The estuarine ecosystem is the connection between the river basin and the ocean. The ecological role of this ecosystem is essential for socioeconomic and subsistence activities. However, this ecosystem faces significant threats from domestic, industrial and agricultural effluents. To assess the influence of factors that could be influencing these impacts, this study investigated the spatio-temporal dynamics of ammonia (NH3) and phosphorous (P) concentration in the lower portion of the river basins located in the most eastern South American region located in Pernambuco State of Brazil. The monitoring data collected between 2005 and 2019 reveal significant NH3 and P concentration variations, influencing annual, seasonal, and spatial factors. The Generalized Addictive Model for Location, Scales, and Shape (GAMLSS) was utilized to assess the data NH3, and P water concentrations often exceed the ideal limits (NH3 ≤ 0.7 mg.L-1 and P ≤ 0.186 mg.L-1). The environmental variables of dissolved oxygen, distance from the coastline, rainfall, and ENSO were the most important factors influencing the concentration of NH3 and P in this portion of South America. The highest concentrations of these nutrients were found principally in the metropolitan sector during the dry season (NH3 = 4.1 mg.L-1 e P = 0.604 mg.L-1). The La Niña phenomenon, particularly during moments of extreme drought (e.g. 2006 and 2017), has led to a significant increase in the concentration of these pollutants, indicating potential risks for the occurrence of eutrophication events in these estuarine ecosystems. Based on our findings, intensifying efforts to sustain and expand the monitoring program is necessary. These measures will enhance the effectiveness of habitat restoration and help achieve optimal environmental conservation.

Northeastern Brazil (NEB) has a high potential for wind energy generation, making it a strategic area for the development of this renewable source. However, the region’s complex wind regime, driven by interactions between large-scale atmospheric systems, local circulations, and coastal topography, presents significant challenges for weather forecasting and wind energy applications. Despite this, detailed assessments of forecast performance using mesoscale models remain limited. The main objective was to develop an efficient strategy that enables satisfactory results by optimizing data assimilation, land use and topography information as well as improvements in physical parameterizations and post-processing, optimizing computational effort. Forecasting conducted during the year 2020 were validated with data from 20 anemometric measurement towers (AMTs), located at strategic points across various wind power complexes. The model’s performance was evaluated using statistical metrics such as MBE, MAE, nRMSE, standard deviation ratio, and correlation. Additionally, the impact of bias removal was assessed using two approaches: one that eliminates the mean error per forecasted time step and another employing artificial intelligence for bias removal training. The results revealed distinct characteristics for each analyzed location, with errors of diverse nature due to the local nuances of the measurements. However, both bias removal approaches showed significant improvements in wind characterization across all complexes.

Northeast Brazil (NEB) is a climatically diverse region that includes semi-arid zones highly vulnerable to droughts and coastal areas frequently affected by extreme rainfall and flooding. These extremes pose significant challenges to water security, agriculture, and infrastructure. Effective climate forecasting in NEB requires a comprehensive understanding of multi-basin interactions, as they play a pivotal role in shaping regional precipitation patterns. Monitoring the simultaneous influences of both the Pacific and Atlantic climate indices is crucial for improving prediction accuracy, given the complex and interconnected nature of ocean-atmosphere dynamics that affect the region. This study investigates 75 years (1948-2022) of Pacific and Atlantic climate modes and their impact on NEB precipitation. Composite analyses were conducted using the 25th and 75th percentiles of sea surface temperature (SST) anomalies to define the warm and cold phases of each climate index. The results show distinct rainfall patterns across the NEB, with delayed responses to different oceanic indices. In Northern NEB (NNEB), the positive phases of Atlantic Meridional Mode (AMM) and El Nino-Southern Oscillation (ENSO) reduce rainfall, while the South Atlantic Ocean Dipole (SAOD) and Tropical South Atlantic (TSA) increase it. In Northern Eastern NEB (ENEBn), the positive phases of the AMM and Nino 1 + 2 decrease rainfall, while the South Atlantic Warm Pool (SAWP) enhances it. Simultaneous influences of the Pacific and Atlantic indices are associated with intense precipitation or drought events.

This study investigated how the extreme rainfall event over eastern Northeast Brazil (ENEB), occurring at the end of May 2022, was induced dynamically using observational and reanalysis data. On a monthly time scale, a wet-spell condition was found over the ENEB region in May 2022, indicated by enhanced onshore-ward moisture flux and a widely spreading positive precipitation anomaly. At a shorter time scale, the ENEB region experienced continually intense rainy days from May 21st to 28th peaking on May 28th. Focusing on the most intense rainfall event on May 28th, a shallow vortex disturbance of a tropical easterly wave can be responsible for this intense event. This easterly wave is initiated over the south tropical Atlantic adjacent to the ENEB region, and we suggest that a strong zonal wind shear zone associated with a synoptic-scale high-pressure system generates the vortex as barotropic instability. Even though the vortex center did not make a landfall over the ENEB region, a part of the vortex band is elongated along the coastal line of the ENEB region and the vorticity and moisture flux convergence intensify drastically over the coastal ENEB region. Reinforced fluid deformation along the coastal line indicates the extension and intensification of the vortex band. The coastal enhancement of vorticity, convergence, and deformation can be interactive, and the sea-land contrast may cause the enhancements due to surface condition change. This study provides a new dynamical insight into the intense precipitation over the ENEB region.

This study investigates the relationship between oceanic and atmospheric parameters and their relation with the occurrence of Coastal Squall Lines (CSL) in the Eastern Amazon. Utilizing a minimalist set of stability and stratification parameters, results indicate a significant coherence in the 8 and 12-month period in bulk parameters, potentially linked to the discharge of the Amazon River and the convective regime of Western Tropical Atlantic. A cross-wavelet analysis shed light on the relation of CSL frequency with the local and remote oceanic stratification and atmosphere stability parameters. Additionally, composite analyses reveal shifts in the distributions of these parameters during CSL occurrences, highlighting the sensitivity of CSL to environmental variables. The environmental variables rely on local and remote drivers, whose interactions still need to be fully addressed. Our results indirectly quantify how these drivers can explain the CSL frequency, with the advantage of bypassing a full assessment of submesoscale processes. These outcomes reveal the need to consider the influence of local shelf sea stratification to enhance the precision of CSL characterization, what can be used to improve the setup of atmospheric models. While this study covers this gap, further research considering the mechanistic approach is needed to improve the understanding of mesoscale convection at the Eastern Amazon.

The seawater fugacity of CO2 (fCO2) has been monitored hourly at an instrumented mooring at 6°S, 10°W since 2006. The mooring is located in the South Equatorial Current and is affected by the equatorial Atlantic cold tongue. This site is characterized by large seasonal sea surface temperature variations (>4°C). The fCO2 is measured by a spectrophotometric sensor deployed at about 1.5 meters deep. Measurements of seawater fCO2, sea surface temperature (SST) and sea surface salinity (SSS) are used to calculate total dissolved inorganic carbon (TCO2) and pH. Total alkalinity (TA) is calculated using an empirical relationship with SSS determined for this region. Satellite chlorophyll-a concentrations at 6°S, 10°W are low (<0.2 mg m-3) but some peaks over 0.8 mg m-3 are sometimes detected in August. Nevertheless, the site is a permanent source of CO2 to the atmosphere, averaging 4.7 ± 2.4 mmol m-2d-1 over 2006-2021. Despite the weakening of the wind, the CO2 flux increases significantly by 0.20 ± 0.05 mmol m-2d-1 yr-1. This suggests that the source of CO2 is increasing in this region. This is explained by seawater fCO2 increasing faster than the atmospheric increase during 2006-2021. Most of the seawater fCO2 increase is driven by the increase of TCO2, followed by SST. The fCO2 increase leads to a pH decrease of -0.0030 ± 0.0004 yr-1. The SST anomalies (SSTA) at 6°S, 10°W are correlated to the Tropical Southern Atlantic (TSA) index and to the Atlantic 3 region (ATL3) index with a correlation coefficient higher than 0.75. The strong positive phase of both ATL3 and TSA, observed towards the end of the time-series, is likely contributing to the strong increase of seawater fCO2.

Pelagic ecosystems around tropical oceanic islands are considered oases of high plankton biomass in the middle of oligotrophic "blue deserts". To understand the dynamics of such a pelagic ecosystem, we used CTD and ADCP data and zooplankton samples taken from the waters off the remote Fernando de Noronha Archipelago (FNA), Tropical Atlantic. We analyzed how the flow and island topography interactions influence the spatial variability of chlorophyll-a fluorescence and zooplankton abundance, biovolume, and normalized biovolume size spectra (NBSS). We used a 500-mu m mesh bongo net to obtain plankton samples in July and August 2010 in areas upstream and downstream of FNA. Zooplankton samples were analyzed with a ZooScan device. Chlorophyll-a peaks and a rise in thermocline indicated a topographic uplift and turbulence downstream of the island, i.e., the "Island Mass Effect". The NBSS presented a mean slope of -1.19 +/- 0.28, and a mean intercept of 3.98 +/- 0.87. There were no significant differences in NBSS slopes and intercepts between upstream and downstream areas. Nevertheless, zooplankton and decapod community structures were significantly different between areas: meroplanktonic communities showed higher abundances and biovolumes downstream (p < 0.05). Zoeae of stenopodid cleaner shrimps, anomuran and brachyuran crabs, and fish eggs were significantly more abundant downstream, indicating a "Larval Island Effect". Distinct peaks in size spectra due to teleost eggs and decapod larvae, downstream of FNA, also indicated a Larval Island Effect. Upstream of the island, there was a higher abundance of gelatinous organisms, holoplanktonic decapods, and advanced stages of brachyuran crabs ("Upstream Island Effect"). Also, copepods, gelatinous organisms, large-sized "other crustaceans" (e.g., euphausiids, amphipods, stomatopod larvae, mysids, etc.), teleost eggs, and stenopodids caused abundance peaks in the size spectra upstream. Our study highlights the need for careful management and conservation of parental spawning stocks of fishes and macroinvertebrates surrounding tropical oceanic islands.

The Eastern Boundary Upwelling System off northwest Africa is among the most productive regions of the ocean. In 2019, two merchant ships equipped with an underway CO2 system sampled the region following exactly the same track from 10 degrees N to 36 degrees N. We determine the sources and sinks of CO2 and the seasonal cycle along the track. A weak permanent upwelling (WPU), a permanent upwelling (PU) and an open ocean regions are identified. The WPU (26 degrees N to 33 degrees N) is a source of CO2 in summer and autumn, and a sink of CO2 in winter and spring. Ther-modynamic warming and cooling processes mainly drive the CO2 variations in this region. The PU (20 degrees N to 26 degrees N) is a sink of CO2 in spring and a source of CO2 in other seasons. This region is the most productive and exhibits the largest variability of the CO2 flux. The supply of CO2 from subsurface waters dominate over the carbon uptake by biology, which leads to a strong outgassing, especially in winter and autumn. A sink of CO2 occurs in spring only in the PU. Near Cape Blanc (20 degrees N) in July 2019, a source of CO2 is observed around 20 degrees N within +/- 1 degrees of latitude and becomes a sink of CO2 a few days later when the ship samples back the same area. South of 18 degrees N, out of the influence of the coastal upwelling, the region is a sink of CO2 in winter only and the region is mainly controlled by physical processes. Using voyages from 2010 to 2022, seawater fCO2 significantly increases at a rate ranging from 1.82 mu atm yr -1 to 2.10 mu atm yr -1 close to the atmospheric increase. This is associated with a pH decrease between 0.0016 and 0.0022 yr -1. Nevertheless, there is no clear trend of the CO2 flux in any region.

Microorganisms are key to balancing marine ecosystems and have complex interactions at the ocean–atmosphere interface, affecting global climate and human health. This research investigated the diversity of cultivable bacteria and fungi in marine bioaerosols in the North Tropical Atlantic Ocean. Using the technique of spontaneous sedimentation in selective culture media, samples were collected during oceanographic expeditions. After isolation and purification, microbial strains were identified by phenotypic and genetic analyses. Fungi isolated included Acrophialophora, Aspergillus, Chrysosporium, Cladosporium, Fonsecaea, Mucor, Rhodotorula, Schizophyllum, Stemphylium, Candida, Curvularia, Cystobasidium, Exophiala, Neotestudina, Penicillium, Pestalotiopsis, and Preussia. The bacterial isolates belonged to the Bacillota, Pseudomonadota, Enterobacteriaceae family, Bacillus genus, and Serratia liquefaciens groups. About 40% of bacteria and 42% of fungi were identified as potential human pathogens, suggesting a relationship between human actions and the microbiota present in bioaerosols on the high seas. Sea surface temperature (SST) and wind speed influenced microorganisms. More studies and analyses in different scenarios should be conducted considering environmental and climate variables in order to deepen knowledge and generate information on the subject, so that standards can be established, and quality parameters determined.

In this work, we aim to evaluate the feasibility and operational limitations of using Sentinel-1 synthetic aperture radar (SAR) data to monitor water levels in the Poço da Cruz reservoir from September 2016–September 2020, in the semi-arid region of northeast Brazil. To segment water/non-water features, SAR backscattering thresholding was carried out via the graphical interpretation of backscatter coefficient histograms. In addition, surrounding environmental effects on SAR polarization thresholds were investigated by applying wavelet analysis, and the Landsat-8 and Sentinel-2 normalized difference water index (NDWI) and modified normalized difference water index (MNDWI) were used to compare and discuss the SAR results. The assessment of the observed and estimated water levels showed that (i) SAR accuracy was equivalent to that of NDWI/Landsat-8; (ii) optical image accuracy outperformed SAR image accuracy in inlet branches, where the complexity of water features is higher; and (iii) VV polarization outperformed VH polarization. The results confirm that SAR images can be suitable for operational reservoir monitoring, offering a similar accuracy to that of multispectral indices. SAR threshold variations were strongly correlated to the normalized difference vegetation index (NDVI), the soil moisture variations in the reservoir depletion zone, and the prior precipitation quantities, which can be used as a proxy to predict cross-polarization (VH) and co-polarization (VV) thresholds. Our findings may improve the accuracy of the algorithms designed to automate the extraction of water levels using SAR data, either in isolation or combined with multispectral images.

Exploring the effects of meteo-oceanographic (MO) events on ships' maneuverability and safety has great potential, since most maritime accidents occur in confined waters, where the speed of ships is low, and the forces of wind and current on ships have particular importance. Therefore, we put forward a methodology that will be used to qualify and classify the risks caused by MO factors to how ships maneuver, dock or undock in a port. The objective is to generate important information for managing risk. The methodology is validated and illustrated step-by-step by applying it in Suape, one of the most important ports in Brazil, where the docking of larger tankers (e.g., Suezmax) was not allowed until recently when dredging was done to fit the specifications of such ships, thereby expanding the port's operations. MO data on Suape were collected and recorded from September 2016 to November 2017 and used for the application. Based on expert opinion and discussion with a Suape pilot, 36 accidental scenarios (ASs) were identified and categorized using preliminary hazard analysis. From these, the seven most severe ASs were selected so as to assess in more detail the frequency and consequences of accidents on human health, the environment, and property, for which the MO statistics for the likelihood of an accident and/or dispersal of an oil spill were used. The results show that the methodology is viable to assess risks caused by bad weather and to communicate these to pilots and competent authorities, thus improving the safety of operations.

Northeast Brazil (NEB) is a susceptible region to the occurrence of extreme rainfall events. Sea surface temperature (SST) is used as an indicator for predicting intense weather events in this region. The westernmost Tropical South Atlantic region, also called Southern Atlantic Warm Pool (SAWP), is characterized by a source of heat and humidity which creates atmospheric instability for the NEB. In June 2010 the eastern coast of NEB (ENEB)was influenced by heavy rainfall, causing flash floods and landslides. On the other hand, 2012 marked the beginning of a period of droughts that affected the whole NEB area. The SAWP temperature in turn recorded anomalous values ​​of + 1ºC (-0.5ºC) in 2010 (2012), respectively, although in June 2012 intense rainfall was recorded in ENEB, even with intense negative SST anomalies. With the Coupled-Ocean-Atmosphere-Wave and Sediment Transport (COAWST) model, simulations were made to characterize 2010 and 2012 atmospheric conditions, modifying the SST input data in both situations. The goal of this work is to assess the meteorological systems that occurred in 2010 and 2012 using observational, reanalysis, and simulated data, as well as to identify changes in atmospheric instability patterns, which are under influences of different SST conditions. We performed four cases, including: a) SST measured in 2010 with 2010 atmospheric conditions; b) SST measured in 2012 with weather conditions of 2010; c) SST measured in 2012 with 2012 weather conditions; d) measured in2010 with atmospheric conditions from 2012. The results showed that SAWP temperature significantly influenced the instability of meteorological systems. The impacts were more significant in the lower layer of the atmosphere, especially in the variables that lead to low-level instabilities. Also, it was observed that warmer atmospheric conditions favor the ocean environment to remain warmer, maintaining the unstable conditions over SAWP.

Oceanographic features influence the early stages of fish to a high degree. We investigated the influence of continental shelf-slope gradient on the ichthyoplankton composition and distribution off Northeastern Brazil. Two oceanographic campaigns were performed during July-August 2010 and 2012. The samplings were performed along three transects composed by three stations, covering the continental shelf and slope areas. Abiotic data were obtained by an ADCP and a CTD. The ichthyoplankton was sampled through diurnal and nocturnal hauls using a 500-µm bongo net from 200 m to the surface. A total of 1634 larvae and 4023 eggs, representing 91 genera and 76 species, were collected. Higher concentrations of fish eggs were found on the continental shelf, probably because of the North Brazil Undercurrent flux. Higher concentrations of larvae were found at night and could be associated with net avoidance or natural variation. Neritic, oceanic and transition groups of species association were determined. Larvae of neritic, demersal and pelagic fishes prevailed on the continental shelf, while larvae of oceanic, mesopelagic and bathypelagic fishes on the continental slope. Melanostomiidae, Scorpaena sp., Lestidium atlanticum, Lampadena sp. and Diaphus sp. were identified as indicators of the continental slope.

Oceanic tropical waters are characteristically oligotrophic. However, current-topography interaction around oceanic islands promotes bio-physical processes, which may enrich surface waters. The ichthyoneuston assemblage at three areas around oceanic islands in the tropical Atlantic was investigated. The aim was to evaluate if the ichthyoneuston was influenced by physical oceanographic processes, such as possible mechanisms of plankton retention promoted by the presence of the islands. Samplings were performed by 20 min long diurnal and nocturnal 500-mu m plankton net hauls using a David-Hempel Catamaran at two transections in each area (Saint Peter and Saint Paul's archipelago, Fernando de Noronha archipelago, and Rocas Atoll). The transections were composed by three stations and were located at opposite sides of the archipelagos (windward and leeward sides of the archipelago). A total of 131 larvae and 3027 eggs, belonging to 16 families and 28 species were collected. Higher densities of eggs were found at the leeward side, which indicates the occurrence of a retention mechanism or spawning at this side. Higher densities of larvae were found at Fernando de Noronha, especially during the nocturnal period. Only one species, Ceratoscopelus warmingii, co-occurred at the three islands. Fernando de Noronha was highlighted as the area with the higher density, abundance and species richness. The waters around this island were positively correlated with chlorophyll -a, which indicates a higher availability of food items and stimulates the selection of this area as a favorable spot for reproduction and early nursery zone. This work highlighted the importance of the relation between abiotic factors and the distribution of fish eggs and larvae inhabiting the neustonic layer around South Atlantic oceanic islands, showing that favorable conditions, e.g. higher phytoplanktonic biomass, may be of fundamental importance to the spawning by adult individuals.

In order to investigate intra- and inter-annual variability of North Brazil Current (NBC) rings, angular momentum eddy detection and tracking algorithm (AMEDA) was used for identification of their occurrence, trajectories, and parameters. Based on 24 years (1993-2016) of geopotential height and geostrophic current fields reanalysis data from ARMOR 3D (1/4 degrees), we identified an average rate of five NBC rings shed by year. The rings present an average lifetime of 15.3 (+/- 5.4) weeks, average speed-based radius (R-max) of 139.8 (+/- 23.6) km, and mean sea surface height anomaly (SSHa) of 9.4 (+/- 4.0) cm. The mean observed maximum azimuthal velocity (V-max) was 0.27 (+/- 0.08) m/s, while the averaged Rossby number (Ro) value was 0.08 (+/- 0.04) and averaged kinetic energy (KE) was of 255.3 (+/- 154.8) cm(2)/s(2). NBC rings have larger dimensions, rotate faster, live less, and transfer more energy in boreal winter months. In contrast, those shed during boreal summer and early fall last longer, have smaller diameters and carry less energy. Besides, the analysis of ring merging pointed that the interaction between NBC rings generated a significantly increase in ring energy (52%), and velocity (22%). Finally, we observed the vertical anomalies temperature and salinity profiles, which indicated a thermocline deepening and sinking of coastal and tropical waters due to NBC rings downwelling. This study emphasizes the robustness and efficiency of AMEDA for studying rings in the ocean and further theorizes possible impacts of NBC ring on ocean physical and biogeochemical features in the Western Tropical North Atlantic.

The surface fugacity of CO2 (fCO2) has been measured hourly at a mooring at 8°N, 38°W, using a spectrophotometric CO2 sensor, from June to October 2013. In September 2013, the fCO2 and the sea surface salinity (SSS) decrease significantly. The high precipitation due to the presence of the Intertropical Convergence Zone (ITCZ) and the propagation of low salinity waters from the Amazon River plume explain the decrease of SSS. Indeed, in fall, the retroflection of the North Brazil Current (NBC) feeds the North Equatorial Counter Current (NECC) and transports Amazon waters to the eastern part of the tropical Atlantic. Simulations from a three dimensional physical and biogeochemical model and observations at the mooring show that the Amazon plume reached the mooring in September 2013. The decrease of fCO2 is associated with a moderate peak of chlorophyll. Over the period of the CO2 observations, the site is a source of CO2 to the atmosphere of 0.65 ± 0.47 mmol m−2 day−1. Although the wind speed is at its lowest intensity in September 2013, the flux over the whole period would be about 14% higher without this month. Every month of September from 2006 to 2017, the model simulates a decrease of dissolved inorganic carbon corresponding to the SSS minimum.

The surface fugacity of CO2 (fCO(2)) has been measured hourly at a mooring at 8 degrees N, 38 degrees W, using a spectrophotometric CO2 sensor, from June to October 2013. In September 2013, the fCO(2) and the sea surface salinity (SSS) decrease significantly. The high precipitation due to the presence of the Intertropical Convergence Zone (ITCZ) and the propagation of low salinity waters from the Amazon River plume explain the decrease of SSS. Indeed, in fall, the retroflection of the North Brazil Current (NBC) feeds the North Equatorial Counter Current (NECC) and transports Amazon waters to the eastern part of the tropical Atlantic. Simulations from a three dimensional physical and biogeochemical model and observations at the mooring show that the Amazon plume reached the mooring in September 2013. The decrease of fCO(2) is associated with a moderate peak of chlorophyll. Over the period of the CO2 observations, the site is a source of CO2 to the atmosphere of 0.65 +/- 0.47 mmol m(-2) day(-1). Although the wind speed is at its lowest intensity in September 2013, the flux over the whole period would be about 14% higher without this month. Every month of September from 2006 to 2017, the model simulates a decrease of dissolved inorganic carbon corresponding to the SSS minimum.

Following the anomalous warming event occurring in the tropical North Atlantic in 2010, higher than usual surface fugacity of CO2 (fCO(2)) was observed. To evaluate the spatial extent of these anomalies and their drivers, and to quantify the sea-air CO2 flux at basin scale, the Mercator-Ocean model is used from 2006 to 2014 within the region 0-30 degrees N, 70-15 degrees W. Model outputs are generally in accordance with underway sea surface temperature, sea surface salinity, and surface fCO(2) recorded by two merchant ships. The anomalous warming of 2010 is well reproduced by the model and is the main driver of fCO(2) anomalies. The first coupled Empirical Orthogonal Function mode, between sea surface temperature and fCO(2), captures more than 70% of the total variance and is characterized by a basin-scale warming associated to positive fCO(2) anomalies. The corresponding principal components are correlated to the Tropical North Atlantic Index and identify 2010 as the year with the highest positive anomaly over 2006-2014. Exceptions to this general pattern are located near the African coast, where the weakening of the coastal upwelling causes negative inorganic carbon anomalies, and close to the Amazon River plume, where fCO(2) anomalies are primarily associated with sea surface salinity anomalies. Although the fCO(2) anomalies of 2010 appear mostly in spring, they affect the annual CO2 budget and lead to an increased CO2 outgassing twice as large (46.2 Tg C per year) as the mean annual flux over the 2006-2014 period (23.3 Tg C per year).

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.

At the mouth of the Amazon River, a widespread carbonate ecosystem exists below the river plume, generating a hard-bottom reef (∼9500 km2) that includes mainly large sponges but also rhodolith beds. The mesozooplankton associated with the pelagic realm over the reef formation was characterized, considering the estuarine plume and oceanic influence. Vertical hauls were carried out using a standard plankton net with 200 μm mesh size during September 2014. An indicator index was applied to express species importance as ecological indicators in community. Information on functional traits was gathered for the most abundant copepod species. Overall, 179 zooplankton taxa were recorded. Copepods were the richest (92 species), most diverse and most abundant group, whereas meroplankton were rare and less abundant. Species diversity (>3.0 bits.ind-1) and evenness (>0.6) were high, indicating a complex community. Small holoplanktonic species dominated the zooplankton, and the total density varied from 107.98 ind. m-3 over the reef area to 2,609.24 ind. m-3 in the estuarine plume, with a significant difference between coastal and oceanic areas. The most abundant copepods were the coastal species ithona plumifera and Clausocalanus furcatus and early stages copepodites of Paracalanidae. The holoplanktonic Oikopleura, an important producer of mucous houses, was very abundant on the reefs. The indicator species index revealed three groups: (1) indicative of coastal waters under the influence of the estuarine plume [Euterpina acutifrons, Parvocalanus crassirostris, Oikopleura (Vexillaria) dioica and Hydromedusae]; (2) characterized coastal and oceanic conditions (Clausocalanus); (3) characterized the reef system (O. plumifera). Two major copepods functional groups were identified and sorted according to their trophic strategy and coastal-oceanic distribution. The species that dominated the coastal area and the area over the rhodolith beds are indicators of the estuarine plume and are mixed with species of the North Brazil Current. These species practically disappear offshore, where occur oceanic species commonly found in other oligotrophic tropical areas. This ecosystem shows a mixture of estuarine, coastal and oceanic communities coexisting in the waters over the Amazon reefs, with no significant differences among these areas. However, the MDS clearly separated the communities along the salinity gradient in the plume.