Alex Costa da Silva

Variação sazonal da estrutura de massas de água na plataforma continental do Amazonas e área oceânica adjacente

This work analyzes hydrographic properties (temperature and salinity) obtained from three oceanographic cruises performed along the Amazon continental shelf and adjacent oceanic areas of the western equatorial Atlantic. Field data covered three distinct periods and river discharge situation: the maximum river outflow during boreal spring (May 1999); the transition flow period (maximum to minimum discharges) during summer (August 2001), and minimum river flow during autumn (November 1997). The analysis of CTD hydrographic profiles identified four water masses: Coastal Water (CW), Tropical Surface Water (TSW), South Atlantic Central Water (SACW) and Antarctic Intermediary Water (AIW). Results suggest that wind shear variability acts over the horizontal distribution of surface water masses (CW and TSW), while the subsurface waters (SACW and AIW) are influenced by seasonal variability of the NBC transport and the presence of anticyclonic rings at the NBC retroflection area. Vertical transects analysis show that SACW is strongly expanded during the transition river flow regime (about 70 m at 49oW and 220 m at 50oW), which corresponds to the period when NBC and North Equatorial Countercurrent (NECC) reach their maximum strengths.

Seasonal changes in the mixed and barrier layers in the western Equatorial Atlantic

Climate is closely related to the dynamics of the surface layer of the tropical Atlantic and the exchange between this latter and the atmosphere, and wearther forecasting will improve with increasing understanding of the processes that govern the relative distribution of thermodynamic properties of the water column. This paper focuses on the isolation of warm surface waters from the cold ones of the deep ocean by a salinity induced barrier layer (BL) in the western equatorial Atlantic (3oS-7oN; 40o-52oW), based on 487 CTD profiles (REVIZEE - 1995-2001). The main process contributing to the seasonal BL formation is the discharge of low salinity waters from the Amazon river. During boreal late winter/spring (Mar-May; high river discharge), deeper isothermal (ZT) and mixed layers (ZM) prevail and the formation of a 16m-thick BL was clearly determined the formation of a salt-induced marked pycnocline within a deeper isothermal layer. However, during the boreal autumn (Oct-Dec; low river discharge), density stratification was mainly determined by temperature distribution (ZM m ZT; BLT = ZM - ZT m 0). There was no clear register of a BL on the Amazon shelf, but a maximum BL (40 m) formed near the shelf break at 45°W.

Coastal Erosion Case at Candeias Beach (NE-Brazil)

ABSTRACT Gomes, G. and Silva, A.C., 2014. Coastal erosion case at Candeias Beach (NE-Brazil). In: Silva, R., and Strusińska-Correia, A. (eds.). The present work is a study of changes in longshore sediment circulation due to the presence of a breakwater which interferes with the beach morphology. The study was done using the SMC software (Sistema de Modelado Costero) as the main tool for simulating the coastal dynamics for the different configurations, as well as for determining the wave climate to be applied at the simulations. The beach environment is a complex dynamic system responsive to the impact of waves and currents through a series of changes that can occur at different time scales and the intervention of human constructions. The focus of the present work is the application of SMC to investigate beach erosion in an area of Candeias Beach, in the metropolitan region of Recife (NE-Brazil), after installation and further modification of a hard coastal structure (breakwater), as well as in a scenario without the breakwater at the same area.

Observações hidrológicas e resultados de modelagem no espalhamento sazonal e espacial da pluma de água Amazônica

In this study, we present surface synoptic data collected during four oceanographic cruises undertaken in March-April 1995, October-November 1997, April-May 1999 and August-September 2001 in the Brazilian Program “REVIZEE/SCORE-NO” and a combination of model results (1/6 deg.). The emphasis of this paper is to point out the monthly changes on the spreading of the Amazon plume over the external Amazon shelf area and the eastern region of the Amazon River. Hydrographic data and model results demonstrated that during March-May, the Amazon plume moved southwestward along the northern coast of Brazil, decreasing during August-September; but this was not observed during October-November. Model results revealed ring signatures shedding from the North Brazil Current (NBC). Results also showed that during August the Amazon plume encircling the NBC retroflection was around 7o N.

Spatial-Temporal Variability of the Thermohaline Properties in the Coastal Region of Fernando de Noronha Archipelago, Brazil

ABSTRACT Assunção, R.V.; Silva, A.C.; Martins, J., and Flores Montes, M., 2016. Spatial-Temporal variability of the thermohaline properties in the coastal region of Fernando de Noronha Archipelago, Brazil. In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and Mc Carroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 512–516. Coconut Creek (Florida), ISSN 0749-0208. Brazilian oceanic islands are areas of great environmental, scientific, economic and strategic interest for the country. A better understanding of the thermohaline and hydrodynamic properties is fundamental to complement studies of chemical and biological processes active on the Fernando de Noronha archipelago, located between 03° 52′S and 32° 25′W. The aim of this work was to verify the coastal thermohaline behavior of the most inhabited part of the island, on a seasonal and spatial scale and how it is associated with the nutrient distribution data. Four campaigns were conducted in 2013 and 2014, two during the wet season and two during the dry season. For each period, data were collect at five stations. The results show that during the rainy season temperature increases and salinity decreases in the surface layer. Spatially no large differences are observed. Regarding to nutrient concentration, seasonal concentrations are quite homogeneous in the waters of the archipelago region. The coastal region was characterized by tropical mass water.

Dynamics of Chlorophyll a and Oceanographic Parameters in the Coastal Zone: Barra das Jangadas-Pernambuco, Brazil

ABSTRACT Otsuka, A.Y.; Feitosa, F.A.N.; Flores-Montes, M.J., and Silva, A., 2016. Dynamics of chlorophyll a and oceanographic parameters in the coastal zone: Barra das Jangadas-Pernambuco, Brazil. The Pernambuco shelf, inserted into the NE-E continental margin of Brazil, is about 187 km long and is characterized by reduced width, shallow depth, gentle slope, relatively warm water, and high salinity. It is influenced to some extent by translittoral rivers, the Jaboatão River being among these. This study aimed to analyze the dynamics of chlorophyll a and hydrological parameters on the Pernambuco inner continental shelf under the influence of the Jaboatão River plume. Bimonthly samplings were carried out during the rainy and dry seasons at one point in the estuarine area and four points along the adjacent inner continental shelf. The parameters evaluated were chlorophyll a, temperature, salinity, transparency, dissolved oxygen, suspended particulate matter, pH, depth, and inorganic nutrients. Most parameters had significant seasonal variation. In the dry period, chlorophyll-a ranged from 2.89 to 34.71 mg m−3 in the estuary and varied from 0.21 to 9.67 mg m−3 on the shelf. In the rainy period, it varied from 0.79 to 12.46 mg m−3 in the estuary and from 0.26 to 4.59 mg m−3 on the shelf. According to a principal components analysis, chlorophyll a showed a direct relationship with oxygen saturation rate and temperature and an inverse relationship with pH, salinity, and water transparency. Two points on the shelf (points 3 and 4) were most influenced by river outflow. The limiting factor for phytoplankton biomass was water turbidity due to the higher values reached in the dry period. The estuarine zone was in a stage of high eutrophication, thus sometimes affecting the waters of the inner shelf. RESUMO A plataforma de Pernambuco está inserida na margem continental nordeste-leste do Brasil, possui cerca de 187 Km de extensão e se caracteriza por ter uma reduzida largura, pouca profundidade, declive suave, águas relativamente quentes, elevada salinidade. Recebe influência de alguns rios translitorâneos, dentre eles, o rio Jaboatão. O presente trabalho apresentou como objetivo analisar a dinâmica da clorofila a e parâmetros hidrológicos na plataforma continental de Pernambuco sob o efeito da pluma do rio Jaboatão. Foram realizadas coletas bimestrais, no período chuvoso e estiagem, em um ponto na zona estuarina e quatro ao longo plataforma continental adjacente. Os parâmetros avaliados foram: clorofila a, salinidade, oxigênio dissolvido, material particulado em suspensão e nutrientes inorgânicos dissolvidos. A maioria dos parâmetros apresentou variação sazonal significativa. A clorofila a no estuário variou de 2,89 à 34,71 mg.m−3 e na plataforma continental de 0,21 à 9,67 mg.m−3 no período de estiagem e, no período chuvoso, apresentou uma variação no estuário de 0,79 à 12,46 mg.m−3 e na plataforma de 0,26 à 4,59 mg.m−3. De acordo com ACP, a clorofila a apresentou uma relação direta com a temperatura e taxa de saturação do oxigênio e inversa com pH, salinidade e transparência da água. Os pontos da plataforma que mais sofreram influência do deságüe fluvial foram os pontos centrais P3 e P4. O fator limitante para a biomassa fitoplanctônica foi a turbidez da água e os maiores teores foram observados no período de estiagem. A zona estuarina encontra-se em um elevado processo de eutrofização antrópica e, desta forma, vem interferindo na qualidade das águas da plataforma continental.

Seasonal and Intraseasonal Variability of Wave Climate on the NE Brazilian Coast using a Nautical Radar System

ABSTRACT Silva, A.C.; Bezerra, C.S.; Barcellos, R.L.; Araújo, M.; Bouchonneau, N. and Manso, V., 2016. Seasonal and intraseasonal variability of wave climate in the NE Brazilian coast by using Nautical Radar System. In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 927–931. Coconut Creek (Florida), ISSN 0749-0208. This paper presents a study about wave climate acting on the Northeast coast of Brazil (Recife, Pernambuco) from the use of X-band nautical radar, which runs through the emission of electromagnetic waves and receives the signal by backscattering the sea surface. The main objective of this work is to obtain information about the wave acting on this coast, by analyzing significant height, period and direction of the incident waves, which will be helpful to generate a solid database for future coastal measures, engineering works of contention for coastal and marine protection. Data were obtained from polar images of X-band nautical radar, from April 2010 to April 2011. By analysing the results, it was possible to observe the joint occurrence of waves wind sea and swell in the region of study. Wind sea waves occur predominantly at 90° - 135°, with higher values at the end of September (3.9 m). Swell waves were more frequent during June, October and December 2010, and February and March 2011. Moreover, we observed a change in direction of the waves and decrease in wave heights along the inner shelf of the coast, caused by variation in bathymetry and the presence of sandstone reefs. The results of this study demonstrated great efficiency in acquiring the physical parameters of waves through the X-band nautical radar system, proving to be an efficient tool for measuring physical parameters of waves in coastal regions.