Southeastern Brazilian Continental Shelf Research Articles

Chemotaxonomy-based mapping of phytoplankton communities in the subtropical Southwestern Atlantic Ocean, with emphasis on the marine cyanobacterium Trichodesmium

The composition and distribution of the phytoplankton community on the southweastern Brazilian continental shelf and continental slope were evaluated through chemotaxonomic analyses (HPLC-CHEMTAX). The samples were collected during five oceanographic cruises from 2012 to 2014 in spring and autumn. Fourteen surface blooms of Trichodesmium (slicks) were registered during the field surveys. The Trichodesmium biomass was estimated by both pigment analyses and microscope counts, with significant correlation found between the methods, except in some slicks. However, myxoxanthophyll, a Trichodesmium pigment biomarker generally used in CHEMTAX, was detectable only in seven samples from stations with Trichodesmium slicks, indicating that their use in pigment chemotaxonomic approaches should be taken with caution, because it could lead to errors in the estimation of Trichodesmium biomass. Four water masses were identified at the surface: Plata Plume Water (PPW), Subtropical Shelf Water (STSW), Shelf Water (SW) and Tropical Water (TW). The identified water masses seem to be the main driving factor influencing the composition, distribution and biomass of phytoplankton groups in the study region. The salty-warm oligotrophic TW, associated with the Brazil Current, was the dominant surface water mass in both autumn and spring. The surface waters in this work were generally associated with low values of both total chlorophyll a (TChl a) and nutrient concentration. In no slicks conditions, surface TChl a concentration was low ranging between 0.04 and 2.44 mg m−3 (mean 0.27 mg m−3) in almost all oceanographic stations. The highest biomass concentrations were recorded in stations under influence of both PPW and STSW. Overall, Prochlorococcus, haptophytes, Synechococcus, and Trichodesmium dominated the phytoplankton community and their contributions were above 70% to total Chl a in both spring and autumn. The other phytoplankton groups (prasinophytes, cryptophytes and dinoflagellates) represented a minor fraction, with values below 15% of the total biomass. A Canonical Correspondence Analysis showed that Prochlorococcus, haptophytes, Synechococcus and Trichodesmium were related with both TW and SW and were also positively associated with weaker water column stability, a deeper mixed layer, temperature and salinity. In turn, cryptophytes, dinoflagellates, prasynophytes and diatoms, mainly associated with STSW and PPW, were positively correlated with higher stability and nutrients (nitrogen and phosphorus), and negatively associated with both temperature and salinity. Our results showed that the pigment analysis (HPLC-CHEMTAX) allowed a detailed mapping of phytoplankton communities' distribution in the south and southeastern Brazilian continental shelf and shelf-break, and that the Trichodesmium biomass, as currently estimated by this approach, should be carefully revised.

Downscaling of the global HadGEM2-ES results to model the future and present-day ocean conditions of the southeastern Brazilian continental shelf

Changes in the regional hydrodynamics of the region of the South Atlantic near the east coast of Brazil were evaluated from the beginning to the end of the century. The analysis was based on the anomalies from two downscaling experiments using the HadGEM2-ES outputs for the historical and RCP4.5 runs from the Coupled Model Inter-comparison Project phase 5. The anomalies between the experiments were collected in a system of two nested grids, with $$1/3^\circ$$ and $$1/12^\circ$$ horizontal resolutions. A northward displacement of the Brazil Current (BC), a southward BC transport intensification, and a 1.44 $$^\circ$$ C increase of the mean values of sea surface temperatures were observed. The sea level rise (SLR) was projected up until 2100 across the study area, and the spatial variations were shown to have an average on SLR rate of 7.30 mm year $$^{-1}$$ for those regions close to the coast. These results highlight the importance of studying climate change and applying methods to enable the evaluation of its effects on coastal zones, especially for regions with few existing studies, such as the Brazilian continental shelf area.

Trichodesmium latitudinal distribution on the shelf break in the southwestern Atlantic Ocean during spring and autumn

AbstractWe report Trichodesmium slicks in the South Atlantic associated with fronts produced by the southward displacement of the Brazil Current. For the first time, a relatively high spatial sampling grid of trichomes density is shown over an undersampled region with regard to Trichodesmium. In this study, the distributions of Trichodesmium along the southeastern Brazilian continental shelf break were characterized during four oceanographic cruises and related to seawater temperature, upper layer nutrient concentrations and wind dynamics. Meridional changes in the densities of trichomes followed an expected trend with higher (lower) values found in warmer (colder) and more saline (less saline) water masses. Between 23° and 28°S, large accumulations of trichomes were associated with high temperature, increased phosphate concentrations (>0.08 μM), nitrogen below 2.4 μM, and low wind speeds (<11 m s−1). Maximum densities of 212.6 × 105 trichomes L−1, which are considerably larger than those reported in other studies in subtropical oceans, occurred at stations showing weak water column stability and higher phosphate levels over the upper 25 m. We suggest that shelf break dynamics, which drive and modulate the intensity of the shelf break upwelling, as well as wind divergence at spatial scales of approximately 600 km2, associated with mesoscale activities, may favor Trichodesmium growth and accumulation. On the other hand, Trichodesmium densities were low at latitudes between 28° and 33°S, likely due to either or both the lowest sea surface temperatures and/or out‐competition by the faster‐growing nondiazotrophs.

The influence of surface low-salinity waters and cold subsurface water masses on picoplankton and ultraplankton distribution in the continental shelf off Rio de Janeiro, SE Brazil

The smallest phytoplankton groups named picoplankton and ultraplankton can be responsible for about 50–80% of the primary production rates in oligotrophic waters, due to their high surface/volume ratios that enables them for competitive growth rates relative to bigger cells under low light and low nutrient availability. The role of picoplankton and ultraplankton in coastal dynamic regions is less clear. This work relates the spatial distribution of autotrophic and heterotrophic components of these communities to the different properties of the water masses in the Southeastern Brazilian Continental Shelf, generally considered oligotrophic. Picoplankton and ultraplankton communities were related to nutrients present in the subsurface South Atlantic Central Water and waters with salinities below 35.5 originated from different estuarine systems. The enhance of autotrophs were also associated with a near shore feature related to topographic effects of São Sebastião Island to the local currents, first reported in this article. A core of higher chlorophyll a concentration, associated with the northeastward current flow at approximately 21m depth below the surface, was identified as a dome-like shape. This core dissipated in the subsequent days suggesting that the flow towards NE was no longer a permanent feature two days after its observation. Locally enhancement of the contribution of picoplanktonic and ultraplanktonic autotrophs was observed in the surface and at the deep chlorophyll maximum depth associated with the chlorophyll core. Heterotrophs were more abundant inside and at the mouth of Guanabara Bay as well as inside Sepetiba Bay where light levels were low.

Inventory of the marine soft bottom macrofauna of São Sebastião Channel, southeastern Brazilian continental shelf

Analysis of macrofauna from 91 quantitative soft-bottom samples (from five surveys) obtained in the Sao Sebastiao Channel at depths ranging from 2 to 45 m yielded 431 species from a total of 38,630 individuals. The present contribution gives a list of the species found in the area and their depth distribution and sedimentary preferences (granulometric characteristics of the sites where they occurred). This is the first complete inventory of the subtidal invertebrate soft-bottom fauna of the Sao Sebastiao Channel, a peculiar marine area under crescent human impact.

A new species and first record of the genus Shoemakerella Pirlot, 1936 (Crustacea: Amphipoda: Lysianassidae) from Brazil.

A new species of the genus Shoemakerella Pirlot, 1936 is described for the Southeastern Brazilian continental shelf. The new species is easily recognized from the others in the genus mainly by the shape of the gnathopod 2. This is the first species of Shoemakerella from Brazilian waters.

Distribution and abundance of Pleuronectiformes larvae off Southeastern Brazil

The objective of this study was the description of the composition, abundance and density in horizontal and vertical distribution of Pleuronectiformes larvae on the southeastern Brazilian continental shelf. The samples were collected with bongo nets and a Multi Plankton Sampler (MPS), both in summer and winter 2002. A total of 352 flatfishes larvae were collected in summer and 343 in winter, representing three families and a total of 13 taxa: Paralichthyidae (Citharichthys cornutus, C. spilopterus, Citharichthys sp., Cyclopsetta chittendeni, Syacium spp., Etropus spp. and Paralichthys spp.), Bothidae (Bothus ocellatus and Monolene antillarum) and Cynoglossidae (Symphurus trewavasae, S. jenynsi, S. plagusia and S. ginsburgi). The most abundant taxa were Etropus spp., Syacium spp. and Bothus ocellatus. Etropus spp. occurred mainly as far out as the 200 m isobath and Syacium spp. from 100 m. B. ocellatus was present mainly in the oceanic zone between Ubatuba and Rio de Janeiro as from the 200 m isobath. The greatest average densities of these species occurred in the strata from 0 to 20 m depth in summer and between 20 and 40 m in winter.

Deep-water rhodolith bed from central Brazilian continental shelf, Campos Basin: coralline algal and faunal taxonomic composition

Rhodolith beds are distributed from the north-eastern to the southeastern Brazilian continental shelf, constituting the largest extension of coralline algal de-posits in the world. Little is known about the deep rho-dolith beds within the Campos Basin: the largest oil pro-duction area in the country and a priority area for marine life conservation. This study illustrates a deep rhodolith bed covering about 15km2 of a 40km2-area in the Peregrino oil field sampled at 100-106m water depth. Coralline algae are the dominant components on the living rhodolith surfaces associated with subordinate bryozoans, cnidarids, brachiopods and porifers. In some inner parts of the coralline algal nodules, encrusting acervulinid fora-minifera are the main nodule contributors. Through accel-erator mass spectrometric analysis, radiocarbon age esti-mates show that the range in ages between the living outer rhodolith parts and within 3mm from it the rhodoliths is ca. 4,700 years. This suggests that a proportion of fossil rhodoliths had been recolonized after periods of burial and/or erosion. The present-day Peregrino rhodolith bed played a fundamental ecological role in the Brazilian con-tinental shelf’s benthic habitats for thousands of years.

Mercury deposition during the previous century in an upwelling region; Cabo Frio, Brazil

To investigate the upwelling influence on Hg biogeochemical cycles and the sedimentological changes during the previous ∼150years, four sediment box-cores were sampled along an inshore offshore transect on the Southeastern Brazilian continental shelf. Mercury values were found to be relatively low, with means ranging between 8.08 and 30.4ngg−1. Mercury fluxes along the sediment cores are directly related to the well documented historical regional activity and global atmospheric deposition. The narrow relationship between mercury and organic carbon suggest that upwelling phenomenon and primary production may play an important role on Hg input and distribution along continental shelf depositional settings.

On the accumulation of organic matter on the southeastern Brazilian continental shelf: a case study based on a sediment core from the shelf off Rio de Janeiro

Sterol and fatty acid biomarkers and isotopic composition (δ13C and δ15N) of bulk organic matter (OM) were quantified in a sediment core to characterize the accumulation of autochthonous OM in an area on the continental shelf adjacent to Rio de Janeiro State. In the sediment surface (0-1 cm) the concentration of total sterols and fatty acids was at least one order of magnitude higher than that measured deeper down in the core and was dominated by labile and planktonic-derived biomarker compounds. These results suggest, as is confirmed by multivariate statistical analysis, the occurrence of an event of enhanced primary production in the water column and efficient export of particles to the bottom. Similar conditions have been observed at Cabo Frio, located 150 km to the north of our study site, during an upwelling event, suggesting that such events may exert a regional influence on primary production on the south-eastern Brazilian continental shelf. Beyond the signatures from this event, the presence of biomarker compounds from vascular plants suggests the additional influence of an outflow from Guanabara Bay at the study site. These results point to the need for further investigation of the relative influence of physical forcings and continental inputs on the biogeochemical processes on the section of the continental shelf considered in the present study.

A new species of Pseudharpinia (Amphipoda: Haustorioidea: Phoxocephalidae) from Southeastern Brazilian continental shelf

A new species of the amphipod family Phoxocephalidae Sars, 1895, Pseudharpinia tupinamba sp. nov., is described from southeastern Brazilian continental shelf. The new species is closely related to the type-species of the genus, P. dentata Schellenberg, 1931 described from Magellan Province, and was misidentified as the latter species by some authors in the past. Pseudharpinia tupinamba sp. nov. differs from P. dentata by the number of articles in the accessory flagellum of antenna 1, ratio of length and width of the propodus of pereopod 6, size of the posteroventral lobe of the basis of pereopod 7, presence of slender setae in posterior margin of epimeral plate 3, presence of a corona of cuticular spines in dorsodistal margin of peduncle of uropod 2, ratio of length of the inner ramus and the first article of outer ramus of uropod 3, ratio of length and width of the telson, and presence of slender setae on the lateral margins of telson. The new described species is the unique of this genus known from the Brazilian continental shelf.

New and little-known cheilostomatous Bryozoa from the south and southeastern Brazilian continental shelf and slope

New and little-known cheilostomatous Bryozoa from the south and southeastern Brazilian continental shelf and slope

New and little-known cheilostomatous Bryozoa from the south and southeastern Brazilian continental shelf and slope

The present paper reports on 22 species collected by the Brazilian Program of Living Resources in the Exclusive Economic Zone (REVIZEE). A new genus and species of Cribrilinidae, Corbuliporina crepida n. gen. et sp., is described, along with seventeen other new species: Chaperia brasiliensis n. sp., Amastigia aviculifera n. sp., Isosecuriflustra pinniformis n. sp., Cellaria subtropicalis n. sp., Melicerita brasiliensis n. sp., Arachnopusia haywardi n. sp., Smittina migottoi n. sp., Hippomenella amaralae n. sp., Rogicka joannae n. sp., Malakosaria atlantica n. sp., Turbicellepora winstonae n. sp., Rhynchozoon coalitum n. sp., Stephanollona angusta n. sp., Stephanollona arborescens n. sp., Aulopocella americana n. sp., Conescharellina cookae n. sp. and Conescharellina bocki n. sp. Chorizopora brongniartii (Audouin, 1826) is recorded for the first time in Brazilian waters and a new combination for Rhynchozoon arborescens Canu & Bassler, 1928 is established. New illustrations and taxonomic remarks are included for two little-known species from Brazil, Rogicka scopae (Canu & Bassler, 1928) and Fenestrulina ampla Canu & Bassler, 1928. A compilation of species recorded from deeper waters of the Brazilian coast is included.

Marine sediments from southeastern Brazilian continental shelf: A 1200 year record of upwelling productivity

A sediment core from the Cabo Frio coastal shelf (−23.19S, −41.8W; 117m depth), was analyzed for TOC, C/N ratio, organic petrography and planktonic foraminiferal content to evaluate variations in local productivity caused by changes in upwelling intensity and its relation to regional and global climatic variations during the last millennium. The Cabo Frio core recorded the last 1200years of sedimentation, with rates varying from 0.11 to 0.32mmyr−1. Foraminiferal and organic geochemical analyses indicate the occurrence of three distinct periods of productivity. From 850AD until 1070AD, foraminifera fluxes consisting primarily of Turborotalita quinqueloba indicate stronger South Atlantic Central Water (SACW) transport onto the shelf, which induced high biological productivity that was also recorded by high TOC and marine palynomorphs content and a low C/N atomic ratio. This period coincided with a northward displacement of the atmospheric Intertropical Convergence Zone (ITCZ) and South Atlantic High (SAH) systems driven by positive temperature anomalies in the North Atlantic Ocean during the Medieval Climate Anomaly (MCA). From 1070 until 1500AD, low TOC flux and planktonic foraminifera fluxes and high C/N atomic ratios suggest a reduction in marine productivity, probably driven by reduced transport of SACW associated with the southward displacement of the SAH and weakening of northeasterly winds. The period between 1500 and 1830AD, which corresponds to the Little Ice Age, is marked by increased fluxes of planktonic foraminifera, principally of Globigerina bulloides and Globigerinita glutinata. These species mark an increase in productivity linked to SACW upwelling, supported by the enhancement of northeasterly winds and southward displacement of the ITCZ and SAH.

Topographic registers of paleo-valleys on the southeastern Brazilian continental shelf

The evolution of paleo-incised-valleys in the São Paulo State region of the southeastern Brazilian continental shelf is presented in this study in relation to the post Last Glacial Maximum (LGM) sea-level rises based on the submarine topography modeled by a detailed Digital Elevation Model and evidences noted in high resolution seismic profiles. The hypothesis that has guided this study is that the set of paleo-valley characteristics (i.e. the fluvial parameters of modern coastal drainage systems, the topographical shape and dimensions of the valleys and of the subsurface channels) may indicate aspects of the relation between the influence of the fluvial and the eustatic variation regime in geomorphological-stratigraphic registers. Models described in the literature sustain the view that faster marine transgressions tend to increase erosion in estuaries, which may explain the lack of registers of paleo-drainage both in topography and the sub-surface in areas with wider shelves. On the other hand, on narrower shelves, with a higher slope angle, the transgression process can preserve, or even enhance, the incised valley registers during shoreface retreat. In the area studied, we observed that the dimensions and form of the continental shelf varies from the northern to the southern part of the area, affecting aspects of the geomorphological registers of the submerged incised valleys.

The Staircase Structure of the Southern Brazilian Continental Shelf

We show some evidences that the Southeastern Brazilian Continental Shelf (SBCS) has a devil′s staircase structure, with a sequence of scarps and terraces with widths that obey fractal formation rules. Since the formation of these features is linked with the sea‐level variations, we say that the sea level changes in an organized pulsating way. Although the proposed approach was applied in a particular region of the Earth, it is suitable to be applied in an integrated way to other shelves around the world, since the analyses favor the revelation of the global sea‐level variations.

Internal Tides in the Southwestern Atlantic off Brazil: Observations and Numerical Modeling

Abstract Data collected from moored instruments, deployed over the southeastern Brazilian continental shelf during the summer and winter months of 2001, show internal tide activity near the shelf break. To help to elucidate the observations, a fully three-dimensional nonlinear primitive equation model is applied to simulate the regional barotropic and baroclinic tides. Two semidiurnal (M2 and S2) and two diurnal (K1 and O1) tidal frequencies are considered. Tidal surface elevations are relatively small over the whole modeled area, reaching maximum values of about 0.40 m for M2 and 0.11 m for O1. Comparison between observed and computed tide elevation and Greenwich phase shows reasonable agreement. When the baroclinic response of the model is investigated, stratification is prescribed using summer and winter climatology data of potential density. In this case, the model response to summer and winter stratifications is very similar and internal tides are generated over the shelf break and slope, with vertical displacements up to 25 m, and seaward propagation. Modeled semidiurnal tidal ellipses agree well with winter and summer observations. Observed diurnal tidal ellipses in the middle of the continental shelf and close to the shelf break during summer show an intensification through the water column that could not be represented by the model. Estimates of the total baroclinic M2 offshore energy flux are about 3.5 and 0.5 MW considering winter and summer stratifications, respectively. Although these quantities are three orders of magnitude less than that estimated for regions known for intense internal tides, they refer to offshore fluxes computed for a very small section of the southeastern Brazilian shelf. This is the first published investigation into internal tides in the southwestern Atlantic Ocean off Brazil.

The contribution of microphytobenthos for scallop Euvola ziczac (Bivalvia: Pectinidae) feeding in a shallow area of the south-eastern Brazilian continental shelf

The general composition and abundance of microalgae in sediment, water column and stomach contents of scallops were studied at two Euvola ziczac beds on the south-eastern inner Brazilian continental shelf. These areas, which support an extensive demersal fishery, are hydrologically dominated by Tropical and Subantarctic Waters and exhibit a summer water intrusion of South Atlantic Central Water (SACW). The same genera of benthic diatoms, mainly <30 μmm, were found on sediment and scallop stomach samples. Despite the seasonal variation of hydrographic conditions, the composition and abundance of main benthic diatoms from sediment and stomachs did not change throughout the year. On the other hand, phytoplankton from the water samples collected above the seabed (mainly pelagic diatoms >30 μm and dinoflagellates) was composed of distinct taxa and presented a high seasonal variation in abundance. The prevalence of microphytobenthos in the scallop diet suggests the importance of this community to the sustainability of this valuable demersal fishery resource.

Taxonomy of Rhabderemia Topsent, 1890 collected from the south-eastern Brazilian continental shelf and slope by Programme REVIZEE (Rhabderemiidae, Poecilosclerida, Demospongiae), with the description of two new species

Three new records (two new species) of Rhabderemia (Rhabderemiidae, Poecilosclerida, Demospongiae) are described from the South-eastern Brazilian coast, collected during Programme REVIZEE (1996–2002)-South Score, off the São Paulo and Santa Catarina State coasts. Rhabderemia uruguaiensis can be recognized by its rhabdostyles which are frequently smaller than 150µm as well as frequently larger than 300µm, and microscleres which are a single category of microstyles smaller than 100µm and small spirosigmata always smaller than 15µm. Rhabderemia besnardi sp. nov. is characterized by possession of two categories of spined microstyles, one category of rugose rhabdostyles and small spirosigmata. Rhabderemia itajai sp. nov. differs from other congeners, because of its rhabdostyles which are never smaller than 300µm, next to microstyles always smaller than 70µm and small spirosigmata always smaller than 10µm.

Osmundea lata (M. Howe & W.R. Taylor) comb. nov. (Ceramiales, Rhodophyta) from the Brazilian south-eastern continental shelf

Specimens of Laurencia lata were dredged from the south-eastern Brazilian continental shelf near Cabo Frio (off the state of Rio de Janeiro) from a depth of 60 m, growing as epiphytes on the rhizoids of Laminaria abyssalis. Detailed examination of the vegetative and reproductive morphology of these specimens revealed anatomical characteristics belonging to the recently resurrected genus Osmundea. Such features include two periaxial cells per vegetative axial segment, spermatangial branches arising directly from apical and epidermal cells in the apical pit of branchlets (filament type), and tetrasporangia cut off from random epidermal cells. On the basis of these features, Osmundea lata (M. Howe & W.R. Taylor) Yoneshigue-Valentin, M.T. Fujii & Gurgel is proposed as a new combination for Laurencia lata. We present detailed observations of the vegetative and reproductive morphology of O. lata, and compare it with related species; its geographical distribution is also discussed.