The sources of the Agulhas Current are the East Madagascar Current (25 Sv), the Mozambique Current (5 Sv) and a recirculated part of the south-west Indian subgyre south of Madagascar (35 Sv). Lutjeharms, M.W. Agulhas Current, where the QUICK scheme was applied to both tracer and momentum advection, the narrow, warm Ag-ulhas Current core was significantly improved, resulting in a much better southwestward penetration of the temperature field, a deficiency noted in an application of HYCOM to the greater Agulhas Current system (Backeberg et al., 2008). The core of the northern Agulhas Current has been found to meander less than 15 km to either side or its mean path by analysing temperature sections across the region between 28°S 30′ and 34°S (Gründlingh, 1983). [6], Large-scale cyclonic meanders known as Natal pulses are formed as the Agulhas Current reaches the continental shelf on the South African east-coast (i.e. By tracking the offshore position of the current core … Beal, 2001: Schouten, 1) is able to estimate the mean position and intensity of the Agulhas Current very well. Agulhas Current core, and 300 m above the steep bottom of the continental slope. When the AC meanders, its width broadens from 88 km (55 mi) to 125 km (78 mi) and its velocity weakens from 208 cm/s (82 in/s) to 136 cm/s (54 in/s). Early concepts and charts of ocean circulation. Temperature sections across the Agulhas Current between 28°30’s and 34°S are analysed to determine the course of the Current down the East Coast of southern Africa. 2. Directly under the core of the Agulhas Current, at a depth of 800 m (2,600 ft), there is an Agulhas Undercurrent which flows equatorward. Along with direct branch currents, this leakage takes place in surface water filaments, and Agulhas Eddies. Matano, R.P., C.G. Mid- to late-Quaternary reseeding of G. menardii in the tropical-subtropical Atlantic. the eastern Agulhas Bank off Natal). Some 30 larger ships were severely damaged or sunk by rogue waves along the South African east-coast between 1981 and 1991. It is estimated that as much as 15 Sv of Indian Ocean water is leaked directly into the South Atlantic. The AC passes 34 km (21 mi) offshore and an ACM can reach 123 km (76 mi) offshore. The undercurrent is more leaky than the Agulhas above, resulting in a relatively well-mixed composition of water masses — at intermediate depth there is a mixture of Antarctic Intermediate Water and Read Sea Water. Bryden, H.L., L.M. EOS, 79, 1, 1, 7-8. Schlax, 1998: Natal pulses and the formation of Agulhas Rings. The current can then more easily detach from the continental slope by interface outcropping, creating a free streamline. It is generally not very wide, usually less than 50 miles, but can be double this. 239p. An ACM induces a strong inshore counter-current. The flow of the Agulhas Current is directed by the topography. A small amount of the Agulhas Leakage joins the North Brazil Current, carrying Indian Ocean water into the North Atlantic Subtropical Gyre. Deep-Sea Research I, 40, 10, 1973-2019. and H.L Bryden, 1999: Duncan, 2003: submitted to the Journal of Oceanography. This heat flux is believed to contribute to the high rate of evaporation in the South Atlantic, a key mechanism in the Meridional Overturning Circulation. Fig. the Agulhas Current as well as the large SST gradients at its inshore boundary should make SST a suitable tracer for tracking the path of the Agulhas Current’s inshore front. 10 Sv of this is relatively warm, salty thermocline water, with the remaining 5 Sv being cold, low salinity Antarctic Intermediate Water. The current reaches its maximum transport near the Agulhas Bank where it ranges between 95-136 Sv. ⋅ Cambridge University Press: Cambridge, UK. The Ifaty coral core location (yellow dot) and the region of dense SST observations (rectangular box) for the Agulhas Current are indicated. Peterson, R.G., L. Stramma, and G. Kortum, 1996: The back to 1850 for the greater Agulhas Current region (Fig. [10] The trajectory of the current was the same during the LGM and that the reduced leakage must be explained by a weaker current. The current reaches its maximum transport near the Agulhas Bank where it ranges between 95-136 Sv. As these pulses moves along the coast on the Agulhas Bank, they tend to pinch off Agulhas rings from the Agulhas Current. The Agulhas Current transport of heat and salt from the Indian Ocean into the South Atlantic around South Africa (Agulhas leakage), can affect the Atlantic meridional overturning circulation (AMOC) and, thus, influence global climate. Agulhas Rings have also been observed as removing larval and juvenile fish from the continental shelf. Indian-Atlantic transfer of thermocline water at the Agulhas Retroflection. Journal of Geophysical Research, 99, 14053-14070. de Ruijter, and J.R.E. This removal of young fish can result in a reduced anchovy catch in the Benguela system if a ring passes through the fishery. Agulhas meanders and Natal pulses 2013, however, noted that changes in temperature and salinity in the Agulhas leakage is at least partly the result of variability in the composition in the current itself and can be a poor indicator of the strength of the leakage. The Cape Cauldron: a regime of turbulent inter-ocean exchange. Lutjeharms, J.R.E., and H.R. J. Geophys. The current core can be seen to fol- 2. (A) Concentration and AR of G. menardii at ODP Site 1087 in the southern Benguela region. Agulhas Current has more inertia so the potential for stretching is larger (related to conservation of the Bernouilli function [Ou and de Ruijter, 1986]). Drifters' positions relative to the core of the Agulhas Current were determined in two steps. Journal of Geophysical Research, 93, 631-635. Geophysical Research Letters, 25, 23, 4361-4364. Steinberg, P.E., 2001: Time-averaged range-directed surface currents derived from ASAR provide an improved map of the mean Agulhas Current flow, clearly showing the location of the Agulhas Current core over the 1000 m isobath and identifying the region at the shelf edge of the north-eastern Agulhas Bank as one of the most variable within the Agulhas Current. southeast Atlantic Ocean: A case study. Deep-Sea Research Part I, 43, 2, 213-238. Boebel, O., C.D. van Ballegooyen, 1988: The Agulhas Return Current flows eastward and exhibits a quasi-stationary meandering pattern of wavelength 500 km between 38° and 40° S. Its core width is about 70 km with an associated transport of 44±5 Sv in the upper 1000 m (Boebel et al., 2003). A better vertical structure and stronger poleward transports in the Agulhas Current core contribute toward a better southwestward penetration of the current, and its temperature field, implying a stronger Indo-Atlantic inter-ocean exchange. Beal, L.M. Its heat transfer into both the midlatitude South Indian Ocean and South Atlantic is of global significance. Journal of Geophysical Research, 104, C3, 5151-5176. The Agulhas Bank is a natural boundary between ocean currents from the Atlantic Ocean, Indian Ocean, and Southern Ocean, resulting in one of the most turbulent waters of the world oceans. Toole, J.M. the Agulhas Current in combination with surface drifters as well as geostrophic currents from satellite altimeters, it is shown that eddies from the Mozambique Channel and south of Madagascar dissipate as they approach the Agulhas Current. Role of the Agulhas Current in Indian Ocean circulation and associated 2.1 Northern Agulhas Current The northern Agulhas Current has been shown to be quite re-markable as a western boundary current for its invariant path. Rae, S. Garzoli, J. Lutjeharms, P. Richardson, T. Rossby, The core of the current is defined as where the surface velocities reaches 100 cm/s (39 in/s), which gives the core an average width of 34 km (21 mi). Leeuwen, P. J., W. P. M. de Ruijter, and J. R. E. Lutjeharms, 2000: Deep-Sea Research II, 50, 13-34. Lutjeharms, J.R.E., O. Boebel, and H.T. This is evident in Fig. [1], The sources of the Agulhas Current are the East Madagascar Current (25 Sv), the Mozambique Current (5 Sv) and a recirculated part of the south-west Indian subgyre south of Madagascar (35 Sv). Both of these factors result in the area being one of enhanced primary productivity as compared to the surrounding waters. [16], The periodicity of the meanders and Natal pulses of the Agulhas is matched by the Agulhas Undercurrent. Strub, D.B. This is the first continuous record of hydrographic variability (SST; δ18O sw ) from the Agulhas Current core region spanning the past 270,000 years. The current follows the continental shelf from Maputo to the tip of the Agulhas Bank (250 km south of Cape Agulhas). Lutjeharms, J.R.E and R.C. C. Schmid and W. Zenk, 1998: [17], Warm core rings are known to have lower primary productivity than surrounding cold waters. [14] The undercurrent is 2,000 m (6,600 ft) deep and 40 km (25 mi) wide and can reach 90 cm/s (35 in/s) at 1,400 metres (4,600 ft), one of greatest speeds observed in any current at this depth, but it also displays a great variance with a transport of 4.2±5.2 Sv. The dominant periods of short-term variability in the Comparison of the three velocity sections of the Agulhas Current Agulhas Rings are no exception, and have been observed to carry waters with low chlorophyll-a concentration water into the South Atlantic. It is estimated that up to 85 Sv (Sv) of the net transport is returned to the Indian Ocean through the retroflection. Lutjeharms, J.R.E. These bulges are occasionally (1-7 times per year) followed by a much larger offshore bulge, known as Natal pulses (NP). van Leeuween, P.T. The Agulhas Current runs close to the shore along the continental shelf and can build up to speeds of 5 knots. of the Agulhas Current, it was shown that for radar incidence angles greater than 30°, the time-averaged map of ASAR range velocities (Fig. [3] Seasonal variations in the region of the Agulhas Retroflection: Studies with Geosat and FRAM. This is the first continuous record of hydrographic variability (SST; δ 18 O sw) from the Agulhas Current core region spanning the past 270,000 … [15] NADW rounds the southern tip of Africa after which the major part (9 Sv) flow eastward and a smaller part (2 Sv) northward through the Agulhas Undercurrent and into the Natal Valley (the basin between South Africa and the Mocambique Plateau); remnants of NADW has been observed in the Mozambique Basin and Channel. [3] Before reaching the Caribbean Sea, this leakage gets heated up by the sun around the equator, and, when finally joining the Gulf Stream, this warm and salty water contributes to the formation of deep water in the North Atlantic. 1). 2009 analysed cores in the South Atlantic deposited during the Last Glacial Maximum (LGM, 20 000 years ago), and concluded that the Agulhas leakage was significantly reduced. Rossby, 2003: Journal of Physical Oceanography, 18, 11, 1570-1583. Interbasin leakage through Agulhas Current filaments. and L.M. Structure and transport of the Agulhas Current and its temporal variability. Deep-Sea Research II, 50, 35-56. [3], Since the Pleistocene, the buoyancy of the South Atlantic thermocline and the strength of the Atlantic meridional overturning circulation has been regulated by the shedding of warm, saline Agulhas Rings. Chelton and M.G. {\displaystyle \cdot } The Social Construction of the Ocean. Lutjeharms, 1994: Natal pulses and the formation of Agulhas Rings. [2] The net transport of the Agulhas Current is estimated as 100 Sv. A hydrographic section across the subtropical South Indian Ocean. The mean peak speed is 136 cm/s (54 in/s), but the current can reach 245 cm/s (96 in/s). At the same time the undercurrent is first squeezed offshore and weakened when the Agulhas moves onshore, then strengthened and forced upward when the Agulhas moves offshore, and finally returns to normal. and B.A. The undercurrent can represent as much as 40% of the Indian Ocean overturning transport. Here velocities averaged 20 cm/s, with a standard deviation of 24 cm/s, along a principal axis oriented 63° from north. This was a repeat experiment from the first ASCA cruise a year earlier to test the hypothesis proposed by Blanke et al. Van Leeuwen, P.J., W.P.M. This is especially notable in the Agulhas Retroflection waters, where chlorophyll-a concentrations tend to be significantly higher than the surrounding South Indian Ocean and South Atlantic Ocean waters. The Agulhas Current (AC) is the strongest western boundary current in the Southern Hemisphere and is key for weather and climate patterns, both regionally and globally. Journal of Geophysical Research, 105, 6425-6436. In the southeast Atlantic Ocean the current retroflects (turns back on itself) in the Agulhas Retroflection due to shear interactions with the strong Antarctic Circumpolar Current, also known as the "West Wind Drift" despite referring to the ocean current rather than to the surface winds. Deep-Sea Research II, 50, 57-86. Srokosz, 1993: These anticyclonic warm core rings are estimated to have a transport of 3-9 Sv each, in total injecting salt at a rate of 2.5 Seasonal variability in the Agulhas Retroflection region. For that reason, mariners who successfully navigated the Cape of Good Hope frequently breathed a sigh of relief. Gordon, A.L., 1985: Van Ballegooyen, R.C., M.L Grundlingh and J.R.E. The Retroflection of the Agulhas Current. Cambridge Studies in International Relations, Path and variability of the Agulhas Return Current. The size of phytoplankton in Agulhas Rings tends to be smaller than in the surrounding water (around 20 µm in diameter).[17]. It flows southward along the southeast coast of Mozambique and the coast of South Africa before turning eastward to join the flow from Africa to Australia. Simionato, W.P. Franzese et al. 106 kg/s and heat at a rate of 45 TW. Roberts, 1988: [9], The provenance of ocean sediments can be determined by analysing terrigenous strontium isotope ratios in deep ocean cores. 3. For the purpose of this particular investigation isopycnal RAFOS floats (Rossby et al., 1986) were launched into the core of the Agulhas Current. An ACM can bulge up to 20 km (12 mi) and a NP up to 120 km (75 mi) from the current's mean position. [16], The Agulhas acts as an oceanic convergence zone. [5] ulhas Current and a southern Agulhas Current. The flow of the Agulhas Current is directed by the topography. [3], Where the Agulhas turns back on itself the loop of the retroflection pinches off periodically, releasing an eddy into the South Atlantic Gyre. The results show that, on average, the Agulhas follows the continental slope with a side-ways meandering displacement of … Since Indian Ocean water is significantly warmer (24-26 °C) and saltier than South Atlantic water, the Agulhas Leakage is a significant source of salt and heat for the South Atlantic Gyre. The current follows the continental shelf from Maputo to the tip of the Agulhas Bank (250 km south of Cape Agulhas). the Southeast Atlantic Ocean: a case study. It is narrow, swift and strong. and the Agulhas Undercurrent. Coordinates: .mw-parser-output .geo-default,.mw-parser-output .geo-dms,.mw-parser-output .geo-dec{display:inline}.mw-parser-output .geo-nondefault,.mw-parser-output .geo-multi-punct{display:none}.mw-parser-output .longitude,.mw-parser-output .latitude{white-space:nowrap}30°00′S 35°00′E / 30.000°S 35.000°E / -30.000; 35.000, Western boundary current of the southwest Indian Ocean that flows down the east coast of Africa, "A time series of Agulhas Undercurrent transport", "Structure and transport of the Agulhas Current and its temporal variability", "Assessing the role of the Subtropical Front in regulating Agulhas leakage at the Last Glacial Termination", "Mesoscale bio-physical interactions between the Agulhas Current and Agulhas Bank, South Africa", "Velocity Structure and Transport of the Meandering vs. Non-Meandering Agulhas Current", "Natal pulses and the formation of Agulhas rings", "Millennial-scale Agulhas Current variability and its implications for salt-leakage through the Indian–Atlantic Ocean Gateway", "The flow field of the subtropical gyre in the South Indian Ocean into the Southeast Atlantic Ocean: a case study", https://en.wikipedia.org/w/index.php?title=Agulhas_Current&oldid=1000460967, Creative Commons Attribution-ShareAlike License, This page was last edited on 15 January 2021, at 05:47. The velocity and vorticity structure of the Agulhas Current at 32°S. Position and Width of the Agulhas Current’s Dynamical Core [5] The AC as portrayed in the 1 Hz along-track altimetry is a strong and narrow flow which exhibits rapid changes in width, speed and position (Figure 2a). The Agulhas Current and the Agulhas Retroflection can give rise to immense "rogue waves" that can even threaten supertankers. Stramma, L. and J.R.E. Boebel, O., T. Rossby, J Lutjeharms, W. Zenk, and C. Barron, 2003: Studying all four cross sections of the Agulhas Current from 30° to 36°S, it seems that the watermass distribution within the current is separated into two distinct regions. Additionally, the convergence tends to increase the concentration of plankton in and around the Agulhas. The Agulhas Current also plays a critical role in global ocean circulation which is why it’s considered important for climatic conditions across the world. and C. Veth, 2002. The remaining water is transported into the South Atlantic Gyre in the Agulhas Leakage. [4], The core of the current is defined as where the surface velocities reaches 100 cm/s (39 in/s), which gives the core an average width of 34 km (21 mi). Here the momentum of the current overcomes the vorticity balance holding the current to the topography and the current leaves the shelf. Tha Natal Pulse: an extreme transient on the Agulhas Current. It is a surface-water current that flows off the east coast of southern Africa between latitudes 25° S and 40° S in a south-westerly direction. Journal of Physical Oceanography, 23, 2107-2124. [15], Below 1,800 m (5,900 ft) a separate layer of the undercurrent can be distinguished: the more coherent North Atlantic Deep Water (NADW) which transports an average of 2.3±3.0 Sv. Observations of the flow in the Mozambique Channel. First, the drifters were colocated to a satellite overpass using a 5-day threshold (according to Bryden et al., 2005, the Agulhas Current has a decorrelation time scale of 10 days). and J. Cooper, 1996: The Agulhas leakage affects the Atlantic thermocline on a decadal timescale and over centuries it can change the buoyancy of the Atlantic thermocline and therefore the formation rates of North Atlantic Deep Water (NADW). Simon et al. Bryden, H.L. Quartly, G.D. and M.A. The Agulhas Current /əˈɡʌləs/ is the western boundary current of the southwest Indian Ocean. In a later deployment, moorings near the core of the Current were terminated deeper. (B) Relative abundance of Agulhas Leakage Fauna (ALF) at Cape Basin ().Note that a new age model for core MD96-2081 was built based on the correlation between the δ 18 O of the benthic foraminifer and … Res., 105, 6425-6436. Due to mass continuity this drives surface waters down, resulting in the upwelling of cold, nutrient rich water south of the current. Journal of Geophysical Research, 99, 14053-14070. The deployments were targeted at key features of the Agulhas Current (core, outside edge and offshore) and all five were deployed within a few hours of each other. Natal pulses move along the coast at 20 km (12 mi) per day. Journal of Geophysical Research, 105, C12, 28585-28593. Donohue, E.A., E. Firing and L. Beal, 2000: [12], The south-east coast of South Africa is on the main shipping route between the Middle-East and Europe/the U.S. and several large ships sustain major damage because of rogue waves in the area where these waves occasionally can reach a height of more than 30 m (98 ft). [8], Surface water filaments are estimated to account for up to 13% of the total salt transport from the Agulhas Current into the Benguela Current and South Atlantic Gyre. Eddy fluxes of heat and salt from the southwest Indian Ocean into the Agulhas Current, surface oceanic current that forms the western boundary current of the southern Indian Ocean. Such a ring shedding can be triggered by a Natal pulse alone, but sometimes meanders on the Agulhas Return Current merge to contribute to the shedding of an Agulhas ring.[7]. [11] Furthermore, it can be predicted that a stronger Agulhas Current will result in a more eastward retroflection and an increased Agulhas leakage.

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