A numerical study of the Plata River plume along the southeastern South American continental shelf

Pimenta, Felipe M.; Campos, Edmo José Dias; Miller, Jerry L.; Piola, Alberto R.

Abstracts

The Rio de la Plata, one of the largest rivers on Earth, discharges into the ocean waters from basin that covers a large area of South America. Its plume extends along northern Argentina, Uruguay, and southern Brazil shelves strongly influencing the ecosystems. In spite of this, little is known about the mechanisms that control it. Here we report results of simulations with POM carried out to investigate the roles of wind and river discharge in Plata plume dynamics. Different outflows were explored, including an average climatological value and magnitudes representative of La Niña and El Niño. Forcing the model with river discharge the average plume speed was directly related to the outflow intensity. The Plata northward extension varied from 850 to 1550 km and for average discharge a band of low salinity waters formed from the estuary up to 30ºN of South Brazilian Shelf. Upwelling and downwelling winds were applied after 130 days. The distribution of low salinity waters over the shelf was more sensitive to the wind direction than to the river outflow variability. Downwelling winds were very capable of advecting the low salinity signal downshelf. Upwelling winds were efficient in eroding the plume, which was basically detached from the coast by Ekman drift. Abnormal plume intrusions toward low latitudes may be a result of the original plume position coupled with events of persistent strong downwelling favorable winds.

Eastern South America Continental Shelf; South Brazilian Shelf; Rio de la Plata; South Brazil Bight; Buoyancy Plume; Princeton Ocean Model

O Rio da Prata, um dos maiores rios da Terra, descarrega no oceano águas de uma bacia de drenagem que cobre uma ampla área da América do Sul. Sua pluma extende-se ao longo do norte da Argentina, Uruguay e sul do Brasil influenciando amplamente os ecossistemas costeiros. A despeito disso, pouco se sabe a respeito dos mecanismos que a controlam. Relatamos aqui simulações conduzidas com o modelo POM na investigação do papel dos ventos e da descarga fluvial na dinâmica da pluma do Prata. Descargas com valores médios climatológicos e magnitudes representativas de El Niño e La Niña foram explorados. Somente sob descarga fluvial, a velocidade média de penetração da pluma ao longo da costa foi diretamente relacionada à vazão. Sua extensão variou entre 850 e 1550 km e no caso da vazão média uma banda de baixa salinidade formou-se desde o estuário até 30ºN na plataforma continental sul brasileira. O efeito de ventos de sudoeste, que causam subsidência, e de nordeste, que promovem a ressurgência costeira, foram investigados após 130 dias de descarga fluvial. Os resultados sugerem que a distribuição de baixa salinidade é muito mais sensível à direção dos ventos do que à descarga fluvial. Ventos de sudoeste são capazes de advectar o sinal de baixa salinidade ao longo da costa. Já os ventos de nordeste demonstram ser eficientes na erosão da pluma, que é destacada da costa por deriva de Ekman. Uma intrusão anormal da pluma de baixa salinidade em direção a baixas latitudes pode ser o resultado da posição original da pluma acoplada a eventos persistentes de fortes ventos de sudoeste.

Plataforma continental leste Sul Americana; Plataforma continental Sul Brasileira; Bacia de Santos; Rio da Prata; pluma costeira; modelagem hidrodinâmica

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Campos, E. J. D.; Lentini, C. A. D.; Miller, J. L. & Piola, A. R. 1999. Interannual variability of the sea surface temperature in the South Brazil Bight. Geophys. Res. Letters,á 26(14):2061û2064.
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Depetris, P. J.; Kempe, S.; Latif, M. & Mook, W. G. 1996. ENSOûControlled flooding in the Paranß River (1904û1991). Naturwissenschaften,á 83:127û129.
Fong, D. A. & Geyer, W. R. 2001. Response of a river plume during an upwelling favorable wind event. J. Geophys. Res, 106 (C1):1067û1084.
Fong, D. A. & Geyer, W. R. 2002. The alongshore transport of freshwater in a surface-trapped river plume. J. Phys. Oceanogr., 32:957û972.
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Garvine, R. W. 1999. Penetration of buoyant coastal discharge onto the continental shelf: A numerical model experiment. J. Phys. Oceanogr., 29:1892û1909.
Garvine, R. W. 2001. The impact of model configuration in studies of buoyant coastal discharge. J Mar. Res., 59:193û225.
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Limeburner, R.; Beardsley, R. C.; Soares, I. D.; Lentz, S. J. & Candela, J. 1995. Lagrangian flow observations of the Amazon River discharge into the North Atlantic. J. Geophys. Res. 100(C2):2401û2416.
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Publication Dates

Publication in this collection
21 July 2009
Date of issue
Dec 2005

History

Accepted
03 Nov 2005
Reviewed
23 Sept 2005
Received
22 June 2005

This work is licensed under a Creative Commons Attribution 4.0 International License.

[1] Assireu, A. T.; Stevenson, M. R. & Stech, J. L. 2003. Surface circulation and kinetic energy in the SW Atlantic obtained by drifters. Continent. Shelf Res., 23:145û157.

[2] Beardsley, R. C.; Limeburner, R.; Yu, H. & Cannon, G. A. 1985. Discharge of the Changjiang (Yangtze River) into the East China Sea. Continent. Shelf Res., 4:57û76.

[3] Blumberg, A. F. & Mellor, G. L. 1987. A description of a threeûdimensional coastal ocean circulation model. In: Heaps, N. S. (Ed.), Threeûdimensional coastal ocean models. Wasnhington, DC., American Geophysical Union. 208p.

[4] Campos, E. J. D.; Gonþalves, J. E. & Ikeda, Y., 1995. Water mass characteristics and geostrophic circulation in the South Brazil Bight û Summer of 1991. J. Geophys. Res., 100 (C9):18537û18550.

[5] Campos, E. J. D.; Ikeda, Y.; Castro, B. M.; Gaeta, S. A.; Lorenzzetti, J. A. & Stevenson, M. R. 1996a. Experiment studies circulation in the Western South Atlantic. In: EOS Transaction, 77:253û259.

[6] Campos, E. J. D.; Lorenzzetti, J. A.; Stevenson, M. R.; Stech, J. L. & B., S. R. 1996b. Penetration of waters from the BrazilûMalvinas Confluence region along the South American continental shelf up to 23║S. Acad. Brasileira de CiÛncias, 68(1):49û58.

[7] Campos, E. J. D.; Lentini, C. A. D.; Miller, J. L. & Piola, A. R. 1999. Interannual variability of the sea surface temperature in the South Brazil Bight. Geophys. Res. Letters,á 26(14):2061û2064.

[8] Castro, B. M. & Lee, T. N. 1995. Windûforced sea level variability on the southeast Brazilian shelf. J. Geophys. Res., 100 (C8):16045-16056.

[9] Chao, S.-Y. 1987. Windûdriven motion near inner shelf fronts. J. Geophys. Res., 92 (C4):3849û3860.

[10] Chao, S.-Y. 1988a. Riverûforced estuarine plumes. J. Phys. Oceanogr., 18:72û88.

[11] Chao, S.-Y. 1988b. Wind-driven motion of estuarine plumes. J. Phys. Oceanogr., 18:1144û1166.

[12] Chao, S.-Y. & Boicourt, W. C. 1986. Onset of estuarine plumes. J. Phys. Oceanogr., 16:2137û2149.

[13] Ciotti, A. M.; Odebrecht, C.; Fillmann, G. & M÷ller, O. O. 1995. Freshwater outflow and Subtropical Convergence influence on phytoplankton biomass on the southern Brazilian continental shelf. Continent. Shelf Res., 15(14):1737û1756.

[14] Csanady, G. T. 1984. Circulation induced by river inflow in well mixed water over a sloping continental shelf. J. Phys. Oceanogr., 14:1703û1711.

[15] Depetris, P. J.; Kempe, S.; Latif, M. & Mook, W. G. 1996. ENSOûControlled flooding in the Paranß River (1904û1991). Naturwissenschaften,á 83:127û129.

[16] Fong, D. A. & Geyer, W. R. 2001. Response of a river plume during an upwelling favorable wind event. J. Geophys. Res, 106 (C1):1067û1084.

[17] Fong, D. A. & Geyer, W. R. 2002. The alongshore transport of freshwater in a surface-trapped river plume. J. Phys. Oceanogr., 32:957û972.

[18] Frami±an, M. B. á& áBrown, O. B. á1996. áStudy áof the Rio de ála áPlata áturbidity áfront, áPart I: áspatial áand temporal distribution. Continent. Shelf Res., 16 (10):1259û1282.

[19] Gan, M. A. & Rao, V. B. 1991. Surface cyclogenesis over South America. Mon. Weath. Rev., 119:1293û1302.

[20] Garvine, R. W. 1987. Estuary, plumes and fronts in shelf waters: A layer model. J. Phys. Oceanogr., 17:1877û1896.

[21] Garvine, R. W. 1999. Penetration of buoyant coastal discharge onto the continental shelf: A numerical model experiment. J. Phys. Oceanogr., 29:1892û1909.

[22] Garvine, R. W. 2001. The impact of model configuration in studies of buoyant coastal discharge. J Mar. Res., 59:193û225.

[23] Geyer, W. R.; Beardsley, R. C.; Lentz, S. J.; Candela, J.; Limeburner, R.; Johns, W. E.; Castro, B. M. & Soares, I. D. 1996. Physical oceanography of the Amazon shelf. Continent. Shelf Res., 16:575û616.

[24] Ghisolfi, R. D. & McKee, W. D. 2003. The effects of the alongshore wind stress on the top-to-bottom front along the Southern Brazilian coast: a two-dimensional modelling approach. Continent. Shelf Res., 23:1401û1424.

[25] Grimm, A. M.; Ferraz, S. E. & T., Gomes, J. 1998. Precipitation anomalies in Southern Brazil associated with El Ni±o and La Ni±a events. J. Climate, 11:2863û2880.

[26] Guerrero, R. A.; Acha, E. M.; Frami±an, M. B. & Lasta, C. A., 1997a. Physical oceanography of the RÝo de la Plata estuary, Argentina. Continent. Shelf Res., 17(7):727û742.

[27] Guerrero, R. A.; Lasta, C. A.; Acha, E. M.; Mianzan, H. W. & Frami±an, M. B. 1997b. Atlas hidrogrßfico del RÝo de la Plata. Montivideo, Comissi¾n Administradora del RÝo de la Plata û Instituto Nacional de Investigaci¾n y Desarrollo Pesquero, 109pp.

[28] Hickey, B. M.; Pietrafesa, L. J.; Jay, D. A. & Boicourt, W. C. 1998. The Columbia River plume study: Subtidal variability in the velocity and salinity fields. J. Geophys. Res., 103(C5):10339û10368.

[29] Houghton, R. W.; Tilburg, C. E.; Garvine, R. W. & Fong, A. 2004. Delaware River plume response to a strong upwelling-favorable wind event. Geophys. Res. Letters,á 31 (L07302).

[30] Kourafalou, V. H.; Lee, T. N.; Oey, L.-Y. & Wang, J. D. 1996a. The fate of river discharge on the continental shelf. 2. Transport of coastal low-salinity waters under realistic wind and tidal forcing. J. Geophys. Res., 101 (C2):3435û3455.

[31] Kourafalou, V. H.; Oey, L.-Y.; Wang, J. D. & Lee, T. N., 1996b. The fate of river discharge on the continental shelf. 1. Modeling the river plume and the inner shelf coastal current. J. Geophys. Res., 101(C2):3415û3434.

[32] Lentini, C. A. D., Podestß, G. G., Campos, E. J. D. & Olson, D. B., 2001. Sea surface temperature anomalies on the Western South Atlantic from 1982 to 1994. Continent. Shelf Res., 21(1):89û112.

[33] Lentz, S. J. 1995. The Amazon river plume during AMASSEDS: Subtidal current variability and the importance of wind forcing. J. Geophys. Res., 100(C2):2377û2390.

[34] Limeburner, R.; Beardsley, R. C.; Soares, I. D.; Lentz, S. J. & Candela, J. 1995. Lagrangian flow observations of the Amazon River discharge into the North Atlantic. J. Geophys. Res. 100(C2):2401û2416.

[35] Matsuura, Y. 1996. Probable causes of recruitment failure of the Brazilian Sardine population in the 1974/75 spawning season. South African J. Mar. Sci., 17:29û35.

[36] Mechoso, C. R. & Iribarren, G. P. 1992. Streamflow in Southeastern South America and the Southern Oscillation. J. Climate, 5:1535û1539.

[37] Mellor, G. L. 1996. Users guide for a threeûdimensional, primitive equation, numerical ocean model. Tech. rep., Program in Atmospheric and Ocean Sciences, Princeton University. 53 p.

[38] Mellor, G. L. & Yamada, T. 1982. Development of a tubulence closure model for geophysical fluid problems. Rev. Geophys Space Phys., 20(4):851û875.

[39] Melo, E.; Pimenta, F. M.; Mendes, D. A. R.; Hammes, G. R.; Araujo, C. E. S.; Franco, D.; Alves, J. H. G. M.; Barletta, R. C.; Souto, A. M. C.; CastelÒo, G. P.; Pereira, N. C. & Branco, F. V. 2003. A real time, on-line coastal information program in Brazil. In: VI Conference on Coastal and Port Engineering in Developing Countries. Colombo, Sri Lanka, p. 14. (published in digital form on compact disc).

[40] Mianzan, H. W.; Acha, E. M.; Guerrero, R. A.; Ramirez, F. C.; Sorarrain, D. R.; Simionato, C. & Borus, J. 2001. South Brazilian marine fauna in the Rio de la Plata estuary: Discussing the barrier hypothesis. In: IX Congreso Latinoamericano de CiÛncias del Mar. p. 210.

[41] M³nchow, A. & Garvine, R. W. 1993. Dynamical properties of buoyancyûdriven coastal current. J. Geophys. Res., 98 (C11):20063û20077.

[42] OÆConnor, W. P. 1991. A numerical model for tides and storm surges in the Rio de la Plata estuary. Cont. Shelf Res., 11 (12):1491û1508.

[43] Oey, L.-Y. & Mellor, G. L. 1993. Subtidal variability of estuarine outflow, plume and coastal current: a model study. J. Phys. Oceanogr., 23:164û171.

[44] Orlanski, I. 1976. A simple boundary condition for unbounded hyperbolic flows. J. Comput.Phys., 21:251û269.

[45] Palma, E. D. & Matano, R. P. 2000. On the implementation of open boundary conditions for a general circulation model: The threeûdimensional case. J. Geophys. Res., 105 (C4):8605û8627.

[46] Pereira, C. S. 1989. Seasonal variability in the coastal circulation on the Brazilian continental shelf (29║Sû35║S). Cont. Shelf Res., 9:285û299.

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