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32 results on '"Lessa, Guilherme C."'

5. Coastal Upwelling and Estuarine Gravitational Circulation: A Feedback System in a Tropical Estuary in the South Atlantic

Author

European Commission, Fonseca, Lucas S., Lessa, Guilherme C., Marta-Almeida, Martinho, Teixeira, Carlos Eduardo P., European Commission, Fonseca, Lucas S., Lessa, Guilherme C., Marta-Almeida, Martinho, and Teixeira, Carlos Eduardo P.

Abstract

This study examines the effects of coastal upwelling on the longitudinal water density gradient within the estuary of Baía de Todos os Santos (BTS), its effect on the gravitational circulation at the estuary entrance, and the reverse effect of gravitational circulation on the coastal upwelling. This investigation was based on a 1-year dataset of observed water temperature, mean velocities, and river discharge, as well as 2 years of numerical simulation of the estuarine flow. The results show that the upwelling regulates the thermohaline field in front of the BTS, decreasing water temperature (up to 3 °C), and increasing density (up to 0.3 kg/m), and have sufficient intensity to more than double the speed, or even establish, the gravitational circulation. It was frequently observed that the water temperature falls after an increase in the subtidal flow shear, suggesting that the estuarine gravitational circulation acts as a facilitator to the upwelling process. Numerical simulations indicate that the coastal upwelling events are also capable of reestablishing the gravitational circulation at times with weak longitudinal density gradient, a scenario that tends to become more frequent and intense in the near future due to the ongoing climate changes.

Published
2024

11. Scientific diving in Brazil: history, present and perspectives

Author

Leite, Tatiana S., primary, Pinheiro, Igor E., additional, Berchez, Flávio, additional, Bertoncini, Áthila A., additional, Cima, Oswaldo M. Del, additional, Demetrescu, Irene E., additional, Francini-Filho, Ronaldo B., additional, Kikuchi, Ruy K.P, additional, Machado, Arthur A., additional, Maia-Nogueira, Rodrigo, additional, Martins, Flavio L., additional, Mendes, Liana F., additional, Rambelli, Gilson, additional, Sampaio, Claudio L.S., additional, Segal, Barbara, additional, Aguiar, Aline A., additional, Auler, Augusto S., additional, Barroco-Neto, José, additional, Bonaldo, Roberta M., additional, Buchmann, Francisco S., additional, Calippo, Flavio, additional, Cesar, Augusto, additional, Gama, Matheus A.C., additional, Ghilardi-Lopes, Natalia, additional, Leão, Zelinda M.A.N., additional, Lessa, Guilherme C., additional, Menegola, Carla, additional, Pinheiro, Hudson T., additional, Rocha, Luiz A., additional, Sabino, José, additional, Seoane, José C.S., additional, Sestokas, Julia, additional, Tiago, Cláudio C., additional, Wegner, Ewerton, additional, and Lotufo, Tito, additional

Published
2023
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16. Long-term Variability of the Salinity Field in a Large Tropical, Well-Mixed Estuary: the Influence of Climatic Trends

Author

Fundação de Amparo à Pesquisa do Estado da Bahia, European Commission, Mariani, Rafael, Lessa, Guilherme C., Marta-Almeida, Martinho, Fundação de Amparo à Pesquisa do Estado da Bahia, European Commission, Mariani, Rafael, Lessa, Guilherme C., and Marta-Almeida, Martinho

Abstract

This work investigates the impact of regional climatic changes upon the salinity field of Todos os Santos Bay (BTS), the third largest estuary in the country. A comprehensive meteorological and oceanographic data set was used, which included more than 50 years of rainfall, river discharge and air temperature, 7 years of hydrodynamic numerical simulations of the bay and adjacent shelf, and 3 years of observations of the salinity field. The results show a clear aridification (less humidity and warmer air temperatures) trend in the last 5–6 decades. In this period, the yearly mean fluvial discharges and total rainfall were reduced by up to 72% and 50%, respectively, of their climatological means, and the air temperature increased by up to 1.25 °C. Less freshwater inflow and higher temperatures caused an increase of the mean surface salinity of 0.6 for the whole bay and 1.2 in the most internal sectors. Hypersalinity events apparently occurred for the first time in the early 1990s, and reached a maximum intensity in 2013 during the worst regional draught in the historical record, when an estuarine density plug was observed. The hypersalinity events were intensified, and not caused by the damming of Paraguaçu River, whose summer discharges have decreased faster than anticipated by previous investigations. The original tropical climate of the region has become more Mediterranean, with relatively less rainfall occurring in the summer. The hydrographic changes of the BTS exemplify similar hydrological and hydrographic processes that might also be underway in tropical areas undergoing climate aridification.

Published
2022

22. The tides and tidal circulation of Todos os Santos Bay, Northeast Brazil: a general characterization

Author

LESSA GUILHERME C., DOMINGUEZ JOSÉ M. L., BITTENCOURT ABÍLIO C.S.P., and BRICHTA ARNO

Subjects
Baía de Todos os Santos, lcsh:Q, Tides, lcsh:Science, Tidal currents
Abstract

The Todos os Santos Bay, located on northeastern Brazil, is the second largest coastal bay in the country, after São Marcos Bay. The three main drainage basins convey an average of 120 m³/s of freshwater towards the bay, the majority of it, however, held by a dam in Paraguaçu River since 1985. The original average freshwater inflow was two orders of magnitude smaller than the estimated tidal discharge through the main bay entrance, and the oceanographic characteristics of the bay, as indicated by bay salinity measurements, are clearly marine. The tides are semi-diurnal, and are amplified up the bay by a factor of 1.5. Shallow water constituents become more important as the tide propagates along Paraguaçu Channel and Paraguaçu River, where they generate time asymmetries that change between spring and neap tides. Currents in the bay are mainly bi-directional, and are stronger during the ebbing tide in most of the bay. Offshore, relatively strong tidal currents appear to be felt in a radius of about 10 km, where they are superimposed on winds driven currents orientated to the southwest.

Published
2001

26. Anais da Academia Brasileira de Ciências

Author

Lessa, Guilherme C., Bittencourt, Abilio Carlos da Silva Pinto, Brichta, Arno, and Dominguez, José Maria Landim

Subjects
Holocene, Stratigraphy, Estuary, Sediment
Abstract

p.573-590 Submitted by Texeira Ana (atanateixeira@gmail.com) on 2012-08-01T12:59:54Z No. of bitstreams: 1 LESSA, GUILHERME C.(2).pdf: 1651726 bytes, checksum: 295960396b0a97d2112835122a8588c7 (MD5) Made available in DSpace on 2012-08-01T12:59:54Z (GMT). No. of bitstreams: 1 LESSA, GUILHERME C.(2).pdf: 1651726 bytes, checksum: 295960396b0a97d2112835122a8588c7 (MD5) Previous issue date: 2000-12 Todos os Santos Bay is a large ( 1000 km2), structurally controlled tidal bay in northeast Brazil. Three main drainage basins debouch into the bay, providing a mean freshwater discharge of 200 m3/s (prior to 1985), or less than 1% of the spring tidal discharge through the bay mouth. Based on the result of several sedimentological studies performed in the 1970's, five surface sedimentary facies were identified inside the bay, namely i) transgressive siliciclastic marine sand facies; ii) transgressive bay sand-mud facies; iii) a transgressive carbonate marine sand facies; iv) regressive bay-mud facies, and v) regressive fluvial sand facies. The spatial distribution of these facies would follow, somewhat closely, the hydrodynamic-energy distribution inside the bay. Seismic profiles along the bay bottom indicate the existence of several paleochannels, 5-10 m deep, blanketed at least by three different sedimentary units. The topmost sedimentary unit, 5-20 m thick, appears to be associated with the regressive bay-mud facies, and assuming that it was laid down within the last 5000 years, sedimentation rates for the central and northeastern part of the bay would average at 2,4 mm/y. Rio de Janeiro

Published
2000
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31. Morphodynamic controls on tides and tidal currents in two macrotidalshallow estuaries, NE Australia

Author

Lessa, Guilherme C.

Subjects
*MANGROVE plants, *ESTUARIES, *COASTAL zone management
Abstract

Field and numerical investigations on the hydrodynamics of shallow estuaries have suggested that the dominant current direction can be assessed through the examination of the water level record. Shorter rising tides induce stronger flood currents, whereas faster falling tides cause stronger ebb currents. Monthly measurements of tides and current velocities in two shallow macrotidal estuaries in eastern Australia show that the hydrodynamics are controlled by two topographical entities, namely the depth of the channel bed across the ebb tidal delta and the elevation of the mangrove banks. Vertical tidal attenuationand asymmetry are related to the degree of tidal truncation at low tide. Lower spring low tide levels increase tidal truncation inside the estuary, causing longer stationary tide levels at low tide and morepronounced tidal attenuation. Neap tides, although still very asymmetric, may propagate freely inside the estuary, as low tide level stays above the elevation of the channel. Velocity measurements show thatthe expected flood dominance, due to the sense of the vertical tidalasymmetry, occurs only during neap tides. As tides rise above the mangrove levels during spring cycles, stronger ebb fluxes are observed,and the system becomes overwhelmingly ebb dominant. Thus, based on current prognostic models for shallow estuary hydrodynamics, the spring-to-neap trend in vertical asymmetry radically opposes the trend in flow regime. [ABSTRACT FROM AUTHOR]

Published
2000

32. Morphodynamic controls on tides and tidal currents in two macrotidal shallow estuaries, NE Australia

Author

Lessa, Guilherme C.

Subjects
*COASTAL zone management, *ESTUARIES, *MANGROVE plants
Abstract

Field and numerical investigations on the hydrodynamics of shallow estuaries have suggested that the dominant current direction can be assessed through the examination of the water level record. Shorter rising tides induce stronger flood currents, whereas faster falling tides cause stronger ebb currents. Monthly measurements of tides and current velocities in two shallow macrotidal estuaries in eastern Australia show that the hydrodynamics are controlled by two topographical entities, namely the depth of the channel bed across the ebb tidal delta and the elevation of the mangrove banks. Vertical tidal attenuationand asymmetry are related to the degree of tidal truncation at low tide. Lower spring low tide levels increase tidal truncation inside the estuary, causing longer stationary tide levels at low tide and morepronounced tidal attenuation. Neap tides, although still very asymmetric, may propagate freely inside the estuary, as low tide level stays above the elevation of the channel. Velocity measurements show thatthe expected flood dominance, due to the sense of the vertical tidalasymmetry, occurs only during neap tides. As tides rise above the mangrove levels during spring cycles, stronger ebb fluxes are observed,and the system becomes overwhelmingly ebb dominant. Thus, based on current prognostic models for shallow estuary hydrodynamics, the spring-to-neap trend in vertical asymmetry radically opposes the trend in flow regime. [ABSTRACT FROM AUTHOR]

Published
2000

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