scholarly journals Inorganic and organic geochemical fingerprinting of sediment sources and ocean circulation on a complex continental margin (São Paulo Bight, Brazil)

2016 ◽  
Author(s):  
Michel Michaelovitch de Mahiques ◽  
Till Jens Jörg Hanebuth ◽  
Renata Hanae Nagai ◽  
Marcia Caruso Bícego ◽  
Rubens Cesar Lopes Figueira ◽  
...  
Keyword(s):  
Organic Matter ◽  
Molecular Markers ◽  
Ocean Circulation ◽  
Western Boundary Current ◽  
Western Boundary ◽  
Boundary Current ◽  
Geochemical Fingerprinting ◽  
Brazil Current ◽  
Shelf Sediments ◽  
Upper Slope

Abstract. In this study, we use inorganic (metals) and organic (bulk and molecular) markers in sediment samples of the southeastern Brazilian margin to investigate the response of geochemical fingerprints to the complex hydrodynamic processes present in the area. Results indicate the potential of export of terrigenous siliciclastic and organic constituents to the upper slope, even in an area with limited fluvial supply. Metal contents and especially the ln(Ti/Al) and ln(Fe/K) ratios make it possible to recognize the extension of shelf sediments toward the upper slope. Potassium, here expressed as ln(K/Sc) and ln(K/Al) ratios used as proxies of illite–kaolinite variations, proved to be an important parameter, especially because it allowed us to decipher the imprint of the northward flow of the Intermediate Western Boundary Current (IWBC) in comparison to the southward flows of the Brazil Current (BC) and Deep Western Boundary Current (DWBC). Using organic matter analyses, we were able to evaluate the extent of terrestrial contributions to the outer shelf and slope, even without the presence of significant fluvial input. In addition, molecular markers signify a slight increase in the input of C4-derived plants to the slope sediments, transported from distant areas by the main alongshore boundary currents, indicating that the terrestrial fraction of the organic matter deposited on the slope has a distinct origin when compared to shelf sediments.

scholarly journals Inorganic and organic geochemical fingerprinting of sediment sources and ocean circulation on a complex continental margin (São Paulo Bight, Brazil)

Ocean Science ◽  
2017 ◽  
Vol 13 (2) ◽  
pp. 209-222 ◽  
Author(s):  
Michel Michaelovitch de Mahiques ◽  
Till Jens Jörg Hanebuth ◽  
Renata Hanae Nagai ◽  
Marcia Caruso Bícego ◽  
Rubens Cesar Lopes Figueira ◽  
...  
Keyword(s):  
Organic Matter ◽  
Molecular Markers ◽  
Ocean Circulation ◽  
Western Boundary Current ◽  
Western Boundary ◽  
Boundary Current ◽  
Geochemical Fingerprinting ◽  
Brazil Current ◽  
Shelf Sediments ◽  
Upper Slope

Abstract. In this study, we use inorganic (metal) and organic (bulk and molecular) markers in sediment samples of the south-eastern Brazilian margin to investigate the response of geochemical fingerprints to the complex hydrodynamic processes present in the area. Results indicate the potential of export of terrigenous siliciclastic and organic constituents to the upper slope, even in an area with limited fluvial supply.Metal contents and especially the ln(Ti ∕ Al) and ln(Fe ∕ K) ratios make it possible to recognise the extension of shelf sediments toward the upper slope. Potassium, here expressed as ln(K ∕ Sc) and ln(K ∕ Al) ratios used as proxies of illite–kaolinite variations, proved to be an important parameter, especially because it allowed us to decipher the imprint of the northward flow of the Intermediate Western Boundary Current (IWBC) in comparison to the southward flows of the Brazil Current (BC) and Deep Western Boundary Current (DWBC). Using organic matter analyses, we were able to evaluate the extent of terrestrial contributions to the outer shelf and slope, even without the presence of significant fluvial input. In addition, molecular markers signify a slight increase in the input of C4-derived plants to the slope sediments, transported from distant areas by the main alongshore boundary currents, indicating that the terrestrial fraction of the organic matter deposited on the slope has a distinct origin when compared to shelf sediments.

scholarly journals THE BIFURCATION OF THE WESTERN BOUNDARY CURRENT SYSTEM OF THE SOUTH ATLANTIC OCEAN

2014 ◽  
Vol 32 (2) ◽  
pp. 241 ◽  
Author(s):  
Janini Pereira ◽  
Mariela Gabioux ◽  
Martinho Marta Almeida ◽  
Mauro Cirano ◽  
Afonso M. Paiva ◽  
...  
Keyword(s):  
High Resolution ◽  
Atlantic Ocean ◽  
Ocean Circulation ◽  
South Atlantic ◽  
Western Boundary Current ◽  
South Atlantic Ocean ◽  
Western Boundary ◽  
Intermediate Water ◽  
Boundary Current ◽  
The South

ABSTRACT. The results of two high-resolution ocean global circulation models – OGCMs (Hybrid Coordinate Ocean Model – HYCOM and Ocean Circulation andClimate Advanced Modeling Project – OCCAM) are analyzed with a focus on the Western Boundary Current (WBC) system of the South Atlantic Ocean. The volumetransports are calculated for different isopycnal ranges, which represent the most important water masses present in this region. The latitude of bifurcation of the zonalflows reaching the coast, which leads to the formation of southward or northward WBC flow at different depths (or isopycnal levels) is evaluated. For the Tropical Water,bifurcation of the South Equatorial Current occurs at 13◦-15◦S, giving rise to the Brazil Current, for the South Atlantic Central Water this process occurs at 22◦S.For the Antarctic Intermediate Water, bifurcation occurs near 28◦-30◦S, giving rise to a baroclinic unstable WBC at lower latitudes with a very strong vertical shearat mid-depths. Both models give similar results that are also consistent with previous observational studies. Observations of the South Atlantic WBC system havepreviously been sparse, consequently these two independent simulations which are based on realistic high-resolution OGCMs, add confidence to the values presentedin the literature regarding flow bifurcations at the Brazilian coast.Keywords: Southwestern Atlantic circulation, water mass, OCCAM, HYCOM. RESUMO. Resultados de dois modelos globais de alta resolução (HYCOM e OCCAM) são analisados focando o sistema de Corrente de Contorno Oeste do Oceano Atlântico Sul. Os transportes de volume são calculados para diferentes níveis isopicnais que representam as principais massas de água da região. É apresentada a avaliação da latitude de bifurcação do fluxo zonal que atinge a costa, permitindo a formação dos fluxos da Corrente de Contorno Oeste para o sul e para o norte emdiferentes níveis de profundidades (ou isopicnal). Para a Água Tropical, a bifurcação da Corrente Sul Equatorial ocorre entre 13◦-15◦S, originando a Corrente do Brasil, e para a Água Central do Atlântico Sul ocorre em 22◦S. A bifurcação daÁgua Intermediária Antártica ocorre próximo de 28◦-30◦S, dando um aumento na instabilidade baroclínica da Corrente de Contorno Oeste em baixas latitudes e com um forte cisalhamento vertical em profundidades intermediárias. Ambos os modelos apresentamresultados similares e consistentes com estudos observacionais prévios. Considerando que as observações do sistema de Corrente de Contorno Oeste do Atlântico Sul são escassas, essas duas simulações independentes com modelos globais de alta resolução adicionam confiança aos valores apresentados na literatura, relacionadosaos fluxos das bifurcações na costa do Brasil.Palavras-chave: circulação do Atlântico Sudoeste, massas de água, OCCAM, HYCOM.

A two-layer approximation to the Brazil Current–Intermediate Western Boundary Current System between 20°S and 28°S

2009 ◽  
Vol 29 (2) ◽  
pp. 154-158 ◽  
Author(s):  
Alexandre M. Fernandes ◽  
Ilson C.A. da Silveira ◽  
Leandro Calado ◽  
Edmo J.D. Campos ◽  
Afonso M. Paiva
Keyword(s):  
Current System ◽  
Western Boundary Current ◽  
Western Boundary ◽  
Boundary Current ◽  
Brazil Current

The ‘sliced-cylinder’ laboratory model of the wind-driven ocean circulation. Part 1. Steady forcing and topographic Rossby wave instability

1975 ◽  
Vol 69 (1) ◽  
pp. 27-40 ◽  
Author(s):  
R. C. Beardsley ◽  
K. Robbins
Keyword(s):  
Boundary Layer ◽  
Ocean Circulation ◽  
Rossby Wave ◽  
Rossby Waves ◽  
Western Boundary Current ◽  
Boundary Layer Transition ◽  
Laboratory Model ◽  
Western Boundary ◽  
Boundary Current ◽  
Topographic Rossby Waves

The nonlinear response of the ‘sliced-cylinder’ laboratory model for the wind-driven ocean circulation is re-examined here in part 1 for the case of strong steady forcing. Introduced by Pedlosky & Greenspan (1967), the model consists of a rapidly rotating right cylinder with a planar sloping bottom. The homogeneous contained fluid is driven by the slow rotation of the flat upper lid relative to the rest of the basin. Except in thin Ekman and Stewartson boundary layers on the solid surfaces of the basin, the horizontal flow in the interior and western boundary layer is constrained by the rapid rotation of the basin to be independent of depth. The model thus effectively simulates geophysical flows through the physical analogy between topographic vortex stretching in the laboratory model and the creation of relative vorticity in planetary flows by the β effect.As the forcing is increased, the flow in both the sliced-cylinder laboratory and numerical models first exhibits downstream intensification in the western boundary layer. At greater forcing, separation of the western boundary current occurs with the development of stationary topographic Rossby waves in the western boundary-layer transition regions. The observed flow ultimately becomes unstable when a critical Ekman-layer Reynolds number is exceeded. We first review and compare the experimental and numerical descriptions of this low-frequency instability, then present a simple theoretical model which successfully explains this observed instability in terms of thelocalbreakdown of the finite-amplitude topographic Rossby waves embedded in the western boundary current transition region. The inviscid stability analysis of Lorenz (1972) is extended to include viscous effects, with the consequence that dissipative processes in the sliced-cylinder problem (i.e. lateral and bottom friction) are shown to inhibit the onset of the instability until the topographic Rossby wave slope exceeds a finite critical value.

scholarly journals Eddy Surface properties and propagation at Southern Hemisphere western boundary current systems

2015 ◽  
Vol 12 (1) ◽  
pp. 135-160 ◽  
Author(s):  
G. S. Pilo ◽  
M. M. Mata ◽  
J. L. L. Azevedo
Keyword(s):  
Southern Hemisphere ◽  
Ocean Circulation ◽  
Surface Characteristics ◽  
Propagation Distance ◽  
Western Boundary ◽  
Boundary Current ◽  
Mean Flow ◽  
Agulhas Current ◽  
Brazil Current ◽  
Great Australian Bight

Abstract. Oceanic eddies occur in all world oceans, but are more energetic when associated to western boundary currents (WBC) systems. In these regions, eddies play an important role on mixing and energy exchange. Therefore, it is important to quantify and qualify eddies occurring within these systems. Previous studies performed eddy censuses in Southern Hemisphere WBC systems. However, important aspects of local eddy population are still unknown. Main questions to be answered relate to eddies' spatial distribution, propagation and lifetime within each system. Here, we use a global eddy dataset to qualify eddies based on their surface characteristics at the Agulhas Current (AC), the Brazil Current (BC) and the East Australian Current (EAC) Systems. We show that eddy propagation within each system is highly forced by the local mean flow and bathymetry. In the AC System, eddy polarity dictates its propagation distance. BC system eddies do not propagate beyond the Argentine Basin, and are advected by the local ocean circulation. EAC System eddies from both polarities cross south of Tasmania, but only anticyclonics reach the Great Australian Bight. Eddies in all systems and from both polarities presented a geographical segregation according to size. Large eddies occur along the Agulhas Retroflection, the Agulhas Return Current, the Brazil-Malvinas Confluence and the Coral Sea. Small eddies occur in the systems southernmost domains. Understanding eddies' propagation helps to establish monitoring programs, and to better understand how these features would affect local mixing.

A laboratory model for the general ocean cicrulation

1969 ◽  
Vol 265 (1168) ◽  
pp. 533-566 ◽  
Keyword(s):  
Ocean Circulation ◽  
Zonal Flow ◽  
Western Boundary Current ◽  
Nonlinear Regime ◽  
Electrochemical Technique ◽  
Laboratory Model ◽  
Western Boundary ◽  
Uniform Density ◽  
Nonlinear Behaviour ◽  
Boundary Current

A laboratory model for the study of a barotropic general ocean circulation has been constructed following the strict geometrical constraints of the B-plane approximation. Fluid is confined by plastic blocks to the volume defined by the intersection of two spherical surfaces, of common centre and slightly different radii with a circular cylinder whose axis intersects the centre of the spheres. The entire system is rotated and an interior circulation is provided by relative rotation of one of the bounding blocks. Uniform density of the rigidly enclosed fluid ensures the irrelevance of laboratory gravity and the absence of centrifugal effects on the flow. Fluid flow is observed with an electrochemical technique. Lines of coloured fluid which move with the local velocity are produced and photographed; velocities are inferred to 5% accuracy. Rossby numbers from 1.3 x 10-4 to 7.7 and Ekman numbers from 3.1 x 10-4 to 3.1 x 10-2 have been achieved. The apparatus can be oriented at an arbitrary mean latitude. The phenomena characteristic of linear subtropical gyres have been observed: a meridional Sverdrup flow, its associated zonal flow and a western boundary current. The existence, structure, and parameter dependencies of these features are in good agreement with the predictions of a general linear boundary layer analysis which has been developed for a thin barotropic ocean. The Sverdrup vorticity balance and the width and structure of the bottom frictional western boundary current have been established within the experimental uncertainties. In the nonlinear regime the position of the centre of the gyre has been measured as it migrates north-westward; a poleward eastern boundary current appears. These results agree with theoretical estimates for the onset of nonlinear behaviour. A long period time dependent flow is observed for high Rossby number. Quantitative studies have been made on an equatorial undercurrent which moves in a direction opposite to the surface forcing velocity. For low Rossby numbers this flow reverses with change in direction of the forcing velocity. In the nonlinear regime, the westward flowing undercurrent developed a streakiness and disappeared; whereas the eastward flowing current remained defined and measurable.

scholarly journals Eddy surface properties and propagation at Southern Hemisphere western boundary current systems

Ocean Science ◽  
2015 ◽  
Vol 11 (4) ◽  
pp. 629-641 ◽  
Author(s):  
G. S. Pilo ◽  
M. M. Mata ◽  
J. L. L. Azevedo
Keyword(s):  
Southern Hemisphere ◽  
Ocean Circulation ◽  
Surface Characteristics ◽  
Propagation Distance ◽  
Western Boundary ◽  
Boundary Current ◽  
Mean Flow ◽  
Data Set ◽  
Brazil Current ◽  
Argentine Basin

Abstract. Oceanic eddies exist throughout the world oceans, but are more energetic when associated with western boundary currents (WBC) systems. In these regions, eddies play an important role in mixing and energy exchange. Therefore, it is important to quantify and qualify eddies associated with these systems. This is particularly true for the Southern Hemisphere WBC system where only few eddy censuses have been performed to date. In these systems, important aspects of the local eddy population are still unknown, like their spatial distribution and propagation patterns. Moreover, the understanding of these patterns helps to establish monitoring programs and to gain insight in how eddies would affect local mixing. Here, we use a global eddy data set to qualify eddies based on their surface characteristics in the Agulhas Current (AC), the Brazil Current (BC) and the East Australian Current (EAC) systems. The analyses reveal that eddy propagation within each system is highly forced by the local mean flow and bathymetry. Large values of eddy amplitude and temporal variability are associated with the BC and EAC retroflections, while small values occur in the centre of the Argentine Basin and in the Tasman Sea. In the AC system, eddy polarity dictates the propagation distance. BC system eddies do not propagate beyond the Argentine Basin, and are advected by the local ocean circulation. EAC system eddies from both polarities cross south of Tasmania but only the anticyclonic ones reach the Great Australian Bight. For all three WBC systems, both cyclonic and anticyclonic eddies present a geographical segregation according to radius size and amplitude. Regions of high eddy kinetic energy are associated with the eddies' mean amplitudes, and not with their densities.

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