North Sea Coast Research Articles

The oldest cereals in the coversand area along the North Sea coast of NW Europe, between ca. 4800 and 3500 cal BC, at the wetland site of ‘Bazel-Sluis’ (Belgium)

The excavations of the multiperiod (Mesolithic-Neolithic) site of Bazel-Sluis in the lower Scheldt valley in Belgium revealed the presence of a number of carbonized cereal grains, of which 24 were radiocarbon dated. These results indicate three chronological clusters, respectively between 4850/4610 – 4530/4330 cal BC; 4430/4250 – 4270/3980 cal BC; and 4050/3840 – 3680/3480 cal BC. In accordance with this chronology the cultural remains on the site are affiliated with the Late Mesolithic, Swifterbant and Michelsberg cultural groups, and display contacts with the Bandkeramik and Rössen cultures. The oldest cereal remains are the oldest thus far recorded in a Mesolithic context in the coversand region of North-Western Europe. When assessed within the framework of the archaeological data from the wider region it seems that these finds are to be explained within a first stage of neolithisation, associated with contacts with the Blicquy and Rössen cultural groups. From ca. 4300 cal BC the Michelsberg cultural group seems to be the main instigator for the further advance of the neolithisation process.

A NEW SAR CLASSIFICATION SCHEME FOR SEDIMENTS ON INTERTIDAL FLATS BASED ON MULTI-FREQUENCY POLARIMETRIC SAR IMAGERY

Abstract. We present a new classification scheme for muddy and sandy sediments on exposed intertidal flats, which is based on synthetic aperture radar (SAR) data, and use ALOS-2 (L-band), Radarsat-2 (C-band) and TerraSAR-X (X-band) fully polarimetric SAR imagery to demonstrate its effectiveness. Four test sites on the German North Sea coast were chosen, which represent typical surface compositions of different sediments, vegetation, and habitats, and of which a large amount of SAR is used for our analyses. Both Freeman-Durden and Cloude-Pottier polarimetric decomposition are utilized, and an additional descriptor called Double-Bounce Eigenvalue Relative Difference (DERD) is introduced into the feature sets instead of the original polarimetric intensity channels. The classification is conducted following Random Forest theory, and the results are verified using ground truth data from field campaigns and an existing classification based on optical imagery. In addition, the use of Kennaugh elements for classification purposes is demonstrated using both fully and dual-polarization multi-frequency and multi-temporal SAR data. Our results show that the proposed classification scheme can be applied for the discrimination of muddy and sandy sediments using L-, C-, and X-band SAR images, while SAR imagery acquired at short wavelengths (C- and X-band) can also be used to detect more detailed features such as bivalve beds on intertidal flats.

ARCHAEOLOGICAL SURVEYS ON THE GERMAN NORTH SEA COAST USING HIGH-RESOLUTION SYNTHETIC APERTURE RADAR DATA

Abstract. We show that high-resolution space-borne Synthetic Aperture Radar (SAR) imagery with pixel sizes well below 1 m2 can be used to complement archaeological surveys in areas that are difficult to access. After major storm surges in the 14th and 17th centuries, vast areas on the German North Sea coast were lost to the sea. Areas of former settlements and historical land use were buried under sediments for centuries, but when the surface layer is driven away under the permanent action of wind, currents, and waves, they appear again on the Wadden Sea surface. However, the frequent flooding and erosion of the intertidal flats make any archaeological monitoring a difficult task, so that remote sensing techniques appear to be an efficient and cost-effective instrument for any archaeological surveillance of that area. Space-borne SAR images clearly show remnants of farmhouse foundations and of former systems of ditches, dating back to the 14th and to the 16th/17th centuries. In particular, the very high-resolution acquisition (staring spotlight) mode of the German TerraSAR/ TanDEM-X satellites allows for the detection of various kinds of residuals of historical land use with high precision. In addition, we also investigate the capability of SARs working at lower microwave frequencies (on Radarsat-2) to complement our archaeological survey of historical cultural traces, some of which have been unknown so far.

Sabellaria spinulosa (Polychaeta, Annelida) reefs in the Mediterranean Sea: Habitat mapping, dynamics and associated fauna for conservation management

Bio-constructions by Sabellaria worms play a key functional role in the coastal ecosystems being an engineer organism and for this reason are the object of protection. The most widespread reef building species along Atlantic and Mediterranean coasts is S. alveolata (L.), while the aggregations of S. spinulosa are typically limited to the North Sea coasts. This paper constitutes the first detailed description of unusual large S. spinulosa reefs in the Mediterranean Sea. Defining current health status and evaluating the most important threats and impacts is essential to address conservation needs and design management plans for these large biogenic structures. Present knowledge on Mediterranean reefs of S. alveolata is fragmentary compared to Northeast Atlantic reefs, and concerning S. spinulosa, this paper represents a focal point in the knowledge on Mediterranean reefs of this species. A one-year study on temporal changes in reef structure and associated fauna is reported. The annual cycle of S. spinulosa reef shows a spawning event in winter-early spring, a period of growth and tubes aggregation from spring-early summer to autumn and a degeneration phase in winter. The variations exhibited in density of the worm aggregation and the changes in the reef elevation highlight a decline and regeneration of the structure over a year. The many ecological roles of the S. spinulosa reef were mainly in providing a diversity of microhabitats hosting hard and sandy bottom species, sheltering rare species, and producing biogenic structures able to provide coastal protection. The Mediterranean S. spinulosa reef does not shelter a distinctive associated fauna; however the richness in species composition underscores the importance of the reef as a biodiversity hot-spot. Finally, the roles of the biogenic formations and their important biotic and physical dynamics support the adoption of strategies for conservation of Mediterranean S.spinulosa reefs, according to the aims of the Habitat Directive.

The potential for dispersant use as a maritime oil spill response measure in German waters

In case of an oil spill, dispersant application represents a response option, which enhances the natural dispersion of oil and thus reduces coating of seabirds and coastal areas. However, as oil is transferred to the water phase, a trade-off of potential harmful effects shifted to other compartments must be performed. This paper summarizes the results of a workshop on the current knowledge on risks and benefits of the use of dispersants with respect to specific conditions encountered at the German sea areas. The German North Sea coast is a sensitive ecosystem characterised by tidal flats, barrier islands and salt marshes. Many prerequisites for a potential integration of dispersants as spill response option are available in Germany, including sensitivity maps and tools for drift modelling of dispersed and undispersed oil. However, open scientific questions remain concerning the persistence of dispersed oil trapped in the sediments and potential health effects.

Impact of Extraction Methods on the Detectable Protein Complement of Metaproteomic Analyses of Marine Sediments.

Metaproteomic analysis targets proteins, the catalytic entities in the habitat, thereby providing direct insights into the metabolic activity of the community studied. A major challenge still remaining for metaproteomics is the effective and comprehensive extraction of proteins from environmental samples, due to their high complexity with respect to organismic diversity and abundance range. Moreover, in certain habitats, the inherent matrix may interfere with protein extraction. In recent years, several studies reported different protein extraction methods for soils known for their complex geochemistry, but only three analyzed marine sediments that generally comprise different though similarly complex geochemistry. In this study, the impact of four different extraction methods was investigated for coastal North Sea and deep sea Pacific Ocean sediments. The extraction methods comprised (i) phenol, (ii) SDS, (iii) a mixture of SDS and phenol, and (iv) urea and thiourea. Prior to extraction, a cell and protein standard (CPS) was added to the sediment samples to trace recovery of proteins from different subcellular locations as well as dissolved BSA. While each extraction method detected distinct peptide complements, SDS-phenol extraction generally achieved highest protein yield and most comprehensive CPS protein identification. Application of two different methods was shown to further improve proteome coverage.

SAR Imaging of Archaeological Sites on Intertidal Flats in the German Wadden Sea

We show that high-resolution space-borne synthetic aperture radar (SAR) imagery with pixel sizes smaller than 1 m2 can be used to complement archaeological surveys on intertidal flats. After major storm surges in the 14th and 17th centuries (“Grote Mandrenke”), vast areas on the German North Sea coast were lost to the sea. Areas of settlements and historical farmland were buried under sediments for centuries, but when the surface layer is driven away under the action of wind, currents, and waves, they appear again on the Wadden Sea surface. However, frequent flooding and erosion of the intertidal flats make any archaeological monitoring a difficult task, so that remote sensing techniques appear to be an efficient and cost-effective instrument for any archaeological surveillance of that area. Space-borne SAR images clearly show remains of farmhouse foundations and of former systems of ditches, dating back to the times before the “Grote Mandrenke”. In particular, the very high-resolution acquisition (“staring spotlight”) mode of the TerraSAR/TanDEM-X satellites allows detecting various kinds of remains of historical land use at high precision. Moreover, SARs working at lower microwave frequencies (e.g., that on Radarsat-2) may complement archaeological surveys of historical cultural traces, some of which have been unknown so far.

Detection of Bivalve Beds on Exposed Intertidal Flats Using Polarimetric SAR Indicators

We propose new indicators for bivalve (oyster and mussel) beds on exposed intertidal flats, derived from dual-copolarization (HH + VV) TerraSAR-X, Radarsat-2, and ALOS-2 images of the German North Sea coast. Our analyses are based upon the Kennaugh element framework, and we show that different targets on exposed intertidal flats exhibit different radar backscattering characteristics, which manifest in different magnitudes of the Kennaugh elements. Namely, the inter-channel correlation’s real (K3) and imaginary (K7) part can be used to distinguish bivalve beds from surrounding sandy sediments, and together with the polarimetric coefficient (i.e., the normalized differential polarization ratio, K0/K4) they can be used as indicators for bivalve beds using multi-frequency dual-copolarization SAR data. Our results show that continuous bivalve bed monitoring is possible using dual-copolarimetric SAR acquisitions at all radar wavelengths.

Geoarchaeological evidence of marshland destruction in the area of Rungholt, present-day Wadden Sea around Hallig Südfall (North Frisia, Germany), by the Grote Mandrenke in 1362 AD

Geophysical and geoarchaeological investigations were carried out in the Wadden Sea of North Frisia (Schleswig-Holstein, Germany) to elucidate major environmental changes that considerably altered the coastal landscape since medieval times. Between the 12th and 14th cent. AD, the present-day tidal flats around the marsh island Hallig Südfall belonged to the historical Edomsharde district and its main settlement Rungholt. For North Frisia, it is well known that during medieval and early modern times, extreme storm surges caused major land losses associated with a massive landward shift of the coastline. Today, cultural traces like remains of dikes, drainage ditches, terps or even plough marks are still visible in the Wadden Sea and provide evidence of the once cultivated marshland.Based on a multi-proxy analysis of sediment cores retrieved from the tidal flat zone around Hallig Südfall and from the Hallig itself, we identified a late medieval paleosol associated with the formerly cultivated marshland most probably belonging to the Edomsharde and local trade centre of Rungholt. Around Hallig Südfall, remains of medieval marsh deposits were found partly eroded and covered by a coarse-grained high-energy deposit including abundant shell debris and artefacts. Based on sedimentological, micropaleontological, geochemical and geochronological data, we conclude that these deposits are associated with the 1st Grote Mandrenke (or St. Marcellus’ flood), an extreme storm surge event in 1362 AD. Our results, for the first time, provide geological evidence of this 1362 AD storm surge for the Wadden Sea of North Frisia. Moreover, marshland on Hallig Südfall dating to the 17th-18th cent. AD was found covered by a thick layer of storm surge sand and shell debris which seems to be associated with one of the major storm event that hit the German North Sea coast in modern times, e.g. the 2nd Grote Mandrenke (or Burchardi flood) in 1634 AD or the Christmas flood in 1717 AD.

Impact of North Atlantic Teleconnection Patterns on Northern European Sea Level

Northern European sea levels show a non-stationary link to the North Atlantic Oscillation (NAO). The location of the centers of the NAO dipole, however, can be affected through the interplay with the East Atlantic (EAP) and the Scandinavian (SCAN) teleconnection patterns. Our results indicate the importance of accounting for the binary combination of the NAO with the EAP/SCAN for better understanding the non-stationary drivers inducing sea level variations along the European coasts. By combining altimetry and tide gauges, we find that anomalously high monthly sea levels along the Norwegian (North Sea) coast are predominantly governed by same positive phase NAO+/EAP+ (NAO+/SCAN+) type of atmospheric circulation, while the Newlyn and Brest tide gauges respond markedly to the opposite phase NAO−/EAP+ combination. Despite these regional differences, we find that coherent European sea level changes project onto a pattern resembling NAO+/SCAN+, which is signified by pressure anomalies over Scandinavia and southern Europe forcing winds to trace the continental slope, resulting in a pile-up of water along the European coasts through Ekman transport. We conclude that taking into consideration the interaction between these atmospheric circulation regimes is valuable and may help to understand the time-varying relationship between the NAO and European mean sea level.

Is the vertical distribution of meiofauna similar in two contrasting microhabitats? A case study of a macrotidal sandy beach

Tides are an important forcing factor of macrotidal sandy beaches because they are directly responsible for the local morphodynamic conditions. Macrotidal beaches may harbor different microhabitats such as sandbars and runnels. We evaluated the influence of tides on the vertical distribution of meiofaunal organisms, particularly nematodes, in these two microhabitats at De Panne Beach, on the North Sea coast of Belgium. The 11 meiofaunal groups found were Acari, Amphipoda, Copepoda, Gastrotricha, Nematoda, Oligochaeta, Ostracoda, Polychaeta, Rotifera, Tardigrada and Turbellaria. The nematodes were identified to species level; the 147 species found included 112 in the sandbar and 117 in the runnel. Only turbellarians and nematodes migrated upward during low tide in the sandbar. The response of the nematodes was species-specific; during low tide, they migrated upward in the sandbar and downward toward deeper layers of the sediment in the runnel. These migration patterns were attributed to the feeding strategies in the sandbar (i.e. possible increase of diatom biomass in the surface layer due to high solar incidence), while environmental variables best explained the migration patterns in the runnel (i.e. preferred grain size and amount of total organic carbon). These results suggest a dissimilar vertical migration of the meiofauna over the tidal cycle in the two microhabitats. We attribute the vertical distribution of nematode species and some other meiofaunal groups to active migration toward preferred sites with more food or better environmental conditions. This study also indicated that other variables such as predation and competition, rather than the commonly studied physical variables should be included in future sampling designs of sandy-beach meiofauna assessments, since the environmental variables measured here could not fully explain the vertical distributions of the major meiofaunal groups or the community as a whole.

Importance of bumblebees (Hymenoptera: Apidae: Bombus spp.) in the diet of European Bee-eaters (Merops apiaster) breeding in oceanic climate

Breeding attempts of European Bee-eater (Merops apiaster) pairs have occasionally been documented far north of the species’ normal range, exceptionally as far as the 17 °C July isotherm. These attempts often failed—in many cases in association with adverse and fluctuating weather conditions, which are thought to lead to, amongst other effects, starvation of the nestlings. This lead to the question: what dietary conditions must be fulfilled for the adults to stay at sites characterized by a cool-wet sea climate and raise chicks successfully? Information regarding this question is very sparse in the literature, but an exceptional opportunity to investigate it arose in 2015 when ten pairs of the species arrived as classic ‘overshooters’ at the Frisian North Sea coast in northwest Germany (53°70′N, 7°88′E) and started to breed. By means of photographic documentation, 1205 prey items were identified; bumblebees (Bombus spp.) were the most abundant prey group representing 38.0% of the items and 60.2% of the total prey mass. A review of 32 European studies (north of the 21 °C July isotherm) on the species’ diet composition revealed that the proportion of bumblebees in the prey increases the more the climate approaches oceanic in character (median of the proportion for adults = 38.6%, for nestlings = 55.0%). As the climate becomes increasingly continental, bumblebees decline in their abundance and importance behind other airborne insect groups (median adults = 16.1%, nestlings = 29.4%). All in all, the following factors may well have been instrumental in successful chick rearing at the Frisian North Sea coast: (1) a manifestly high abundance of bumblebees as a basic food supply, (2) considerable insect diversity (and abundance) in the main feeding habitat, and (3) the presence of beehives to provide an emergency food supply during cold and rainy weather when no other aerial insects were flying.

Photochemical oxidation of dimethylsulphide to dimethylsulphoxide in estuarine and coastal waters

Dimethylsulphide (DMS) photo-oxidation and dimethylsulphoxide (DMSO) photoproduction were estimated in 26 laboratory irradiations of coastal samples from NE England (Tyne estuary) and W Scotland (Loch Linnhe and River Nant at Taynuilt). Pseudo-first order rate constants of DMS photo-oxidation (0.038 h−1 to 0.345 h−1) and DMSO photo-production (0.017 h−1 to 0.283 h−1) varied by one order of magnitude and were lowest in the coastal North Sea. Estuarine samples (salinity S < 30) had a mean DMSO yield of 96 ± 16% (n = 14), consistent with 1:1 M conversion via photosensitised oxidation by singlet oxygen. Photochemical rate constants were strongly correlated with coloured dissolved organic matter (CDOM) absorption coefficients at 350 nm, a350. Variations in a350 explained 61% (R2 = 0.61, n = 26) and 73% (R2 = 0.73, n = 17) of the variability in DMS photo-oxidation and DMSO production, respectively. However, CDOM normalised photochemical rate constants increased strongly towards coastal waters exhibiting lowest CDOM absorbance, indicating water samples of marine character (S > 30) to be most reactive with respect to DMS photo-oxidation. Estimates of water column averaged DMS photo-oxidation rate constants, obtained by scaling to mean daily irradiance (July, NE England) and mid-UV underwater irradiance, were 0.012 d−1, 0.019 d−1, and 0.017 d−1 for upper estuary (S < 20), lower estuary (20 < S < 30) and coastal waters (S > 30), at the lower end of previous observations. Comparing our water column averaged DMS photo-oxidation rate constants with estimated DMS losses via air-sea gas exchange and previously reported biological consumption implies that DMS photochemical removal is of only minor importance in our study area.

Long-term temporal and spatial changes in the richness and relative abundance of the inshore fish community of the British North Sea Coast

Changes in temporal and spatial composition of the British inshore North Sea fish community are reviewed. Sampling from the cooling water filter screens of power stations bordering the North Sea commenced in the early 1960s. To date, a total of 112 marine fish species have been recorded, a high proportion of the total inshore fish species complement of shallow North Sea British waters. The unrecorded top predators, such as large sharks, swordfish and tuna are not regularly observed in waters <20m deep. The greatest species number (92) is reported from fully marine waters in East Anglia. A group of 18 ubiquitous, high abundance, taxa form a core inshore community throughout the region in both estuarine and marine waters. They show a high level of concordance in relative abundance along the British east coast from the 1970s to the present. A second group of 20 species are abundant, but more restricted in habitat. Where they do occur, this group are usually always present and form together with the ubiquitous taxa the local core community. The third group of 67 species, are never abundant and are restricted in occurrence both spatially and temporally. Total species richness declines between 50 and 56°N, probably because high summer temperatures allow the southern North Sea to support summer migrants entering via the English Channel. Since the 1960s there has been a notable recovery in fish diversity and abundance in large industrialised estuaries such as the Thames and the Firth of Forth. Linked to spawning and nursery habitat gain, smelt, Osmerus eperlangus, and bass, Dicentrarchus labrax, have greatly increased in abundance. There is no evidence for a decline in species richness since the 1970s. However, elasmobranch species number has declined while two species Raja clavata and Scyliorhinus canicula have remained abundant and one, Mustelus asterias, has increased in abundance. It is argued that overexploitation and habitat destruction remain, as they have been for the last 300years, the most serious threats to the health of North Sea inshore fish communities. There are no clear signs that climate change is causing species loss, although it may be influencing relative species abundance as species at the southern edge of their range such as the viviparous blenny, Zoarces viviparous, have declined in the southern British North Sea. Power station water temperature records do not show a warming trend, in some estuarine locations temperature has declined with reduced thermal pollution; the temperature record cannot explain the observed major changes in fish relative abundance observed since the 1970s.

Hot Spots of Nitrification in the Elbe Estuary and Their Impact on Nitrate Regeneration

Estuaries act as an organic matter and nutrient filter in the transition between the land, rivers and the ocean. In the past, high nutrient and organic carbon load and low oxygen concentration made the Elbe River estuary (NW Europe) a sink for dissolved inorganic nitrogen. A recent reduction in loads and subsequent recovery of the estuary changed its biogeochemical function, so that nitrate is no longer removed on its transition towards the coastal North Sea. Nowadays in the estuary, nitrification appears to be a significant nitrate source. To quantify nitrification and determine actively nitrifying regions in the estuary, we measured the concentrations of ammonium, nitrite and nitrate, the dual stable isotopes of nitrate and net nitrification rates in the estuary on five cruises from August 2012 to August 2013. The nitrate concentration increased markedly downstream of the port of Hamburg in summer and spring, accompanied by a decrease of nitrate isotope values that was clearest in summer exactly at the location where nitrate concentration started to increase. Ammonium and nitrite peaked in the Hamburg port region (up to 18 and 8 μmol L−1, respectively), and nitrification rates in this region were up to 7 μmol L−1 day−1. Our data show that coupled re-mineralization and nitrification are significant internal nitrate sources that almost double the estuary’s summer nitrate concentration. Furthermore, we find that the port of Hamburg is a hot spot of nitrification, whereas the maximum turbidity zone (MTZ) only plays a subordinate role in turnover of nitrate.

Top-down control of carbon sequestration: grazing affects microbial structure and function in salt marsh soils.

Tidal wetlands have been increasingly recognized as long-term carbon sinks in recent years. Work on carbon sequestration and decomposition processes in tidal wetlands focused so far mainly on effects of global-change factors such as sea-level rise and increasing temperatures. However, little is known about effects of land use, such as livestock grazing, on organic matter decomposition and ultimately carbon sequestration. The present work aims at understanding the mechanisms by which large herbivores can affect organic matter decomposition in tidal wetlands. This was achieved by studying both direct animal-microbe interactions and indirect animal-plant-microbe interactions in grazed and ungrazed areas of two long-term experimental field sites at the German North Sea coast. We assessed bacterial and fungal gene abundance using quantitative PCR, as well as the activity of microbial exo-enzymes by conducting fluorometric assays. We demonstrate that grazing can have a profound impact on the microbial community structure of tidal wetland soils, by consistently increasing the fungi-to-bacteria ratio by 38-42%, and therefore potentially exerts important control over carbon turnover and sequestration. The observed shift in the microbial community was primarily driven by organic matter source, with higher contributions of recalcitrant autochthonous (terrestrial) vs. easily degradable allochthonous (marine) sources in grazed areas favoring relative fungal abundance. We propose a novel and indirect form of animal-plant-microbe interaction: top-down control of aboveground vegetation structure determines the capacity of allochthonous organic matter trapping during flooding and thus the structure of the microbial community. Furthermore, our data provide the first evidence that grazing slows down microbial exo-enzyme activity and thus decomposition through changes in soil redox chemistry. Activities of enzymes involved in C cycling were reduced by 28-40%, while activities of enzymes involved in N cycling were not consistently affected by grazing. It remains unclear if this is a trampling-driven direct grazing effect, as hypothesized in earlier studies, or if the effect on redox chemistry is plant mediated and thus indirect. This study improves our process-level understanding of how grazing can affect the microbial ecology and biogeochemistry of semi-terrestrial ecosystems that may help explain and predict differences in C turnover and sequestration rates between grazed and ungrazed systems.

Genesis of soils from Holocene tidal deposits at the North Sea coast

The Southern North Sea coast has served as an exemplification to analyse and discuss the genesis of soils from Holocene tidal deposits. The accumulation wedge of Holocene tidal deposits at the North Sea coast is artificially embanked for the most part. In the enclosed area (hinterland) a variety of different soils developed. Disparate models attempting to explain the genesis of these soils deduce genesis of hinterland soils from recent foreland conditions, disregarding that geogenic preconditions have fundamentally changed. By consolidating and reviewing established literature we show that differences in geogenic preconditions are the initiating key for a feasible model. Describing geogenic preconditions to infer pedogenic processes, we develop a model comprising four different development pathways. High settling velocities and regular flooding, as present in the foreland, cause high inputs of mineral sediments and carbonate, moderate sulfur dynamics and thus the development of calcareous soils. Synsedimentary decalcification prevails in irregularly flooded areas due to enduring low sedimentation rates, low carbonate inputs and moderate sulfur dynamics under alternating redox states, as mainly proposed for the unobstructed landscape. High contents of soil organic matter (SOM) facilitate intensive sulfur dynamics creating potential acid sulfate soils (PASS), which become extreme acid upon oxidation (actual acid sulfate soils (AASS)). A great gradient in depositional conditions, occurring at unobstructed plain coasts, enables the deposition of deflocculated fine-grained sediments which promotes the formation of very compact soils with low water conductivities. Although this proposed model is based mainly on conditions known from the German North Sea coast, it is shown that shaping geogenic and pedogenic processes are applicable to other humid coastal regions around the world.

Sensitivity of Risk-Based Maintenance Planning of Offshore Wind Turbine Farms

Inspection and maintenance expenses cover a considerable part of the cost of energy from offshore wind turbines. Risk-based maintenance planning approaches are a powerful tool to optimize maintenance and inspection actions and decrease the total maintenance expenses. Risk-based planning is based on many input parameters, which are in reality often not completely known. This paper will assess the cost impact of this incomplete knowledge based on a case study following risk-based maintenance planning. The sensitivity study focuses on weather forecast uncertainties, incomplete knowledge about the needed repair time on the site as well as uncertainties about the operational range of the boat and helicopter used to access the broken wind turbine. The cost saving potential is estimated by running Crude Monte Carlo simulations. Furthermore, corrective and preventive (scheduled and condition-based) maintenance strategies are implemented. The considered case study focuses on a wind farm consisting of ten 6 MW turbines placed 30 km off the Danish North Sea coast. The results show that the weather forecast is the uncertainty source dominating the maintenance expenses increase when considering risk-based decision-making uncertainties. The overall maintenance expenses increased by 70% to 140% when considering uncertainties directly related with risk-based maintenance planning.

Fossil bog soils (‘dwog horizons’) and their relation to Holocene coastal changes in the Jade Weser region, southern North Sea, Germany

After the deceleration of the postglacial marine transgression, the German North Sea coast was subject to deposition of a complex pattern of subtidal to terrestrial facies. This study aims at reconstructing these facies changes in the ‘Land Wursten’ region (Lower Saxony) by focussing on so-called dwog horizons (incipient soil horizons of the pre-engineered salt marshes). We explore their implications for relative sea-level reconstructions and their indication for early settlement activities. Archive drilling data (1960, provided by the ‘Landesamt fur Bergbau, Energie und Geologie’) were analysed to create five high-resolution stratigraphic cross sections. Three new drilling records were subjected to sedimentological and microfaunal investigations and interpreted to verify and calibrate the archive data. Two dwog horizons were found and 14C-AMS dated. We found basal salt marsh deposits inundated by a high-energy event and covered by tidal flat sediments. The thick tidal flat unit is again overlain by salt marsh deposits indicating the transition from a shallow marine to a terrestrial environment where dwogs were developed and covered by episodic marine incursions. The ages of the dwogs (1128–969 cal BC; cal AD 1426–1467) do not correlate with known layers of adjacent settlement sites and are critically discussed. However, we show that they correlate with phases of stagnant regional relative sea level (RSL) and can be used as RSL indicators. The combined archive and modern data provide valuable information for the RSL reconstruction and palaeoenvironmental changes. However, further research is recommended to accomplish more detailed information about coastal response during the Holocene sea-level changes and implications for settlement dynamics.

Impacts of Past Climate and Environmental Change: The Effects on Prehistoric and Roman Coastal Saltmaking in Lincolnshire, UK

As an example of the effect of climate and environmental and, therefore, landscape change on archaeological sites this paper sets out the positions of known prehistoric and Roman salterns in Lincolnshire (Eastern England) and the present condition and archaeological potential of such sites. Their current position – some recorded as surface finds and some sealed by later sedimentation – demonstrates the dynamic nature of wetland landscapes in various parts of Lincolnshire. Both freshwater and marine deposits have at times affected the salterns, sometimes in restricted zones and sometimes over extensive areas. Also considered are methodologies for discovering such sites. The paper is a case study of one type of coastal site in Lincolnshire and serves as an example of the localised and complex chronology of sedimentation and/or erosion episodes in just one area. It may reflect wider changes around the North Sea coast and raises issues of generic importance.