Dutch North Sea Research Articles

Testing non-destructive spectrometric methods for the identification and distinction of archaeological pine wood tar and birch bark tar

Archaeological findings prove the appearance and use of birch bark tar since the Middle Palaeolithic. The production and use of birch bark tar and pine wood tar has overlapped since at least the late Neolithic, but probably for much longer. The reliable chemical identification of such archaeological tar residues can offer valuable insights into, for example, ancient technical complexity, trade and culture. In this context, the scarcity of these mainly organic residue findings in the archaeological record bears the need for non-destructive analytical tools. However, there is currently no systematic proposed way for this purpose. We aim here to verify the organic nature and test the reliability of the identification of archaeological pine wood tar and birch bark tar with a combination of SEM-EDS, FTIR microspectroscopy in reflectance mode and XRD. We examined a set of experimental adhesive replicas of pine tar and birch tar in pristine form, but also after a three-year-long weathering experiment. Additionally, we studied a set of archaeological samples, consisting of Mesolithic bone/antler points with adhering hafting residues, form the Dutch North Sea. This research shows that degradation negatively influences the reliable verification and identification of the organic residue constituents significantly. SEM-EDS as a starting point of analysis verifies the residue’s organic nature, but it cannot be used to identify birch or pine tar. XRD can identify crystalline additives in the adhesive mixture, like ochre and wax, as well as phases related to the artefact’s environment of burial and provenance. Micro-FTIR is also capable of verifying the organic matter of the residue constituents. The differentiation of birch and pine tars is hindered by vibrational modes occurring in neighbouring wavenumbers for both tars, and by the limited research on degradation markers indicative of thermal treatment to prove tar production. Until reference collections also account for degradation and include a wide variety of adhesives, results of FTIR collected in reflectance mode are best treated with some caution.

Guardians of the seabed: Nature-inclusive design of scour protection in offshore wind farms enhances benthic diversity

In the past, a large part of the seabed of the southern North Sea was covered by hard substrates, including oyster beds, coarse peat banks, and glacial erratics. Human activities, particularly bottom trawl fisheries, led to the disappearance of most of these hard substrates, resulting in the loss of its associated diverse benthic life as well. However, the introduction of human-made structures such as offshore wind farms in the North Sea, offers a chance to provide habitat of similar functionality as the former hard substrates. The offshore wind farm infrastructure generally contains layers of rock material deployed at the base of the wind turbine foundations and cable crossings, so-called scour protection, aiming to prevent seabed erosion. The scour protection offers a unique habitat for rock-dwelling benthic organisms in an otherwise mostly soft-bottom environment. By designing the scour protection to be more nature-inclusive, the biodiversity of benthic life can be increased. In this study we examined the effect of substrate material and grading of the scour protection on the epibenthic biodiversity in situ. This was done by deploying research cages containing crates (n = 15) with different types of substrates (concrete, granite, and marble) on the scour protection within an offshore wind farm in the Dutch North Sea. The study revealed a significant (p < 0.05) positive relation between available substrate surface (pebble size) and taxonomic richness. Furthermore, a biological trait assessment of living habits (Tube dwelling, Burrowing, Free living, Crevice dwelling, Epi/endobiotic, and Attached) revealed variations in habit modes across substrate types, with marble and concrete samples showing greatest divergence. Marble samples contained a higher prevalence of tube dwelling organisms, whereas concrete samples contained a relatively higher prevalence of free living, epi/endobiotic and crevice dwelling organisms. The findings support the value of nature-inclusive scour protection designs, emphasizing that both taxonomic and functional diversity can be enhanced by increasing the available surface area of the scour protection and incorporating a variety of substrate types. By adopting these nature-inclusive design components, the coexistence of renewable energy production and a diverse marine benthic community can be further optimized.

Modeling Form Roughness Induced by Tidal Sand Waves

AbstractTide‐dominated sandy shelf seas, such as the Dutch North Sea, are covered by sand waves. Yet, basin‐scale hydrodynamic models do not include any sand wave information because their grid sizes are too coarse to resolve sand waves individually. We explore the possibility of parametrizing the effects of sand waves on the larger‐scale tidal flow by means of a form roughness. Specifically, our aim is to see to what extent the flow over a sand wave field can be reproduced by that over a flat seabed with an increased effective roughness (accounting for both grain and form roughness). To do so, we use two process‐based hydrodynamic models: a second order perturbation approach, and Delft3D. Both models demonstrate that the presence of sand waves causes amplitude decrease and phase shift of the tidal flow. We explore the dependencies of form roughness on different sand wave characteristics (wavelength, height and asymmetry). Shorter and higher sand waves cause a higher form roughness, while our analysis does not reveal any dependency on sand wave asymmetry. Notably, the consideration of a tidal flow, characterized by several tidal constituents, each represented by an amplitude and a phase, results in a more complex form roughness analysis than in a fluvial setting, where the flow is unidirectional and steady. We thus obtain an amplitude‐based form roughness and a phase‐based form roughness, each yielding a different value, yet displaying the same qualitative dependencies.

Robust validation of trends and cycles in sea level and tidal amplitude in the Dutch North Sea

In this paper I present a new method for analyzing long series of observed sea levels. My method provides insight in sea level and the changes over time that are required by practicing engineers, assigned the design of new, modified or renovated structures along the coast.&#x0D; After extensively reviewing earlier research of sea level and tide, I present my method. The analysis relies on the application of classic harmonic analysis, which is made operational in a script in the programming language Python. Rigorous statistical testing is introduced to test the significance of trends and cycles in sea level and tide. This application of harmonic analysis and the introduction of formal statistical testing appear both to be new in this field.&#x0D; The method is tested on six locations in the Dutch North Sea, all with continuous sea level records of at least 130 years. The results of the statistical quality tests are shown in this paper. Subsequently, I show my findings related to mean sea level, lunar and solar tide and wind setup.&#x0D; Subsequently I analyze the long-term trends and cycles in Mean Sea Level. Long-period cycles with periods equal to the oceanic perigean and nodal tide are found to be important for a correct interpretation of sea level over time. Statistical tests show that acceleration of the rate of sea level is not significant up to 2021; the last year in the dataset.&#x0D; I compare my results with contemporary projections of sea level rise. The comparison reveals that in the Dutch North Sea the projected rates of rise are a factor two or more higher than the empirical rates established in this paper.

Fouling community composition on a pilot floating solar-energy installation in the coastal Dutch North Sea

The increasing need for renewable energy has led to the transition of renewable energy devices to the marine environment. Currently, mainly offshore wind farms have been completely developed and are operational in the North Sea. The solar energy sector is also rapidly evolving and floating photovoltaics are continuously created and deployed. In this study, we investigated the colonisation patterns and community changes with time of fouling fauna on the first floating photovoltaics in the coastal Dutch North Sea. Samples were collected by divers from the underwater side of 4 floaters, coated with different anti-fouling techniques (Intersleek, GreenPowerNano PPDura, Finsulate and Pato) at two different moments, shortly after the deployment of the floaters and approximately a year later. In total, 72 fouling taxa were identified on the floaters, from which ca. 11% are known to be non-indigenous species for the region. The anti-fouling coating Intersleek seemed to work the most efficiently against fouling colonisation, since the fouling community sampled from this floater contained the least taxa. However, the small number of samples collected from the different floaters did not allow for a direct comparison between the anti-fouling coatings. The communities evolved with time, with young communities accommodating a larger number of individuals and old communities having less individuals but higher biomass, indicating that the organisms become bigger in size and compete for the available space. Nevertheless, the communities had not reached a stable climax yet, while this process might take multiple years due to the dynamic environment in which floating photovoltaics are deployed. Monitoring the fouling communities occurring on floating photovoltaics in the North Sea for a long-term is necessary to understand the effects of these new man-made structures on the marine environment, especially since floating photovoltaics are moving to offshore locations and will be possibly co-located with offshore wind farms in the future.

Performance of European oysters (Ostrea edulis L.) in the Dutch North Sea, across five restoration pilots

IntroductionThe European flat oyster (Ostrea edulis) is a biogenic reef former, internationally recognised as threatened and declining in the NE Atlantic by OSPAR and one of the focal species in nature inclusive designs in offshore windfarms in The Netherlands. Oyster reefs offer habitat to many other benthic hard substrate and fish species and provide ecosystem functions such as shelter and feeding grounds. European flat oyster reefs have disappeared from the Dutch North Sea in the early 1900s due to overfishing and diseases but are now subject of nature restoration under the Dutch Marine Strategy.MethodSince 2018, pilot projects have started in the Dutch North Sea to restore European flat oysters at suitable locations, such as offshore windfarms or natural reefs, which are protected from bottom trawling. We compared European flat oyster performance in five pilot projects, using translocated adult oysters sourced from Ireland, Norway, and the Netherlands. The aim of this research was to assess the performance of translocated oysters between pilots, to assess the installation and monitoring techniques, and to come forward with recommendations for future pilot projects.ResultsWe found that translocation of both foreign sourced flat oyster populations (Ireland and Norway in nearshore and offshore areas) and local oysters (in nearshore areas) result in good oyster performance. Oysters were able to grow (max 3.67 mm/month) and reproduce (larvae present) in their new environment. We found that growth rate was explained by origin and average water temperature, to a lesser extent by number of months, location and salinity and not to other environmental factors such as pH and O2. Correlations between growth and environmental conditions need to be considered with caution, since not all pilots were sampled just before and after the growing season. Oysters were Bonamia-negative at the start and end of the pilots, indicating that the offshore Dutch North Sea is still Bonamia-free.Discussion, conclusions, recommendationsBy the year 2050 more than ten new offshore farms will be constructed in the Dutch North Sea and some sites will be suitable for oyster restoration. We conclude that local and foreign sourced oysters performed well at all locations. Based on the success and failure of the different outplacement and monitoring techniques, we provide recommendations on good practice for the future, including developing standardized monitoring protocols. This will enable better inter-site comparisons in upcoming oyster restoration pilots.

The dynamic lives of osseous points from Late Palaeolithic/Early Mesolithic Doggerland: A detailed functional study of barbed and unbarbed points from the Dutch North Sea.

Osseous barbed and unbarbed points are commonly recovered from the Dutch North Sea and other Mesolithic sites of northern Europe. Interpreted as elements of projectile weaponry, barbed points are considered by archaeologists to be a technological innovation in the hunting equipment of hunter-gatherers. However, debate about their exact use and identification of the targeted prey species is still ongoing. To shed light on the function of these tools, we analysed a sample of 17 artefacts from the Netherlands with a multi-disciplinary approach encompassing morphometric, functional, and chemical analysis. 14C-AMS dating yielded the oldest date for a barbed point from the Dutch coast (⁓13000 cal. BP). The observation of microwear traces preserved on the tools provides solid evidence to interpret the function of barbed and unbarbed points. We show that there were two distinct tool categories. 1) Barbed points hafted with birch tar and animal or vegetal binding were likely projectile tips for terrestrial and aquatic hunting. We provide strong clues to support the link between small barbed points and fishing using wear traces. 2) Points without barbs served as perforators for animal hides. Our results highlight the importance of use-wear and residue analysis to reconstruct prehistoric hunting activities. The functional interpretation of projectile points must also rely on microwear traces and not merely on the association with faunal remains, historical sources, and ethnographic comparisons.

Palaeostress state around a rising salt diapir inferred from seismic reflection data

A 3D seismic volume and borehole data from the Dutch North Sea are used to investigate the palaeostress state around a rising salt diapir. The results show radial, polygonal and keystone faults around the diapir of interest, which are separated into eight zones based on their geometry, strike and overall distribution. Principal fault families include: a) 400–3500 m long radial faults developed in flanking and corner areas of the salt diapir, and known to have accommodated the stretching resulting from its rise, b) 200–1500 m long polygonal faults providing a record of the stress conditions farther from radial faults, and c) 1000–1800 m long keystone faults controlled by the rise of a buried salt pillow during Paleogene tectonic inversion. Stress inversions for 10,401 interpreted faults reveal that the maximum principal palaeostress (σ1) is close to vertical, whereas intermediate and minimum principal palaeostresses (σ2 and σ3) are sub-horizontal, though variable in their magnitudes and orientations. Palaeostresses in flanking zones of the salt diapir show marked differences when compared with corner zones, but the combination of minimum principal palaeostresses from all flanking and corner zones formed a triangular stress ring around the salt diapir. Importantly, the width of this stress ring was not only associated with the rise of the salt diapir, but also largely influenced by adjacent salt structures. Additionally, minimum principal palaeostresses estimated from polygonal fault systems are nearly normal to the boundary between polygonal and radial faults, implying that the rise of the salt diapir influenced the stress field in the outer part of its flanks. Stress inversion is shown here as a key method to understand the palaeostress state around the salt diapirs with triangular geometry and multiple growth stages, providing insights into their evolving stress states. This work also has implications to the analysis of salt diapirs, and their adjacent strata, in areas posed for carbon sequestration, gas storage, and the production of oil and gas.

Hybrid modelling to improve operational wave forecasts by combining process-based and machine learning models

Operational wave forecasting plays an important role in ensuring safe navigation and in the prediction of tidal windows for harbour approach channels. The underlying nearshore process-based wave models need to be accurate for a wide range of different conditions, from more common mild wave conditions to the occasional high energy (storm) conditions. In this work, an innovative hybrid modelling approach is proposed to improve the accuracy of operational wave forecasts. An operational wave model is combined with a machine learning model which is trained using wave measurements within the wave model domain. This hybrid modelling approach is applied to the Dutch North Sea, covering four major harbour approach channels.The final hybrid operational wave model results in a significant average error decrease compared to just the process-based model, amounting to 21.7% for the wave energy density and 25.3% for the wave direction. The error reduction for the spectral wave parameters is even larger, with a 33.3% smaller error in spectral wave height and a 38.8% smaller error in spectral wave period. As this approach is generically applicable to spectral wave models, it contains the potential for significant improvements in operational modelling.

Applicability of the gape monitor to study flat oyster (Ostrea edulis) feeding behaviour

Innovative techniques are needed to assess oyster performance in flat oyster reef restoration projects. A valve gape monitor, a device that continuously measures opening and closing of live bivalves, can potentially be used as an effective method to determine survival and behaviour of the European flat oyster Ostrea edulis. The method has been successfully used in combination with a number of bivalve species to investigate valve gape activity in response to environmental factors. In this study, eight O. edulis were equipped with valve gape sensors in order to relate gape to environmental conditions such as food availability. Valve gape activity was monitored under controlled laboratory conditions, with and without food, in a concrete basin in the Oosterschelde and in the field (Voordelta, Dutch North Sea). Under controlled laboratory conditions, oysters clearly responded to changes in food availability. Starved oysters closed their valves significantly longer than oysters that received food, and the relative gape width in fed oysters was larger. In the concrete basin (Oosterschelde), a positive correlation between valve opening and Chlorophyll-a was found. Additionally, valve gape activity and tidal movement appeared to be linked. When exposed to a full tidal cycle (Voordelta), a negative correlation between valve opening and Chlorophyll-a was found. However, there was no correlation between valve gape and current velocity. In autumn, longer periods of inactivity were seen, but when valves opened, the valve gape was larger. These data indicate that valve gape can provide valuable information on behaviour (gape frequency and gape width), but also show that it is not necessarily a good proxy for feeding rate. Nevertheless, these results show that the gape monitor can be used to determine the natural behaviour of flat oysters under field conditions, and that gape opening provides information on behaviour and the stress response of bivalves to environmental conditions.

Food for thought: A realistic perspective on the potential for offshore aquaculture in the Dutch North Sea

Food for thought: A realistic perspective on the potential for offshore aquaculture in the Dutch North Sea

The Dutch fisheries sector and the North Sea Accord: Unpacking stakeholder participation in multi-levelled marine governance

Integrated, participatory forms of marine governance can form a basis of stakeholder support on which to base increasingly complex marine planning efforts, in the EU and beyond. Yet such stakeholder support is often the product of a constellation of external factors at the local, national and international level as well as of the internal organisation of a given interest group. This paper presents a qualitative study of an outlier case, examining the question why the Dutch fisheries sector was the only involved interest group which was unable to give its full support to the 2020 North Sea Accord. Through in-depth, semi-structured interviews with participants in the Dutch North Sea Accord negotiation, ratification and implementation process as well as with representatives of local fisheries organisations, the authors identified crucial factors which contributed to the division within the sector over the ratification of the Accord. Such factors include perceived inconsistencies in the double closure to conventional fisheries of both wind parks and marine protected areas, disagreements over the practical aspects of the transition fund and the decommissioning scheme, and varying degrees in which Brexit influenced local fisheries organisations. More fundamentally, a parallel, equally multileveled division within the Dutch fisheries sector over the desirability of participatory marine governance at the national level was identified. Such findings demonstrate the importance of understanding not just a given (marine) policymaking process, but also participants therein, in their own multileveled context, in order to explain a particular policy outcome or functioning of a given marine governance structure.

Spatial patterns in age‐ and colony‐specific survival in a long‐lived seabird across 14 contrasting colonies

Demographic rates such as recruitment and survival probability can vary considerably among populations of the same species due to variation in underlying environmental processes. If environmental processes are spatially correlated, nearby populations are expected to have more similar demographic rates than those further apart. Breeding populations and foraging ranges are spatially segregated in colonial seabirds, making them ideal for studying spatial patterns in demographic rates and their effects on local population dynamics. Here we explored variation in age‐dependent survival probabilities across 14 colonies of Herring GullsLarus argentatusbreeding along the Dutch North Sea coast. We used long‐term mark–recapture data of marked fledglings to estimate survival, and estimated spatial autocorrelation of survival probabilities. We assessed whether survival until recruitment age or until 10 years old (close to their expected lifespan) explained variation in population trajectories of each colony. Juvenile and adult survival showed a strong, but different, north‐to‐south gradient in survival probability, with lower juvenile but higher adult survival in northern colonies than southern colonies, whereas the spatial pattern of immature survival was less distinct. Neither recruitment nor the proportion of 10‐year‐old adults alive predicted whether a colony collapsed, declined, remained stable or increased. The distinct spatial pattern in survival suggests variation in regional food availability, which do not seem to drive local population dynamics. The absence of a link between survival and colony trajectories implies that connectivity between populations plays an important role affecting population dynamics.

Food Choice and Prey Selection by Great Cormorants Phalacrocorax carbo in a Shallow Coastal Zone in the Dutch Delta Area: Importance of Local Flatfish Stocks

Coastal breeding Great Cormorants Phalacrocorax carbo foraging in a shallow part of the Dutch North Sea preyed upon abundant marine demersal fish species. In 2010–2012 intensive fish surveys were performed in the Voordelta area and in 2009–2015 Cormorant pellets were sampled in the breeding colony of Breede Water, Voorne, four times per year between March and September. In total 48 fish species were detected in the diet, 38 being marine species. Mainly flatfish were consumed, and European Plaice, Common Dab and Common Sole were the most important prey according to fish mass. Experimental trawling revealed 65 species of fish of which gobies, Herring, Whiting, Sprat, European Plaice and Common Dab were the most abundant. Compared to the trawl data, Cormorants showed a preference for Common Dab and Common Sole and for other solitary bottom fish like sandeels and Shorthorn Sculpin. These species were all common in the area. With respect to uncommon and rare species, no preferential selection was recorded. Densities of flatfish were highest in foraging areas closest to the breeding colony and possible depletion effects were only recorded in Common Dab. This diurnal species was already being preyed upon early in the season. Nocturnal foraging habits in other flatfish species, in combination with burrowing behaviour and rounded body shape are effective anti-predator traits and this was reflected in lower frequencies of these species in the Cormorants' diet. Consumption of freshwater fish by Cormorants at the beginning of the breeding period enabled an early start to breeding, and the increasing availability of flatfish in late spring matched the peak demand of rearing nestlings. The almost exclusive predation on flatfish was probably caused by the near-bottom foraging behaviour of most Cormorants and this habit made the birds feed on other abundant demersal fish species as well, such as Whiting, sandeels, Shorthorn Sculpin, Lesser Weever and dragonet species. And although numerous in the system, this bottom-oriented feeding behaviour of Cormorants therefore resulted in a very limited predation on pelagic fish species. In total we estimate an annual extraction by Cormorants of some 100 tonnes of fish being c. 77,600 kg flatfish and c. 20,700 kg other marine fish. Although with a foraging range partly outside the coastal zone, the extraction of fish by Harbour Seals Phoca vitulina and Grey Seals Halichoerus grypus outnumbered that of Cormorants by a factor of 9. As seals are known flatfish consumers, this suggests that there is competition between mammalian and avian predators on demersal fish stocks in the coastal zone.

Unambiguously defined and recognized seabed protection targets are necessary for successful implementation of MPAs

Bottom-impacting fisheries affect benthic marine ecosystems through extraction of resources and physical habitat impact. To protect natural values against human impacts, marine protected areas (MPAs) are being implemented. In practice, however, these do not necessarily provide full protection against bottom-impacting fisheries. Sometimes only certain types of fishing are prohibited, or only during certain periods of the year. In the Netherlands currently 20% of the North Sea is declared MPA. Most areas include ambiguously defined conservation goals for the seafloor, such as protection against ‘note-worthy’ impact. The government, fishermen and NGOs state that respectively 4%, 20% and less than 1% of the Dutch North Sea floor is currently protected against bottom-impacting fisheries. These diverging perspectives hamper successful communication, and result in different views on whether the Netherlands meets (inter)national targets. This paper reveals the fact-base and rationale behind these different perspectives, and illustrates these in more detail for three areas in the Dutch North Sea. We suggest five steps to help avoid miscommunication, operationally define Dutch MPAs and ensure their effectiveness; (1) explicitly specify protection goals beforehand, (2) substantiate why and how the protection goals under (1) will be reached with the proposed measures, (3) define measurable targets, (4) ensure enforcement and (5) monitor closely and adapt when needed. The explicit fact-base presented in this paper aims to contribute to a constructive discussion about protection goals and necessary measures, and prevents Babylonian confusion. Recent new developments concerning the ‘North Sea Agreement’, as well as the EU Biodiversity Strategy for 2030, have the potential to solve several of the abovementioned challenges.

Using machine learning and beach cleanup data to explain litter quantities along the Dutch North Sea coast

Abstract. Coastlines potentially harbor a large part of litter entering the oceans, such as plastic waste. The relative importance of the physical processes that influence the beaching of litter is still relatively unknown. Here, we investigate the beaching of litter by analyzing a data set of litter gathered along the Dutch North Sea coast during extensive beach cleanup efforts between the years 2014 and 2019. This data set is unique in the sense that data are gathered consistently over various years by many volunteers (a total of 14 000) on beaches that are quite similar in substrate (sandy). This makes the data set valuable to identify which environmental variables play an important role in the beaching process and to explore the variability of beach litter concentrations. We investigate this by fitting a random forest machine learning regression model to the observed litter concentrations. We find that tides play an especially important role, where an increasing tidal variability and tidal height leads to less litter found on beaches. Relatively straight and exposed coastlines appear to accumulate more litter. The regression model indicates that transport of litter through the marine environment is also important in explaining beach litter variability. By understanding which processes cause the accumulation of litter on the coast, recommendations can be given for more effective removal of litter from the marine environment, such as organizing beach cleanups during low tides at exposed coastlines. We estimate that 16 500–31 200 kg (95 % confidence interval) of litter is located along the 365 km of Dutch North Sea coastline.

Climate change and intensifying human use call for a monitoring upgrade of the Dutch North Sea

Regulatory monitoring of the Dutch part of the southern North Sea does not provide sufficient information to understand the observed changes in the physical, chemical and ecological environment. As a result, the Dutch North Sea policy and management is not appropriately supported by data. The monitoring lacks explicit objectives for integrated management and knowledge enhancement about system functioning. Ecological processes are not included in the programs. There is neither integration of monitoring of physical, chemical and biological parameters, nor is there integration of regulatory monitoring, project monitoring and applied in-depth research. In the meantime, the effects of climate change, the upscaling of renewable energy, and plans for intensifying offshore aquaculture make appropriate monitoring even more urgent. The Dutch North Sea management is therefore faced with the challenge of adapting the current monitoring without compromising continuity. This can be done by making monitoring hypothesis-driven, setting up an integrated monitoring strategy based on regulatory and project-based monitoring, combining structure and process measurements, applying new smart automated techniques, increased use of modelling and remote sensing, and conducting in-depth measurement campaigns. As the North Sea is bordered by several countries, such a renewed effort should be done in coordination with these countries.

Origin of shallow gas in the Dutch North Sea — Seismic versus geochemical evidence

In the Dutch offshore, we have observed numerous acoustic anomalies, usually bright spots, in seismic data of Cenozoic deltaic deposits. When associated with shallow gas, these bright spots are good indicators of resource potential, drilling hazard, or seabed methane emissions. We apply a combined seismic and petrophysical assessment to qualify the bright spots as direct hydrocarbon indicators (DHIs) for shallow gas and to exclude alternative sources of seismic anomalies. In some cases, we use other DHIs such as flat spots, velocity push-downs, transmission, and attenuation effects as estimators for gas saturation. A long-standing discussion concerns the sourcing and migration of shallow gas. Although vertical seismic noise trails (chimneys) tend to be seen as proof that shallow gas originates from the migration of deeper sourced thermogenic gas, the geochemical and isotope analyses almost exclusively indicate that the gas is of microbial origin and generated in situ in the Cenozoic strata. We conclude that the observed “chimneys” are most likely transmission effects, that is, artifacts that do not represent migration pathways of gas. Hence, we believe that for the Dutch offshore, the presence of shallow biogenic gas is not indicative of leakage of deeper thermogenic petroleum plays and cannot be used as an exploration tool for these deeper targets.

Emerson helps produce green H2 in Dutch North Sea

Emerson helps produce green H2 in Dutch North Sea

Distribution and flight heights of Sandwich Terns Thalasseus sandvicensis during different behaviours near wind farms in the Netherlands

ABSTRACT Flight heights and behaviour of 1460 Sandwich Terns Thalasseus sandvicensis in the Dutch North Sea were recorded with a laser range finder during ship-based surveys in 2020 and 2021. Over 87% of all Sandwich Terns were flying below 20 m, and fewer than 1.5% were recorded above 40 m, leading to a two-fold increase in the collision risk model estimates for the Borssele offshore wind farm in the Netherlands compared to the current standard flight height distributions.