Marcus Silva | Universidade Federal de Pernambuco (original) (raw)

Papers by Marcus Silva

Ocean Science, 2011

High-resolution hydrographic observations of temperature and salinity are used to analyze the for... more High-resolution hydrographic observations of temperature and salinity are used to analyze the formation and distribution of isothermal depth (Z T), mixed depth (Z M) and barrier layer thickness (BLT) in a section of the southwestern Atlantic (0 • 30 N-14 • 00 S; 31 • 24-41 • 48 W), adjacent to the northeastern Brazilian coast. Analyzed data consists of 279 CTD casts acquired during two cruises under the Brazilian REVIZEE Program. One occurred in late austral winter (August-October 1995) and another in austral summer (January-April 1997). Oceanic observations are compared to numerical modeling results obtained from the French Mercator-Coriolis Program. Results indicate that the intrusion of subtropical Salinity Maximum Waters (SMW) is the major process contributing to the seasonal barrier layer formation. These waters are brought by the South Equatorial Current (SEC), from the subtropical region, into the western tropical Atlantic boundary. During late austral winter southeastern trade winds are more intense and ITCZ precipitations induce lower surface salinity values near the equator. During this period a 5-90 m thick BLT (median = 15 m) is observed and BLT > 30 m is restricted to latitudes higher than 8 • S, where the intrusion of salty waters between 8 •-12.3 • S creates shallow mixed layers over deep (Z T ≥ 90 m) isothermal layers. During austral summer, shallow isothermal and mixed layers prevail, when northeasterly winds are predominant and evaporation overcomes precipitation, causing saltier waters at the surface/subsurface layers. During that period observed BLT varies from 5 to 70 m and presents thicker me

Human and Ecological Risk Assessment: An International Journal, 2013

ABSTRACT Despite the fast growth of underwater oil and gas exploration in low latitude regions, v... more ABSTRACT Despite the fast growth of underwater oil and gas exploration in low latitude regions, very few experimental data acquisition and modeling studies involving gas release in tropical and shallow waters are found in literature. In this article, a dataset of geophysical and gas release measurements obtained from an in situ experiment conducted off the Northeast Brazil coast are used as a baseline for evaluating the GASOCEAN blowout model. Hydrological and hydrodynamic data were collected for distinct seafloor gas plume releases (3000 to 9000 L/hr) during neap/spring tides of summer/dry and winter/wet periods. Simulation results indicate that the gas plume is horizontally displaced by the horizontal current as it rises through seawater column. The extreme situation provided a critical radius (maximum horizontal displacement) from the gas release source of 35.2 m. The comparison between the measured and the calculated data showed that the model satisfactorily represented the main features of the gas release, such as the displacement (11.6–35.2 m), diameter (1.2–2.8 m) and ascending time (1.1–1.6 min) of the plumes. Although the mean plume widths have the same order of magnitude between the measurements and the calculations, improvements may enhance the model's performance during the earlier plume development.

Frontiers in Marine Science, 2021

The hydrodynamics and the occurrence of topographic upwelling around the northern Brazilian seamo... more The hydrodynamics and the occurrence of topographic upwelling around the northern Brazilian seamount chain were investigated. Meteorological and physical oceanographic data collected under the REVIZEE-NE Program cruises around the Aracati Bank, the major and highly productive seamount in the area, were analyzed and used to force and validate simulations using the 3D Princeton Ocean Model (3D POM). The Tropical Water mass in the top 150-m layer and the South Atlantic Central Water (SACW) beneath it and down to a depth of 670 m was present. The thickness of the barrier layer varied seasonally, being thinner (2 m) during the austral spring (October–December) and thicker (20 m) during the austral autumn (April–June) when winds were stronger. The surface mixed and isothermal layers in the austral winter (July–September) were located at depths of 84 and 96 m, respectively. During the austral spring, those layers were located at depths of 6 and 8 m, respectively. The mean wind shear energy...

Remote Sensing

Oil spill detection and mapping (OSPM) is an extremely relevant issue from a scientific point of ... more Oil spill detection and mapping (OSPM) is an extremely relevant issue from a scientific point of view due to the environmental impact on coastal and marine ecosystems. In this study, we present a new approach to assess scientific literature for the past 50 years. In this sense, our study aims to perform a bibliometric and network analysis using a literature review on the application of OSPM to assess researchers and trends in this field of science. In methodological terms we used the Scopus base to search for articles in the literature, then we used bibliometric tools to access information and reveal quantifying patterns in this field of literature. Our results suggest that the detection of oil in the sea has undergone a great evolution in the last decades and there is a strong relationship between the technological evolution aimed at detection with the improvement of remote sensing data acquisition methods. The most relevant contributions in this field of science involved countries...

Tropical Oceanography, 2011

Brazilian Journal of Oceanography, 2005

Climate is closely related to the dynamics of the surface layer of the tropical Atlantic and the ... more 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 (Z T) and mixed layers (Z M) 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 riv...

Ocean Science Discussions, 2009

Brazilian Journal of Aquatic Science and Technology, 2008

The Pirapama system in Pernambuco, Northeast Brazil, is one of the last major sources of adequate... more The Pirapama system in Pernambuco, Northeast Brazil, is one of the last major sources of adequate water supply in the state. A reservoir was constructed to store water for domestic, agricultural and industrial use. However, the formation of the reservoir pool flooded the marginal vegetation, starting an organic matter mineralization process, which resulted in eutrophication of the waters and depletion of dissolved oxygen concentrations, reaching anoxic conditions near the reservoir bed. This water body is also impacted by upstream inputs of domestic sewage, agricultural runoff and effluents from sugar-cane mills and distilleries. This work applied a one-dimensional vertical approach (CE-QUAL-R1) in order to simulate the formation of the reservoir pool, analysing the different operational alternatives. Eutrophication, anoxia and stratification potentials were studied. Water quality data obtained during 17 months are used to adjust the model rates and parameters. After model calibration-validation, hypothetical operational scenarios were simulated, taking into account different ways for water pumping (outtake elevations) and for discharging outflow excess (spillways or bottom outlet). Strong anoxic conditions (DO concentrations of less than 1.0 mg.L-1), associated to high eutrophication levels (high PO 4 and Chlorophyll-a concentrations), were found in all simulated scenarios. Regarding water quality conditions in the reservoir, the use of bottom outlet for reservoir water releases presented better results than the other operational alternatives, since it makes possible releasing anoxic waters from the deepest layers of the reservoir pool. However, in these conditions, the water quality downstream from the reservoir was severely compromised.

Surface and vertical thermal structures, heat budget in the surface mixing layer, and mass transp... more Surface and vertical thermal structures, heat budget in the surface mixing layer, and mass transports are explored in the southwestern tropical Atlantic (5°S-25°S / 20°W-47°W). That region, where part of the South Equatorial Current (SEC) enters at its eastern border, is of prime interest by feeding many western boundary currents along the eastern Brazilian edge, and by contributing to the climatic variability over the Northeast Brazil. The Regional Ocean Model System (ROMS) is used here to simulate a seasonal cycle of the ocean circulation with an isotropic horizontal grid resolution of 1/12 o and 40 terrain-following layers. Such a high-resolution regional model allows illustrating the complexity of meso-scales phenomena which occur in that region. Model results are compared with the very first annual series of observed thermal profiles available in the region thanks to the three PIRATA-SWE moorings recently deployed. Simulated thermal structure at the upper ocean layers agrees with in-situ data set. Seasonal evolutions of atmospheric and oceanic balances involving in the mixing layer heat budget are locally discussed. The magnitude of oceanic components (mainly the vertical diffusion and the horizontal advection) is about of the same order than of atmospheric forcing, and practically always opposes to it, with some local and seasonal timing differences. Simulated meridional transports across three zonal sections extending from continent to PIRATA sites provide new insight in the knowledge of the western boundary current system. Another section running along the PIRATA-SWE array indicates how the divergence of SEC is complex. This result encourages the need and future expansion of the observational PIRATA array system in that region.

The southwestern tropical Atlantic (05°S-25°S/20°W-47°W), where part of the South Equatorial Curr... more The southwestern tropical Atlantic (05°S-25°S/20°W-47°W), where part of the South Equatorial Current (SEC) enters at its eastern border, is of particular interest as it is fed by many western boundary currents along the eastern Brazilian continental shelf. However, the long-term variability of the dynamics in this region, which are also important as they contribute to the climate over northeastern Brazil, is largely unknown. We use the Regional Ocean Model System (ROMS) here for the first time in this area to simulate the ocean circulation with an isotropic horizontal grid resolution of 1/12°and 40 terrain-following layers. As a primary evaluation of the ROMS configuration, we explore surface and vertical thermal structures, the surface mixed layer, and mass transports within the upper levels. Interannual variability results are compared with the first two-year series of observed thermal profiles derived from the three PIRATA-SWE moorings. The simulated thermal structure in the upper ocean layers agrees well with in-situ data. ROMS simulations point out a broad and relatively weak SEC flow composed of a sequence of more or less defined near-surface cores. The westward SEC transport for the upper 400 m along the PIRATA-SWE section, calculated from the ROMS simulation for 2005-2007, shows an average volume transport of 14.9 Sv, with a maximum observed in JFM (15.7 Sv), and a minimum during MJJ (13.8 Sv). ROMS results indicate that the 2005-2007 seasonal near-surface westward SEC transport is modulated by the zonal wind variability. Three zonal sections extending from the American continent to the PIRATA buoy sites confirm that stronger northward NBUC transport and decreasing BC transport were achieved during May 2006 and May 2007, i.e. at the time the sSEC bifurcation reaches its southernmost position. On the other hand, the maximum southward BC flow was verified during January 2006, January 2007 and March 2007, with a minimum northward NBUC flow in December 2005 and October/December 2006, corresponding to the period when the sSEC bifurcation reaches its lowest latitude (OND). Sea Surface Height (SSH) and the surface Eddy Kinetic Energy (EKE) derived from simulations and AVISO Rio05 product point out the highest surface meso-scale activity (EKE P 50 cm 2 s À2) along the cSEC and NBUC/BC patches. Preliminary results provide additional ingredients in the complexity of the SEC divergence region and encourage us to conduct a more detailed exploration of the dynamics of this region using the ROMS. This also shows the need to continue, extend, and vertically upgrade the observational PIRATA-SWE array system, especially with more levels of salinity measurements and the installation of current measurements.