The vertical variability of the ocean in Santos Basin
Keywords:
dynamic modes, vorticity corridor, oceanography, pre-salt, Santos BasinAbstract
The Brazil Current (BC) flows southwestward as a vertically stratified and organized western boundary jet in the Brazilian shelf-break region ranging from Vitória-Trindade Seamount Chain (CVT) at 20oS to the Brazil-Malvinas Confluence (CBM) region at 38-40oS. Along this distance, the southward BC’s mass transport grows vertically. The upper ocean western boundary flow (~ 1000m) is characteristically baroclinic northward of 25ºS and more barotropic southward of 30ºS. Both domains show intense mesoescale activity due to the passage of eddies and meanders, superimposed upon oceanic large-scale recirculation features which influence the oceanic circulation in the Santos Basin Pre-salt cluster blocks area 300km off the coast. Based on a 2-year current data series of an oceanographic mooring array at Lula Field, and based on repeated hydrographic data (seawater temperature, salinity and, N2 profiles) we used statistical and dynamical orthogonal modes in order to approach the local vertical variability. We verified that 85% of it is explained by EOF-1. This variability is essentially of the 1st baroclinic mode. Great part of it occupies the first 400-600m of the water column, with no predominant direction. We also found a remarkable water column seasonal stratification. Albeit of the relative weaker mean flows (0.1-0.2m s-1), the study area is eddy-dominated which are geostrophically adjusted to the 1st baroclinic mode. Furthermore, we observed that the significant directional variability over the São Paulo Plateau occurs far away from the mean current jets that flow parallel to the continental shelf morphology. These are the main characteristics that define the vertical variability pattern of the oceanic flows of the Santos Basin Pre-salt cluster area.
References
BELO, W. C. A recirculação interna do Giro Subtropical do Atlântico Sul e a circulação oceânica na região do Pólo Pré-sal da Bacia de Santos. 2011. 378 f. Tese (Doutorado) – Universidade de São Paulo, São Paulo, 2011.
BÖEBEL, O.; DAVIS, R. E.; OLLITRAUT, M.; PETERSON, R. G.; RICHARD, P. L.; SCHIMID, C.; ZENK, W. The intermediate depth circulation of the Western South Atlantic. Geophysical Research Letters, Washington, v. 26, n. 21, p. 33293332, Nov. 1999.
CALADO, L.; SILVEIRA, I. C. A.; GANGOPADHYAY, A.; CASTRO, B. M. Eddyinduced upwelling off Cape São Tomé (22o S, Brazil). Continental Shelf Research, Oxford, v. 30, n.1011, p. 11811188, June 2010.
EVANS, D. L.; SIGNORINI, S. R. Vertical structure of the Brazil Current. Nature, London, v. 315, p. 4850, May 1985.
FLIERL, G. R. Models of vertical structure and calibration of twolayer models. Dynamics of Atmospheres and Oceans, Amsterdam, v. 2, n. 4, p. 341381, Aug. 1978.
FORRISTAL, G. Z.; COOPER, K. C. Design profiles using empirical orthogonal function (EOF) and inverse FORM methods. In: ANNUAL OFFSHORE TECHNOLOGY CONFERENCE, 29., 1997, Houston. Proceedings… Houston: Offshore Technology Conference, 1997. p. 1121, OTC 8267.
GARFIELD, N. The Brazil Current at subtropical latitudes. 1990. 122 f. Tese (Doutorado) – University of Rhode Island, Kingston, 1990.
GODOI, S. S. Dinâmica quase-geostrófica do sistema Corrente do Brasil no embaiamento de São Paulo (23,5-27o S). 2005. 133 f. Tese (Doutorado) – Universidade de São Paulo, São Paulo, 2005.
GORDON, A. L.; GREENGROVE, C. L. Geostrophic circulation of the Brazil–Falkland confluence. Deep-Sea Research Part A. Oceanographic Research Papers, Oxford, v. 33, n. 5, p. 573585, May 1986.
HOURY, S.; DOMBROWSKY, E.; DE MEY, P.; MINSTER, J. F. BruntVäisälä frequency and rossby radii in the South Atlantic. Journal of Physical Oceanography, Boston, v. 17, n. 10, p. 16191626, Oct. 1987.
JEANS, R. G.; FELD, G. A method for deriving extreme current profiles to support design of deep water drilling risers. In: INTERNATIONAL CONFERENCE ON OFFSHORE MECHANICS AND ARTIC ENGINEERING, 20., 2001, Rio de Janeiro. Proceedings… Rio de Janeiro: ASME, 2001. p. 112, OMAE01/OFT1181.
JOHNSON, D. R.; BOYER, T. P.; GARCIA, H. E.; LOCARMINI, R. A.; BARANOVA, O. K.; ZWENG, M. M. World Ocean Database 2009 Documentation. Edited by Sydney Levitus. NODC Internal Report 20, NOAA Printing Office, Silver Spring, MD. 175 p. Disponível em: <http://www.nodc.noaa.gov/OC5/WOD09/pr_wod09.html>. Acesso em: 2013.
LIMA, J. A. M.; RIBEIRO, E. O.; CECCOPIERI, W.; MATHESON, G. G. Directional extreme current profiles based on complex Empirical Orthogonal Functions (CEOF) for offshore design. In: INTERNATIONAL CONFERENCE ON OCEAN, OFFSHORE AND ARCTIC ENGINEERING, 28., 2009, Honolulu. Proceedings… Honolulu: ASME, 2009. OMAE200979467.
MASCARENHAS, A. S.; MIRANDA, L. B.; ROCK, N. J. A study of oceanographic conditions in the region of Cabo Frio. In: COSTLOW JR., J. D. Fertility in the Sea. New York: Gordon & Breach, 1971. p. 285308. v. 1,
MATTOS, R. A. Feições de meso e grande escalas da Corrente do Brasil ao largo do sudeste brasileiro. 2006. 126 f. Dissertação (Mestrado) – Universidade de São Paulo, São Paulo, 2006.
MÉMERY, L.; ARHAN, M.; ALVAREZSALGADO, X. A.; MESSIAS, M. J.; MERCIER, H.; CASTRO, C. G.; RIOS, A. F. The water masses along the western boundary of the south and equatorial atlantic. Progress in Oceanography, Oxford, v. 47, n. 1, p. 6998, Oct. 2000.
MÜLLER, T. J.; IKEDA, Y.; ZANGENBERG, N.; NONNATO, L. V. Direct measurements of western boundar y currents off Brazil between 20oS and 28oS. Journal of Geophysical Research, Richmond, v. 103, n. C3, p. 54295437, Mar. 1998.
PETERSON, R. G.; STRAMMA, L. Upperlevel circulation in the South Atlantic Ocean. Progress in Oceanography, Oxford, v. 26, n. 1, p. 173, 1991.
SCHMID, C.; SIEDLER, G.; ZENK, W. Dynamics of intermediate water circulation in the subtropical South Atlantic. Journal of Physical Oceanography, Boston, v. 30, p. 31913211, Dec. 2000.
SIGNORINI, S. R. On the circulation and the volume transport of the Brazil Current between the Cape of São Tomé and Guanabara Bay. Deep-Sea Research, Oxford, v. 25, n. 5, p. 481490, May 1978.
SILVEIRA, I. C. A.; SCHMIDT, A. C. K.; CAMPOS, E. J. D.; GODOI, S. S.; IKEDA, Y. A Corrente do Brasil ao largo da costa leste brasileira. Revista Brasileira de Oceanografia, São Paulo, v. 48, n. 2, p. 171183, 2000a.
SILVEIRA, I. C. A.; BROWN, W. S.; FLIERL, G. R. Dynamics of the North Brazil Current retroflection from the WESTRAX observations. Journal of Geophysical Research, Richmond, v. 105, n. C12, p. 28.55928.583, 2000b.
SILVEIRA, I. C. A.; CALADO, L.; CASTRO, B. M.; CIRANO, M.; LIMA, J. A. M.; MASCARENHAS, A. S. On the baroclinic structure of the BrazilCurrent –intermediate western boundary current system at 22º23ºS. Geophysical Research Letters, Washington, v. 31, n. 14, July 2004.
SILVEIRA, I. C. A. O sistema corrente do Brasil na Bacia de Campos, RJ. 2006. 160 f. Tese de Livre Docência – Universidade de São Paulo, São Paulo, 2006.
SILVEIRA, I. C. A.; LIMA, J. A. M.; SCHMIDT, A. C. K.; CECCOPIERI, W.; SARTORI, A.; FRANCISCO, C. P. F.; FONTES, R. C. F. Is the Meander Growth in the Brazil Current System off southeast Brazil due to baroclinic instability? Dynamics of Atmospheres and Oceans, Amsterdam, v. 45, n. 34, p. 187207, Aug. 2008.
SOUTELINO, R. G. A origem da corrente do Brasil. 2008. 101 f. Dissertação (Mestrado) – Universidade de São Paulo, São Paulo, 2008.
SOU T EL I NO, R . G .; SI LV EI R A , I . C. A .; GANGOPADHYAY, A.; MIRANDA, J. A. Is the Brazil Current eddydominated to the north of 20°S? Geophysical Research Letters, Washington, v. 38, n. 3, Feb. 2011.
STRAMMA, L.; ENGLAND, M. On the water masses and mean circulation of the South Atlantic Ocean. Journal of Geophysical Research, Richmond, v. 104, n. C9, p. 2086320883, Sept. 1999.
WOODS HOLE GROUP. Data qualification for Santos Basin. East Falmouth: Woods Hole Group, 2009. Relatório Técnico. EEPTM/GEO IRL3A26.001000931TDO004
ZEMBA, J. C. The structure and transport of the Brazil Current between 27o and 36o South. 1991. 160 f. Tese (Doutorado) – Institute of Technology and Woods Hole Oceanographic Institution, Massachusetts, 1991.
