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Middle Triassic deposition in Northwest Europe occurred in the enclosed Germanic Basin, which extended from its connection with Tethys in eastern Poland to eastern England. A detailed lithostratigraphic subdivision of the middle Triassic Dowsing Dolomitic Formation of the U.K. Southern North Sea and subsurface eastern England is presented, based on petrophysical logs, well cuttings and limited core. This subsurface lithostratigraphy is linked to the established outcrop lithostratigraphy of eastern England by means of a surface gamma-ray profile at Kirton Brickworks, Nottinghamshire. The outcrop lithostratigraphy is thereby accurately correlated with that of the basin centre in north Germany. The major tectonic elements active during middle Triassic deposition in the Southern North Sea area are identified, including previously unreported differential subsidence in an extension of the Dutch Broad Fourteens Basin in the U.K. Sector. The basinwide Hardegsen unconformity marks the base of the middle Triassic. A transgressive phase resulted first in the deposition of lacustrine pro-delta mudstones towards the basin centre, followed by the deposition of a more extensive thin marine mudstone which formed the base of the middle Triassic over most of the U.K. Southern North Sea area. Two regressive cycles followed. Each started with deposition of the cyclic, hypersaline-marine halites (the Main and Upper Röt Halites), followed by sabkhas, then playa mudflat/lagoonal deposits. At the start of the Muschelkalk deposition, restricted marine conditions were established in the Southern North Sea area. These were followed by a further regressive sequence of hypersaline-marine halites (the Muschelkalk Halite), sabkhas, and finally playa mudstones. The establishment of continental sedimentation across the whole of the Germanic Basin marked the end of the middle Triassic. The cyclicity within the Germanic Basin correlates with the published coastal onlap charts, indicating its origin is eustatic fluctuations in Tethys.

Ostracods were obtained from two cores in the southern North Sea area: the Sand Hole and Swarte Bank Formations of Tappin (1991) in BGS borehole 81/52A, cored from the Inner Silver Pit, southern North Sea, and a core from Shoeburyness in Essex, borehole S 1. The faunal assemblages in 131-181/52A were dominated by Sarsicytheridea punctillata, Elo/sonella concinna and Acanthocvthereis clunelmnensis. The assemblages recovered reflect a transition from glacio-marine conditions in the Swarte Bank Formation up into a cold-temperate marine environment in the Sand Hole Formation with deteriorating temperatures indicated at the top of the interval studied. In BHSI a freshwater to brackish transition occurred in the core, the freshwater section being dominated by Darwinula slevensoni and llyocypris spp., and the brackish section by Cyprideis torosa and C ytheromor pha fiiscata. The palaeoecology of the ostracod assemblages recovered is compared to other palaeoecological data from the same sections in each core and to ostracod data from other Hoxnian/l lolsteinian sites in north western Europe. These data are also discussed in the light of evidence indicating that there was a barrier across the southern North Sea when the sediments examined were deposited. Sarsicytheridea spp. and (yprideis terosa were used for trace element (Mg: Ca, Sr: Ca) and stable isotope (cS'"O, ö'3C) analyses. A calibration equation for the calculation of temperature from Mg: Ca ratio was successfully established from analysis of modern Sarsicytheridea. Modern Sr: Ca data could not be used to establish a calibration for salinity since there was too much scatter in the data. (' prideis torosa has been used for trace element and stable isotope work by other authors who have published relationships between ('yprideis and the water chemistry. Ostracods were also analysed down core to examine the changing ratios of Mg and Sr as a proxy for temperature and salinity changes in the I-loxnian of the southern North Sea. In BH81/52A, Mg: Ca data indicated a deterioration in temperature from 36.20 m to the top of the section studied of 9°C. Oxygen stable isotopic analyses from the same species, measured through the same core intervals, did not exhibit a trend, but their values were indicative of normal marine salinities. Carbon stable isotope analyses, performed at the same time as the oxygen analyses, indicate that there may have been high productivity in the region of deposition of the Sand Hole Formation, implying deposition in a region of freshwater influence. However, C/N analyses indicated that the sediments in the Inner Silver Pit were deposited under fully marine conditions. In III ISI, both the Mg: Ca and Sr: Ca data suggested that salinity had increased upcore. Ilowever, there was a lot of scatter in the data, indicating that the estuarine environment, under which the palaeoecology suggests the sediments were deposited, was a highly fluctuating one. These data compare favourably with previously published records. Published partition coefficients were used to compare the trace element data obtained to mean river and seawater values.

The Pliocene world c.5.3 Ma to c.2.58 Ma exhibited a relatively stable climate with a warmer global mean surface temperature than present-day by ~2 °C to 3 °C, and palaeoclimate analysis from this interval is used to understand climate drivers in ‘warmer world’. Previous oxygen isotope thermometry investigations of Pliocene southern North Sea Basin (SNSB) Aequipecten opercularis from the Coralline Crag Formation in Suffolk, UK repeatedly reveal evidence of a cold-temperate climate regime. Contrastingly, other biological proxies record a warm-temperate/sub-tropical regime. This investigation concentrated on oxygen, carbon and microgrowth increment widths (MIWS) of fossil shell material from Pliocene SNSB spanning an interval of~4.4 Ma to ~2.5 Ma. The study sites included shallow marine Pliocene formations from the western and eastern SNSB, the Ramsholt Member of the Coralline Crag Formation, Suffolk UK, and the Luchtbal Sands and Oorderen Sands Members of the Lillo Formation, Belgium, and the Oosterhout Formation in the Netherlands. Oxygen isotopic palaeotemperature results showed cooler summer temperatures than presently in the SNSB, which were reflective of a cool-temperate regime. There was no evidence of warm-temperate or sub-tropical summer palaeotemperatures in the Pliocene SNSB as suggested by other planktonic proxies. This investigation discussed the possible causal factors for the cooler – than- expected winter and summer palaeotemperatures in the ‘warmer’ Pliocene world as recorded by this proxy. Discrepancies between the cool summer benthic palaeotemperatures from the bivalves and the warmer sub-tropical or warm-temperate summer palaeotemperature estimations from planktonic biological proxies was rectified by the application of a theoretical summer stratification factor (SSF). However, rectifying the discrepancies between cooler (cold-temperate) benthic winter palaeotemperatures and the warmer winter palaeotemperatures from other proxies was difficult because stratification does not occur during the winter. Dormancy behaviours in the warm- temperate –sub-tropical organisms was proposed as a suitable mechanism to allow their coexistence with the cool-tolerant bivalves, which were able to grow and feed underneath the thermocline during the summer months. Therefore, the investigation showed how the Pliocene SNSB exhibited a greater seasonality than occurs presently in the SNSB. The driver for the cooler winter temperatures in the Pliocene SNSB was not identified. Localised explanations including continental wind effects, interannual variations in MOC strength, and increased storm activity in the winter bringing cooler water into the SNSB were all suggested as potential drivers. Global features of climate including interglacial/glacial cycles and orbital forcing effects were factors also proposed for the overall mixed palaeotemperature signal in the Pliocene SNSB.

One of the most promising mitigation strategies for greenhouse gas accumulation in the atmosphere is carbon capture and storage (CCS). Deep saline aquifers are seen as the most efficient carbon dioxide (CO2) storage sites, mainly because of their vast size and worldwide distribution. Injecting CO2 into brine filled media will cause a physical and chemical disequilibrium in the formation. This PhD thesis documents the investigation of some of the resulting effects which occur at the beginning of the injection, during the injection period and millions of years after injection. When CO2 is injected into a brine filled reservoir, large amounts of in situ brine will be displaced away from the injection well. This causes a pressure increase in the vicinity of the well which may compromise the injection process. The simulation of this pressure increase was performed with the black-oil simulator Eclipse10 (Schlumberger) while using a number of recent formulas to predict the mutual dissolution and the fluid properties of CO2 and brine. The results show that the pressure increase can exceed the maximum sustainable pore pressure and will cause fracturing of the reservoir formation. The pore pressure increase is dependent on parameters such as temperature and salinity because they change the fluid properties of the CO2 and brine, but also the capability of the fluids to dissolve mutually. The mutual dissolution has generally a pressure reducing effect although its impact is regarded to be overestimated. This is mainly because reservoir engineering software cannot simulate the shock front realistically. Undulations, which appear on the injection pressure profile are not a result of model instabilities but can either be related to enhanced mutual dissolution due to grid effects, or to the software which may overestimate or underestimate the pressure and dissolution. A detailed investigation of those undulations is vital for the interpretation of the injection pressure. High fluid pressure can be an important parameter for the estimation of the CO2 storage capacity of saline aquifers such as the offshore Bunter Sandstone Formation, in the UK southern North Sea. Based on fluid pressure, the 1 storage capacity was calculated using the ECLIPSE compositional simulation package and a simple analytical equation. The estimated storage capacity is 6.55 to 7.17 Gt of CO2 calculated with the analytical and the numerical approach respectively. By comparing the results, the differences are relatively moderate and therefore the application of the numerical simulator is not regarded as necessary. This is mainly due to the effective pressure flow which prevents pressure accumulations underneath the cap rock. Although the CO2 storage capacity of the Bunter Sandstone Formation remains high, a previous survey, which was not based on fluid pressure, calculated a storage capacity approximately twice as high as the results presented here. In theory, due to the increase in CO2 concentration, CO2 bearing carbonate minerals could precipitate when CO2 is injected into an aquifer such as the Rotliegend aquifer in the southern North Sea. Geochemical models often predict a relatively rapid growth of carbonate minerals as the most secure form of long term engineered CO2 storage. But validation of model-results remains difficult due to the long periods of time involved. Natural analogue studies can bridge the gap between experiments and real-world storage. The Fizzy field, a southern North Sea (UK) gas accumulation with a high natural CO2 content (c. 50%) provides an ideal opportunity to study the long term effect of CO2 related mineral reaction. However all such reservoirs contain ‘normal’ diagenetic dolomite, so that distinguishing sequestration related dolomite is a challenge. CO2 was stepwise extracted from dolomite from both the Fizzy field and the Orwell Rotliegend sandstone in order to reveal any zonation of the crystals which could be related to enhanced dolomite precipitation due to the high CO2 concentration. According to the method between 0 and 22 % of the dolomite in the Fizzy field precipitated due to the high CO2 concentration. Therefore, between 0 and 19 % of the CO2, which is related to the relatively recent high CO2 concentration, is ‘trapped’ in the ‘sequestration dolomite’. The wide range of this estimate is mainly related to rock heterogeneity.

We report a 40 year record of eutrophication and hypoxia on an estuarine ecosystem and its recovery from hypereutrophication. After decades of high inorganic nutrient concentrations and recurring anoxia and hypoxia, we observe a paradoxical increase in chlorophyll-a concentrations with decreasing nutrient inputs. We hypothesise that algal growth was inhibited due to hypereutrophication, either by elevated ammonium concentrations, severe hypoxia or the production of harmful substances in such a reduced environment. We study the dynamics of a simple but realistic mathematical model, incorporating the assumption of algal growth inhibition. It shows a high algal biomass, net oxygen production equilibrium with low ammonia inputs, and a low algal biomass, net oxygen consumption equilibrium with high ammonia inputs. At intermediate ammonia inputs it displays two alternative stable states. Although not intentional, the numerical output of this model corresponds to observations, giving extra support for assumption of algal growth inhibition. Due to potential algal growth inhibition, the recovery of hypereutrophied systems towards a classical eutrophied state, will need reduction of waste loads below certain thresholds and will be accompanied by large fluctuations in oxygen concentrations. We conclude that also flow-through systems, heavily influenced by external forcings which partly mask internal system dynamics, can display multiple stable states.

The eutrophication of the Southern Bight of the North Sea has been benefitting to the prymnesiophyte Phaeocystis globosa (P. globosa). This species is a known high dimethylsulfoniopropionate (DMSP) producer whose bloom accounts for 95% of spring phytoplankton biomass. An increase in DMS(P) and its oxidation product dimethylsulfoxide (DMSO) cellular contents have been frequently observed in cellular stress conditions. To test this, we have first analysed the natural distribution of DMS(P,O) cellular contents in the North Sea. Secondly, we have measured DMS(P,O) cellular contents in monospecific cultures of several key species of the North Sea and their responses to salinity variations. Our main working hypothesis is that DMSP acts as an osmoregulator and/or as an antioxidant, depending on the species. The DMS(P,O) annual cycle in the Southern Bight of the North Sea revealed a seasonality linked to the spring phytoplankton communities succession: (1) colonial diatoms (reappearing in autumn), (2) Chaetoceros spp. (3) P. globosa, (4) large-size summer diatoms (mainly Guinardia spp.), and (5) dinoflagellates. Spatial gradients of DMS(P) were related to those of phytoplankton biomass, itself related to the inputs of nutrients from the Scheldt estuary. It also discharges suspended matter in which DMSO may have been produced by anaerobic oxidation of DMS. Laboratory measurements confirmed a large variability in DMSP cellular contents between the six studied diatoms (Nitzschia closterium, Skeletonema costatum, Thalassiosira rotula, Chaetoceros socialis, Chaetoceros debilis, and Guinardia delicatula), low producers in comparison with P. globosa and even more with Heterocapsa triquetra (Dinoflagellate). In particular, communities 2 and 4 have lower DMSP cellular contents than community 1 (N. closterium, S. costatum and T. rotula). Senescence induces a decrease in DMSP/DMSO suggesting an oxidative stress caused by nutrients and/or light limitation in DMSP producers. In S. costatum, DMSP seems to play an osmoregulatory role and is oxidised into DMSO in hyposaline conditions. In P. globosa and H. triquetra, an oxidative stress appears in hypo- and hypersaline conditions diverging from their salinity optimum. / Doctorat en Sciences / info:eu-repo/semantics/nonPublished

Les diatomées sont une composante majeure des écosystèmes marins et sont caractérisées par une grande diversité. L’objectif général de cette thèse est d’étudier les facteurs de contrôle des diatomées dans la Zone Côtière Belge (ZCB). Pour ce faire, la modélisation par groupes fonctionnels et l’approche basée sur les traits sont combinées :la première fournit un cadre écosystémique utile pour étudier les interactions des diatomées avec les compartiments biotiques et abiotiques de l’écosystème, et la seconde permet de représenter de façon efficace leur diversité fonctionnelle.<p><p>Dans un premier temps, puisque la taille est reconnue comme un trait majeur affectant de nombreux aspects de la valeur sélective du phytoplancton, la dépendance au biovolume de différents traits des diatomées a été établie sur base d’observations disponibles dans la littérature. Cette revue a montré qu’un compromis sépare les diatomées sur base de leur biovolume :les petites espèces sont meilleures compétitrices pour l’acquisition des ressources mais plus sensibles au broutage, et inversement. <p>Sur cette base, un ré-analyse d’un jeu de données incluant des comptages et mesures de biométrie avec l’identification de 68 taxons dans la ZCB entre 1992 et 2000 a été réalisée, avec une attention particulière pour la structure en termes de taille de la communauté de diatomées. Un regroupement des diatomées en fonction de leur biovolume a été réalisé sur base de leur évolution saisonnière typique. L’analyse de leur évolution temporelle suggère que la communauté des diatomées est composée d’assemblages avec une évolution saisonnière et interannuelle distinctes qui répondent vraisemblablement différemment aux conditions environnementales.<p>Afin d’étudier plus en profondeur les facteurs environnementaux contrôlant la structure en termes de taille de la communauté des diatomées dans la ZCB, le module diatomées du modèle MIRO, qui représente l’écosystème planctonique de la ZCP, a été modifié afin d’inclure les dépendances à la taille de quatre traits des diatomées. Cet outil reproduit correctement l’évolution saisonnière du biovolume moyen de la communauté, qui est caractérisé par de plus petites diatomées au printemps qui maximisent l’acquisition de ressources tandis que la prévalence du broutage en été induit une transition vers des espèces plus grandes. Le modèle a également été exploité pour étudier la gamme de tailles viables dans la ZCB en fonction des conditions environnementales. <p>Les résultats du modèle basés sur les traits ont ensuite été analysés sur la période 1992-2000. Les simulations ont mis en évidence les interactions complexes entre les processus physiques, de contrôles par les ressources et par le broutage, qui sont susceptibles de déterminer la variabilité interannuelle de la structure en termes de taille des diatomées dans la ZCB. La comparaison de ce modèle adaptatif avec un modèle plus conventionnel qui ne représente pas de diversité interne aux diatomées suggère que le premier produit une réponse légèrement plus flexible que le dernier, mais que la rigidité de la réponse simulée demeure un problème avec le modèle adaptatif qui reste incapable de représenter des évènements extrêmes de biomasse ou de structure de la communauté. Cela suggère que des développements supplémentaires du modèle sont nécessaires, en particulier du module zooplancton.<p>Finalement, une fonction écologique particulière est abordée dans une dernière section de cette thèse :la production d’une neurotoxine par certaines diatomées du genre Pseudo-nitzschia. Cette fonction a été incluse comme un métabolisme secondaire dans un modèle idéalisé de la croissance de Pseudo-nitzschia afin d’étudier les facteurs contrôlant la production de la toxine. Il est notamment montré que l’environnement lumineux est déterminant lorsque les conditions menant à la production de toxine sont rencontrées. <p><p>/<p><p>Diatoms are a key component of marine ecosystems and are characterized by an important diversity. The general objective of this thesis is to investigate the bottom-up and top-down controls of diatoms in the Belgian Coastal Zone (BCZ). This is done through the integration of their functional diversity into a coherent framework. In order to achieve this, Plankton Functional Type modelling and trait-based approaches are combined: the former provides an ecosystem context convenient to study the interactions of diatoms with biotic and abiotic compartments, and the latter allows an efficient representation of their functional diversity. <p><p>As a first step, since size is recognized as a master trait shaping many aspects of phytoplankton fitness, the cell volume dependences of diatom functional traits were compiled from observations available in the literature. This review showed that a trade-off distinguishes diatoms on the basis of their cell volume: smaller species are better competitor for resource acquisition but sensitive to grazing, and inversely. <p>On this basis, a re-analysis of a dataset including diatom cell counts and biometry with the identification of 68 taxa in the BCZ over the 1992-2000 period was carried out, with a focus on the size structure of the diatom community. A clustering of diatoms according to their cell volume was realized on the basis of their average seasonality. Investigation of their time evolution suggested that the diatom community in the area is composed of assemblages with distinct seasonal and interannual evolution that likely respond differently to environmental conditions.<p>In order to further investigate the bottom-up and top-down constrains on the size structure of the diatom community in the BCZ, the diatom module of the MIRO model, which represents the planktonic ecosystem of the BCZ, was modified in order to accommodate size-dependences of four diatom functional traits. This tool adequately reproduced the seasonal evolution of the mean cell volume of the diatom community, which is characterized by smaller diatoms in spring that maximize resource acquisition while the prevalence of grazing pressures in summer induces a shift towards larger species. The model was also used to investigate the range of viable diatom sizes in response to the bottom-up and top-down pressures in the BCZ.<p>Results of the trait-based adaptive model were then analysed over the 1992-2000 period. Simulations evidenced the complex interactions between physical, bottom-up and top-down processes that are likely to govern the interannual variability in the size structure of diatom in the area. Comparison of the adaptive model with a more conventional model resolving no diversity within diatoms suggested that the former produces a slightly more flexible response than the latter, but showed that the rigidity of the simulated response persists with the adaptive model which remains unable to catch extreme biomass and community structure events. This calls for further developments of other compartments of the model, more particularly zooplankton.<p>Finally, a peculiar ecological function is addressed on its own in the last section of this thesis: the toxigenicity of some species of the genus Pseudo-nitzschia. This function was added as a secondary metabolism in an idealized model of Pseudo-nitzschia growth in order to investigate the factors affecting toxin production. It notably showed that light was determinant under conditions leading to its production.<p> / Doctorat en Sciences agronomiques et ingénierie biologique / info:eu-repo/semantics/nonPublished

De part l'importance et la diversité des pressions anthropiques en mer du Nord, les mammifères marins en tant que prédateurs supérieurs se trouvent de plus en plus exposés à ces activités (trafic maritime, activités industrielles et portuaires, surpêche, pollution chimique, etc.). Les campagnes d'observation SCANS et SCANS II mises en place en 1994 et 2005 pour estimer l'abondance des petits cétacés, ont mis en évidence un changement majeur dans la distribution du marsouin commun (Phocoena phocoena) en mer du Nord avec un déplacement du Nord vers le Sud. Ce changement peut être lié à une migration de ses proies préférentielles en mer du Nord et/ou à une afaptation de son régime alimentaire par rapport à la disponibilité des proies. Parallèlement, à ces modifications de distribution spatiale, un nombre croissant d'échouage de marsouin commun en Manche Orientale et sur les côtes belges a été observé depuis une dizaine d'années avec une augmentation conséquente ces deux dernières années. Pour étudier les causes responsables de ces échouages, un des objectifs de cette étude a été d'évaluer l'état de la contamination chimique des animaux échoués en relation avec l'état sanitaire des individus. L'analyse de deux familles de composés chimiques (éléments traces métalliques et polluants organiques persistants) sur des animaux échoués sur la période 2006-2013 révèlent des concentrations significativement plus élevées dans les organies des animaux présentant des pathologies que celles obtenues chez les animaux sains. Cette tendance a déjà été observée en Atlantique Nord pour le marsouin. Les comparaisaons des niveaux de concentration mesurées avec ceux d'études antérieures effectuées sur des marsouins échoués dans la même zone ou dans le Golfe de Gascogne suggèrent que l'augmentation du nombre de marsouins échoués n'est pas liée à une dégradation du milieu en terme de pollution chimique. Pour déterminer le régime alimentaire du marsouin commun, trois techniques complémentaires ont été utilisées : l'analyse des contenus stomacaux, des isotopes stables (carbone et azote) et des acides gras dans différents tissus. Pour ces deux dernières méthodes, les signatures obtenues pour le marsouin ont été comparées à celles de leurs proies potentielles. Les résultats ont mis en évidence la présences des gobies, merlans, lançons, sprats, trisopterus sp., harengs et sardines comme proies potentielles. Le déplacement des marsouins du nord jusqu'au sud de la mer du Nord a été attribué à la baisse de l'abondance du lançon dans le nord, ainsi qu'à la ré-invasion du sud de la mer du Nord par la sardine, probablement suite au changement climatique. Enfin, cette étude confirme la nécessité d'utiliser une approche multi-analyses qui intègre des informations complémentaires à différentes échelles de temps pour étudier le régime alimentaire de ces prédateurs supérieurs. / The North Sea is heavely impacted by human activities such as overfishing and pollution. Due to their position as top predators in the ocean, marine mammals are becoming increasingly affected by anthropogenic activities. The large-scale surveys SCANS in 1994 and SCANS II in 2005 that were held in the North Sea to estimate the abundance of small cetaceans highlighted a major shift in the distribution of harbour porpoises (Phocoena phocoena) from the northern parts of the North Sea to its eastern parts. Alongside, over the past few decades harbour porpoises stranding has increased in the southern North Sea particularly along the French and Belgian coastal waters. Since the contaminant exposure presents, among others, a potential threat to harbour porpoises inhabiting the North Sea, the first objective of the present study was to assess the contamination status of this species in the southern North Sea. On the other hand, the distribution and abundance of marine mammals is expected to follow the distribution of their main prey species. Hence, the second objective of this study was to investigate whether the changes in the distribution of porpoises in the southern North Sea may be a result of the changes in prey availability. Moreover, the third objective was to evaluate the interest of combining three methods to investigate the diet of harbour porpoises : stomach contents, stable isotopes (carbon and nitrogen) and fatty acids analyses. First, the contamination status was evaluated through the determination of two components of chemical contaminants (metals and persistent organic pollutants) in tissues of harbour porpoises stranded along the southern North Sea between 2006 to 2013. Several chemical contaminants presented higher concentrations in diseased animals compared to healthy animals. In addition, some metallic contaminants showed bioaccumulation with age. Comparison with previous study suggests that the population status of harbor porpoises in term of chemical concentration has been stable from 1994 to 2013. This work suggested that the increase in the number of stranded individuals is not related to the decline in the quality of the environment. Secondly, the shift in the abundance of harbour porpoises was evaluated and interpreted in the light of prey species abundance. Three techniques were used in order to determine the diet of porpoises. Results highlighted the presence of gobies, whiting, sandeel, sprat, trisopterus sp., herring and sardine as potential preys. The shift of the abundance of porpoises form the northern parts of the North Sea to its southern parts was attributed to the sandeel abundance decline in the northern parts of the North Sea along with the re-invasion of the southern North Sea by the sardine species, probably in response to climate change. Finally, the value of a multi-approach dietary analysis was evaluated. Besides overcoming the limitations of each method, combining different techniques that integrate diet over days and weeks allowed gaining more complete understanding of harbour porpoise's diet.