Outer Stations Research Articles

Contamination Assessment of Sediments and Bivalves in Estuaries of the Southern Iberian Peninsula

Human activities directly impact estuaries, where the biota is exposed to sediment contamination. A contamination assessment was carried out in several estuaries in the Southern Iberian Peninsula. Sediment samples were analyzed for the presence of metals/metalloids, and bioaccumulation tests were conducted with clams (Ruditapes philippinarum). Huelva Estuary had the highest contamination levels, while the inner bay of Cádiz and the outer stations of the estuaries from Guadiana, Guadalquivir, Palmones, and Guadarranque were the lesser contaminated. All sampling points (except Huelva) had low contamination levels of As and Cd, but they had high concentrations of Cu. The elements Pb, Cd, Zn, Cu, As, and Hg displayed correlations between the concentrations in sediments and the biota. High bioaccumulation of Zn, Cu, and As was observed in Huelva and Barbate. Important insights into the sediment contamination in Southern Iberian Peninsula estuaries suggest greater management and conservation efforts in these critical ecosystems.

Determination of Settling Velocity for Cohesive Sediments Using a Settling Column Experiment—Case Study: Ca Mau, Vietnam

The settling velocity (Ws) is a fundamental parameter in sediment dynamics, particularly in the coastal zones as estuarine and mangrove ecosystems, where various physical processes interact to influence sediment transport and deposition. Determining settling velocity is essential for understanding and predicting sediment transport, erosion–deposition processes in coastal environments. This study aims to determine the settling velocity and examines how sediment concentration affects settling velocity, using empirical models. The study applies these methods to compute the settling velocity of fine sediments in Ca Mau, Vietnam, which were collected in the Song Doc area (Western) in August 2014 and Rach Goc area (Eastern) in August 2015. The particle size analysis results indicate that the sediment samples from Western Ca Mau are coarser than those from Eastern Ca Mau, with sand ratios of 42.78% and 7.08% at the outer station, and 19.09% and 4.39% at the mangroves, respectively. The results also show that the average settling velocity of the sediment samples from Western Ca Mau is higher than that of the samples from Eastern Ca Mau. Specifically, the settling velocity in Western Ca Mau is 2.80 × 10−4 m s–1 at the outer station and 1.68 × 10−4 m s–1 at the mangroves. Meanwhile, in Eastern Ca Mau, the settling velocity of the sediment samples is 1.99 × 10−4 m s–1 at the outer station and 1.42 × 10−4 m s–1 at the mudflat-mangrove. Hence, it can be seen that the settling velocity of cohesive sediments corresponds well with the sediment’s particle size.

A Journey towards Self-discovery in Joseph Conrad’s The Heart of Darkness

The research paper sheds light on the self-discovery of Charles Marlow and considers it as a journey of initiation which extends itself to the new unending existence. There is no time and space in it, which remains vacant for advent of a new life. It examines the pursuit of Kurtz, the head of the inner station. This study objectifies both inner and outer stations for a new experiment. This is seen as a self-discovery of one’s inner spirit. These pictures, in the novella, adopt a method depicting both figurative and literal meanings. It is obviously a pursuit of self-discovery focused on the discovery of Africa and the impact of imperialism. It develops two stations are one the people and another their colonial rule. Basically, Marlow’s journey appears to be as if Joseph Conrad presents himself as a cloak of true journey. The paper portrays the physical journey in the Heart of Darkness in which the inner and outer realities are complementary to each another. The inner journey has a profound effect on unconscious thoughts and actions. It shows Marlow’s capability to differentiate between good and evil since he observes how progress implies the moral sense of judgment.

Assessing the spatial distribution of meiofaunal communities in Krossfjord, Svalbard Archipelago: Foraminifera diversity as a key component

The study furnishes an insight into the ecology of meiofauna through an elaborate examination of the living Foraminifera in the Krossfjorden system of the Svalbard Archipelago. Samples collected during the Summer Phase Indian Arctic Expeditions of 2017 and 2018 were analyzed to reveal novel insights into the distribution, abundance and species composition of living Foraminifera in this less studied fjord system. The investigation uncovered a rich and diverse meiofaunal community consisting of ten taxonomic groups, among which living Foraminifera emerged as a prominent component. The spatial patterns of Foraminifera distribution were examined, revealing their preferences for specific habitats and environmental conditions within the Krossfjorden system. The Shannon diversity index (H’) indicates good overall diversity of foraminifera in the Krossfjord region, with H’ ranging from 4.49 to 4.891 in 2017 and from 3.885 to 4.984 in 2018. The research discovered noteworthy inequalities in the distribution of Foraminifera species amid inner and outer stations, as inferred by PERMANOVA analysis (p<0.05). The foraminiferan species Nonionellina labradorica was the dominant species in outer, middle and inner zones in the fjord, while species Lobatula lobatula, Quinqueloculina seminulum, Hormosinella sp., and Procerolagena sp. played significant roles in driving the dissimilarity between outer, middle, and inner zones. Environmental factors accounted for a substantial 83.1% of the variations observed in foraminiferan species distribution across four CCA axes. The fluctuations in potential temperature, sand fraction, chlorophyll-a, C:N ratio, organic matter, and salinity have had a noteworthy effect on the distribution of species. These findings underscore the susceptibility of Foraminifera and the broader meiofaunal community to the impacts of environmental variations in this rapidly changing Arctic ecosystem. The outcomes of this research provide a crucial baseline for understanding the ecological dynamics of meiofaunal communities in the Krossfjorden system, contributing to predicting future changes in benthic habitats, including the potential repercussions for meiobenthic productivity.

Controlling the Molecular Shuttling of pH‐Responsive [2]Rotaxanes with Two Different Stations

AbstractA novel synthesis of degenerate [2]rotaxanes with two different amine stations is presented. Variable‐temperature 1H NMR and rotating‐frame nuclear Overhauser effect correlation spectroscopy experiments revealed that the addition of trifluoroacetic acid initiates molecular shuttling. The activation barrier for the motion remained constant even when the amine in the outer station was changed. Conversely, the addition of camphorsulfonic acid caused a rotational motion, which was demonstrated by synthesizing a new [2]rotaxane without an outer station and examining its molecular behavior in the presence of acid.

First record of microplastic in the environmental matrices of a Mediterranean marine cave (Bue Marino, Sardinia, Italy)

This study investigates for the first time the presence of microplastics in sediment, water, and benthic organisms (foraminifera) of a marine cave in the Gulf of Orosei (Sardinia, Italy). Microplastics were found in all water, and sediment samples with similar shapes, sizes, and compositions; identified items were mainly fragments and fibers constituted by PVC and polyethylene. Their provenance was supposed to be predominantly from the sea than from the seasonal freshwater supplies from the karst system. Foraminiferal assemblages were mainly constituted by calcareous hyaline taxa in the outer station, while in the inner ones, the agglutinated Eggerelloides advenus was dominant. FTIR analyses on agglutinated shells identified polyethylene. Microplastic items are collected by the foraminifers and sediment grains building the shell chambers. This is the first study providing evidence that marine caves may be collectors of microplastics and that, in these habitats, microplastics enter the biotic matrix at the protist's level.

The investigation on daytime conjugate hemispheric asymmetry along 100°E longitude using observations and model simulations: New insights

The hemispherical asymmetry of the low latitude region along 100°E ± 5°E is scrutinized for the year 2015 at magnetically conjugate points on seasonal and intra-seasonal time scales. Two conjugate Ionosonde station pairs are selected- one pair in the inner valley (from SEALION) and the other in the outer edges of the EIA region. The anomaly in the stations is estimated using the difference of low latitude NmF2 from the dip equatorial NmF2 in the same meridian. A monthly average scheme is used instead of a seasonal mean, as the month-to-month variations are found to provide intricate details. The anomaly at the conjugate stations is highly asymmetric even during the equinoctial months of March and October, whereas it is nearly symmetric during April. During June/July, the morning time hemispheric asymmetry (larger on the winter side) temporarily reduces in the midday period and then reverses sign (larger in summer) in the afternoon. The NmF2 observations suggest a close relation of hemispheric symmetry to the position of the subsolar point with respect to the dip equator and a shift/expansion of the trough region of the EIA towards the summer hemisphere. The inter-hemispheric comparison of the hmF2 suggests a strong modulating influence of meridional winds at both the inner and outer stations which depend strongly on the relative position of the subsolar point with respect to the field line geometry. Theoretical (SAMI3/SAMI2) and empirical model (IRI) simulations show a meridional movement of the EIA region with the subsolar point. The winter to summer hemisphere movement of the EIA trough and crest region is also reproduced in the GIM-TEC along 100°E for 2015. This shifting or tailoring of the trough and the crest region is attributed primarily to the meridional wind field, which varies with the shifting position of subsolar point relative to the field line geometry. The seasonal and intra-seasonal difference in the NmF2 hemispheric asymmetry is attributed to the misalignment of the two centers of power viz., the thermospheric/neutral processes and the electromagnetic forces, due to the geographic-geomagnetic offset in this longitude.

Sources and dynamics of suspended particulate matter in a large-river dominated marine system: Contributions from terrestrial sediments, biological particles, and flocculation

Elucidating the sources and dynamics of suspended particulate matter (SPM) in large-river dominated estuarine and coastal areas is challenging, because these areas are characterized not only by high turbidity with complex terrestrial sediment transportation and deposition processes, but also by high primary production and plankton biomass. In addition, flocculation occurring near the river mouth can also markedly modify SPM dynamics, and its roles in affecting SPM concentrations, variations, and inherent properties remain inadequately addressed. In July 2016, an exceptional flood event occurred in the Changjiang (Yangtze) River basin, and a cruise on the Changjiang River Estuary and the adjacent shelf area was conducted. During this cruise, we deployed instrument of OBS (optical backscatter sensor) and LISST (laser in situ scattering and transmissometry) at 87 stations to study the SPM variations in 32 size classes (2.5–500 μm) and to elucidate the contributions of terrestrial sediments, biological particles, and flocculation to SPM sources and dynamics. The entire water columns at inner stations and the seawaters in the lower-depth waters at outer stations were found to be generally dominated by terrestrial SPM with smaller sizes. The waters in the upper depths at the outer stations were generally occupied by autochthonous and biological SPM with larger sizes, which mostly showed maximum values in the subsurface layers and were closely associated with fluorescence. In two stations near the river mouth and estuarine salinity front, the SPM, also with larger sizes, probably experienced flocculation. The findings from this study may greatly improve our understanding of SPM sources and dynamics under the multiple influences of physical and biogeochemical processes in large-river dominated estuarine and coastal areas.

Coastal gradients of small microplastics and associated pollutants influenced by estuarine sources

Small microplastics (SMPs) in the gulf of Cadiz was sampled at 5 m depth by pumping it through the ship's pipe system and filtered through a 45 μm mesh size net. Our study reveals that higher densities have been found (130 mg·m−3) compared to other regions worldwide and these densities decreased from the coastline to the outer stations, showing a general coastal gradient influenced by estuarine outflows. SMPs with a size range between 45 and 193 μm were predominant and most of them composed by polyethylene and polypropylene. The metals associated with the MPs were mainly Na (21.1%), K (11.3%), Fe (8.5%), Ca (2.1%), Cr (1.8%), Zr (13.3%) and Hf (0.7%). The high proportion of Zr compared to Fe, which is different from what can be found in the environment, suggests that this metal is intrinsic to the materials used in catalytic processes during plastic production.

Ecological role and phylogenetic position of a new habitat-forming species (Canalipalpata, Sabellidae) from the Mediterranean mesophotic soft bottoms

This study presents a description of Bispira riccardi sp. nov., a new habitat-forming sabellid polychaete from the mesophotic NW Mediterranean Sea. Individuals, up to 20 cm long, show a peculiar morphology of radioles, thoracic uncini, companion chaetae and ventral shield of the collar. The phylogenetic position of this new taxon in the genus Bispira has been validated using nuclear (18S rRNA) and mitochondrial (COI) markers.Aggregations of B. riccardi sp. nov. were found by ROV on horizontal muddy bottoms between 56 and 85 m, in areas subjected to high trophic inputs. Patches are fragmented and dense (up to 943 individuals m−2) probably accounting for various hectares. A 5-days continuous monitoring, carried out using an autonomous lander, revealed that the contraction of the branchial crown was positively affected by temperature and current, rapidly responding to meteorological events. The filtering activity and high density of these fields suggest a considerable impact on the pelagic-benthic coupling and the amount of organic matter in the sediments. Indeed, meiofaunal abundance and diversity within the aggregations resulted significantly higher than in outer stations. These findings highlight the undisclosed potential of the deep Mediterranean Sea for sabellid diversity and their importance as habitat-forming species on mesophotic soft bottoms.

Eutrophication Driven by Aquaculture Fish Farms Controls Phytoplankton and Dinoflagellate Cyst Abundance in the Southern Coastal Waters of Korea

We examined the dynamics of dinoflagellate cyst and phytoplankton assemblages in eutrophic coastal waters of Korea, adjacent to fish and shellfish farms. Water temperature showed seasonality, whereas salinity and pH remained relatively consistent. Dissolved inorganic nutrient levels were higher in September and at the inner stations, where aquaculture fish farms are located than those in May and at the outer stations. Canonical correspondence analysis and artificial neural network analysis revealed multiple environmental factors that affect the distribution of phytoplankton and dinoflagellate cysts. Diatoms dominated in the phytoplankton assemblages, while the protoperidinioid group dominated in the dinoflagellate cyst assemblages. Cyst abundance was higher at the outer stations than at the inner stations due to transport by fast currents, and phytoplankton abundance was positively correlated with cyst abundance. An increase in diatom abundance led to an increase in heterotrophic/mixotrophic cyst abundance, indicating that excessive uneaten food and urinary waste from the fish farms caused eutrophication in the study region and fast growth of diatoms, thereby contributing to the growth of heterotrophic/mixotrophic dinoflagellates and consequently, high abundance of heterotrophic/mixotrophic dinoflagellate cysts.

Food source diversity, trophic plasticity, and omnivory enhance the stability of a shallow benthic food web from a high‐Arctic fjord exposed to freshwater inputs

AbstractUnder climate change, many Arctic coastal ecosystems receive increasing amounts of freshwater, with ecological consequences that remain poorly understood. In this study, we investigated how freshwater inputs may affect the small‐scale structure of benthic food webs in a low‐production high‐Arctic fjord (Young Sound, NE Greenland). We seasonally sampled benthic invertebrates from two stations receiving contrasting freshwater inputs: an inner station exposed to turbid and nutrient‐depleted freshwater flows and an outer station exposed to lower terrestrial influences. Benthic food web structure was described using a stable isotope approach (δ13C and δ15N), Bayesian models, and community‐wide metrics. The results revealed the spatially and temporally homogeneous structure of the benthic food web, characterized by high trophic diversity (i.e., a wide community isotopic niche). Such temporal stability and spatial homogeneity mirrors the high degree of trophic plasticity and omnivory of benthic consumers that allows the maintenance of several carbon pathways through the food web despite different food availability. Furthermore, potential large inputs of shelf organic matter together with local benthic primary production (i.e., macroalgae and presumably microphytobenthos) may considerably increase the stability of the benthic food web by providing alternative food sources to locally runoff‐impacted pelagic primary production. Future studies should assess beyond which threshold limit a larger increase in freshwater inputs might cancel out these stability factors and lead to marked changes in Arctic benthic ecosystems.

Evaluation of bioavailability of trace metals through bioindicators in a urbanized estuarine system in southeast Brazil

The mussel Perna perna is one of the most used bioindicators of coastal areas and the most economically exploited species in Brazil through mariculture. In the present study, P. perna was used to investigate metal pollution in the estuarine area of Vitória Bay. Four sampling sites were located along an estuarine branch of Vitória Bay and stations were sampled during three campaigns. Trace metals in the tissues of P. perna were evaluated as well as dissolved trace metals and other ancillary variables in the water column. Dissolved Cd, Pb, Cu, Ni, and Fe concentrations surpassed the tolerance limits stablished by legislation in all the sampling campaigns. P. perna exhibited concentrations in disagreement with the Brazilian legislation for Cr and As. A general trend of higher concentrations in outer stations was observed for most metals, what suggested the occurrence of flocculation process in the lower estuary, reducing the concentrations of dissolved elements and increasing their bioavailability for the biota through the particulate form. Cd was highlighted with elevated concentrations in dissolved fraction but not detected in P. perna, probably due to chlor-complex formation under influence of more saline waters. Al, Ba, Mn, Fe, Cu, Zn, Ni, Cr, Pb, and As were considered bioavailable, once they were accumulated in the mussels' tissues. Hazard index (HI) and target cancer risk (TCR) showed that the consumption of mussels from the study area offers health risk issues, being iron and arsenic the main contributors for the high indexes.

Recolonization patterns of benthic assemblages after relict sand dredging in the central Tyrrhenian sea

AbstractRecolonization patterns of benthic assemblages after relict sand dredging were investigated in an area offshore of Capo d’Anzio (central Tyrrhenian Sea). Surveys were performed before, during, and after dredging in 2007. Sampling stations were located within and outside the dredging site in water depths between 40 and 56 m. Defaunation due to sand extraction was the main impact observed in the inner stations and in stations located in proximity of the dredging site. At the inner stations, 9 months after dredging, a significant increase in species richness and diversity was observed: the sediment removal led to an increase of the sandy sediment fraction, favouring the settlement of sabulicolous species. A decrease in number of individuals and species was also observed in most of the outer stations, probably due to fine sediment redeposition. Recolonization of macrobenthic assemblages was essentially achieved at inner stations both in terms of abundance and species richness, while at outer stations it was still in progress. Results of this study, providing a picture of recovery times and processes in the Tyrrhenian Sea, could be used to develop predictions of the effects of future offshore sand dredging projects in comparable areas. Monitoring programs and research have a key role to provide a more detailed overview of biological recovery processes and times in different regions and with different dredging intensity.

Natural and anthropogenic impacts on long-term meiobenthic communities in two contrasting nearshore habitats

The present study investigated the spatiotemporal distributions of meiofauna and corresponding environmental variables in two different subtidal environments. The two habitats represent unique geographical localities; (1) Jinhae Bay for semi-enclosed industrial bay (under anthropogenic pressure) and (2) Samcheok coast for open sea area (rather in natural condition) in Korea. Biotic and abiotic data were seasonally collected from six monitoring stations in each area for 3 years (2013–16) at two study areas and all the data were comparatively analyzed. First, abiotic data such as sediment properties and water quality parameters showed significant variations in time (season/year) and space (site/area) cross the study areas and within sites in each area. Second, meiofauna assemblages, such as number of taxa, abundance, and composition, greatly varied between seasons and localities, reflecting (in)direct association(s) to local activities and/or environmental gradients. Of note, the Jinhae Bay community was directly influenced by a hypoxia during summer season. In general, the site-specific variations rather prevailed masking seasonal fluctuations, indicating significance of both oceanographic settings and terrestrial land use activities. Among the environmental parameters measured, sediment grain size appeared to be the key factor in determining the meiofaunal assemblages and distributions, particularly under natural condition shown at Samcheok. Altogether, clear separations in meiofaunal community cross sites (inner vs. outer stations) and areas (enclosed industrial bay vs. open sea) implied anthropogenic pressures and certain impacted boundaries. In addition, association of benthic communities to anthropogenic environments seemed to prevail in macrofaunal community, being simultaneously influenced by abiotic seasonal fluctuations. Overall, two contrasting nearshore habitats exhibited typical spatiotemporal distributions of subtidal benthic communities being collectively influenced by anthropogenic stresses and site-specific environmental gradients.

The Effect of Deep Oceanic Flushing on Water Properties and Ecosystem Functioning Within Atolls in the British Indian Ocean Territory

Within atolls, deep water channels exert significant control over local hydrodynamic conditions; which are important drivers of planktonic distributions. To examine planktonic responses to oceanography, this study tested the effect of proximity and exposure to deep oceanic flushing through these channels on water properties and planktonic assemblages across four atolls (Diego Garcia, Salomon, Egmont and Peros Banhos) in the British Indian Ocean Territory Marine Reserve. As this is the largest, most isolated and sparsely inhabited atoll complex in the world, it provides the perfect experimental conditions to test the effect of oceanic flushing without confounding factors related to anthropogenic development. Results are discussed in the context of ecosystem functioning. A total of 30 planktonic taxa and 19,539 individuals were identified and counted. Abundance was significantly different between atolls and significantly greater within inner regions in all atolls except southeast Egmont. Planktonic assemblage composition significantly differed between atolls and between inner and outer stations; exhibiting higher similarity between outer stations. Within outer stations of Diego Garcia, Peros Banhos and Egmont, evidence suggesting oceanic flushing of cold, saline and dense water was observed, however a longer time series is required to conclusively demonstrate tidal forcing of this water through deep water channels. Planktonic variability between inner and outer atoll regions demonstrates that broad comparisons between oceanic and lagoon regions fail to capture the complex spatial dynamics and hydrodynamic interactions within atolls. Better comprehension of these distributional patterns is imperative to monitor ecosystem health and functioning, particularly due to increasing global anthropogenic pressures related to climate change. The extensive coral bleaching described in this paper highlights this concern.

Seasonal cycle of zooplankton abundance and biomass in Hamsilos Bay, Sinop, Southern Black Sea, Turkey

ABSTRACTIn this investigation, zooplankton was studied between July 2015 and June 2016 in Hamsilos Bay to examine spatial and temporal variations in abundance, biomass and taxonomic composition. The recorded mean zooplankton abundance and biomass were 3770.35 ind. m−3 and 25.06 mg m−3 in the inner station, 3928.11 ind. m−3 and 28.19 mg m−3 in the middle station and 3948.22 ind. m−3 and 28.74 mg m−3 in the outer station, respectively. The high abundance and biomass values observed in September 2015 were attributed to Oithona davisae (4575 ind. m−3 at the inner station) and Penilia avirostris (33.4 mg m−3 at the outer station), respectively. Copepoda was the most abundant during the entire period of the survey. In terms of abundance and biomass, Copepoda was followed by meroplankton and Cladocera. Most species within the zooplankton community exhibited evident seasonality throughout the year in Hamsilos Bay. This was particularly apparent for O. davisae, Centropages ponticus, Cladocera and meroplankton, which were abundant in summer–autumn, and for Pseudocalanus elongatus, which was more abundant during winter and spring. It has been determined that O. davisae, which is a non-indigenous cyclopoid copepod species of the Black Sea, has successfully inhabited southern Black Sea and has established a permanent population in this area.

Use of a species-rich and highly eutrophic tropical estuary in the South Atlantic by Pleuronectiformes (Teleostei: Acanthopterygii)

Abstract: A total of 1,471 specimens of 16 species of flatfishes (Pleuronectiformes) were caught during 48 sampling campaigns between July 2005 and June 2007 at ten stations in Guanabara Bay, Rio de Janeiro, Brazil. Paralichthyidae was the dominant family, with Etropus crossotus as the dominant species. The outer stations, especially those on the western side of the lower estuary, were distinguished as a result of their higher abundance of flatfishes and number of species. The spatial distribution of E. crossotus and its population structure indicate that this species is an estuarine resident despite the apparent reduction in its area of occupation within the estuarine complex. Among the other species, nine were classified as marine stragglers (Achirus declivis, Bothus ocellatus, Cyclopsetta chittendeni, Etropus longimanus, Paralichthys orbignyanus, P. patagonicus, Syacium micrurum, Symphurus diomedeanus and Trinectes paulistanus) and three as estuarine opportunists (Bothus robinsi, Citharichthys macrops and Syacium papillosum); another three could not be classified due to the small number of captures or lack of previous data (S. tessellatus, A. lineatus and C. spilopterus).

Feeding ecology of capelin (Mallotus villosus) in a fjord impacted by glacial meltwater (Godthåbsfjord, Greenland)

Capelin (Mallotus villosus) is an important trophic node in many Arctic and sub-Arctic ecosystems. In Godthabsfjord, West Greenland, the zooplankton community has been shown to change significantly from the inner part of the fjord, which is impacted by several glaciers to the shelf outside the fjord. To what extent this gradient in zooplankton composition influences capelin diet during their summer feeding in the fjord is yet unknown. To investigate this, we analysed stomach content of capelin (8–14 cm) sampled using a pelagic trawl at three stations in outer (GF3), mid (GF7) and inner (GF10) part of Godthabsfjord in May and August 2013. In May, the copepod nauplii numerically dominated the diets, but euphausiids contributed > 92% by carbon mass at all stations. In August, calanoid copepods were the most important prey numerically and by carbon mass. Smaller copepod species became more important towards the inner stations, whereas the large Calanus species dominated in the outer stations. There was also a trend in decreasing stomach carbon content towards the inner stations, and on the individual level, variation in stomach content was strongly negatively related to the proportion of small copepods in the diet. This suggests that the inclusion of small copepods in the diet cannot compensate for the absence of larger euphausiids and copepods. Therefore, any change in the ecosystems that favours these at the expense of larger zooplankton and euphausiids is likely to impact capelin feeding negatively with consequences for the whole ecosystem.

Nutrient and carbon dynamics under the water mass seasonality on the continental shelf at the South Brazil Bight

Abstract The enrichment of the euphotic zone and the production of organic matter (OM) are induced by wind-driven processes that change the water mass distribution in the central inner and mid continental shelf of Santa Catarina State (27°18′–27°37′S), South Brazil Bight (23–28.5°S). During austral summer, the Ekman transport by north-eastern winds is balanced by onshore bottom intrusions of the nutrient-rich South Atlantic Central Water (SACW), while during austral winter, the Plata Plume Water (PPW) reaches the region, which is pushed northward by south-eastern winds. Between 2014 and 2016, six oceanographic campaigns were conducted at the isobaths of 30 and 50 m, one in the early fall of 2014, others in the summers of 2015 and 2016, and in each winter of the stated years. The aim was to investigate the spatio-temporal variability of nutrients (nitrate + nitrite, ammonium, phosphate and silicate), and composition of the particulate organic matter (POM), i.e. particulate organic carbon and nitrogen, in relation to the water masses dynamics. In summer of 2015 and 2016, the SACW reached all over the bottom layers of the studied area, while in 2014, it only reached the outer stations. The SACW intrusion was reflected by relatively high phosphate (0.61 ± 0.29 μM), silicate (9.51 ± 4.34 μM), and notably high nitrate (4.21 ± 2.83 μM) concentrations. The POM composition revealed the deep chlorophyll-a maximum at intermediate and bottom layers, indicating new primary production associated with the nutrient-rich SACW. The denitrification was identified in bottom water by nitrogen loss (up to 9.66 μM) associated with the low dissolved oxygen saturation (DO%) (53.07 ± 7.8%). In winter, the PPW reached the region in the surface, especially in 2015 and 2016, with high silicate concentrations (8.36 ± 2.46 μM). Nitrate (1.69 ± 0.92 μM) and phosphate (0.46 ± 0.23 μM) were mainly related to regeneration processes in the bottom layers associated with low DO% (78.25 ± 7.55%). In summer, the SACW presented higher potential for biological production against Subtropical Shelf Water (STSW), while in winter, the STSW was higher than the PPW. Besides the new nutrient supply associated with wind-driven water mass dynamics, the nutrients regeneration contributed to the food chain structure via a regenerated primary production.