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International audience; This study focuses on analysing the potential impact of the Amazon and Pará Rivers on the salinity, temperature and hydrodynamics of the Western Tropical North Atlantic (WTNA) region between 60.5°-24°W and 5°S-16°N. The Regional Ocean Model System (ROMS) was used to simulate ocean circulation with 0.25°horizontal resolution and 32 vertical levels. Two numerical experiments were performed considering river discharge and river input. Temperature and salinity distributions obtained numerically were compared with Simple Ocean Data Assimilation (SODA) and in situ observations from the Prediction Research Moored Array in the Tropical Atlantic (PIRATA) buoys located at 38°W8°N and 38°W12°N. Surface currents were compared with Surface Currents from Diagnostic model (SCUD). Once we verified that model results agreed with observations, scenarios with and without river discharges were compared. The difference between both simulations in the Sea Surface Temperature distribution was smaller than 2°C, whereas the Sea Surface Salinity (SSS) changed by approximately 8 psu in the plume area close to the coast from August to December and reaching SSS differences of approximately 4 psu in the region of the North Equatorial Counter Current (NECC). The surface current velocities are stronger in the experiment with river discharge, mainly in the NECC area from September to December and close to the coast in June to August. The results show that river discharges also cause a phase shift in the zonal currents, anticipating the retroflection of the North Brazil Current by two months and enhancing eastward NECC transport, which is in agreement with observations. The Mixed Layer Depth and Isothermal Layer Depth in the presence of river discharge is 20-50 m shallower over the entire extension of the Amazon plume compared with the situation without continental inflows. As a consequence, stronger Barrier Layers develop in the river plumes, reducing the Oceanic Heat Content in the WTNA.

A high-resolution nutrient biochemistry and carbonate system surface synoptic data set from the N-NE Brazilian continental shelf was reanalyzed to fill a gap in the time series of the carbonate system in the region and to allow us to perform a historical analysis of its evolution in recent years. We used data collected from 7 oceanographic cruises (n = 852) undertaken between March 1995 and September 2001 during the Brazilian Program "REVIZEE" in the North (N) and Northeast (NE) Economical Exclusive Zones of Brazil. Measured temperature and salinity data, which exhibited strong fluctuations (25.5 degrees C - 29.5 degrees C and 13.2-37.4 units, respectively), showed significant differences between the N and NE campaigns. The concentrations of dissolved inorganic nitrogen (DIN), PO4- and SiO2- were higher in the N region than in the NE region, mainly due to fluvial transport, and nitrogen: phosphorus (N:P) ratios of < 16 and oxygen supersaturation were observed within the Amazon plume. The concentrations of riverine nutrients in the N region support primary production occurring in the offshore plume area. The calculated total alkalinity (1031-2437 mol kg(-1)) values showed strong spatial variations that were mainly associated with the Amazon plume. The calculated pCO(2) values reached 423 mu atm offshore in the NE region during boreal winter. The calculated sea-air CO2 fluxes (average: + 0.3 +/- 1.7 mmol m(-2) d(-1); range: -1.2 to + 2.0 mmol m(-2) d(-1)) showed spatial and temporal variations, with negative values (sink) in the region of the Amazon River plume and positive values (source) offshore in the NE region (4 degrees S to 12 degrees S). The variability in the sea-air CO2 fluxes in the N and NE regions was explained by variations in biological activity and the thermodynamic effect of temperature, respectively. The analysis of available data, complemented with those presented here, indicated that the surface water pCO(2) values showed a positive temporal trend (+ 1.10 +/- 0.2 mu atm yr(-1)) in the NE region during the period of 1987-2010. This rate of increase is lower than that verified to have occurred in the atmosphere (+1.72 +/- 0.01 mu atm yr(-1)) during the same period.

International audience; This study is focused on analyzing the behavior of oil/gas plumes from blowouts into deepwater, located at the northern Brazil continental shelf. The Regional Ocean Modeling System (ROMS) model is used to simulate ocean dynamics in the region 60.5°-24.0°W/5°S-16°N with 0.25° of resolution, 32 vertical levels and considering the discharges of the Amazon and Pará Rivers. The ROMS output are compared to Simple Ocean Data Assimilation (SODA) dataset. Three points were selected to make the numerical simulations, located at (50°W, 5.25°N), (44.5°W, 0.5°N) and (42.75°W, 1°S). The time step suggested by Lee and Cheung (1990) was adjusted due to the particular oceanographic conditions at each point, in which, the initial velocity tends to zero and the coefficient 0.1 of the original equation was replaced by 0.0250 and 0.0375. All the plumes behaved as type 3. The seasonal current speed was small from the bottom to the surface, usually not exceeding 0.25 ms-1; the maximum displacement of the plumes from its point of origin was not greater than 1 m. The mean plumes diameter on the surface ranged 54 - 79.7 m and the arrival time to the surface was from 7.25 to 8.05 hours.; O estudo está focado na análise do comportamento das plumas de vazamento de óleo/gás em águas profundas, localizadas na plataforma continental do norte do Brasil. O modelo Regional Ocean Modeling System (ROMS) é utilizado para simular a dinâmica oceânica na região 60.5°-24°W/5°S-16°N com 0.25° de resolução, 32 níveis verticais e considerando as descargas dos rios Amazonas e Pará. A saída do modelo ROMS é comparada com o conjunto de dados SODA (Simple Ocean Data Assimilation). Três pontos foram selecionados para fazer as simulações numéricas, localizados em (50°W, 5.25°N), (44.5°W, 0.5°N) e (42.75°W, 1°S). O passo do tempo sugerido por Lee e Cheung (1990) foi ajustado devido às condições oceanográficas particulares em cada ponto, em que a velocidade inicial tende a zero. O coeficiente 0.1 da equação original foi substituído por 0.0250 e 0.0375. Todas as plumas se comportaram como tipo 3. A velocidade de corrente sazonal foi pequena do fundo á superfície, não excedendo 0.25 ms-1 ; o deslocamento máximo das plumas de seu ponto de origem não foi maior do que 1 m. O diâmetro médio das plumas na superfície variou de 54 a 79.7 m e o tempo de chegada à superfície foi de 7.25 a 8.05 horas.

The spatial and temporal variations of the flux of CO2 were determined during 2007 in the Recife estuarine system (RES), a tropical estuary that receives anthropogenic loads from one of the most populated and industrialized areas of the Brazilian coast. The RES acts as a source of nutrients (N and P) for coastal waters. The calculated CO2 fluxes indicate that the upstream inputs of CO2 from the rivers are largely responsible for the net annual CO2 emission to the atmosphere of +30 to +48 mmol m(-2) day(-1), depending on the CO2 exchange calculation used, which mainly occurs during the late austral winter and early summer. The observed inverse relationship between the CO2 flux and the net ecosystem production (NEP) indicates the high heterotrophy of the system (except for the months of November and December). The NEP varies between -33 mmol m(-2) day(-1) in summer and -246 mmol m(-2) day(-1) in winter. The pCO(2) values were permanently high during the study period (average similar to 4,700 mu atm) showing a gradient between the inner (12,900 mu atm) and lower (389 mu atm) sections on a path of approximately 30 km. This reflects a state of permanent pollution in the basin due to the upstream loading of untreated domestic effluents (N/P = 1,367:6 mu mol kg(-1) and pH = 6.9 in the inner section), resulting in the continuous mineralization of organic material by heterotrophic organisms and thereby increasing the dissolved CO2 in estuarine waters.