW recirculates into the Gulf Stream, while some remains in the DWBC. High CFCs in the subtropics indicate recirculation in the subtropics. ULSW that remains in the DWBC dilutes as it moves equatorward. Deep convection in the Labrador Sea during the late 1980s and early 1990s resulted in CLSW with a lower CFC concentration due to downward mixing. Convection allowed

680-432: The DWBC, but maintain their high CFCs. The ULSW eddies erode rapidly as they mix laterally with this warmer saltier water. The lower waters mass of NADW form from overflow of the Greenland-Iceland-Scotland Ridge. They are Iceland-Scotland Overflow Water (ISOW) and Denmark Strait Overflow Water (DSOW). The overflows are a combination of dense Arctic Ocean water (18%), modified Atlantic water (32%), and intermediate water from

714-583: The Nordic seas (20%), that entrain and mix with other water masses (contributing 30%) as they flow over the Greenland-Iceland-Scotland Ridge. The formation of both of these waters involves the conversion of warm, salty, northward-flowing surface waters to cold, dense, deep waters behind the Greenland-Iceland-Scotland Ridge. Water flow from the North Atlantic current enters the Arctic Ocean through

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748-518: The Southeast Atlantic associated with more eddies and rings being formed leading to stronger leakage. The Agulhas leakage can potentially play a role in global climate because of its impact on the strength of the AMOC . The leakage can modify the AMOC through: The leakage brings relatively warm and saline water into the Atlantic basin which has two contrary effects on the density. Around

782-553: The Southern tip of Africa, the heat input has a dominant effect resulting in a negative density anomaly. Further northward propagation leads to atmospheric heat loss and only the salinity anomaly remains which is manifested as a positive density anomaly. The associated buoyancy forcing enhances the Atlantic meridional density gradient giving rise to the North Atlantic Deep Water (NADW) formation which strengthens

816-582: The Tropical Atlantic to the Mid and High Latitude Atlantic. In the conveyor belt model of thermohaline circulation of the world's oceans, the sinking of NADW pulls the waters of the North Atlantic drift northward. However, this is almost certainly an oversimplification of the actual relationship between NADW formation and the strength of the Gulf Stream /North Atlantic drift. NADW has

850-666: The continental shelf and filaments peeled directly from the main current. After reaching the Atlantic, the leakage enters the Cape Cauldron and the majority of the leakage propagates further north-westwards through the Benguela Current , South Equatorial Current , and finally crosses the equator along with the North Brazil Current . It then joins the Loop Current and the Gulf Stream . Part of

884-753: The leakage follows the extension of the Indian-Atlantic supergyre to the Pacific Ocean. A small part of it follows the " cold water route ", by looping along the Antarctic Circumpolar Current and entering the Atlantic through the Drake Passage . The Agulhas Current represents a western boundary current which is primarily driven by a positive wind stress curl. The presence of the African continent allows for

918-478: The leakage was more intense during interglacial periods . Those periods are characterized by a southward shift of the Subtropical Front associated with stronger leakage. Paleoclimate data suggest that the strength of the leakage is positively correlated with the sea surface temperature, which is higher during interglacials. Moreover, the strength of the leakage was shown to be linked to the strength of

952-485: The shallower Iceland-Faeroe Rise. ISOW has a low CFC concentrations and it has been estimated from these concentrations that ISOW resides behind the ridge for 45 years. As the water flows southward at the bottom of the channel, it entrains surrounding water of the eastern North Atlantic, and flows to the western North Atlantic through the Charlie-Gibbs Fracture Zone , entraining with LSW. This water

986-666: The south of the gyre, NADW flows under the Gulf Stream, where it continues along the DWBC until it reaches another gyre in the subtropics. Lower North Atlantic Deep Water (LNADW), originating in the Greenland and Norwegian seas, brings high salinity, oxygen, and freon concentrations towards to the Romanche Trench , an equatorial fracture zone in the Mid-Atlantic Ridge (MAR). Found at depths around 3,600–4,000 m (11,800–13,100 ft), LNADW flow east through

1020-570: 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 C/ C, and chlorofluorocarbons (CFCs). CFCs are anthropogenic substances that enter

1054-484: The southward flow of the current. Beyond Cape Agulhas , further southward propagation is no longer maintained by the western boundary. With large inertia , the current reaches the latitude of maximum westerlies (40°S) associated with neutral wind stress and loops back into the Indian Ocean (Agulhas retroflection). Without sufficient inertia, it turns westwards and leaks into the Atlantic Ocean. The strength of

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1088-555: The southward inertia and the position of the Subtropical Front (STF) are the key factors in the generation of the Agulhas leakage. Both of them are primarily controlled by the strength and the pattern of the wind field over the Indian Ocean. Generation of the Agulhas rings is also an important driver of the leakage. This depends on instabilities , topography, and mesoscale non-linear dynamics. The strength and location of

1122-623: The surface of the ocean from gas exchange with the atmosphere. This distinct composition allows its path to be traced as it mixes with Circumpolar Deep Water (CDW), which in turn fills the deep Indian Ocean and part of the South Pacific . NADW and its formation is essential to the Atlantic Meridional Overturning Circulation (AMOC), which is responsible for transporting large amounts of water, heat, salt, carbon, nutrients and other substances from

1156-525: The trench over Antarctic Bottom Water —the trench is the only opening in the MAR where inter-basin exchange is possible for these two water masses. It is believed that North Atlantic Deep Water formation has been dramatically reduced at times during the past (such as during the Younger Dryas or during Heinrich events ), and that this might correlate with a decrease in the strength of the Gulf Stream and

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