Sampling epifauna, a necessity for a better assessment of benthic ecosystem functioning: an example of the epibenthic aggregated species Ophiothrix fragilis from the Bay of Seine

Sampling the sea bottom surface remains difficult because of the surface hydraulic shock due to water flowing through the gear (i.e., the bow wave effect) and the loss of epifauna organisms due to the gear’s closing mechanism. Slow-moving mobile epifauna, such as the ophiuroid Ophiothrix fragilis, form high-density patches in the English Channel, not only on pebbles like in the Dover Strait or offshore Brittany but also on gravel in the Bay of Seine (>5000 ind m⁻²). Such populations form high biomasses and control the water transfer from the water column to the sediment. Estimating their real density and biomass is essential for the assessment of benthic ecosystem functioning using trophic web modelling. In this paper, we present and discuss the patch patterns and sampling efficiency of the different methods for collecting in the dense beds of O. fragilis in the Bay of Seine. The large Hamon grab (0.25 m⁻²) highly under-estimated the ophiuroid density, while the Smith McIntyre appeared adequate among the tested sampling grabs. Nowadays, diving sampling, underwater photography and videos with remote operated vehicle appear to be the recommended alternatives to estimate the real density of such dense slow-moving mobile epifauna.     

Generation mechanisms for mesoscale eddies in the Gulf of Lions: radar observation and modeling

Coastal mesoscale eddies were evidenced during a high-frequency radar campaign in the Gulf of Lions (GoL), northwestern Mediterranean Sea, from June 2005 to January 2007. These anticyclonic eddies are characterized by repeated and intermittent occurrences as well as variable lifetime. This paper aims at studying the link between these new surface observations with similar structures suggested at depth by traditional acoustic Doppler current profiler measurements and investigates the eddy generation and driving mechanisms by means of an academic numerical study. The influence of the wind forcing on the GoL circulation and the eddy generation is analyzed, using a number of idealized configurations in order to investigate the interaction with river discharge, buoyancy, and bathymetric effects. The wind forcing is shown to be crucial for two different generation mechanisms: A strong northerly offshore wind (Mistral) generates a vortex column due to the bathymetric constraint of a geostrophic barotropic current, which can surface after the wind relaxes; a southerly onshore wind generates a freshwater bulge from the Rhône river discharge, which detaches from the coast and forms a well-defined surface anticyclonic eddy based on buoyancy gradients. These structures are expected to have important consequences in terms of dispersion or retention of biogeochemical material at local scales.     

Salt diapirs without well defined boundaries – a feasibility study of semi‐automatic detection

Prestack depth imaging of seismic data in complex areas such as salt structures requires extensive velocity model updating. In many cases, salt boundaries can be difficult to identify due to lack of seismic reflectivity. Traditional amplitude based segmentation methods do not properly tackle this problem, resulting in extensive manual editing. This paper presents a selection of seismic attributes that can reveal texture differences between the salt diapirs and the surrounding geology as opposed to amplitude‐sensitive attributes that are used in case of well defined boundaries. The approach consists of first extracting selected texture attributes, then using these attributes to train a classifier to estimate the probability that each pixel in the data set belongs to one of the following classes: near‐horizontal layering, highly‐dipping areas and the inside of the salt that appears more like a low amplitude area with small variations in texture. To find the border between the inside of the salt and the highly‐dipping surroundings, the posterior probability of the class salt is input to a graph‐cut algorithm that produces a smooth, continuous border. An in‐line seismic section and a timeslice from a 3D North Sea data set were employed to test the proposed approach. Comparisons between the automatically segmented salt contours and the corresponding contours as provided by an experienced interpreter showed a high degree of similarity.     

Experimental study of the carbonation of partially serpentinized and weathered peridotites

Carbonation of partially serpentinized and weathered peridotites was studied experimentally under hydrothermal conditions (T: 200 °C, P_CO2: 130-180 bars). Experiments were performed in a closed system using whole rock drill core samples (height: 1 cm, diameter: 1 cm) as starting material. The initial samples were composed mainly of meshwork serpentine, relicts of primary olivine and an olivine weathering product (deweylite assemblage). Two types of solutions, each with a total salt content corresponding to that of average seawater (35 g/L dissolved salts), were used: (1) a Na-Ca-Cl solution (12.5 g/L CaCl₂ + 22.5 g/L NaCl) and (2) a NaCl solution (35 g/L NaCl). After 15-25 days of experimental treatment, the samples were partly covered with carbonates. In addition, noticeable carbonation reactions had occurred below the sample surfaces within zones with thicknesses up to 250 μm. In the Na-Ca-Cl solution, both the olivine relicts and the deweylite assemblage were partly replaced by calcite along the surrounding serpentine veins. However, the extent of calcitization was found to be considerably larger for the deweylite assemblage than for the olivine. Bulk fluid analyses show an increase in the Mg and Si concentrations with reaction time. In the NaCl solution, the deweylite assemblage was partly dissolved resulting in large voids within the reaction zone. In contrast, the olivine was replaced by magnesite. Under the conditions of our experiments, the meshwork serpentine was not reactive, but aided fluid infiltration into the rock samples. The experimentally produced microtextures closely resemble those found in natural examples. Our study elucidates the mechanisms by which carbonates form in ultramafic rocks under relatively high P_CO2-T conditions and particularly in the presence of Ca-bearing aqueous solutions. The existence of a serpentine meshtexture and the presence of weathering products formed from primary Mg-silicates may have significant beneficial effects on in situ CO₂ mineral sequestration in ultramafic rocks.     

On the use of IPCC-class models to assess the impact of climate on Living Marine Resources

The study of climate impacts on Living Marine Resources (LMRs) has increased rapidly in recent years with the availability of climate model simulations contributed to the assessment reports of the Intergovernmental Panel on Climate Change (IPCC). Collaboration between climate and LMR scientists and shared understanding of critical challenges for such applications are essential for developing robust projections of climate impacts on LMRs. This paper assesses present approaches for generating projections of climate impacts on LMRs using IPCC-class climate models, recommends practices that should be followed for these applications, and identifies priority developments that could improve current projections. Understanding of the climate system and its representation within climate models has progressed to a point where many climate model outputs can now be used effectively to make LMR projections. However, uncertainty in climate model projections (particularly biases and inter-model spread at regional to local scales), coarse climate model resolution, and the uncertainty and potential complexity of the mechanisms underlying the response of LMRs to climate limit the robustness and precision of LMR projections. A variety of techniques including the analysis of multi-model ensembles, bias corrections, and statistical and dynamical downscaling can ameliorate some limitations, though the assumptions underlying these approaches and the sensitivity of results to their application must be assessed for each application. Developments in LMR science that could improve current projections of climate impacts on LMRs include improved understanding of the multi-scale mechanisms that link climate and LMRs and better representations of these mechanisms within more holistic LMR models. These developments require a strong baseline of field and laboratory observations including long time series and measurements over the broad range of spatial and temporal scales over which LMRs and climate interact. Priority developments for IPCC-class climate models include improved model accuracy (particularly at regional and local scales), inter-annual to decadal-scale predictions, and the continued development of earth system models capable of simulating the evolution of both the physical climate system and biosphere. Efforts to address these issues should occur in parallel and be informed by the continued application of existing climate and LMR models.     

Editorial: Reflections from Ireland

Responses of governance systems to change in coastal and marine ecosystems vary from country to country around the globe. Lessons can be learned from country specific case studies, as national governments strive to adapt and respond to issues of concern. This short paper highlights the benefits of a country-specific, special edition of Marine Policy, with a focus on Ireland. Despite the uniqueness of socio-ecological setting, many of the issues faced by policy makers in Ireland, such as the reconciliation of economic development and conservation needs, are shared elsewhere. This special edition was produced at the end of the ‘Celtic Tiger’ in Ireland. As a result, it reflects an era when economic development was very much a priority. The same period represented an unparalleled investment in marine science since the foundation of the State in 1922. Despite this, the papers in the Special Edition point to varying degrees of progress in policy integration and implementation. Papers covering a range of sectors (fisheries, ocean energy, conservation and fisheries) and disciplines (economics, science and management) will be of interest to academics, policy makers, students and practitioners of marine policy.     

In situ U/Pb dating of impact‐produced zircons from the Vargeão Dome (Southern Brazil)

The Vargeão impact structure was formed in the Serra Geral basaltic and rhyodacitic to rhyolitic lava flows of southern Brazil, that belong to the Paraná‐Etendeka large igneous province. The Chapecó‐type rhyodacites contain small baddeleyite crystals recently dated at 134.3 (±0.8) Ma, which is regarded as the age of this acid volcanism coeval to the flood basalt eruption. Inside the impact structure, a brecciated rhyodacitic sample displays fine veinlets containing numerous lithic fragments in a former melt. This impact breccia contains newly formed zircons, either in the veins or at the contact between a vein and the volcanic matrix. The zircons are 10–50 μm in length, clear and nearly unzoned. In situ laser‐ablation dating of the zircons provides a concordant Early Aptian age of 123.0 ± 1.4 Ma that is regarded as the age of the impact event. As in situ age determination ensures the best possible selection of the analyzed mineral grains, the methodology employed in this study also represents a promising method for dating other impact structures.     

Provenance of Pleistocene Rhine River Middle Terrace sands between the Swiss–German border and Cologne based on U–Pb detrital zircon ages

Detrital zircon U–Pb age distributions derived from samples representing ancient or relatively young large-scale continental drainage networks are commonly taken to reflect the geochronological evolution of the tapped continental area. Here, we present detrital zircon U–Pb ages and associated heavy mineral data from Pleistocene Rhine River Middle Terrace sands and equivalents between the Swiss–German border and Cologne in order to test the commonly assumed Alpine provenance of the material. Samples from eight localities were analyzed for their heavy mineral assemblages. Detrital zircon U–Pb ages were determined by laser ablation inductively coupled mass spectrometry on selected samples from five locations along the Rhine River. The zircon age populations of all samples show a similar distribution, their main peaks being between 300 and 500 Ma. Minor age populations are recognized at 570 and 1,070 Ma. The 300–400 Ma maximum reflects the Variscan basement drained by or recycled into the Rhine River and its tributaries. The 400–500 Ma peak with predominantly Early Silurian ages points to Baltica or to the mid-German crystalline rise as original sources. One distinct peak at c. 570 Ma probably represents input from Cadomian terranes. The Precambrian U–Pb ages are compatible with derivation from sources in Baltica and in northern Gondwana. The heavy mineral populations of Middle Terrace sands and equivalents are characterized to a variable extend by garnet, epidote, and green hornblende. This association is often referred to as the Alpine spectrum and is considered to be indicative of an Alpine provenance. However, hornblende, epidote, and garnet are dominant heavy minerals of collisional orogens in general and may also be derived from Variscan and Caledonian units or from intermittent storage units. A remarkable feature of the detrital zircon age distribution in the Rhine River sediments from the Swiss–German border to Cologne is the absence of ages younger than 200 Ma and in particular of any ages reflecting the Alpine orogeny between c. 100 and 35 Ma. Sediments from rivers draining the equally collisional Himalaya orogen contain detrital zircons as young as 20 Ma. Our results question the assumption that Pleistocene Rhine River sediments were directly derived from the Alps. The lag time between the formation and deposition age of the youngest zircon in the studied Pleistocene Rhine River deposits is 200 Ma. Together with the absence of Alpine zircon ages, this stresses that detrital zircon age data from ancient sedimentary units found in poorly understood tectonic or paleogeographic settings need to be interpreted with great care, one could miss an entire orogenic cycle.