The Amazon generates the world's largest offshore river plume, which covers extensive areas of the tropical Atlantic. The data and samples in this study were obtained during the oceanographic cruise Camadas Finas III in October 2012 along the Amazon River-Ocean Continuum (AROC). The cruise occurred during boreal autumn, when the river plume reaches its maximum eastward extent. In this study, we examine the links between physics, biogeochemistry and plankton community structure along the AROC. Hydrographic results showed very different conditions, ranging from shallow well-mixed coastal waters to offshore areas, where low salinity Amazonian waters mix with open ocean waters. Nutrients, mainly NO3− and SiO2−, were highly depleted in coastal regions, and the magnitude of primary production was greater than that of respiration (negative apparent oxygen utilization). In terms of phytoplankton groups, diatoms dominated the region from the river mouth to the edge of the area affected by the North Brazil Current (NBC) retroflection (with chlorophyll a concentrations ranging from 0.02 to 0.94 mg m−3). The North Equatorial Counter Current (NECC) region, east of retroflection, is fully oligotrophic and the most representative groups are Cyanobacteria and dinoflagellates. Additionally, in this region, blooms of cyanophyte species were associated with diatoms and Mesozooplankton (copepods). A total of 178 zooplankton taxa were observed in this area, with Copepoda being the most diverse and abundant group. Two different zooplankton communities were identified: a low-diversity, high-abundance coastal community and a high-diversity, low-abundance oceanic community offshore. The CO2 fugacity (fCO2sw), calculated from total alkalinity (1,450 < TA < 2,394 μmol kg−1) and dissolved inorganic carbon (1,303 < DIC < 2,062 μmol kg−1) measurements, confirms that the Amazon River plume is a sink of atmospheric CO2 in areas with salinities <35 psu, whereas, in regions with salinities >35 and higher-intensity winds, the CO2 flux is reversed. Lower fCO2sw values were observed in the NECC area. The ΔfCO2 in this region was less than 5 μatm (−0.3 mmol m−2 d−1), while the ΔfCO2 in the coastal region was approximately 50 μatm (+3.7 mmol m−2 d−1). During the cruise, heterotrophic and autotrophic processes were observed and are indicative of the influences of terrestrial material and biological activity, respectively.

This study was undertaken in the coastal zone of the state of Pernambuco adjacent to the Recife port area, which corresponds to the inner shelf. This research aimed to analyze the dynamics of chlorophyll-a and several other environmental variables. Sampling was undertaken bimonthly on the surface from September 11th to May 10th, thus including the rainy and dry periods, and during low tide in spring tide. The parameters analyzed were chlorophyll-a, salinity, temperature, transparency, dissolved oxygen, oxygen saturation rate, pH, suspended solids, dissolved inorganic nutrients. Phytoplankton biomass ranged from 13.48 to 145.09 mg m-3 in the estuarine area and on the inner shelf, the variation being from 0.24 to 19.29 mg m-3 in the dry season and from 0.78 to 5.20 mg m-3 in the rainy season. PCA showed a direct relationship of chlorophyll-a with ammonia, phosphate and transparency and an inverse relationship with suspended particulate matter and nitrate. Biomass did not vary significantly different as a result of seasonal or spatial dynamics. The estuary of the Capibaribe River is considered highly impacted, and as it forms the Recife port basin, it joins with two more strongly eutrophic water bodies, the Beberibe River and the Pina Basin, leading to an amplification of its influence on the adjacent shelf. In terms of the river plume's dispersion in the Port of Recife, the presence of a dike causes some disturbance in the direction of the current, limiting the plume to the area close to the coast and influences the oceanographic variables on the inner continental shelf.

Este trabalho teve o objetivo de caracterizar o estuário do rio Botafogo (Itamaracá-PE) a partir da análise da clorofila a e alguns parâmetros ambientais. Foram feitas coletas mensais, em três pontos de amostragem ao longo do estuário, no período de abril/07 a março/08, em diferentes estágios e em maré de sizígia. Foi utilizada a garrafa de Kitahara na camada superficial da água para a análise de biomassa, Secchi, salinidade, oxigênio dissolvido, DBO, nutrientes, material particulado em suspensão. A biomassa fitoplanctônica variou sazonalmente, com maiores concentrações no período chuvoso e em baixa-mar. Os valores em média estiveram abaixo de 20 mg.m-3 , e a fração menor que 20 µm foi a que mais contribuiu para o ecossistema. A ACP mostrou uma correlação direta da clorofila com os nutrientes e inversa com a salinidade e oxigênio dissolvido. O ambiente dessa forma mostrou uma qualidade ambiental ainda satisfatória, porém em processo moderado de eutrofização. Palavras chave: sazonalidade, biomassa fitoplanctônica, parâmetros hidrológicos, área costeira.

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The watershed of the Amazon River discharges about 120,000 m 3 •s −1 of freshwater into the adjacent platform and oceanic region. The aim of this work was to analyze the distribution of oceanographic parameters, chlorophyll a and primary productivity under the influence of the Amazon River plume, during the period of greatest extension of the Amazon plume. Collections were carried out in September 14 in 16 stations including continental platform and oceanic region. It was possible to observe superficial currents along the coast in the northwest direction, but with less intensity and currents with greater speeds towards the east due to the North Brazil Current retroflexion at this time of the year, transporting the plume to the central Atlantic Ocean. The spatial influence of the plume was observed in the salinity, which ranged from 28 to 36.75, although the high precipitation in the region may also have contributed as a source of freshwater. However, the sampled region showed strong negative linear correlation of silicate, chlorophyll a and primary productivity with salinity. The primary productivity values ranged from 0.04 to 18.81 mg C m −3 day −1 , whereas chlorophyll a concentrations ranged from 0.15 mg•m −3 to 1.83 mg•m −3 , decreasing their values as they move away from the coast. The Amazon River plume can reach and influence the oceanographic and biological parameters in a large area of this oligotrophic region. However, the results also suggest that the export of material from the adjacent coastal region is another determinant of the region's productivity.

The Suape coastal zone has suffered since the 1980s the effects of anthropogenic action due to the construction of the industrial complex of Suape. This work aimed to evaluate the environmental conditions and possible eutrophication processes of the area. Six campaigns were carried out, three in the dry season (November 2015, January and April 2016) and three in the rainy season (July 2015, July and August 2016). Water samples were collected at the surface during low tide and high tide, in neap tides. Salinity ranged from 19.75 to 37.20, the dissolved oxygen rate ranged from 61.75 to 125.90% and chlorophyll-a from 0.02 to 3.48 mg m−3. Water transparency, temperature, nitrate and silicate presented significant seasonal variation, the concentrations of nutrients being higher in the rainy season and the others in the dry season. Water transparency, salinity, dissolved oxygen saturation and chl-a <20 µm showed significant differences for tide, being higher at high tide, and at low tide for chl-a of <20 µm. The low content of dissolved inorganic nutrient salts and chl-a were indicative of an area still free of eutrophication. Anthropogenic changes in the environment have led to greater marine interference and consequently to a reduction of the productive capacity of the system.

The aim of the current study was to evaluate the productive capacity of the phytoplankton community and other environmental variables in the estuarine area of Suape; while considering the constant morphological, sedimentological and hydrological changes, the site has been facing due to the implementation and expansion of an industrial and port complex. The study comprised 6 campaigns: 3 in the dry season and 3 in the rainy season. Water samples were collected from the surface layer of the internal and external portions of the estuarine bay during low spring tides. The salinity ranged from 32.20 to 37.10, the water temperature ranged from 26.60˚C to 29.40˚C, and the oxygen saturation rate ranged from 58.5% to 114.5%. There was significant seasonal variation. The nitrite concentration was higher during the rainy season, whereas the ammonia concentration was higher during the dry season; the higher ammonia concentration helped increase chlorophyll-a levels and rates of primary productivity, which ranged from 0.02-2.45 mg•m −3 and from 0.34 to 4.32 mg•C•m −3 •h −1 , respectively. Chlorophyll-a < 20 μm was the fraction of biomass most commonly present in the estuarine ecosystem, accounting for 88.6% of the chlorophyll-a-containing biomass, and this reflected the low nutrient content in the water and indicated that the area was free from eutrophication processes. The decrease of rainfall during the sampling months and the anthropogenic changes in the environment led to reduced continental contributions, increased marine interference, nutrient dilution and loss of phytoplankton production capacity in Suape Bay, which severely damaged other trophic links in the ecosystem.

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