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.

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RESUMO.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). ABSTRACT. 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.