Middle Shelf Waters Research Articles

Ecological Indicative Stressors of Native vs. Non-Native Fish in an Ultra-Oligotrophic Region of the Mediterranean Sea

In the present study, we investigated the different ecological characteristics of native and non-native demersal fish collected in 2014–2015 on the shelf of the Antalya Gulf in the Eastern Mediterranean Sea. Lessepsian migrants originating from the Indo-Pacific Ocean were classified as non-indigenous species (NIS) and the other species, which were mostly Atlanto-Mediterranean, were classified as indigenous species (IS). The results showed that the faunistic characteristics of IS and NIS differed significantly in space but only partly over time. The density and species diversity of the IS increased with the seafloor depth, while the opposite pattern was observed for the NIS, which were found mostly in shallow waters. Proximity to rivers and Posidonia oceanica meadows and the presence of a marine protected area (MPA) were also important factors determining the differences in the ecological characteristics of IS and NIS. The ecological ordination of the fish assemblages in the canonical correspondence analysis (CCA) space was V-shaped for the IS and =-shaped for the NIS, and it was mainly determined by bottom depth. Altogether, the ordination took the shape of a double strikethrough (V) due to the NIS filling an available niche. Hierarchically, the NIS (“occupiers”) and IS (“resisters”) shared the shallowest waters, while the middle-shelf waters were occupied by NIS (“gapers”) and IS (“escapers”) separately. The upper shelf was occupied only by IS (“homekeepers”) and “minorities” of NIS. Finally, we identified eight factors as ecological indicators of NIS and IS: bottom depth, bottom vegetation status, fish hierarchy, key species, water productivity, fish trophic level, life strategy and morphometry.

Contrast the distribution, transformation, and degradation of dissolved and particulate organic matter in the South Yellow Sea, the East China Sea, and its adjacent Kuroshio Current

The distribution and bioavailability of dissolved and particulate organic matter (DOM and POM) were determined throughout the water column in sampling transects across the South Yellow Sea (SYS), East China Sea (ECS), and its adjacent Kuroshio Current (KC) during March–April 2017. The carbon (C), nitrogen (N), and amino acids (AA) levels in DOM and POM, as well as other parameters including temperature, salinity, nutrients, chlorophyll-a, and biological parameters (heterotrophic bacteria, Synechococcus, and picoeukaryotes), were used in the multi-factor analysis to explore the underlying factors contributing to the distribution patterns and degrading status of DOM and POM. The AA contents in POM (PAA) were higher at shallower depths than the deep ones, whereas total dissolved amino acids (TDAA) levels showed minor variation with depth. Specifically, glycine and serine in the PAA were selectively preserved throughout the water column. High levels of heterotrophic bacteria were associated with high temperature and high levels of ammonium in shelf waters, indicating a spot for intensive remineralization of organic nitrogen. High concentrations of bulk organic parameters (POC and PON) were found more along the coast and correlated with arginine and alanine. The Kuroshio surface water was short of PAA, POC, and PON compared with the coastal and middle shelf water. The bioavailability of surface POM indicated by the percentages of AA in POC (PAA-C%) and PON (PAA-N%) was much higher in KC than in shelf and coastal waters. This study found the distinctive characterization of bioavailability and degradation status between KC and its adjacent seas.

Hypoxic Effects on the Radiocarbon in DIC of the ECS Subsurface Water

AbstractDissolved inorganic carbon (DIC) in the East China Sea (ECS) is physically and chemically affected by the northward intrusion of the Kuroshio Branch Current (KBC) and the Changjiang River (CR) outflow. We trace these processes using dual DIC isotopic compositions (Δ14C and δ13C) along transects that begin in the CR and estuary, and extend out into middle shelf waters of the ECS. We especially focus on frequently occurred nearshore hypoxia, as they appeared in the summer of 2017. The Δ14C values (28.8‰–35.3‰) from the ECS mid‐shelf water were comparable to the reported value from the Kuroshio Current (KC) at the continental slope (34.4‰ ± 7.4‰), but Δ14C values in the CR (−173.6‰ & −162.3‰) were substantially lower than observations made in 2014. We also found that the Δ14C of DIC in the bottom waters along the inner shelf, including hypoxic area, decreased from 25.0‰ to 18.5‰, from south to north. Water masses mixing between the CR and the ECS mid‐shelf waters with and without organic carbon degradation can be identified in plots of Δ14C versus DIC‐1. With simple mixing calculations, we show that the northward decreasing Δ14C of inner shelf bottom water is caused by downward transport of DIC with low Δ14C value mediated by biological process from the surface, as opposed to simple physical mixing.

Hydrogen peroxide in tropical shelf Waters: The Northern South China Sea Shelf

The distribution of hydrogen peroxide was determined at 28 stations in four transects across the Northern South China Sea Shelf-sea (NoSoCS) in June 2010. The average concentration in the top 10m ranged between 0.063 and 0.231µM. Among the hydrographic regimes: the inner shelf outside the influence of upwelling, the inner shelf under the influence of upwelling, the middle shelf, the outer shelf and the open South China Sea, the highest concentration was found in the day-time in the inner shelf outside of the influence of upwelling and the lowest concentration was found in the night-time in the inner shelf under the influence of upwelling. The average concentration at the day-time stations in each hydrographic regime was invariably higher than the corresponding concentration at the night-time stations. Across the shelf, the concentration was the highest in the inner shelf. The variations in the concentrations of hydrogen peroxide and total organic carbon (TOC) in the different hydrographic regimes followed a similar pattern. All these behaviors are consistent with the photochemical production of hydrogen peroxide, using dissolved organic matter as the chromophore, as a primary control on its occurrence in the surface waters. Moreover, at day-time stations at different locations in the NoSoCS and at a single location sampled through the day, the relationship between the concentration of hydrogen peroxide and the product of the concentration of TOC and the time-integrated irradiance at the time of sample collection fell on two distinct linear lines with different slopes and intercepts: one for mostly the inner and middle shelf waters and the other for mostly the water in the open northern SCS. These relationships suggest that the light history, the pre-existing concentration of hydrogen peroxide, and, the concentration and the photochemical efficiency of the dissolved organic matter in the production of hydrogen peroxide play major roles in determining the temporal and spatial variations in the concentration of hydrogen peroxide in the surface waters in the day-time. In the sub-surface, a notably large fraction, about one-third, of the profiles of hydrogen peroxide did not follow the typical distribution of a quasi-exponential decrease in concentration with depth. Almost all the profiles at the stations in the slope where the internal waves were most active were atypical. At these stations, the concentration of hydrogen peroxide was generally elevated down to about 100m, well beyond the depths where solar irradiance was plentiful. Superimposed on these elevated concentrations was a persistent sub-surface maximum, with concentrations reaching about 0.5µM, at 80m. While the origin of these atypical distributions is not yet clear, dark biological production and the action of internal waves conceivably could have contributed to their occurrence.

Differential use of the Argentine shelf by wintering adults and juveniles southern giant petrels, Macronectes giganteus, from Patagonia

To study habitat use and at-sea movements of southern giant petrels (SGP) during non-breeding period, we deployed 15 satellite transmitters (six adults, nine juveniles) at Isla Arce and Isla Gran Robredo colonies in Patagonia, Argentina. Birds were instrumented during 81.4 ± 37 days. Adult birds used 74% of the Argentine shelf concentrating mainly at the shelf break, middle shelf waters, and the surroundings of the colony. After fledging, juveniles spread to the Argentine, Uruguayan and Brazilian shelves within the South Atlantic. Adults alternated at-sea excursions (12 ± 5 days) with periods at the colony of 3 ± 0.3 days. Contrarily, juveniles moved first to the shelf break and then traveled northwards reaching the south of Brazil. There was some spatial overlap between age classes, but only during the first 30 days after juveniles had fledged; thereafter there was not overlap between the areas used by both age classes. The Argentine shelf is widely used by different species offering a suitable environment for foraging; this may be why adults SGP from Patagonian colonies spend all year-round within the Argentine shelf. The identification of used areas of non-breeding SGP fills a gap in the species knowledge contributing not only to the preservation the species, but also to the management of marine areas globally recognized as important for many other Procellariiformes.

Blooms of Azadinium cf. spinosum Elbrächter et Tillmann (Dinophyceae) in northern shelf waters of Argentina, Southwestern Atlantic

Azadinium spinosum has been identified as a species producer of azaspiracids (AZAs), marine toxins reported to cause human poisoning etiologically similar to diarrheic shellfish poisoning. AZAs are accumulated by molluscs via food web which, in turn, may cause human poisoning after consumption of contaminated shellfish. In this study, the presence of a species of the genus Azadinium, A. cf. spinosum, is reported for the first time in the Southwest Atlantic ocean, and two blooms in northern shelf waters of Argentina are analysed. Both blooms occurred during spring in succesive years and developed along extensive areas (up to 60km transection) of the middle shelf and near the shelf break in 1990, and also near the shelf break during 1991. The extended shelf break front of the Argentine Sea developed during spring and summer is a highly productive area rich in exploited marine resources. In November 1990, a first bloom (up to 9.03×106cellsL−1) produced heavy discolorations, and morphological and taxonomical studies showed that the causing organism was a new dinoflagellate genus. During September 1991 plankton composition and abundance along a transect from the coast to the Malvinas Current were analysed. Results showed that this dinoflagellate was the most important species in middle shelf waters, with high biomass and abundance values (up to 3×106cellsL−1) surpassing those of various chain-forming diatom Thalassiosira species, typical of the spring bloom. The description of this new taxon, according to the thecal analysis performed at that time by light and scanning electron microscopy, corresponds with little morphological differences to the thecal tabulation, cell morphology and dimensions of the recently described Azadinium spinosum. Taking into account these minor differences and due to the lack of both DNA sequence data and AZAs production, we decided to name it A. cf. spinosum. The phagotrophic dinoflagellate Gyrodinium fusus has shown to be an important grazer of A. cf. spinosum during the first bloom, suggesting that its grazing activity could have acted as a modeling factor in population levels of its prey. The presence of A. cf. spinosum in this area opens several questions as that related to toxin production given the regional importance of bivalve commercial fisheries.

Biomass of autotrophic dinoflagellates under weak vertical stratification and contrasting chlorophyll levels in subantarctic shelf waters

Both the biomass of autotrophic dinoflagellates and its contribution to total chlorophyll were found to increase significantly with seawater temperature and the level of stratification in southern Patagonian waters during spring and winter. The highest peak of biomass corresponded to a single species, Prorocentrum minimum (Pavillard) Schiller, and was detected in middle shelf waters, coinciding with the primary productivity and CO2 uptake maxima reported for the area under spring conditions.

Origins of the subsurface ammonium maximum in the Southeast Bering Sea

Abstract In the Bering Sea, it has long been argued that ammonium-rich bottom water from the middle shelf of Bristol Bay is tidally diffused seaward resulting in a mid-depth ammonium tongue over the outer shelf. Weak horizontal mean flows in the region (relative to an especially strong tidal component) support this contention. We examined the distribution of ammonium further north in the vicinity of the Pribilof Islands. On the middle shelf, bottom waters had concentrations of 4–7 μmol kg−1, and over the outer shelf there was a mid-depth ammonium tongue. Optimal multiparameter analysis of hydrographic data suggested that bottom waters from the middle shelf were prevalent across the outer shelf, and could account for this ammonium tongue. Drifter tracks demonstrated that middle shelf water was incorporated into a westward flow along the shelf break south of St. George Island, and mean flows derived from several decades of drifter tracks also show prominent cross-shelf advection in the region. This was consistent with a scalar argument suggesting that, in the vicinity of the Pribilof Islands, the seaward movement of middle shelf water, and loss of nitrogen over the middle shelf, was the result of advection rather than tidally driven lateral diffusion.

Phosphorus speciation and budget of the East China Sea

Water samples collected from the inner (<50 m), middle (50–200 m) and outer (>200 m) shelves of the East China Sea (ECS) were analyzed to investigate the importance of dissolved inorganic phosphorus (DIP), dissolved organic phosphorus (DOP) and particulate inorganic phosphorus (PIP) in the water column. Concentrations of DIP, DOP and PIP ranged 0.05–3.01 μM, 0.01–0.54 μM and 0.18–13.94 ı̀mol g −1, respectively. Higher values were generally found in the inner shelf. Significantly higher concentrations of suspended particulate matter (SPM) (mean value 16.87 mg l −1) and PIP (mean value 11.59 μmol g −1) were found near the bottom along the inner shelf and was attributed to re-suspension of sediments. DIP was the major form of dissolved P, accounting for more than 70% of the total dissolved P (TDP) pool in inner and middle shelf waters. However, the DOP concentration generally exceeded the DIP concentration in the surface layer (<100 m) of the outer shelf. PIP was 10–20% of the total P pool (TDP+PIP) in the inner shelf and decreased markedly to less than 1% in the outer shelf. It was also found that the higher the concentrations of SPM and of particulate iron, the higher the percentage of P bound by particles. The phosphorus budget on the ECS was also calculated by employing a box model based on the balance of the water mass and phosphorus mass. The model results revealed that the Kuroshio Surface Water, the Kuroshio Tropical Water, the Kuroshio Intermediate Water and the Taiwan Strait Water annually import approximately 8.6±5.7×10 9 mol, 6.7±5.6×10 9 mol, 28.9±22.2×10 9 mol, and 22.8±13×10 9 mol P, respectively, into the ECS. These imports of P are primarily transported in the dissolved phase. In contrast, the input of P, 11.8±2.3×10 9 mol P yr −1, from the Changjiang River is chiefly transported in the solid phase. The Shelf Surface Water annually exports 44.5±27.3×10 9 mol P out of the ECS, predominately in the dissolved phase. The ECS is a phosphorus sink with approximately 34.3±21.5×10 9 mol P yr −1 deposited in the sediments. Finally, the results of the present study suggested that PIP and DOP could not be ignored when studying the geochemistry of P in the inner and outer shelf, respectively, of the ECS.

Phytoplankton spatial distribution patterns along the western Antarctic Peninsula (Southern Ocean)

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 261:21-39 (2003) - doi:10.3354/meps261021 Phytoplankton spatial distribution patterns along the western Antarctic Peninsula (Southern Ocean) Irene A. Garibotti1,*, María Vernet2, Martha E. Ferrario3, Raymond C. Smith4, Robin M. Ross5, Langdon B. Quetin5 1Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales, CRICyT, CONICET, CC 330, 5500 Mendoza, Argentina 2Scripps Institute of Oceanography, University of California, San Diego, La Jolla, California 92093-0218, USA 3Facultad de Ciencias Naturales y Museo, Universidad Nacional de La Plata, 1900 La Plata, Argentina 4Institute for Computational Earth System Science and 5Marine Science Institute, University of California, Santa Barbara, California 93106, USA *Email: ireneg@lab.cricyt.edu.ar ABSTRACT: This paper describes spatial distribution patterns of the phytoplankton community (composition, cell abundance and biomass concentration) in relation to local environmental conditions in the Southern Ocean. Sampling was performed during summer 1997 off the coast of the western Antarctic Peninsula between Anvers Island and Marguerite Bay. Phytoplankton was characterized by relatively low biomass throughout most of the study area and was dominated by nanoalgae (<20 µm). Phytoplankton varied along an on-offshore gradient, with decreasing total cell abundance, chlorophyll a (chl a) concentration and carbon biomass toward the open ocean. Chl a concentration showed surface or subsurface maxima in coastal and middle-shelf waters, and deep maxima between ~40 and 100 m in oceanic waters. Across-shelf variability in phytoplankton correlated with vertical stability in the water column, which appears to be the major parameter affecting phytoplankton community structure in the area. We hypothesize that the deep chl a maximum offshore may be associated with iron limitation in near-surface waters and higher iron concentration in Œwinter waters¹ (subsurface remnant of Antarctic Surface Waters). On a smaller spatial scale, a cluster analysis showed great regional variability in phytoplankton assemblages. The area was divided into 4 main regions based on differences in the phytoplankton composition and concentration. Three peaks in phytoplankton abundance were found on a north-to-south gradient in near-shore waters: a Cryptomonas spp. bloom near Anvers Island, a small unidentified phytoflagellate bloom in Grandidier Channel, and a diatom bloom in Marguerite Bay. These assemblages resemble different stages of the phytoplankton seasonal succession, and may be related to the progressive sea-ice retreat, which might have regulated the timing of the onset of the phytoplankton seasonal succession in a north-south gradient. Biological environmental factors, such as seeding of the water column by epontic algae and selective zooplankton herbivory, are hypothesized to affect community composition in coastal regions. We conclude that large-scale variability in phytoplankton community structure is related to water column physical conditions and possibly iron availability, while mesoscale variability, as seen in coastal waters, is more likely due to seasonal succession of different algae groups. KEY WORDS: Western Antarctic Peninsula · Phytoplankton spatial variability · Seasonal progression · Environmental gradients · Palmer LTER Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 261. Online publication date: October 17, 2003 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2003 Inter-Research.

The occurrence of Calanidae species in waters off Argentina

As food of planktivorous fish and likely good predictors of natural perturbations, members of the family Calanidae are recognised to be key species in ecosystems worldwide. The distribution and seasonal relative abundance of the Calanidae species occurring in the Argentine Sea were reviewed from published and unpublished data collected over the last three decades. Species are also figured in order to elucidate any possible taxonomic uncertainty. Calanoides cf. carinatus, Calanus australis and Calanus simillimus are the most abundant calanids in the region. The former two species typically inhabit inner and middle shelf waters decreasing offshore, while Calanus simillimus is distributed in the middle and outer shelf, its abundance increasing towards the shelf-break. The southern limit of the distribution of Calanoides cf. carinatus appears to be ∼46° S. Calanus australis is the most common large copepod in coastal and inner shelf waters off southern Patagonia. Neocalanus tonsus and Calanoides patagoniensis are a much rarer species. The latter is recorded in the southwestern Atlantic, for the first time, immediately east of Magallanes Strait and the Beagle Channel. The taxonomic status and worldwide biogeographic distribution of the region's calanids are briefly described and the patterns identified off Argentina are discussed in relation to the major hydrographic characteristics.

Long-term mean and event-related pigment distributions during the unstratified period in South Atlantic Bight outer margin and middle shelf waters

Phytoplankton pigment distributions in the South Atlantic Bight (SAB) during the unstratified period (November through April) and dynamics influencing these distributions are examined using multi-year Coastal Zone Color Scanner (CZCS) and Advanced Very High Resolution Radiometer (AVHRR) coverage, oceanographic and meteorological data from buoys and coastal stations, and Fleet Numerical Meteorology and Oceanography Center (FNMOC) wind fields. We examine: (1) long-term mean and event-related pigment distributions along the outer margin in relation to Gulf Stream and meteorological forcing, and (2) spatial coherence in pigment field temporal variation along the outer margin itself and between the outer margin and adjacent regimes. The highest mean unstratified period CZCS-derived chlorophyll (CZCS-Chl) is in the central SAB, immediately inshore of the region of the Gulf Stream offshore mode/Charleston Gyre. The highest event-related pigment concentrations are associated with the development of large-scale pigment field features, exhibiting along-shore orientation and association with development of temperature (SST) fronts. The role of wind and Gulf Stream forcing is supported in event studies of these features. Coherent temporal variation in CZCS-Chl is evident at along-shelf scales greater than that typical of Gulf Stream frontal eddies, particularly in the central SAB, where the coherence scale exceeds 600 km. Distinct pigment field coherence between the central SAB outer margin (ca. 400 km along-shore) and the Charleston Gyre/Gulf Stream offshore mode region is evident. The pigment field of middle shelf waters also exhibits significant coherence with that of the outer margin. The results show that non frontal eddy processes are important in determining the mean and event-related pigment distributions, as well as the spatial scale of coherent pigment field variation during the unstratified period.

Paleoenvironment of a Diverse Marine Vertebrate Fauna from the Yazoo Clay (Late Eocene) at Copenhagen, Caldwell Parish, Louisiana: ABSTRACT

ABSTRACT The vertebrate fauna from the exposures of the Tullos Member, Yazoo Clay (Jackson Group, Late Eocene) at Copenhagen represents the most diverse assemblage documented from Louisiana and is one of the richest faunas known from the Tertiary of the Gulf coastal plain. Studies of the diverse assemblage of marine vertebrates revealed 70 vertebrate species, including 14 sharks, 5 rays, 46 teleosts (34 based on otoliths), 3 reptiles, and 2 mammals. Over 8,000 specimens have been collected making paleoenvironmental interpretations possible. The Copenhagen fauna has the greatest abundance and diversity of vertebrate species in comparison to previously described Jackson faunas in Louisiana, Texas, Arkansas, Mississippi, Alabama, Georgia, and Florida. Open marine conditions are suggested by the occurrence and variety of open-water and pelagic species such as the sharks Isurus, Abdounia, and Alopias, teleosts such as Bregmaceros, Cylindracanthus, Myripristis, Sphyraena, and Xiphiorhynchus, and cetaceans. Paleoecologic comparisons to extant species support an interpretation of an inner shelf deepening to middle shelf upsection as pelagics increase. The Yazoo Clay's invertebrate macrofauna which consisted mainly of oysters, corals, crabs, gooseneck barnacles, comatulid crinoids, and other rare bivalves and gastropods is not especially helpful for paleoecologic comparisons to the vertebrate fauna. However, diverse and abundant foraminiferal and ostracode microfaunas in the Yazoo Clay support an interpretation of deposition in middle shelf waters as suggested by the vertebrate distribution.

Response of South Carolina continental shelf waters to wind and Gulf Stream forcing during winter of 1986

The South Carolina shelf water response to strong winter atmospheric forcing and Gulf Stream variations over the slope is discussed with the aid of a comprehensive set of atmospheric and oceanic observations made during project GALE (Genesis of Atlantic Lows Experiment). A mixed response is observed to wind and Gulf Stream forcing. Subtidal variability of inner and middle shelf waters is primarily a barotropic, forced response to coherent, synoptic scale, alongshore winds. This response is not trapped over the shelf, as has been found for other wide, non‐equatorial shelves, but is also significant at the shelf edge, possibly because of the comparable widths of the shelf and slope. The outer shelf also shows a significant Gulf Stream influence. The Gulf Stream appears to have two preferred position modes, either onshore, with the stream flowing over the Charleston bump and along the shelf break, or offshore, when the stream can be located up to 100 km east of the shelf break; transition between the two states is rapid. Subtidal variability in the outer shelf is dominated by weekly period frontal eddies and meanders when the stream is in an onshore mode, and by persistent southward flow when the stream is offshore. This southward flow is produced by enlarged cyclonic eddies with upwelled centers located over the slope between the offshore Stream and the shelf edge, sometimes referred to as the Charleston gyre. Positive mean alongshore sea level slopes at the shelf edge, due to the persistence of the cyclonic gyres, are geostrophically balanced by mean onshore flow, which transports upwelled waters onto the shelf, enhancing the biological productivity of the area relative to other regions of the South Atlantic Bight.

Response of Florida Atlantic shelf waters to Hurricane David

Water level data, bottom pressures and temperature, and current records are used to document the response to Hurricane David of inner and middle shelf waters along the Atlantic coast of Florida near latitude 27°30′N. Available data records extend from well before the storm to well after its passage on September 3, 1979, to put hurricane effects in proper perspective. Highest water levels recorded in the Fort Pierce Inlet nearby indicate values about 60 cm above normal high water levels. Bottoms pressure fluctuations corrected for atmospheric pressure variations suggest a storm surge over the inner shelf of approximately 100 cm above the normal high water mark. Longshore current components over both the inner and the middle shelf rise briefly to about twice the normal maximum speeds. A distinct upwelling event is recorded in both inner and middle shelf waters as the storm moved through the study area. Near‐bottom temperatures along the 10‐ and 26‐m isobaths decrease to just under 17°C and 9°C, respectively, and remain low for a period of about a week. Temperature variations in near‐surface waters over the middle shelf are dominated by near‐inertial period internal wave activity and hurricane effects are negligible. Data suggest that hurricane effects in the hydrographic variables were apparent for only 1–2 weeks following the passage of a storm.