On the discontinuous nature of the Mozambique Current
Keywords:
Mozambique Current, Mozambique Channel, Mozambique Eddies, Western boundary currents, oceanic modelling
Abstract
The concept of a spatially continuous western boundary current in the Mozambique Channel has historically been based on erroneous interpretations of ships’ drift. Recent observations have demonstrated that the circulation in the Channel is instead dominated by anti-cyclonic eddies drifting poleward. It has therefore been suggested that no coherent Mozambique Current exists at any time. However, satellite and other observations indicate that a continuous current – not necessarily an inherent part of Mozambique Eddies – may at times be found along the full Mozambican shelf break. Using a high-resolution, numerical model we have demonstrated how such a feature may come about. In the model, a continuous current is a highly irregularly occurring event, occurring about once per year, with an average duration of only 9 days and with a vertical extent of about 800 m. Surface speeds may vary from 0.5 m/s to 1.5 m/s and the volume flux involved is about 10 Sv. The continuous current may occasionally be important for the transport of biota along the continental shelf and slope.References
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27.Swart NC, Lutjeharms JRE, Ridderinkhof H, De Ruijter WPM. Observed characteristics of Mozambique Channel eddies. J Geophys Res. 2010;115:C09006. http://dx.doi.org/10.1029/2009JC005875
28.Bryden HL, Beal LM, Duncan LM. Structure and transport of the Agulhas Current and its temporal variability. J Oceanogr. 2005;61:479–492. http://dx.doi.org/10.1007/s10872-005-0057-8
2.Michaelis G. Die Wasserbewegung an der Oberfläche des Indischen Ozeans im Januar und Juli. Veröff. [The movement of water on the surface of the Indian Ocean in January and July]. Berlin: Institut für Meereskunde, Universität Berlin; 1923. German.
3.Duncan CP, Schladow SG. World surface currents from ship’s drift observations. Int Hydrogr Rev. 1981;58:101–112.
4.Wyrtki K. Oceanographic atlas of the International Indian Ocean Expedition. Washington DC: National Science Foundation; 1971.
5.Lutjeharms JRE. A quantitative assessment of year-to-year variability in water movement in the South-west Indian Ocean. Nature. 1972;239:59–60.
6.Sætre R, Jorge da Silva A. The circulation of the Mozambique Channel. Deep-Sea Res. 1984;31:485–508. http://dx.doi.org/10.1016/0198-0149(84)90098-0
7.Sætre R. Surface currents in the Mozambique Channel. Deep-Sea Res. 1985;32:1457–1467. http://dx.doi.org/10.1016/0198-0149(85)90097-4
8.Biastoch A, Krauß W. The role of mesoscale eddies in the source regions of the Agulhas Current. J Phys Oceanogr. 1999;29:2303–2317. http://dx.doi.org/10.1175/1520-0485(1999)029<2303:TROMEI>2.0.CO;2
9.De Ruijter WPM, Ridderinkhof H, Lutjeharms JRE, Schouten MW, Veth C. Observations of the flow in the Mozambique Channel. Geophys Res Lett. 2002;29:1401–1403. http://dx.doi.org/10.1029/2001GL013714
10.Schouten MW, De Ruijter WPM, Van Leeuwen PJ, Ridderinkhof H. Eddies and variability in the Mozambique Channel. Deep-Sea Res II. 2003;50:1987–2003. http://dx.doi.org/10.1016/S0967-0645(03)00042-0
11.Ridderinkhof H, De Ruijter WPM. Moored current observations in the Mozambique Channel. Deep-Sea Res II. 2003;50:1933–1955. http://dx.doi.org/10.1016/S0967-0645(03)00041-9
12.Harlander U, Ridderinkhof H, Schouten MW, De Ruijter WPM. Long-term observations of transport, eddies, and Rossby waves in the Mozambique Channel. J Geophys Res. 2009;114:C02003. http://dx.doi.org/10.1029/2008JC004846
13.Ridderinkhof H, Van der Werf PM, Ullgren J, Van Leeuwen PJ, Van Aken HM, De Ruijter WPM. Seasonal and interannual variability in the Mozambique Channel from moored current observations. J Geophys Res. 2010;115:C06010. http://dx.doi.org/10.1029/2009JC005619
14.Penven P, Lutjeharms JRE, Florenchie P. Madagascar: A pacemaker for the Agulhas Current system? Geophys Res Lett. 2006;33:L17609. http://dx.doi.org/10.1029/2006GL026854
15.Quartly GD, Srokosz MA. Eddies in the southern Mozambique Channel. Deep-Sea Res II. 2004;51:69–83. http://dx.doi.org/10.1016/j.dsr2.2003.03.001
16.Jaquemet S, Le Corre M, Quartly GD. Ocean control of the breeding regime of the sooty tern in the southwest Indian Ocean. Deep-Sea Res I. 2007;54:130–142. http://dx.doi.org/10.1016/j.dsr.2006.10.003
17.Weimerskirch H, Le Corre M, Jaquemet S, Potier M, Marsac F. Foraging strategy of a top predator in tropical waters: Great frigatebirds in the Mozambique Channel. Mar Ecol Progr Ser. 2004;275:297–308. http://dx.doi.org/10.3354/meps275297
18.Schouten MW, De Ruijter WPM, Van Leeuwen PJ. Upstream control of Agulhas ring shedding. J Geophys Res. 2002;107(C8):3109. http://dx.doi.org/10.1029/2001JC000804
19.Biastoch A, Böning C, Lutjeharms J, Scheinert M. Mesoscale perturbations control inter-ocean exchange south of Africa. Geophys Res Lett. 2008;35:L20602. http://dx.doi.org/10.1029/2008GL035132
20.Lutjeharms JRE, Jorge Da Silva A. The Delagoa Bight eddy. Deep-Sea Res. 1988;35:619–634. http://dx.doi.org/10.1016/0198-0149(88)90134-3
21.Biastoch A, Böning CW, Scheinert M, Lutjeharms JRE. The Agulhas system as a key region of the global circulation. In: Nagel WE, Kröner DB, Resch MM, editors. High Performance Computing in Science and Engineering '08. Heidelberg: Springer, 2008; p. 459–469.
22.Madec G. NEMO ocean engine. Technical Report 27. Paris: Institute Pierre Simon Laplace; 2006.
23.Large WG, Yeager SG. Diurnal to decadal global forcing for ocean and sea-ice models: The data sets and flux climatologies. NCAR Technical Note NCAR/ TN-460 + STR. Boulder, CO: National Centre for Atmospheric Research; 2004.
24.Debreu L, Vouland C, Blayo E. AGRIF: Adaptive grid refinement in Fortran. Comput Geosci. 2008;34:8–13. http://dx.doi.org/10.1016/j.cageo.2007.01.009
25.Barnier B, Madec G, Penduff T, et al. Impact of partial steps and momentum advection schemes in a global ocean circulation model at eddy permitting resolution. Ocean Dyn. 2006;56:543–567. http://dx.doi.org/10.107/s10236-006-0082-1
26.Biastoch A, Beal L, Lutjeharms JRE, Casal TGD. Variability and coherence of the Agulhas Undercurrent in a high-resolution ocean general circulation model. J Phys Oceanogr. 2009;10:2417–2435. http://dx.doi.org/10.1175/2009JPO4184.1
27.Swart NC, Lutjeharms JRE, Ridderinkhof H, De Ruijter WPM. Observed characteristics of Mozambique Channel eddies. J Geophys Res. 2010;115:C09006. http://dx.doi.org/10.1029/2009JC005875
28.Bryden HL, Beal LM, Duncan LM. Structure and transport of the Agulhas Current and its temporal variability. J Oceanogr. 2005;61:479–492. http://dx.doi.org/10.1007/s10872-005-0057-8