Atlantic Shelf Research Articles

A Model for Paleoamerican Coastal Zone Preference for the Atlantic Slope of Eastern North America Since the Last Glacial Maximum

ABSTRACTPaleoamerican colonization models have emphasized the importance of coastal zones for provisioning hunter gatherers with a diverse range of subsistence resources. This article expands on recent research by Lowery et al. 2012, and presents a model to explain the distribution of Clovis points across the Atlantic slope of Eastern North America. Marine transgression since the last glaciation has submerged large tracts of the Atlantic continental shelf. Global bathymetric data was used to estimate the Clovis age shoreline from Delaware to Florida. Clovis biface data for modern coastal areas, obtained from the Paleoindian database of the Americas, was compared to the slope of the paleo-shoreline to predict coastal zone preference. Results indicate a relationship between point distribution and coastal zone type. Areas where major rivers with high-quality tool-stone intersect broad coastal zones served important roles to Clovis subsistence adaptations. The potential exists for early Paleoamerican sites along the continental shelf submerged beneath 55–75 m of the Atlantic Ocean. Modern coastal regions with high densities of Clovis points may serve as analogues for identifying earlier sites that have been submerged as a result of marine transgression.

Dinoflagelados del Eoceno medio a superior de las cuencas Punta Del Este y Colorado, latitudes medias del Atlántico sudoccidental

The analysis of middle Eocene dinoflagellate cyst assemblages from sites at Punta del Este (~36°S, Uruguay) and Colorado (~38°S, Argentina) basins allows to interpret ocean circulation patterns on the South American Shelf prior to the opening of the Drake Passage. The assemblages contain endemic-Antarctic taxa such as Enneadocysta, Deflandrea, Vozzhennikovia and Spinidinium, which are also dominant in several circum-Antarctic sites, located southern 45°S. Enneadocysta dictyostila is the most abundant species recorded from the studied sites and the unique member of the endemic assemblage apparently tolerant to warm surface waters. The presence of endemic taxa at mid latitudes has been related to a strong clockwise subpolar gyre favoured by the partial continental blockage of the Tasmanian Gateways and the Drake Passage. The distribution of the dinoflagellate cyst assemblages along the South Atlantic Ocean Shelf can be explained by a similar dynamical mechanism induced by a cyclonic subpolar gyre on the South Atlantic Ocean. The western boundary current of this gyre, starting on the west Antarctic continental slope, would follow a similar path to the present Malvinas Current on the Patagonian slope, which introduce cold oceanic waters to the shelf and intensifies the northward shelf transport. In the same way, during the middle Eocene the western boundary current of a proto-Weddell Gyre transported the circum-Antarctic waters and the endemic taxa northward along the Southwestern Atlantic Shelf. The opening and deepening of the Tasmanian Gateway and Drake Passage and the development of an incipient Antarctic Circumpolar Current during the latest Eocene-Oligocene disrupted the subpolar gyres and promoted the extinction of the endemic species. © 2016 by the Sociedade Brasileira de Paleontologia.

Footprint of roman and modern mining activities in a sediment core from the southwestern Iberian Atlantic shelf

A 5-m long sediment core (VC2B), retrieved in the Southwestern Iberian Atlantic shelf, at 96m water depth, was used to assess major changes in climate and human activities during the last 9.7kyrs. Analytical measurements included sedimentological (mean grain size, and the contents of sand, silt and clay), geochemical (major, minor, trace and rare earth elements; REEs) and chronological (210Pb and 14C) parameters. Two episodes of increment of fine-grained particles, occurring at 3050BCE and 1350CE, suggest the retreat of the coast line to the present level and the beginning of a wetter phase associated with the “Little Ice Age”. The North American Shale Composite (NASC)-normalized REE-pattern detected in the shelf is similar to that found in the Guadiana estuarine sediments. The possibility of this estuary as a contributor to the sediment load deposited in the adjacent coastal zone was indicated. Trace elements were significantly correlated with Al until 1850CE, pointing that grain-size rules its distribution in sediments. The depth variation of As, Cu and Pb enrichment factors relative to background values shows two periods of intense human activity that can be mainly linked to mining: (i) across the Roman Period, marked by low enrichments; and (ii) starting on the second half of the 19th century until nowadays with significantly increased enrichments, especially of Pb and Cu. In addition to As, Cu and Pb, this period is also marked by high enrichments of Hg and Zn. Despite the decrease/closure of sulphide massive deposits mining exploitation (e.g., São Domingos, Las Herrerias) during the second half of the 20th century, results showed ongoing input of Pb, Cu, As, Hg and Zn to coastal sediments. Thus, the legacy of contamination by these elements, mainly from leaching of slags and tailings, and remobilization/reworking of contaminated estuarine sediments, is still recorded in marine sediments.

Holocene oscillations of Southwest Atlantic shelf circulation based on planktonic foraminifera from an upwelling system (off Cabo Frio, Southeastern Brazil)

The Brazil Current (BC) is a relevant feature in the Atlantic Meridional Overturning Circulation (AMOC). Its behavior during slowdown or intense AMOC remains poorly known because of the lack of paleoceanographic records, especially for the Holocene. Here, we investigate changes in a western boundary upwelling system (Cabo Frio, off Southeastern Brazil) which are driven by variations in the BC and NE winds during the last 9 kyr. To assess the variability of the BC, we used δ18O, Mg/Ca, and assemblages of planktonic foraminifera. Our results indicate five oceanographic phases during the last 9 kyr. During Phase I (from 9.0 to 7.0 cal kyr BP), the BC diverged offshore from the modern upwelling area because of the low sea level, increasing the influence of shelf waters and coastal upwelling plumes on foraminifera assemblages. Phase II (7.0–5.0 kyr BP) was marked by the approach of the internal front of the BC with low intensity and episodes of strong productivity that were linked primarily to the upwelling of the South Atlantic Central Water (SACW) and/or Subpolar Shelf Waters (SPSWs) (cold). Phase III (5.0–3.5 kyr BP) was a transition, marking a large oceanographic and climatic change from the weakening of the AMOC. The internal front of the BC became warm and subsurface SACW upwelling was stronger. In Phase IV (3.5–2.5 kyr BP), the BC acquired its modern dynamics, but weak NE winds weakened the SACW’s contribution to upwelling events. Finally, in Phase V (last 2.5 kyr BP), the NE winds reintensified, promoting frequent episodes of upwelling and intrusion by SPSWs during the Medieval Climate Anomaly.

The JEBAR term: Model calculations for the northeastern Atlantic shelf

The JEBAR term: Model calculations for the northeastern Atlantic shelf

Determining the effective parameters of a Shallow-Water bottom from wideband signal spectra under conditions of hydrodynamic variability

We propose a method for determining the effective parameters of the upper marine sediment layer on extended tracks from the spectra of wideband signals in conditions of hydrodynamic variability. As an example, we consider the Shallow Water 2006 experiment on the Atlantic shelf of the United States, which used signals with a band of 300 ± 30 Hz received by a vertical array. The length of the track was ~20 km at a sea depth of ~80 m. Frequency-mode analysis of the received signals showed that spatiotemporal fluctuations of the wave medium lead to random changes in mode amplitudes while retaining the relative stability of the mode phase difference. This is the basis of the proposed method, which makes it possible to determine the track-averaged values of the sound velocity in the bottom and density of the bottom under conditions of hydrodynamic variability.

Polychaete distribution on the southwestern Atlantic continental shelf

ABSTRACTDiversity and distribution of polychaetes on the southeastern Brazilian Shelf (SBS) adjacent to the city of Santos were studied. The study area is situated in the vicinity of Santos Bay with its estuarine complex and other small rivers along the coast. A total of 16,274 specimens belonging to 214 polychaete species were found at 21 sampling stations during two different periods. Two communities occur along the shelf and were related firstly to sediment characteristics. Prionospio dayi (Spionidae) was dominant in the inner shelf community that was characterized by well-sorted, very fine sand. The outer shelf community was found in muddy sediments with high organic matter content and was dominated by subsurface deposit feeders, like Petersenaspis capillata (Sternaspidae) and Leitoscoloplos kerguelensis (Orbiniidae), and by large carnivores such as Aglaophamus sp. (Nephtyidae) and Sigambra sp. (Pilargidae). A transition zone of mixed sediments presenting high diversity and richness was found between these communities. The characteristics of bottom water and food quality in the sediment were important to divide the inner shelf into two sub-areas. Nearshore sampling stations (A group) were more influenced by freshwater input, mainly during summer. This influence is not conspicuous at stations close to 30 m depth (B group). However the effect of South Atlantic Central Water mass (SACW) intrusion on the benthic system was observed on the inner shelf – B group during the summer. The summer intrusion of SACW onto the inner shelf may explain the higher quality of organic matter that resulted in an increase in polychaete abundance and richness.

Atlantic surfclam connectivity within the Middle Atlantic Bight: Mechanisms underlying variation in larval transport and settlement

Larval transport and settlement have been shown in various studies to be essential in determining population abundance and connectivity for benthic invertebrates. This transport is influenced by both the physical environment and biological behavior. The Atlantic surfclam, Spisula solidissima, is a commercially important benthic invertebrate fishery species along the U.S northeastern coast. In this study, a physical circulation model is coupled to a surfclam larval model to investigate the dynamics of larval transport and settlement within the Middle Atlantic Bight (MAB) shelf in 2006. The main physical mechanisms causing variability in larval transport and settlement are also examined. Model results show that surfclam larvae released from July to early October experience relatively larger settlement rates, due to higher average temperatures experienced by larvae. Larval along-shore transport exhibits a mean down-coast pattern following the coastal current from the northeast to the southwest, with most high-frequency (period of 2–10 days) variations caused by fluctuations in the along-shore surface wind stress, and with seasonal variations speculated to be driven mainly by changes in the across-shelf density gradient. Larval across-shelf movement is highly correlated with the along-shore surface wind stress mediated by coastal upwelling and downwelling episodes, but the correlation is further dependent on the vertical distribution of the larvae, particularly their position relative to the thermocline. Most surfclam larvae released from the Middle Atlantic shelf stay below the thermocline and experience a net onshore transport during the summer-stratified season when upwelling-favorable wind forcing dominates. A proposed critical value of water temperature at the thermocline successfully regulates the observed patterns of vertical distribution of surfclam larvae and their across-shelf movement off the New Jersey and South Virginia shelves; that is, when the water temperature at the thermocline is above the critical value (19.0 °C), surfclam larvae tend to escape the warm surface layer to concentrate below the thermocline and follow the across-shelf movement of bottom water, and vice versa. These results provide an important insight into the general mechanism of how physical environmental factors interact with biological behavior of the larvae to influence larval transport, connectivity and population dynamics, and also indicate the potential impact of large-scale climate change on benthic species and coastal ecosystems.

Distribution and dynamics of two species of Dinophyceae producing high biomass blooms over the French Atlantic Shelf

The frequency and distribution of high biomass blooms produced by two dinoflagellate species were analysed along the French continental shelf from 1998 to 2012. Two species were specifically studied: Karenia mikimotoi and Lepidodinium chlorophorum. Based on remote-sensing reflectances at six channels (410, 430, 480, 530, 550 and 670nm), satellite indices were created to discriminate the species forming the blooms. A comparison with observations showed that the identification was good for both species in spite of a lower specificity for L. chlorophorum. The overall analysis of the satellite indices, in association with some monitoring data and cruise observations, highlights the regularity of these events and their extent on the continental shelf. L. chlorophorum blooms may occur all along the South Coast of Brittany. All the coastal areas under the influence of river plumes and the stratified northern shelf area of the Western English Channel appear to be areas of bloom events for both species. These two species are likely to be in competitive exclusion as they share the same spatial distribution and the timing of their bloom is very close. Finally, due to the scarcity of off-shore observations, these satellite indices provide useful information regarding HABs management and the development of a warning system along the French coast.

Sensitivity of Northwest North Atlantic Shelf Circulation to Surface and Boundary Forcing: A Regional Model Assessment

ABSTRACTThe northwest North Atlantic shelves, influenced by both North Atlantic subpolar and subtropical gyres, are among the most hydrographically variable regions in the North Atlantic Ocean and host biologically rich and productive fishing grounds. With the goal of simulating conditions in this complex and productive region, we implemented a nested regional ocean model that includes the Gulf of Maine, the Scotian Shelf, the Gulf of St. Lawrence, the Grand Banks, and the adjacent deep ocean. Configuring such a model requires choosing external data to supply surface forcing and initial and boundary conditions, as well as the consideration of nesting options. Although these selections can greatly affect model performance and results, they are rarely systematically investigated. Here we assessed the sensitivity of our regional model to a suite of atmospheric forcing datasets, to sets of initial and boundary conditions constructed from multiple global ocean models and a larger scale regional ocean model, and to two variants of the model grid — one extending farther off-shelf and resolving Flemish Cap topography. We conducted model simulations for a 6-year period (1999–2004) and assessed model performance relative to a regional climatological dataset of temperature and salinity, to observations collected from multiple monitoring stations and cruise transect lines, to satellite sea surface temperature (SST) data, to coastal sea level estimates, and to descriptions and estimates of regional currents from literature. Based on this model assessment, we determined the model configuration that best reproduces observations. We find that although all surface forcing datasets are capable of producing model SSTs close to observed, the different datasets result in significant differences in modelled sea surface salinity (SSS), with the European Centre for Medium-range Weather Forecasts’ (ECMWF) global atmospheric reanalysis (ERA-Interim) performing best. We also find that initial and boundary conditions based on global ocean models do not necessarily produce a realistic circulation, whereas using climatological initial and boundary conditions (constructed from long-term, monthly-mean output from a larger scale regional model) improves model performance. Through this model assessment, we determine the model configuration that best reproduces observations and gain generally applicable insight into the factors that are key to accurate model performance.

Miocene uplift of the NE Greenland margin linked to plate tectonics: Seismic evidence from the Greenland Fracture Zone, NE Atlantic

Tectonic models predict that, following breakup, rift margins undergo only decaying thermal subsidence during their post-rift evolution. However, post-breakup stratigraphy beneath the NE Atlantic shelves shows evidence of regional-scale unconformities, commonly cited as outer margin responses to inner margin episodic uplift, including the formation of coastal mountains. The origin of these events remains enigmatic. We present a seismic reflection study from the Greenland Fracture Zone – East Greenland Ridge (GFZ-EGR) and the NE Greenland shelf. We doc- ument a regional intra-Miocene seismic unconformity (IMU), which marks the termination of syn-rift deposition in the deep-sea basins and onset of: (i) thermo-mechanical coupling across the GFZ, (ii) basin compression, and (iii) contourite deposition, north of the EGR. The onset of coupling across the GFZ is constrained by results of 2-D flexural backstripping. We explain the thermo-mechanical coupling and the deposition of contourites by the forma- tion of a continuous plate boundary along the Mohns and Knipovich ridges, leading to an accelerated widening of the Fram Strait. We demonstrate that the IMU event is linked to onset of uplift and massive shelf-progradation on the NE Greenland margin. Given an estimated middle-to-late Miocene (ca. 15-10 Ma) age of the IMU, we speculate that the event is synchronous with uplift of the East and West Greenland margins. The correlation between margin uplift and plate-motion changes further indicates that the uplift was triggered by plate tectonic forces, induced perhaps by a change in the Iceland plume (a hot pulse) and/or by changes in intra-plate stresses related to global tectonics.

Enhanced warming of the Northwest Atlantic Ocean under climate change

AbstractThe Intergovernmental Panel on Climate Change (IPCC) fifth assessment of projected global and regional ocean temperature change is based on global climate models that have coarse (∼100 km) ocean and atmosphere resolutions. In the Northwest Atlantic, the ensemble of global climate models has a warm bias in sea surface temperature due to a misrepresentation of the Gulf Stream position; thus, existing climate change projections are based on unrealistic regional ocean circulation. Here we compare simulations and an atmospheric CO2 doubling response from four global climate models of varying ocean and atmosphere resolution. We find that the highest resolution climate model (∼10 km ocean, ∼50 km atmosphere) resolves Northwest Atlantic circulation and water mass distribution most accurately. The CO2 doubling response from this model shows that upper‐ocean (0–300 m) temperature in the Northwest Atlantic Shelf warms at a rate nearly twice as fast as the coarser models and nearly three times faster than the global average. This enhanced warming is accompanied by an increase in salinity due to a change in water mass distribution that is related to a retreat of the Labrador Current and a northerly shift of the Gulf Stream. Both observations and the climate model demonstrate a robust relationship between a weakening Atlantic Meridional Overturning Circulation (AMOC) and an increase in the proportion of Warm‐Temperate Slope Water entering the Northwest Atlantic Shelf. Therefore, prior climate change projections for the Northwest Atlantic may be far too conservative. These results point to the need to improve simulations of basin and regional‐scale ocean circulation.

Towards a functional characterization of rocky reefs marine habitats

Event Abstract Back to Event Towards a functional characterization of rocky reefs marine habitats María Rodríguez González1*, Natalí D. Lazzari1, Laura Palacín Fernández1, Jose A. Sanabria1 and Mikel A. Becerro1 1 Spanish Scientific Research Council, Natural Products and Agrobiology Institute CSIC, Spain Habitat heterogeneity is a major component of biodiversity as it determines species distribution and abundance. Habitat loss, with its associated loss of species, food resources, and ecosystem functioning, is identified as one of the major threats to marine biodiversity. Traditionally, the analysis of taxonomic diversity dominates community level approaches. But species losses or additions can generate major or minor impacts in multiple ecosystem processes depending on their functional traits. Recently, there are an increasing number of researches that approach ecosystem dynamics based on species functional traits. Yet, we still have no description of habitats based on their functional characteristics. Here, we carried out a functional level characterization of the different habitats present on Spanish littoral reefs. We have used underwater visual census that follow the Reef Life Survey methodology to quantify fish, invertebrate, and sessile communities in more than 250 locations scattered over the Spanish and Portuguese coasts. We have quantified the sessile community with over 5.000 photoquadrats distributed along five marine ecoregions: Alboran Sea, Macaronesian, Saharan upwelling, South European Atlantic Shelf and Western Mediterranean. We have described 16 functional traits, including algae, sessile animals, and substrate types. These traits have allowed us to determine 13 functional marine habitats differentially distributed over the coast of Portugal, Spain, and associated archipelagos. The largest functional habitat covers 18% of the rocky reefs and it is dominated by corticated macrophytes (28%), filamentous algae (20%), and bare rock (18%) functional groups. Functional habitats dominated by leathery functional group and filamentous functional group account of 2% and 3% of rocky reefs and are not represented in marine protected areas. Our results suggest that Spain and Portugal have a large number of functional habitats heterogeneously distributed in their coastal waters. Because each habitat is restricted to a specific range in the functional space, effective conservation of each habitat is mandatory to maximize the functional diversity of rocky reefs. Our characterization of functional habitats is a first approach to increase our understanding of the functional diversity of marine benthic communities, which can lead to more effective conservation actions. Keywords: Marine habitat, functional groups, Rocky reef, Biodiversity, conservation Conference: XIX Iberian Symposium on Marine Biology Studies, Porto, Portugal, 5 Sep - 9 Sep, 2016. Presentation Type: Oral Presentation Topic: 1. ECOLOGY, BIODIVERSITY AND VULNERABLE ECOSYSTEMS Citation: Rodríguez González M, Lazzari ND, Palacín Fernández L, Sanabria JA and Becerro MA (2016). Towards a functional characterization of rocky reefs marine habitats. Front. Mar. Sci. Conference Abstract: XIX Iberian Symposium on Marine Biology Studies. doi: 10.3389/conf.FMARS.2016.05.00068 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 18 May 2016; Published Online: 02 Sep 2016. * Correspondence: Miss. María Rodríguez González, Spanish Scientific Research Council, Natural Products and Agrobiology Institute CSIC, San Cristóbal de La Laguna, Santa Cruz de Tenerife, 38206, Spain, maria.rguez92@hotmail.com Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers María Rodríguez González Natalí D Lazzari Laura Palacín Fernández Jose A Sanabria Mikel A Becerro Google María Rodríguez González Natalí D Lazzari Laura Palacín Fernández Jose A Sanabria Mikel A Becerro Google Scholar María Rodríguez González Natalí D Lazzari Laura Palacín Fernández Jose A Sanabria Mikel A Becerro PubMed María Rodríguez González Natalí D Lazzari Laura Palacín Fernández Jose A Sanabria Mikel A Becerro Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Marine resilience distribution in the Alboran Sea ecoregion

Event Abstract Back to Event Marine resilience distribution in the Alboran Sea ecoregion Jose A. Sanabria1*, Natalí D. Lazzari1, María Rodríguez González1 and Mikel A. Becerro1 1 Spanish Scientific Research Council, Natural Products and Agrobiology Institute, Spain The Alboran Sea is an ecoregion in between the South European Atlantic Shelf and the Western Mediterranean ecoregions. Oceanographic conditions in the Alboran Sea are strongly influenced by Atlantic and Mediterranean currents, which suggest that this particular ecoregion could function as a transition zone from Atlantic to Mediterranean biodiversity. The Alboran Sea ecoregion is a major contributor to species richness of temperate seas and it is consider a biodiversity hotspot, but we know very little about the resistance and resilience of this region, i.e., the capacity of the region to resist to and recover from disturbance. Both resistance and resilience are critical components for a healthy ocean and a warranty to ensure effective conservation. Our study used a resilience framework to calculate an index based on a number of indicators that are known to directly affect the resilience of temperate benthic communities. Our results showed that marine resilience increased progressively and significantly from western to eastern Alboran Sea. Maximum resilience values occurred on marine protected areas. Whether the high resilience values of protected communities are a cause or a consequence of protection remains unclear, but our study supports the hypothesis that protection increases the capacity of the system to recover from disturbance and sets forth a number of hypotheses prone to experimental testing. Keywords: resilience, Alboran Sea, Marine diversity, protected areas, Rocky reef Conference: XIX Iberian Symposium on Marine Biology Studies, Porto, Portugal, 5 Sep - 9 Sep, 2016. Presentation Type: Poster Presentation Topic: 1. ECOLOGY, BIODIVERSITY AND VULNERABLE ECOSYSTEMS Citation: Sanabria JA, Lazzari ND, Rodríguez González M and Becerro MA (2016). Marine resilience distribution in the Alboran Sea ecoregion. Front. Mar. Sci. Conference Abstract: XIX Iberian Symposium on Marine Biology Studies. doi: 10.3389/conf.FMARS.2016.05.00156 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 18 May 2016; Published Online: 03 Sep 2016. * Correspondence: Mr. Jose A Sanabria, Spanish Scientific Research Council, Natural Products and Agrobiology Institute, San Cristobal de La Laguna, Santa cruz de Tenerife, 38206, Spain, jose.sanabria@csic.es Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Jose A Sanabria Natalí D Lazzari María Rodríguez González Mikel A Becerro Google Jose A Sanabria Natalí D Lazzari María Rodríguez González Mikel A Becerro Google Scholar Jose A Sanabria Natalí D Lazzari María Rodríguez González Mikel A Becerro PubMed Jose A Sanabria Natalí D Lazzari María Rodríguez González Mikel A Becerro Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Subglacial processes from drumlins in Clew Bay, western Ireland

AbstractInterpretation of subglacial processes and environments can be usefully informed by the stratigraphy and structures of sediments preserved within drumlins, and the down‐ice variability of these sediments. Drumlins in Clew Bay, western Ireland, were formed by westward late Pleistocene ice flow onto the Atlantic shelf, but the depositional processes and environments of these sediments remain uncertain. This study describes and interprets the drumlin stratigraphy and sediment properties and structures from two drumlins on the south side of Clew Bay. Drumlin sediments are dominated by massive to stratified diamicton deposited subglacially by deformation of flows of varying rheology. Folds, shears and clastic dikes within the sediments suggest active subglacial water flow related to variations in ice flow and ice‐bed coupling. The distal ends of the drumlins are dominated by stratified diamicton and gravel units with sandy interbeds. These sediments reflect deposition in a leeside subglacial cavity formed coevally with bedform development. A model is proposed that can account for sediment stratigraphic patterns and drumlin formation. Copyright © 2015 John Wiley & Sons, Ltd.

Tsunami propagation over a wide, shallow continental shelf caused by the Storegga slide, southeastern North Sea, Denmark

The large Storegga slide, which occurred on the Norwegian Atlantic shelf ∼8150 yr ago, triggered a tsunami that has been identified in sediment deposits along the coasts of Greenland, Norway, the Faroe Islands, the Shetland Islands, Scotland, and the northernmost coasts of England, but hitherto not along the southeastern shores of the North Sea. It has generally been assumed that the shallow continental shelf of the North Sea attenuated and dissipated the energy of the tsunami before it reached those coastlines. We used radiocarbon and optically stimulated luminescence dating as well as stratigraphic, lithologic, chemical, and palynological analyses of sediment cores to identify tsunami deposits on the barrier island of Romo located on the southwestern North Sea coast of Denmark. We show that tsunami sediments were deposited in a freshwater paleolake that is located ∼16 m below present-day mean sea level. The tsunami sediment run-up was between 1.5 m and 5.5 m above the contemporaneous sea level. Our results demonstrate that the Storegga slide tsunami propagated across the wide (>500 km) and relatively shallow (depth <95 m) continental shelf of the North Sea and resulted in run-up along adjacent coastlines. In contradiction to earlier theoretical studies, the coastline of the southeastern North Sea cannot be regarded as being sheltered from impacts of North Atlantic tsunami incidents.

Seabed geomorphology of the Porcupine Bank, West of Ireland

ABSTRACTA new map of the seabed geomorphology on the Porcupine Bank, located at the western edge of the north-eastern Atlantic shelf west of Ireland, uses high-resolution multibeam bathymetric and backscatter data as well as numerous shallow seismic profiles to identify individual landforms. They are described based on their acoustic signature on the various datasets. The landforms comprise sharp-crested ridges, mounds and outcrops often associated with and expressing underlying bedrock topography; sand waves highlighting modern currents directions; and iceberg scours with strongly preferred orientations. The map is intended as baseline evidence to test models of the palaeoceanographic and palaeoglaciological history of the Porcupine Bank.

Macroecological analysis of the fish fauna inhabiting Cymodocea nodosa seagrass meadows.

In this study, patterns in the taxonomic richness and composition of the fish fauna inhabiting Cymodocea nodosa seagrass meadows were described across their entire distribution range in the Mediterranean Sea and adjacent Atlantic Ocean. Specifically, the study tested whether there are differences in the composition of fish assemblages between those ecoregions encompassed by the distribution range of C. nodosa, and whether these differences in composition are connected with differences in bioclimatic affinities of the fish faunas. A literature review resulted in a total of 19 studies, containing 22 fish assemblages at 18 locations. The ichthyofauna associated with C. nodosa seagrass meadows comprises 59 families and 188 species. The western Mediterranean (WM) Sea has the highest species richness (87 species). Fish assemblages from the Macaronesia-Canary Islands, the Sahelian Upwelling, South European Atlantic Shelf and the WM differ, in terms of assemblage composition, relative to other ecoregions. In contrast, the composition of the fish fauna from the central and eastern Mediterranean overlaps. There is a significant serial correlation in fish assemblage composition between adjacent ecoregions along the distribution range of C. nodosa. Dissimilarities in assemblage composition are connected with the geographical separation between locations, and the mean minimum annual seawater temperature is the environmental factor that explains most variation in fish assemblage composition.

Cetacean acoustic survey using towed array in the western South Atlantic shelf break

Passive acoustic towed array during ship surveys has being applied to increase the knowledge about cetacean. From 2012 to 2015, towed arrays were used to investigate cetacean distribution along the western South Atlantic shelf break. Research cruises were performed between 26°S and 38°S over the continental shelf break and slope. Acoustic tracklines comprised an average of 780 nm of effort per survey. Hydrophone arrays (Auset®) were towed 150 and 300 m behind the vessel. The system was configured to give a variable frequency response from 1592 (High Pass Filter) to 100,000 Hz. Acoustic data were recorded as .wav files. Concurrent environmental and GPS data were logged automatically using WinCruz software. Visual positive identifications were associated to the acoustic recordings. The .wav files were analyzed using partially automated detections tools complemented with visual and acoustical searched for species confirmation whenever possible. A total of nine cetacean species were acoustically detected. The most frequently species were Physeter macrocephalus, Delphinus delphis, Stenella longirostris, Orcinus orca, and Globicephala sp.. Additional studies are needed to describe acoustic parameters of the various species present in this region in order to improve automated detection systems. [This study was supported by Instituto Aqualie and was funded by BG Group and Chevron Brasil Upstream Frade LTDA.]

Nitrogen and carbon stable isotope variation in northeast Atlantic fishes and squids

Nitrogen and carbon stable isotope data are frequently used to describe the origins and transformations of organic matter. Nitrogen stable isotopes (δ15N) in tissue are used to estimate species' trophic levels, the extent of omnivory, food chain length, and community‐wide relationships between body size and trophic level; the latter leading to estimates of predator–prey mass ratios for parameterization, calibration, and validation of food web models. Carbon stable isotopes (δ13C) are used to identify pathways linking producers and consumers and for studies of migration and movement. Collectively, δ15N and δ13C, often with other stable isotopes such as δ34S, may be used to define the contribution of different producers and pathways to consumer production, to assess the trophic impacts of invasive species and habitat modification, and to predict past habitat use, movements, and migrations. Stable isotope data often complement dietary data (e.g., from stomach contents) in food web studies, because stable isotope composition is indicative of assimilated diet over months to years, depending on species, size, environment, and tissue type. There are relatively few large‐scale compilations of δ15N and δ13C data for marine species from offshore habitats, but such data facilitate comparative analysis and research into food web structure and function. The data provided comprise 5535 records for individuals of 62 species of fish and squid weighing 0.3 g to 17 920 g and sampled from the northeast Atlantic shelf seas (Celtic Sea, North Sea, Irish Sea, Channel) from 2002 to 2010. For every sampled individual the record lists: species name, date of sampling, position of sampling, body mass, percentage nitrogen in muscle tissue, percentage carbon in muscle tissue, and δ15N and δ13C natural abundance in muscle tissue. Awareness of, and access to, these data should catalyze and facilitate new research with stable isotopes, to improve understanding of marine biology, food web ecology, and human impacts on the environment.