Luiz Bruner de Miranda

Condições hidrográficas na plataforma continental ao largo de Ubatuba: variações sazonais e em média escala

As caracteristicas hidrograficas da regiao ao largo de Ubatuba, pesquisadas em periodos quase-sinoticos de verao (dezembro, 1985) e de inverno (julho, 1986), mostraram padroes distintos de distribuicao de massas de agua. Dois dominios com caracteristicas fisicas diferentes foram identificados sobre a plataforma continental: um interior e costeiro, e outro exterior, separados por uma zona frontal bem definida pelo campo de temperatura para o inverno. O dominio interior tem, durante o verao, uma estraficacao de massa em duas camadas, determinada principalmente pelo desenvolvimento da termoclina sazonal nesta epoca do ano, enquanto que no inverno a estratificacao dessa regiao e bem mais homogenea. No verao a camada superficial (profundidades menores do que 20 m) de toda a regiao e ocupada basicamente pela Agua Costeira (AC), que se mistura com a Agua Tropical (AT) mais ao largo; nesta epoca do ano observa-se, na camada subsuperficial, predominância da Agua Central do Atlântico Sul (ACAS), cuja mistura vertical com a AC e somente observada nas proximidades da costa. No inverno a ACAS nao penetra muito sobre a plataforma continental, e na camada superficial ocorre uma intrusao acentuada de AT no dominio exterior, sendo o dominio interior ocupado principalmente pela AC, a qual interage com a ACAS apenas na zona frontal que delimita a regiao de ocorrencia dessas massas de agua. Com base nesses padroes de distribuicao de massas de agua e do campo de massas, bem como nas condicoes meteorologicas de regiao vizinha, e sugerido um modelo de circulacao cuja dinâmica e controlada pelo vento e pela acao da Corrente do Brasil. Essa acao da Corrente do Brasil sobre o dominio exterior e, provavelmente, responsavel pela presenca dos vortices com caracteristicas de vortices frontais observados nas duas epocas do ano. Esses vortices, cuja extensao horizontal nas profundidades de 25 e 50 m e bem definida nas estruturas termica e halina, tem provavelmente um importante papel na troca de massas de agua entre a costa e o talude, contribuindo para o enriquecimento das aguas da plataforma continental atraves dos movimentos ascendentes que ocorrem em seu nucleo.

On the origins of the North Brazil Current

The analysis of the hydrographic data obtained during the “Nordeste III” (NEIII) survey by the R/V Almirante Saldanha (Brazilian Navy) between May 4 and July 12, 1986, is reported in this work. Distributions of geostrophic speeds and transports (relative to 1000 m) reveal the North Brazil Current (NBC) and other major features of the tropical Atlantic circulation west of 30°30′W between 4°S and 10°30′S. The well-developed NBC appears in all analyzed crossisobath sections bordering the Brazilian continental slope between 10°S and 5°S, transporting an average of 21 Sv. The velocity core of the NBC is found to be centered at about 100–200 m, instead of at the surface, as previously thought. The central branch of the South Equatorial Current (CSEC) enters the study region at about 5°S–6°S and separates into two portions. The northern portion of the CSEC transports about 15 Sv northwestward, and north of 5°S, it coalesces with the NBC to form a 300-km-wide current that transports more than 36 Sv equatorward. The southern branch of the CSEC transports 14 Sv southwestward until about 9°30′S, where it makes a cyclonic turn to the north and merges with northward flow from the southernmost branch of South Equatorial Current (SSEC). The high-salinity signature of waters from the SSEC appears in the NBC, indicating that it is formed to the south of the study area. By contrast, historical ship drift and Lagrangian drifter observations suggest that the NBC and the Brazil Current are formed at the bifurcation of the CSEC. This apparent contradiction is explained by the surface Ekman drift which obscures the geostrophic flow patterns.

Circulation and mixing due to tidal forcing in the Bertioga Channel, São Paulo, Brazil

Bertioga Channel is a partially mixed (type 2) tidal estuary on the coastal plain of São Paulo, Brazil. Hourly current and salinity measurements during neap and spring tides in July 1991 yielded information about the physical structure of the system. Peak along-channel velocities varied from 40 cm s−1 to 60 cm s−1 during flood tides and from 70 cm s−1 to 100 cm s−1 during ebb tides. Net vertical velocity profiles indicate that the net current reverses directions at a depth of 2.5–3.0 m in the halocline. Due to appreciable fortnightly tidal modulation, the estuary alternates from being highly stratified (type 2b) during neap tides, with advection and diffusion contributing equally to the net upstream salt flux, to being moderately stratified (type 2a) during spring tides, when 90% of the net upstream salt transport is the result of effective tidal diffusion. Decomposition of the salt flux indicates that the relative contribution to the upstream salt transport by gravitational circulation shear is greater than the oscillatory tidal flux by a factor of 2.6 during neap tides. The oscillatory tidal flux is generated by the correlation of the tidal components of the u-velocity and salinity and is responsible for approximately the same amount of upstream salt transport, during neap and spring tides. However, during spring tides, this oscillatory term is greater than the other salt flux terms by a factor of 1.4. The total salt transport, through a unit width of the section perpendicular to the flow, was within 2% of the sum of the seven major decomposed, advective and dispersive terms. On the assumption that the Bertioga Channel is laterally homogeneous, the results also indicate that the estuary is not in steady state with respect to salt flux.

Instantaneous transport of salt, nutrients, suspended matter and chlorophyll-a in the tropical estuarine system of Santos

The contribution of the polluted Sao Vicente and Santos estuarine channels to the eutrophication of Santos bay was assessed through the quantification of instantaneous transport of salt, dissolved inorganic nitrogen (DIN) and phosphate, organic and inorganic matter (OSM and ISM) and chlorophyll-a (Chl-a), during dry (austral winter- August/ 1999) and rainy (austral summer- January/2000) seasons. Samplings were carried out during spring and neap tides, in flood and ebb phases, in two transversal sections at the mouths of the Sao Vicente and Santos channels. Instantaneous transport values generally indicated importation of salt to the estuarine channels, exportation of DIN to the bay, mainly as N-NH4, at a maximum rate of 1155.1 g s-1 during the rainy season; importation of phosphate during the dry season (maximum of 385 g s-1) and exportation of ISM, OSM and Chl-a during periods of greater freshwater discharge. These results demonstrate the great contribution made by the Santos and Sao Vicente estuaries to the eutrophication of Santos bay, especially in the rainy season.

Circulation and suspended particulate matter transport in a tidally dominated estuary: caravelas estuary, Bahia, Brazil

The circulation and transport of suspended particulate matter in the Caravelas Estuary are assessed. Nearly-synoptic hourly hydrographic, current (ADCP velocity and volume transport) and suspended particulate matter data were collected during a full semidiurnal spring tide, on the two transects Boca do Tomba and Barra Velha and on longitudinal sections at low and high tide. On the first transect the peak ebb currents (-1.5 ms-1) were almost twice as strong as those of the wider and shallow Barra Velha inlet (-0.80 ms-1) and the peak flood currents were 0.75 and 0.60 ms-1, respectively. Due to the strong tidal currents both inlets had weak vertical salinity stratification and were classified with the Stratification-circulation Diagram as Type 2a (partially mixed-weakly stratified) and Type 1a (well mixed). Volume transports were very close, ranging from -3,500 to 3,100 m3s-1 at the ebb and flood, respectively, with a residual -630 m3s-1. The concentration of the suspended particulate matter was closely related to the tidal variation and decreased landwards from 50 mg.L-1 at the estuary mouth, to 10 mg.L-1 at distances of 9 and 16 km for the low and high tide experiments, respectively. The total residual SPM transport was out of the estuary at rates of -18 tons per tidal cycle.

Forma da correlação T-S de massas de água das regiões costeira e oceânica entre o Cabo de São Tomé (RJ) e a Ilha de São Sebastião (SP), Brasil

Characteristics of the structure and sea water properties on the continental shelf and waters adjacent to the continental slope, were studied based on the temperature-salinity (T-S) relationships. The water sampling was carried out with standard methods in a network of hydrographie stations worked in five-time intervals (5-10 days), from January 1970 through February 1971. The classification review of the water masses used under regional conditions confirm that the Subtropical-Deep (STDW), Subtropical (STW) and South Atlantic Central (SACW) Water Masses are different nomenclature for the same water mass; the latter is suggested to indicate a water mass with a thermohaline index given by (20.0 oC; 36.36 ‰), observed underneath the Tropical Water Mass. This salinity value is slightly higher than the modified thermohaline index of the SACW (36.20 ‰), and can be used with great simplification in volumetric studies in the area. Polynomial expressions of the mean T-S curve, whose coefficients were computed with the least squares method, were given for practical applications. From these applications, alternative methods for the determination of the thermohaline derivative and constant density ratio (Rρ = αdT/βdS) were obtained.

Hidrodinâmica e transporte de material particulado em suspensão sazonal em um estuário dominado por maré: Estuário de Caravelas (BA)

The objective of the present paper is to characterize the hydrodynamics and the suspended particulate matter (SPM) in the Caravelas Estuary under different tidal and river regimes. Four hydrographic campaigns were carried out comprising a complete semi-diurnal tidal cycle, comprising neap and spring tidal phases, and during dry and wet seasons. Water level, current speed and direction, salinity, temperature and turbidity were recorded in an anchored station near to the estuarine mouth. The residual SPM flux and the mechanisms of transport were calculated. The higher SPM concentrations were recorded during the spring tidal phase. During neap tides, the net SPM flux was up-estuary, although with low scale. During spring tides the tidal currents are strongly ebb dominant, and the net flux can be either up- or down-estuary. The estuary was classified as well mixed or weakly stratified. The hydrography and the sediment balance are firstly modulated by the tidal range, and the fresh water inflow is negligible.

Physical and chemical aspects of transient stages of the upwelling at southwest of Cabo Frio (Lat. 23ºS - Long. 42ºW)

As observacoes oceanograficas realizadas em fevereiro de 1971, na plataforma continental entre Cabo Frio e a Ponta de Guaratiba, mostraram a presenca e a atenuacao de efeitos do fenomeno de ressurgencia observados na superficie. A analise detalhada da distribuicao termica na camada superficial evidencia que o processo fisico responsavel pela atenuacao desse fenomeno foi a adveccao de uma corrente costeira de aguas quentes, fluindo para leste. A componente zonal dessa corrente costeira atingiu nas proximidades da costa o valor maximo de 5 mn. dia 1 e a sua intensidade decresceu com o aumento da distancia a costa, anulando-se aproximadamente sobre a isobata de 100 m. Os efeitos do fenomeno de ressurgencia na superficie, observados ao largo da Ponta de Saquarema, eram claramente indicados pelos minimos de temperatura (17oC) e da concentracao de oxigenio dissolvido (4,2 ml/l) bem como pelo maximo na concentracao de fosfato (0,6 µg-at/l), que sao caracteristicos de aguas mais profundas. No intervalo de tempo (4-7 dias) decorrido entre as observacoes, verificou-se nao somente aumentos de temperatura e do oxigenio dissolvido, como tambem um decrescimo na concentracao de fosfatos de aproximadamente 50% de seu valor inicial.

Estudo da circulação e dos processos de mistura no extremo sul do mar de Cananéia: condições de dezembro de 1991

Foram analisados dados de correntes e de propriedades hidrograficas amostradas durante tres ciclos completos de mare, em dezembro de 1991. O maximo valor da componente longitudinal da velocidade da corrente variou, para as condicoes de enchente e de vazante, de 50 a -100 cm/s com esses extremos precedendo de 1,0 a 1,5 horas a ocorrencia dos instantes de mare alta e baixa, respectivamente. A componente transversal de velocidade mostrou que a circulacao secundaria predominava na direcao leste com nucleos de maxima de ate 30 cm/s em profundidades medias, enquanto que no sentido oposto (para oeste) essa componente apresentou valores maximos proximos a -10 cm/s na camada de superficie. A variabilidade da salinidade indicou uma quase homogeneidade vertical e durante a enchente o seu maximo (34,5-35,0 %o) precede a mare alta com uma defasagem de 1,0-2,0 horas. Entretanto, durante a vazante, a mare baixa precede o minimo de salinidade (29,5-30,5 %o) com defasagens entre 2 e 3 horas. Nao obstante a regiao estudada ser parte de um complexo sistema estuarino de planicie costeira, o extremo sul do Mar de Cananeia foi classificado, de acordo com o Diagrama Estratificacao-circulacao, como parcialmente misturado e fracamente estratificado (Tipo 2a). O movimento resultante reverte a 2,5 m de profundidade e quase 100% do fluxo de sal estuario acima e devido a difusao turbulenta.

Numerical study of circulation and thermohaline structure in the São Sebastião channel

The Princeton Ocean Model (POM) was adapted to Sao Sebastiao Channel (SSC) by nesting three numerical grids so as to study the seasonal changes of its circulation and thermohaline structure. Through monthly average conditions, the numerical model simulated reasonably the typical conditions of spring, summer, autumn and winter, filling the bottom channel with South Atlantic Central Water (SACW) in spring and in summer. In autumn and in winter this mass of water is not found, nevertheless its weaker signs appear in autumn, season in which the stronger signs of Tropical Water (never more than 50%) are found. Northeasterly winds on the Southeast Continental Shelf (SECS) grid are essential so that the SACW enters SSC. The bottom circulation obtained in SSC is essentially to northeast and associated to the intrusion of the SACW forced first by the northeasterly winds in SECS and second by the pressure force always bigger at the south entrance than in the north entrance and always bigger in summer than in winter. The superficial currents are southwestward, weakening in autumn and intensifying towards summer, with its maximum in this season.