Abstract The Brazil-Malvinas Confluence (BMC) is a significant biological frontier where distinct currents meet, fostering optimal conditions for phytoplankton development. In this study we tested the hypothesis that eddys promote an increase in phytoplankton biomass at the Brazil-Malvinas Confluence (BMC), altering species diversity. Phytoplankton were collected with Niskin bottles and nutrient concentrations assessed at two depths (Surface and Deep Chlorophyll Maximum Layer – DCML) in areas outside and under the influence of Cold-Core (CCE) and Warm-Core (WCE) Eddies. Environmental variables were determined in situ using a CTD profiler. Four regions were separated based on environmental variables and phytoplankton species, namely, the Brazil Current (BC), Malvinas Current (MC), CCE, and WCE. Species diversity was higher in the eddies. The conditions of the WCE were different from those of the CCE, with low temperature and salinity and high cell density values in the latter. The phylum Bacillariophyta was predominant in terms of species richness in all regions and was responsible for the higher cell density in the MC, while dinoflagellates were dominant in the BC and eddies. Therefore, eddy activity alters the structure, diversity and biomass of the phytoplankton community in the BMC. BrazilMalvinas BMC (BMC meet development BMC, , Surface DCML ColdCore Cold Core CCE (CCE WarmCore Warm (WCE Eddies profiler namely BC, (BC) MC (MC) eddies latter Therefore structure (BC (MC

Abstract Measurements of the marine carbonate system on tropical and subtropical continental margins are poorly distributed in space and time, with many uncertainties persisting regarding the role of carbon exchanges at the ocean-atmosphere interface in these areas. To calculate sea-to-air CO 2 fluxes in Marine Ecoregions along the Brazilian continental margin (4°N to 34°S), we used data from the Surface Ocean CO 2 Atlas (SOCAT v2020), collected up to 400 km from the coast, at the surface (5 m), between 1991 and 2018, with the aim of investigating the role of ecoregions as potential sinks or sources of atmospheric CO 2. The temperature and salinity of seawater presented variability in the north-south direction mainly because of the broad latitudinal range, reflecting typical patterns of tropical (T = 27.4°C ±1.49; S = 36.4 ±1.91) and subtropical waters (T = 22.8°C ±3.41; S = 35 ±2.91), in addition to the greater or lesser influence of river inputs in each ecoregion. The pCO 2 values in the surface waters varied from 121.81 (Amazon) to 478.92 μatm (Eastern), differing significantly between ecoregions and showing an expected decadal increasing trend, both in the atmosphere and in the seawater. The calculated values of CO 2 fluxes showed non-homogeneous spatio-temporal variations, from -24.37 mmol m-2 d-1 (Rio Grande) to 9.87 mmol m- 2 d-1 (Southeastern). Throughout the analyzed time series, we observed that the Northeast, Amazon and Eastern ecoregions acted predominantly as sources of CO 2 and the Southeastern ecoregions and, mainly, Rio Grande, acted predominantly as sinks of atmospheric CO 2. oceanatmosphere ocean areas seatoair sea air 4°N 4N N 4 34°S, 34S 34°S , 34 34°S) SOCAT v2020, v2020 v v2020) 40 coast 5 ( m, m m) 199 2018 northsouth north south range T 274C C 27 ±1.49 149 1 49 364 36 36. ±1.91 191 91 228C 22 8 ±3.41 341 3 41 ±2.91, 291 ±2.91 ±2.91) ecoregion 12181 121 81 121.8 (Amazon 47892 478 92 478.9 Eastern, (Eastern) trend nonhomogeneous non homogeneous spatiotemporal spatio temporal variations 24.37 2437 24 37 -24.3 m2 d1 d d- Grande 987 9 87 9.8 Southeastern. . (Southeastern) series Northeast v202 19 201 ±1.4 14 ±1.9 ±3.4 29 ±2.9 1218 12 121. 4789 47 478. (Eastern 24.3 243 -24. 98 9. (Southeastern v20 20 ±1. ±3. ±2. 24. -24 v2 ±1 ±3 ±2 -2 ± -

Multiple environmental problems are caused by the accumulation of nitrogen (N) and phosphorus (P) in river water on its way to the ocean. The objective of this work was to determine the N and P loads in 12 hydrographic basins that flow into estuaries along the northeastern coast of Brazil using established methods. Additionally, natural and anthropogenic loads trends in the hydrographic basins of 12 tropical rivers in northeastern Brazil over 27 years (1990-2016) were evaluated. The results indicated an annual average increase of +1.1% in population density, while precipitation showed no significant trend. The anthropogenic loads were 21 and 112 times higher than natural inputs for N and P, respectively. Anthropogenic sources accounted for ~ 96% of all contributions. The positive trends of these loads (mainly wastewater) represented an annual average increase of 1.1% for N and 1.2% for P, for all river basins included in this study. These percentages represent average annual loads of 251 t N yr-1 and 54.8 t P yr-1. The time series of N and P in the study region showed trends that point to a constant increase, implying a greater contribution of these loads to the adjacent coastal region year after year. (N (P ocean 1 methods Additionally 2 19902016 1990 2016 (1990-2016 evaluated 11 +1.1 density trend respectively 96 contributions mainly wastewater 1.1 1.2 25 yr1 yr yr- 548 54 8 54. yr1. 1. 1990201 199 201 (1990-201 +1. 9 5 199020 19 20 (1990-20 +1 19902 (1990-2 + (1990- (1990 (199 (19 (1 (

Resumo O intenso preparo e revolvimento do solo em cultivos, com o tempo, reduz a quantidade e a qualidade da matéria orgânica do solo. Diante desse contexto, este trabalho teve como objetivo determinar os estoques de carbono do solo e frações lábeis sob sistema agroflorestal (SAF) e topossequências em brejo de altitude, em Taquaritinga do Norte, Pernambuco, Brasil. O estudo foi desenvolvido na fazenda Yaguara, e as áreas estudadas foram mata nativa com 4,57 ha e plantio de café sombreado com mata nativa com 25,59 ha. As amostras de solos foram coletadas em quatro trincheiras 1,5 x 1,5 x 0,60 m, com distância de 50 metros. Foram coletados solos nas profundidades de 0-20, 20-40 e 40-60 cm, seguido de análises químicas, físicas e densidade para determinação dos estoques de carbono no solo e frações lábeis. A área com café sombreado apresentou maiores valores de estoques de carbono no solo nas profundidades de 0-20 cm e 20-40 cm. Na profundidade de 40-60 cm, a topossequência de topo do SAF apresentou maior estoque de carbono com 11,73 Mg ha-1, seguido da área com vegetação nativa com 10,6 Mg ha-1 , encosta com 9,23 Mg ha-1 e pedimento com 7,00 Mg ha-1. Verificou-se que a topossequência de topo com café sombreado exibiu maior estoque de carbono lábil na profundidade 0-20 cm com o valor de 1,06 Mg ha-1, sucedido das áreas de pedimento (SAF) com 0,88 Mg ha-1, mata nativa com 0,79 Mg ha-1e encosta com 0,67 Mg ha-1. No entanto, a área de vegetação nativa apresentou o maior valor de carbono lábil na profundidade de 40-60 cm. Concluiu-se que a área com café sombreado na topossequência topo mostrou grande capacidade para elevar os estoques de carbono total e estoques de carbono lábil da matéria orgânica do solo. cultivos tempo contexto (SAF altitude Norte Pernambuco Brasil Yaguara 457 4 57 4,5 2559 25 59 25,5 15 1 5 1, 060 0 60 0,6 m metros 020, 020 20, 20 2040 40 20-4 4060 40-6 químicas 0-2 1173 11 73 11,7 ha1, ha1 106 10 6 10, ha- 923 9 23 9,2 700 7 00 7,0 ha1. 1. Verificouse Verificou se 06 1,0 088 88 0,8 079 79 0,7 ha1e hae 1e 067 67 entanto Concluiuse Concluiu 45 4, 255 2 25, 0, 02 204 20- 406 40- 0- 117 11, 92 9, 70 7, 08 8 07

Abstract Intense soil preparation and disturbance in crops, over time, reduces the quantity and quality of soil organic matter. Given this context, this work aimed to determine soil carbon stocks and labile fractions under agroforestry system (AFS) and toposequences in an altitude marsh, Taquaritinga do Norte, Pernambuco, Brazil. The study was carried out at the Yaguara farm, and the areas studied were native forest with 4.57 ha and coffee plantation in shade with native forest with 25.59 ha. Soil samples were collected in four trenches measuring 1.5 x 1.5 x 0.60 m, with a distance of 50 meters. Soils were collected at depths of 0-20, 20-40 and 40-60 cm, followed by chemical, physical and density analyzes to determine soil carbon stocks and labile fractions. The area with shaded coffee showed higher values of soil carbon stocks at depths of 0-20 cm and 20-40 cm. At a depth of 40-60 cm, the AFS top toposequence showed the highest carbon stock with 11.73 Mg ha-1, followed by the area with native vegetation with 10.6 Mg ha-1, slope with 9.23 Mg ha-1 and pediment with 7.00 Mg ha-1. It was found that the top toposequence with shaded coffee exhibited a greater stock of labile carbon at depth 0-20 cm with a value of 1.06 Mg ha-1, followed by the bedding areas (SAF) with 0.88 Mg ha-1, native forest with 0.79 Mg ha-1 and slope with 0.67 g kg-1. However, the area of native vegetation showed the highest value of labile carbon at a depth of 40-60 cm. It was concluded that the area with shaded coffee in the top toposequence showed great capacity to increase total carbon stocks and labile carbon stocks of soil organic matter. crops time matter context (AFS marsh Norte Pernambuco Brazil farm 457 4 57 4.5 2559 25 59 25.5 15 1 5 1. 060 0 60 0.6 m meters 020, 020 20, 20 2040 40 20-4 4060 40-6 chemical 0-2 1173 11 73 11.7 ha1, ha1 1, 106 10 6 10. 923 9 23 9.2 ha- 700 7 00 7.0 ha1. 06 1.0 SAF (SAF 088 88 0.8 079 79 0.7 067 67 kg1. kg1 kg kg-1 However 45 4. 255 2 25. 0. 02 204 20- 406 40- 0- 117 11. 92 9. 70 7. 08 8 07 kg-

Abstract A scientific cruise between November 15 and December 18, 2019 aboard R/V Vital de Oliveira collected offshore seawater samples at 59 stations between the states of Ceará and Bahia. The objective was to identify hydrocarbon levels potentially associated with the mysterious oil spill that reached the northeastern coast of Brazil. Median concentrations of aliphatic hydrocarbons (AHs, 0.79 µg L-1) and polycyclic aromatic hydrocarbons (PAHs, 5.39 ng L-1) do not indicate contamination by crude oil and are comparable to baseline levels previously found in other areas of the Brazilian continental margin. The detailed composition of both groups of hydrocarbons revealed that some samples were contaminated during sampling and/or handling on-board. The data set presented herein highlights the difficulty in tracking small oil patches spread over a huge ocean area and, more importantly, the need for improving protocols of national research vessels used to collect seawater samples for trace organic analyses.

Abstract: This paper focused on the use of the biogeochemical LOICZ (Land Ocean Interactions in the Coastal Zone) to investigate the dynamics of DIN and DIP nutrients among three highly urbanized tropical estuaries (Barra das Jangadas (BJ), Recife (RE) and Timbó (TB)), located in the northeastern region of Brazil. The input data were obtained through in situ measurements (2007) and governmental agency databases (2001-2007). The balances of the non-conservative elements showed that the RE and TB systems alternated between sources and sinks during the observation periods (0.2-0.8 mmoles DIP m-2 d-1 and 0.1-10 mmoles DIN m-2 d-1). The metabolism rates in the systems indicated that the BJ system was autotrophic during the two observation periods (10-26 mmoles C m-2 d-1), while the RE system was heterotrophic (9-12 mmoles C m-2 d-1). The river discharge rates observed during the period 2001-2007 showed averages ranging from 9.4±3.8 to 18.4±7.7 m3s-1. Measurements of the trophic status in the RE system during 2007 characterized the system as eutrophic, thereby demonstrating high levels of chlorophyll-a and inorganic nutrients. The applications of balance sheets modeling proved to be very useful toward understanding the dynamics of estuarine systems dominated by large urban centers.

Resumo A suscetibilidade dos ambientes costeiros às mudanças nos ciclos biogeoquímicos do carbono e nutrientes impulsionados pela pressão antrópica e mudanças climáticas é um verdadeiro desafio para a comunidade científica. Este artigo avaliou os efeitos de um evento de precipitação extrema sobre os parâmetros de oxigênio, nutrientes e do sistema carbonato em dois estuários tropicais poluídos. As amostras de água superficial foram retiradas sazonalmente ao longo de um gradiente de salinidade nos estuários do Capibaribe e Barra de Jangadas, a fim de investigar a variabilidade espacial e sazonal dos nutrientes dissolvidos, clorofila-a, oxigênio dissolvido, alcalinidade total, carbono inorgânico, pressão parcial de CO2 (pCO2) e fluxos de CO2. O aumento da influência ribeirinha causada pelas inundações fluviais durante a estação de precipitação extrema aumentou as concentrações de nitrogênio nas plumas dos estuários, que também apresentaram valores reduzidos de salinidade, alcalinidade e oxigênio dissolvido. Na pluma do Capibaribe o valor médio de fluxo de CO2 também mudou, passou de - 4,01 mmolC m-2 d-1 durante a estação seca, para um fluxo médio positivo de + 5,7 mmolC m-2 d-1 durante a estação chuvosa. Dentro dos estuários, os valores de BOD5,20 e fosfato dissolvido foram maiores durante a estação seca (p<0,0001) e apresentaram correlação positiva com os blooms fitoplanctônicos que atingiram um valor de chl-a de 85 mg m-3 no Capibaribe. A alta alcalinidade encontrada em ambos os estuários, com valores médios entre estações seca e chuvosa, respectivamente, de 1808 a 1373 µmol kg-1 no estuário Capibaribe e 1616 a 1058 µmol kg-1 no estuário Barra de Jangadas, pode atuar como um amortecedor para o processo de acidificação costeira devido à eutrofização. O aumento da descarga dos rios levou a um maior transporte de matéria orgânica e nutrientes para o litoral, diminuindo a disponibilidade de oxigênio e deslocando o estado metabólico da pluma estuarina para heterotrófico, enquanto aumentou a qualidade da água dentro dos estuários devido ao aumento de descarga promovido pela precipitação extrema.

Abstract The susceptibility of coastal environments to shifts in the biogeochemical cycles of carbon and nutrients driven by anthropogenic pressure and climate change is a real challenge for the scientific community. This paper evaluated the effects of an extreme rainfall event over the nutrients and carbonate parameters in two polluted tropical estuaries. Surface water samples were taken seasonally along a salinity gradient in the Capibaribe and Barra de Jangadas estuaries in order to investigate the spatial and seasonal variability of dissolved nutrients, chlorophyll-a, dissolved oxygen, total alkalinity, inorganic carbon, partial pressure of CO2 (pCO2) and CO2 fluxes. The increased riverine influence caused by the fluvial flooding during the extremely rainy season augmented the nitrogen concentrations in the plumes, which also presented reduced salinity, alkalinity and dissolved oxygen values. In the Capibaribe plume it has also shifted the mean CO2 flux value of - 4.01 mmolC m-2 d-1 during the dry season, to a positive mean flux of + 5.7 mmolC m-2 d-1 during the rainy season. Within the estuaries the BOD5,20 and dissolved phosphorus values were higher during the dry season (p<0.0001), they showed positive correlation with the phytoplanktonic blooms that reached a chl-a value of 85 mg m-3 in the Capibaribe. The high alkalinity found in both estuaries, with mean values between dry and wet seasons respectively from 1808 to 1373 µmol kg-1 in the Capibaribe estuary and 1616 to 1058 µmol kg-1 in Barra de Jangadas estuary, may act as a buffer to the process of coastal acidification due to eutrophication. The increased rivers discharge lead to a greater transport of organic matter and nutrients to the coast, decreasing the oxygen availability and shifting the metabolic status of the estuarine plume to heterotrophic, whereas increased the water quality within the estuaries due the flushing promoted by the extreme rainfall event.

Nine surface water surveys were performed in the Formoso estuary (Brazil) during 2012-2013 mainly in summer and winter periods and during spring tide. Temporal variations of temperature, salinity, phosphate, silicate, total alkalinity, dissolved inorganic carbon, partial pressure of CO2 (pCO2) and water-air CO2 fluxes were analyzed. Low rates of water-air CO2 fluxes (4.7 ± 8.0 mmol C m-2 d-1) were estimated despite the different climate conditions. pCO2 values ranged from 190 to 988 matm. These values are lower than those observed in other tropical estuaries. CO2 fluxes presented in this study contribute to the characterization of humid tropical estuarine systems, thus filling an important geographical information gap.

O arquipélago de São Pedro e São Paulo (ASPSP) está localizado próximo ao Equador, no oceano Atlântico. O objetivo deste estudo foi avaliar variações espaciais nos padrões de abundância da comunidade de Copepoda, e da biomassa e produção das três espécies de Calanoida mais abundantes no ASPSP. Amostras de plâncton foram coletadas com rede com 300 µm de abertura de malha, ao longo de quatro transectos (norte, leste, sul e oeste do ASPSP), com quatro estações cada. Todos os transectos exibiram uma tendência de redução da densidade dos Copepoda com o aumento da distância do ASPSP, provado estatisticamente para o Norte. A densidade variou de 3,33 a 182,18 ind.m−3, e diferenças também foram observadas entre o primeiro perímetro (primeira faixa de distância circular) e os demais. A biomassa total variou de 15,25 a 524,50 10−3 mg C m−3e a produção de 1,19 a 22,04 mg C m−3d−1. A biomassa e produção de Undinula vulgaris (Dana, 1849),Acrocalanus longicornis Giesbrecht, 1888 eCalocalanus pavo (Dana, 1849) apresentaram diferenças entre alguns transectos. Uma tendência de declínio da biodiversidade e produção com o aumento da distância do arquipélago foi observada, sugerindo que pequenas feições como o ASPSP podem afetar a comunidade em áreas oceânicas oligotróficas tropicais.

The Saint Peter and Saint Paul Archipelago (SPSPA) are located close to the Equator in the Atlantic Ocean. The aim of this study was to assess the spatial variations in the copepod community abundance, and the biomass and production patterns of the three most abundant calanoid species in the SPSPA. Plankton samples were collected with a 300 µm mesh size net along four transects (north, east, south and west of the SPSPA), with four stations plotted in each transect. All transects exhibited a tendency toward a decrease in copepod density with increasing distance from the SPSPA, statistically proved in the North. Density varied from 3.33 to 182.18 ind.m−3, and differences were also found between the first perimeter (first circular distance band) and the others. The total biomass varied from 15.25 to 524.50 10−3 mg C m−3 and production from 1.19 to 22.04 10−3 mg C m−3d−1. The biomass and production of Undinula vulgaris (Dana, 1849), Acrocalanus longicornis Giesbrecht, 1888 andCalocalanus pavo (Dana, 1849) showed differences between some transects. A trend of declining biodiversity and production with increasing distance from archipelago was observed, suggesting that even small features like the SPSPA can affect the copepod community in tropical oligotrophic oceanic areas.

Este trabalho se focalizou na dinâmica de nutrientes de um estuário tropical na costa nordeste brasileira, usando o protocolo LOICZ de balanços biogeoquímicos. Nós descrevemos a metodologia e os pressupostos subjacentes a este modelo. Os dados de entrada (precipitação e evaporação mensal, vazão do rio, e as concentrações de sal, fósforo e nitrogênio) foram obtidos durante as campanhas de campo no estuário de Barra das Jangadas - Brasil durante um período de 5 anos (1999 a 2003). Os resultados indicam grandes entradas de nutrientes ao sistema. O modelo mostrou que a variação sazonal do Metabolismo do Ecosistema (NEM) indica que o sistema passa de uma fase de produção de líquido da matéria orgânica, durante a estação seca (-0,5 mmoles C m-2 d-1) para uma mineralização líquida durante a estação chuvosa (-19 mmol m-2 C d-1). Sugerimos que o sistema varia ligeiramente entre autotrófica e heterotrófica durante o ano, devido ao regime de chuvas, as atividades antrópicas na bacia (densidade populacional e as plantações de cana de açúcar), e as cargas ribeirinhas de DIP associadas. A alta carga de N e P per capita, indica uma alta densidade populacional e um alto runoff. A aplicação da modelagem de balanço de fluxos foi útil para o entendimento da dinâmica de nutrientes em um pequeno estuário tipicamente tropical

This paper focuses on the nutrient dynamics of a tropical estuary on the northeastern Brazilian coast, studied using the LOICZ biogeochemical budgeting protocol. We describe the methodology and assumptions underlying this model. Input data (monthly for rainfall, evaporation, river discharge, and concentrations of salt, phosphorus and nitrogen) were obtained during field campaigns in the Barra das Jangadas Estuary (BJE) over a 5 years period (1999 to 2003). Mass balance results indicate large inputs of nutrients to the system. The model shows that the seasonal variation of the Net Ecosystem Metabolism (NEM) indicates that the system passes from a stage of organic matter liquid production and mineralization during the dry season (-0.5 mmoles C m-2 d-1) to liquid mineralization during the rainy season (-19 mmoles C m-2 d-1). We suggest that the system varies slightly between autotrophy and heterotrophy during the year due to the rainfall regime, human activities in the basin (density population and sugarcane plantations), and associated DIP riverine loads. High per capita loads of N and P indicate a high population density and high runoff. The application of flux balance modeling was useful to understand the nutrient dynamics of this typical small tropical estuary

ABSTRACT This paper presents a hydrobiological time series at Barra de Jangadas estuary in Northeastern Brazil. Studies were carried out during seven consecutive days from a spring to a neap tide, in one fixed station during the dry (January) and rainy (July) seasons, in 2001. The meteorology (rainfall, evaporation, wind intensity), hydrology (temperature, salinity, pH, dissolved oxygen-DO and relative saturation, BOD5, nutrients (NH3+NH4, NO2-, NO3-, PO4-3, SiO2)), bathymetry, current intensity and, chlorophyll-α, were studied. The principal component analysis (PCA) explained 80% of the total variance showing an inverse relationship between nutrients and DO, salinity and pH. This analysis showed a positive correlation between low tide and nutrients, indicating anthropogenic pollution. The water temperature presented low seasonal variation, similar to chlorophyll-α, which presented values over 20 mg m-3, characterizing a eutrophic environment. Higher salt concentrations were registered during the dry season with no vertical stratification. DO varied significantly in both seasons. Total dissolved inorganic nitrogen and dissolved inorganic Phosphorus values in July were in general 2 to 5 times higher than values registered in January, respectively. The average N/P ratio varied from 35:1 in January to 8:1 in July, being both phosphate and nitrogen limiting for phytoplankton growth. Night/day differences showed that in January, ammonia decreased in higher proportion than the other nitrogen compounds indicating assimilation by the autotrophic organisms during the day.

RESUMEN Este trabajo muestra los resultados de series temporales en el estuario de Barra de Jangadas en el Noreste de Brasil. El estudio fue realizado durante siete días consecutivos desde una marea de sicigia a una de cuadratura, en una estación fija durante el periodo seco (enero) y lluvioso (julio), en 2001. Se analizaron parámetros meteorológicos (precipitación pluviométrica, evaporación, intensidad de los vientos), hidrológicos (temperatura, salinidad, pH, oxígeno disuelto-OD y tasa de saturación, DBO5, nutrientes (NH3+NH4, NO2-, NO3- , PO4-3, SiO2)), batimetría, intensidad de las corrientes y clorofila-α. El análisis de componentes principales (ACP), explicó el 80% de la varianza total, mostrando una relación inversa entre nutrientes y OD, salinidad y pH. Este análisis mostró una correlación positiva entre la bajamar y los nutrientes, indicativo de polución de origen antropogénica. La temperatura del agua varió poco estacionalmente, similar a la clorofila-α que caracterizó un ambiente eutrófico con valores superiores a 20 mg m-3. Mayores concentraciones de sal ocurrieron en el mes estival y sin mostrar estratificación vertical. El oxígeno disuelto varió significativamente entre ambos períodos. Los valores totales de nitrógeno y fósforo inorgánico disuelto en julio fueron en promedio 2 y 5 veces superiores a los de enero, respectivamente. Las medias de N:P variaron de 35:1 en enero a 8:1 en julio, siendo ambos, el fosfato y el nitrógeno limitantes para el crecimiento del fitoplancton. Diferencias día/noche evidenciaron que, en enero, el amonio decreció en mayor proporción que el resto de los compuestos nitrogenados, indicativo de la asimilación por los organismos autotróficos durante el día.

Neste estudo são apresentadas as análises espaciais e temporais dos dados sinóticos coletados durante quatro campanhas oceanográficas do programa “REVIZEE/SCORE-N” realizadas em março-abril de 1995, outubro-novembro de 1997, abril-maio de 1999 e agosto-setembro de 2001. Em complemento às análises dos dados hidrológicos, foram utilizados resultados do modelo numérico CLIPPER - Experimento ATL6 (1/6 deg.). A ênfase deste artigo é avaliar o deslocamento sazonal e espacial da pluma de água Amazônica nas regiões localizadas à sudoeste, noroeste e em frente à foz do rio Amazonas. Dados hidrológicos e resultados do modelo demonstram que durante os meses de março-maio a pluma do rio Amazonas move-se para sudoeste, ao longo da costa norte brasileiro, tendendo a diminuir o deslocamento da pluma para sudoeste durante os meses de agosto-setembro. De outubro a novembro, não foi observado ou registrado o deslocamento da pluma para sudoeste. Resultados do modelo revelam anéis gerados pela retroflexão da Corrente Norte do Brasil (CNB) em torno de 7º N, e também a influência de água proveniente do rio Amazonas em volta desses anéis durante o mês de agosto.

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.

O estuário do rio Amazonas é notável na Plataforma Continental do Amazonas, onde a presença das águas fluviais foi detectada, mesmo durante o período da diminuição da descarga desse rio, pelos baixos valores de salinidade e altos valores de nutrientes. Contudo, a presença das águas oceânicas também foi marcante. Em relação às fases do ciclo do nitrogênio, o nitrogênio orgânico dissolvido foi a forma predominante, seguido do nitrogênio total particulado, nitrato, amônia e nitrito. Os dados de clorofila a indicaram uma área eutrófica onde há nitrogênio embora os valores da anomalia do nitrogênio inorgânico dissolvido tenham mostrado que ocorre maior remoção do que adição dessa forma nitrogenada na área em estudo. Os resultados das simulações com o modelo bidimensional MAAC-2D confirmaram que as águas ricas em nutrientes são deslocadas para noroeste (dois núcleos em 2,5°N-50°W e 4°N-51°W), pela ação de uma CNB mais forte durante o período de decaimento da vazão dos rios. No período de vazão máxima, estas lentes de águas ricas de nutrientes distribuem-se próximo de 0,5°N-48,5°W, bem como ao longo da plataforma Amazônica rasa (20m-50m profundidade, 1°N-3,5°N), como resultado do espalhamento da água doce de origem continental.

The Amazon River estuary is notable at the Amazon Continental Shelf, where the presence of the large amount of water originating from the Amazon during the river's falling discharge period was made evident by the low salinity values and high nutrient levels. Even so, the presence of oceanic waters in the shelf area was significant. Dissolved organic nitrogen was the predominant species of the nitrogen cycle phases, followed by total particulate nitrogen, nitrate, ammonium and nitrite. The chlorophyll a data in the eutrophic area indicated that there is sufficient nitrogen in the area to withstand productivity, though dissolved inorganic nitrogen removal processes are faster than regeneration or mineralization. The anomalous amounts of inorganic dissolved nitrogen showed more removal than addition. The simulations with the bidimensional MAAC-2D model confirmed that high nutrient waters are displaced northwest-ward (two cores at 2.5ºN-50ºW and 4ºN-51ºW) by the stronger NBC during falling river discharge. During high river flow period these nutrient-rich lenses are distributed around 0.5ºN-48.5ºW as well as along the shallow Amazonian shelf (20m-50m depth, 1ºN-3.5ºN), as a result of the spreading of Amazon freshwater outflow.

Este trabalho tem como objetivo analisar a variabilidade sazonal das propriedades termohalinas na Plataforma Continental do Maranhão (PCM) e área oceânica adjacente. Foram considerados dois diferentes períodos, associados às distintas características de forçantes atmosféricas e continentais - Novembro/1997 e Junho/1999. Os resultados foram baseados na análise simultânea de dados hidrográficos obtidos a partir de cruzeiros oceanográficos do Programa "REVIZEE/SCORE-NO'', complementados com informações oriundas de satélites e de resultados de modelagem numérica oceânica. Na região da Plataforma Continental Interna (limitada pela isóbata de 50 m), as distribuições de salinidade e temperatura são principalmente afetadas pelo aporte continental de água doce, sobretudo no mês de Junho/1999. Na região oceânica adjacente à Plataforma Continental (ao longo da quebra da plataforma), as distribuições de TSM podem ser explicadas com base na influência da Corrente Norte do Brasil (CNB). Os resultados numéricos e as observações hidrográficas confirmam que a profundidade da camada de mistura na região oceânica adjacente à PCM é fortemente condicionada à posição e à intensificação dos núcleos de salinidade máxima, que por sua vez são influenciados pela variabilidade sazonal da CNB.

The objective of this work is to characterize the spacial variability of the thermohaline surface properties in the Maranhão continental shelf and adjacent oceanic area, during two different periods, associated to the distinct characteristics of atmospheric and continental forcings - November/1997 and June/1999. This paper presents the results of simultaneous shipboard measurements collected during oceanographic cruises of the program "REVIZEE/SCORE-NO''. Numerical model outputs and satellite data complement the results of hydrographical observations. In the inner shelf (limited at isobath 50 m), the distributions of salinity and temperature are mainly affected by fresh water discharge (observed during June/1999). The distributions of SST in the adjacent oceanic region can be explained by the influence of the North Brazil Current (NBC). Model results and hydrographic observations indicate that the mixed layer depth in the oceanic region adjacent to the Maranhão continental shelf is influenced by seasonal variability of the NBC transport associated with the position and the intensification of the high salinity core of the NBC.

O clima está fortemente relacionado com a dinâmica da camada superficial do Atlântico tropical e com as trocas entre esta e a atmosfera, e a previsão do tempo melhorará à medida em que ganhemos um melhor entendimento dos processos que governam a distribuição relativa das propriedades termodinâmicas na coluna d'água. O presente trabalho focaliza o isolamento das águas quentes superficiais das águas frias profundas pela camada de barreira (CB) induzida pela salinidade no Atlântico Equatorial Oeste (3ºS-7ºN; 40º-52ºW), com base em 487 perfis de CTD (REVIZEE - 1995-2001). O principal processo que contribue para a formação sazonal da CB é a descarga fluvial de águas doces do rio Amazonas. Durante o final do inverno/primavera boreal (Mar-Mai; alta descarga), prevalecem camadas isotérmica (Z T) e de mistura (Z M) mais profundas e a formação de uma CB com 16m de espessura foi governada pelo estabelecimento de uma forte picnoclina induzida pela salinidade, no interior da camada isotérmica. Entretanto, durante o outono boreal (Out-Dez; baixa descarga), estratificações em densidade foram principalmente controladas pela distribuição de temperatura (Z M m Z T; ECB = Z M - Z T m 0). Embora não tenha registrado uma CB sobre a plataforma Amazônica, uma CB máxima (40m) foi formada próxima à quebra da plataforma a 45°W.

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 river discharge), density stratification was mainly determined by temperature distribution (Z M m Z T; BLT = Z M - Z T 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.