Search Results (9)

Several skate and ray species are widely distributed in European Atlantic waters but many aspects still remain unknown: stock structure, species dynamics, migration movements, and spawning areas. Rays are vulnerable to overfishing and are bycatch species in the bottom fisheries in European waters of the International Council for the Exploration of the Sea (ICES). At least eight species of skate and rays inhabit north and northwestern Iberian waters. In offshore waters of the continental shelf, the most abundant is the thornback ray, Raja clavata, followed by R. montagui and Leucoraja naevus. In shallower waters, the most abundant species are R. undulata, R. microocellata, and R. brachyura. Some elasmobranchs are considered to have high survival rates, including the skates. In European waters, several studies have estimated the survival of discarded rays caught by different gear types. These species are usually discarded due to their small sizes or lack of fishing quota. Several commercial species are under an exemption for the landing obligation due to their high survivability when discarded in southwestern European waters. The estimates of the specific composition of landing skates are arduous to obtain due to the difficulties of certifying the identification of landed rays. This study presents the survival rates of discarded skates and rays caught by commercial trawlers and gillnetters operating in north Atlantic Spanish waters. Our results indicate that approximately 66.8% and 100% of sampled rays caught by bottom trawlers and trammel nets, respectively, survive fishing and handling operations on board. Detailed quantitative and biological data of species on catches and discards in Galician fisheries are also presented. Following the ICES recommendations, a tagging program has been carried out to improve knowledge of the status and spatial movements of species. Understanding the patterns of discarding and survivability rates could be used to reduce the fishing impact on skate and ray stocks. Full article

A feed-forward neural network (FFNN) was used to estimate the monthly climatology of partial pressure of CO₂ (pCO_2W) at a spatial resolution of 1° latitude by 1° longitude in the continental shelf of the European Arctic Sector (EAS) of the Arctic Ocean (the Greenland, Norwegian, and Barents seas). The predictors of the network were sea surface temperature (SST), sea surface salinity (SSS), the upper ocean mixed-layer depth (MLD), and chlorophyll-a concentration (Chl-a), and as a target, we used 2 853 pCO_2W data points from the Surface Ocean CO₂ Atlas. We built an FFNN based on three major datasets that differed in the Chl-a concentration data used to choose the best model to reproduce the spatial distribution and temporal variability of pCO_2W. Using all physical–biological components improved estimates of the pCO_2W and decreased the biases, even though Chl-a values in many grid cells were interpolated values. General features of pCO_2W distribution were reproduced with very good accuracy, but the network underestimated pCO_2W in the winter and overestimated pCO_2W values in the summer. The results show that the model that contains interpolating Chl-a concentration, SST, SSS, and MLD as a target to predict the spatiotemporal distribution of pCO_2W in the sea surface gives the best results and best-fitting network to the observational data. The calculation of monthly drivers of the estimated pCO_2W change within continental shelf areas of the EAS confirms the major impact of not only the biological effects to the pCO_2W distribution and Air-Sea CO₂ flux in the EAS, but also the strong impact of the upper ocean mixing. A strong seasonal correlation between predictor and pCO_2W seen earlier in the North Atlantic is clearly a yearly correlation in the EAS. The five-year monthly mean CO₂ flux distribution shows that all continental shelf areas of the Arctic Ocean were net CO₂ sinks. Strong monthly CO₂ influx to the Arctic Ocean through the Greenland and Barents Seas (>12 gC m⁻² day⁻¹) occurred in the fall and winter, when the pCO_2W level at the sea surface was high (>360 µatm) and the strongest wind speed (>12 ms⁻¹) was present. Full article

The fast development of the offshore energy industry becomes an essential component of resilient economies in most of the countries around the North Sea, addressing an increasing demand for cost-efficient and environmentally safe energy sources. Offshore wind farms are planned to be installed further away from the coasts to ensure stronger and more stable wind resources in this region. Oil and gas extraction infrastructures are also planned to move into deeper areas of the continental shelf and continental shelf slopes to explore new fields. These deeper areas of the ocean are characterised by harsh environmental conditions: stronger winds, larger waves and strong shelf slope currents, inducing considerably larger loads on offshore structures. This study brings together operational physical oceanography and the mathematics of fluid-structure interactions to estimate the likelihood of extreme environmental loads on offshore structures in the North Sea. We use the state-of-the-art Met Office high resolution ocean forecasting system, which provides high-frequency data on ocean and tidal currents, wave heights and periods and winds at a ~7 km horizontal resolution grid, spanning the North–West European Shelf. The Morison equation framework is used to calculate environmental loads on various types of offshore structures that are typically employed by the offshore industries in the North Sea. We use hourly data for a 2-year period to analyse the spatio-temporal variability of mean and extreme hydrodynamic loads and derive the relative contributions of currents, waves and winds in the region. The results indicate that waves dominate extreme hydrodynamic forces on the shallow shelf, whereas the current contribution is important at the shelf break and in the English Channel. Full article

Offshore oil and gas operations carry a high risk of explosions, which can be efficiently prevented in many cases. The two most used approaches for prevention are: (1) the “International Electrotechnical Commission System for Certification to Standards Relating to Equipment for Use in Explosive Atmospheres” (IECEx) and (2) European “Atmosphere Explosible” (ATEX) schemes. The main shortcoming for the IECEx scheme is in the fact that it does not cover nonelectrical equipment, while for the ATEX scheme, it is due to the allowed self-certification for a certain category of equipment in areas with a low probability of explosions, as well as the fact that it explicitly excludes mobile offshore drilling units from its scope. An advantage of the IECEx scheme is that it is prescribed by the US Coast Guard for protection against explosions on foreign mobile offshore drilling units, which intend to work on the US continental shelf but have never operated there before, with an additional requirement that the certificates should be obtained through a US-based Certified Body (ExCB). Therefore, to avoid bureaucratic obstacles and to be allowed to operate with minimized additional costs both in the US and the EU/EEA’s offshore jurisdictions (and very possibly worldwide), all mobile offshore drilling units should be certified preferably as required by the US Coast Guard. Full article

The impact of tides on the Bay of Biscay dynamics is investigated by means of an ocean model twin-experiment, consisted of two simulations with and without tidal forcing. The study is based on a high-resolution ($1/{36}^{\circ }$) regional configuration of NEMO (Nucleus for European Modelling of the Ocean) performing one-year simulations. The results highlight the imprint of tides on the thermohaline properties and circulation patterns in three distinct dynamical areas in the model domain: the abyssal plain, the Armorican shelf and the English Channel. When tides are activated, the bottom stress is increased in the shelf areas by about two orders of magnitude with respect to the open ocean, subsequently enhancing vertical mixing and weakening stratification in the bottom boundary layer. The most prominent feature reproduced only when tides are modelled, is the Ushant front near the entrance of the English Channel. Tides appear also to constrain the freshwater transport of rivers from the continental shelf to the open ocean. The spectral analysis revealed that the tidal forcing contributes to the SSH variance at high frequencies near the semidiurnal band and to the open ocean mesoscale and small-scale features in the presence of summer stratification pattern. Full article

Significant amounts of anthropogenic radionuclides were introduced in ocean waters following nuclear atmospheric tests and development of the nuclear industry. Dispersion of artificial dissolved radionuclides has been extensively measured for decades over the North-European continental shelf. In this area, the radionuclide measurement and release fluxes databases provided here between 1982 and 2016 represent an exceptional opportunity to validate dispersion hydrodynamic models. This work gives accessibility to these data in a comprehensive database. The MARS hydrodynamic model has been applied at different scales to reproduce the measured dispersion in realistic conditions. Specific methods have been developed to obtain qualitative and quantitative results and perform model/measurement comparisons. Model validation concerns short to large scales with dedicated surveys following the dispersion: it was performed within a two- and three-dimensional framework and from minutes and hours following a release up to several years. Results are presented concerning the dispersion of radionuclides in marine systems deduced from standalone measurements, or according to model comparisons. It allows characterizing dispersion over the continental shelf, pathways, transit times, budgets and source terms. This review presents the main approaches developed and types of information derived from studies of artificial radiotracers using observations, hydrodynamic models or a combination of the two, based primarily on the new featured datasets. Full article

In northern Europe, beach erosion, coastal flooding and associated damages to engineering structures are linked to mid-latitude storms that form through cyclogenesis and post-tropical cyclones, when a tropical cyclone moves north from its tropical origin. The present work analyses the hydrodynamic forcing and morphological changes observed at three beaches in the north coast of Northern Ireland (Magilligan, Portrush West’s southern and northern sectors, and Whiterocks), prior to, during, and immediately after post-tropical cyclone Katia. Katia was the second major hurricane of the active 2011 Atlantic hurricane season and impacted the British Isles on the 12–13 September 2011. During the Katia event, offshore wave buoys recorded values in excess of 5 m at the peak of the storm on the 13 September, but nearshore significant wave height ranged from 1 to 3 m, reflecting relevant wave energy dissipation across an extensive and shallow continental shelf. This was especially so at Magilligan, where widespread refraction and attenuation led to reduced shore-normal energy fluxes and very minor morphological changes. Morphological changes were restricted to upper beach erosion and flattening of the foreshore. Longshore transport was evident at Portrush West, with the northern sector experiencing erosion while the southern sector accreted, inducing a short-term rotational response in this embayment. In Whiterocks, berm erosion contributed to a general beach flattening and this resulted in an overall accretion due to sediment influx from the updrift western areas. Taking into account that the post-tropical cyclone Katia produced £100 m ($157 million, 2011 USD) in damage in the United Kingdom alone, the results of the present study represent a contribution to the general database of post-tropical storm response on Northern European coastlines, informing coastal response prediction and damage mitigation. Full article

Electrification of offshore oil and gas installations on the Norwegian continental shelf is one of several options to decrease the CO₂ emitted from these installations. However, there is an ongoing debate regarding how the increased electricity consumption will influence the CO₂ emissions in the power market, both in the short-run and in the long-run. This paper aims to address the issue and investigate the feasibility of the electrification of a large offshore area in the North Sea in comparison to standard concepts to supply energy offshore. A novel integrated model was developed for the purpose that includes and combines a process model of the offshore power generation units and a model of the European power system. The integration of the two models allows to simultaneously simulate the behavior of the offshore energy conversion systems and the effect of electrification on the onshore power system. The outcomes of the analysis show that the environmental performance of electrification is strongly affected by the selected approach to quantify the CO₂ emissions associated with power from shore. Taking standard methods to supply offshore energy as basis for comparison, the marginal effect of electrification would result in increased CO₂ emissions (+40%), while the average effect would entail large reductions in CO₂ emissions (−48% to −90%), the extent of which depends on the geographical scope selected. An analysis on the economics of electrification indicates that its economic viability would be challenging and would not be favoured by a strong European commitment towards environmental policies since the expected increase of power price will outbalance the gains for the reduced emission costs. Full article

Sediment maps developed from categorical data are widely applied to support marine spatial planning across various fields. However, deriving maps independently of sediment classification potentially improves our understanding of environmental gradients and reduces issues of harmonising data across jurisdictional boundaries. As the groundtruth samples are often measured for the fractions of mud, sand and gravel, this data can be utilised more effectively to produce quantitative maps of sediment composition. Using harmonised data products from a range of sources including the European Marine Observation and Data Network (EMODnet), spatial predictions of these three sediment fractions were generated for the north-west European continental shelf using the random forest algorithm. Once modelled these sediment fraction maps were classified using a range of schemes to show the versatility of such an approach, and spatial accuracy maps were generated to support their interpretation. The maps produced in this study are to date the highest resolution quantitative sediment composition maps that have been produced for a study area of this extent and are likely to be of interest for a wide range of applications such as ecological and biophysical studies. Full article