Eastern North Sea Research Articles

Morphology and distribution of the Miocene dinoflagellate cyst operculodinium? Borgerholtense louwye 2001, emend.

The extinct, organic‐walled, proximochorate dinoflagellate cyst Operculodiniuml borgerholtense Louwye 2001 was first described from Miocene shallow‐marine deposits of northern Belgium, and has since been documented from the Miocene of the eastern North Atlantic, North Sea, Austria, Hungary, and Egypt. Conventional and confocal light microscopy and scanning electron microscopy are used to reveal new details of the archeopyle, wall structure, and ornament. The archeopyle is shown to have well‐defined rather than rounded angles, a distinction we consider significant in assigning this species only provisionally to the genus. Operculodiniuml borgerholtense was a euryhaline neritic species highly tolerant of environmental stress, a feature consistent with its morphological variability. Present records indicate a tropical‐subtropical to temperate paleoclimatic distribution. It ranges from the upper Lower Miocene to upper Middle Miocene, and promises to be a useful Stratigraphic marker particularly in neritic settings where adverse paleoenvironmental factors have excluded other species.

Determination of the diversity of Rhodopirellula isolates from European seas by multilocus sequence analysis.

In the biogeography of microorganisms, the habitat size of an attached-living bacterium has never been investigated. We approached this theme with a multilocus sequence analysis (MLSA) study of new strains of Rhodopirellula sp., an attached-living planctomycete. The development of an MLSA for Rhodopirellula baltica enabled the characterization of the genetic diversity at the species level, beyond the resolution of the 16S rRNA gene. The alleles of the nine housekeeping genes acsA, guaA, trpE, purH, glpF, fumC, icd, glyA, and mdh indicated the presence of 13 genetically defined operational taxonomic units (OTUs) in our culture collection. The MLSA-based OTUs coincided with the taxonomic units defined by DNA-DNA hybridization experiments. BOX-PCR supported the MLSA-based differentiation of two closely related OTUs. This study established a taxon-area relationship of cultivable Rhodopirellula species. In European seas, three closely related species covered the Baltic Sea and the eastern North Sea, the North Atlantic region, and the southern North Sea to the Mediterranean. The last had regional genotypes, as revealed by BOX-PCR. This suggests a limited habitat size of attached-living Rhodopirellula species.

Variability in transport of fish eggs and larvae. II. Effects of hydrodynamics on the transport of Downs herring larvae

A 10-layered, finite-volume advection-dispersion model with real-time meteorological and freshwater runoff drivers investigated the interannual differences in the transport of Downs her- ring Clupea harengus L. larvae in the southern North Sea. Simulations were carried out for the win- ters of 1989 and 1996 to 2003. As they grew, the concentrations of herring larvae developed vertical behaviour. Meteorological forcing transported Downs herring larvae to the nursery grounds in the eastern North Sea with large interannual differences. Diel vertical movement was relatively un- important in the transport of larvae in the hydrographically mixed southern North Sea. Year classes with less transport of larvae from the hatching area (which was generally warmer) were associated with greater abundances of young Downs herring in the ICES International Bottom Trawl Survey. This implies that retention, rather than dispersal or delivery of larvae to nursery grounds, is associ- ated with the determination of year class strength in Downs herring.

MORPHOLOGY AND DISTRIBUTION OF THE MIOCENE DINOFLAGELLATE CYST OPERCULODINIUM? BORGERHOLTENSE LOUWYE 2001, EMEND.

Abstract The extinct, organic-walled, proximochorate dinoflagellate cyst Operculodinium? borgerholtense Louwye 2001 was first described from Miocene shallow-marine deposits of northern Belgium, and has since been documented from the Miocene of the eastern North Atlantic, North Sea, Austria, Hungary, and Egypt. Conventional and confocal light microscopy and scanning electron microscopy are used to reveal new details of the archeopyle, wall structure, and ornament. The archeopyle is shown to have well-defined rather than rounded angles, a distinction we consider significant in assigning this species only provisionally to the genus. Operculodinium? borgerholtense was a euryhaline neritic species highly tolerant of environmental stress, a feature consistent with its morphological variability. Present records indicate a tropical—subtropical to temperate paleoclimatic distribution. It ranges from the upper Lower Miocene to upper Middle Miocene, and promises to be a useful stratigraphic marker particularly in ne...

Essential and non-essential elements in tissues of harbour porpoises (Phocoena phocoena) stranded on the coasts of the North and Baltic Seas between 2004–2006

This study on harbour porpoises (Phocoena phocoena) stranded along the coasts of the Eastern North and Western Baltic Sea as well as in the river Elbe during 2004-2006, evaluated concentrations of 20 essential and non-essential elements (Ag, Al, As, Ca, Cd, Co, Cr, Cu, Fe, K, Li, Mg, Mn, Mo, Ni, Pb, Se, Sn, V, Zn) in liver and muscle samples. Tissue samples of 22 porpoises were taken during post-mortem investigations at the Research and Technology Centre (FTZ) in Büsum, Germany. A multi element method utilizing microwave accelerated acid digestion for sample preparation and collision/reaction cell inductively coupled plasma mass spectrometry (CC-ICP-MS) was used for element quantification. All 20 elements investigated could be determined in liver and muscle tissues except for Al in muscle samples. Furthermore the concentrations in liver tissues were higher compared to muscle tissues. While sex specific differences were observed only for Cu concentrations in liver tissue, age-dependent relationships were obtained for nine elements. Differences between juveniles and adults were found for Ag, Al, Co, Mn, Mo, Se, Sn, Pb, and V concentrations in liver, as well as Sn concentrations in muscle tissues. Furthermore, As and Sn concentrations in liver and muscle showed differences between the stranding locations. This multi-element study on harbour porpoises gives baseline information to concentrations of essential and non-essential elements in tissue to develop reference ranges for health status determination as well as the assessment of the pollutant body burden.

Resolving fine-scale spatio-temporal dynamics in the harbour porpoise Phocoena phocoena

With the development of human activities in offshore shelf waters, the harbour porpoise Phocoena phocoena has become a focal species in relation to management of human activities and marine habitat conservation efforts. In this study, acoustic and visual time series of harbour porpoise occurrence were analysed from the Horns Reef area, eastern North Sea, aiming at resolving periodic- ity, spatial scale of aggregation and habitat drivers in porpoises. A total of 51 fine-scale surveys and 474 d of hydrophone deployment at 2 stations were analysed by partial least squares regression and spatial modelling in relation to synoptic (spatio-temporal) data derived from a local, high-resolution hydrodynamic model. Small-scale changes in local currents reflecting upwelling driven by the inter- action of the semi-diurnal tidal currents with the steep slopes of the bank were the main habitat driver identified from the acoustic as well as the survey data. Spatial modelling based on selected key predic- tor variables showed the distribution of harbour porpoises to alternate between 2 upwelling cells de- pending on the direction of tidal currents. The size of upwelling cells was less than 10 km, matching the small-scale spatial structure of survey data as revealed by geostatistical analysis. The findings may have great implications for the design of future protected areas for harbour porpoises, and they indi- cate that the overlap between areas of concentration of the species and areas targeted by fisheries and the offshore wind industry could be avoided without major changes to current management practices.

Unambiguous identification of pectenotoxin-1 and distribution of pectenotoxins in plankton from the North Sea

Lipophilic phycotoxins in size-fractionated plankton net tows (20 μm mesh-size) were measured on-board during a month-long oceanographic cruise in North Sea coastal waters. Tandem mass spectrometry coupled to liquid chromatography (LC–MS/MS) was employed for the detection and quantification of a broad spectrum of known and putative phycotoxins. For pectenotoxins (PTXs) the following ion masses ([M + NH 4] +) were monitored: m/ z 876 for PTX-2, m/ z 892 for PTX-11 and PTX-13, and m/ z 874 for PTX-12 and PTX-14. The PTX levels in net plankton were highest along the Danish north coast, but levels over 50 ng per net tow were also detected on the southern Scottish East coast and in the northern Skagerrak. Abundance of PTXs was highly correlated with the occurrence of the marine dinoflagellate Dinophysis spp. Whereas in the eastern North Sea PTX-2 was the most abundant PTX, in the western North Sea PTX-1 was the major component, but it was also present in lower proportions in the Norwegian and Danish waters than in the western North Sea. Isobaric PTX-11 was absent or only detected at trace levels throughout the entire cruise, and PTX-13 and PTX-14 were not detected at all. The identity of PTX-1 was confirmed by comparison of retention time and mass spectrum of the North Sea phytoplankton sample to PTX-1 previously isolated from shellfish. Statistical analysis showed the best correlation between the occurrence of PTX-1 and Dinophysis acuminata cell concentration. Nevertheless, we could not rule out the possibility of metabolic transformations of PTXs by organisms that have grazed upon Dinophysis. Such biotransformations could conceivably occur in heterotrophic dinoflagellates or ciliates, or even via oxidation in copepod fecal pellets. In any case, this study confirmed the presence of PTX-1 in the plankton and is the first definitive report of this toxin in the North Sea.

Long-term trends in mercury and PCB congener concentrations in gannet (Morus bassanus) eggs in Britain

Gannet (Morus bassanus) eggs from Bass Rock (North Sea) and Ailsa Craig (eastern Atlantic) were monitored for PCB congeners (1990-2004) and total mercury (1974-2004). Congener profiles for both colonies were dominated by PCBs 153, 138, 180, 118 and 170. All declined in concentration at Ailsa Craig but some (153, 170, 180) remained stable or increased slightly at Bass Rock. Egg congener concentrations at Bass Rock were typically 10-fold higher than at Ailsa Craig by 2002, and Principal Component Analysis indicated that colony differences were driven by the dominant congeners. Egg mercury concentrations were significantly lower at Bass Rock than at Ailsa Craig and temporal trends differed, there being a significant decline at Ailsa Craig but a marginal increase at Bass Rock. Our results suggest there may be differences in contamination between the eastern Atlantic and North Sea and/or there are colony differences in prey selection and associated contaminant loads.

Climate change impact on extreme wave conditions in the North Sea: an ensemble study

An analysis of today’s mean and extreme wave conditions in the North Sea and their possible future changes due to anthropogenic climate change are presented. The sea state was simulated for the 30-year period 2071–2100 using the wave model WAM and an ensemble of wind field data sets for four climate change realizations as driving data. The wind field data sets are based on simulation outputs from two global circulation models (GCMs: HadAM3H and ECHAM4/OPYC3) for two emission scenarios (A2 and B2, Intergovernmental Panel on Climate Change, Special Report on Emission Scenarios). They were regionalized by the Swedish Meteorological and Hydrological Institute using the regional climate model RCAO. The effects of the climate realizations on the sea state statistics were assessed by analyzing the differences between the patterns in the four CGM/emission scenario combinations and those in two control simulations representing reference wave climate conditions for the 30-year period 1961–1990. The analysis of the four emission scenario/GCM combinations has shown that the future long-term 99 percentile wind speed and significant wave height increase by up to 7% and 18%, respectively, in the North Sea, except for significant wave height off the English coast and to the north in the HadAM3H-driven simulation. The climate change response in the ECHAM4/OPYC3-forced experiments is generally larger than in the HadAM3H-driven simulations. The differences in future significant wave height between the different combinations are in the same order of magnitude as those between the control runs for the two GCMs. Nevertheless, there is agreement among the four combinations that extreme wave heights may increase in large parts in the southern and eastern North Sea by about 0.25 to 0.35 m (5–8% of present values) towards the end of the twenty first century in case of global warming. All combinations also show an increase in future frequency of severe sea state.

Cenozoic palaeogeography and isochores predating the Neogene exhumation of the eastern North Sea Basin

Denmark is a key region for studies of the Cenozoic development of Scandinavia because Paleocene to Upper Miocene sediments crop out across the country and because it is possible to correlate these occurrences with the up to 3 km thick Cenozoic succession of the North Sea Basin. However, the reason why the Cenozoic deposits occur close to the surface of the Earth in Denmark is that the sediments have been exhumed from their cover of younger rocks. This implies that a reconstruction of the Cenozoic development across Denmark – involving both burial and exhumation – must rely on sedimentological and seismic studies of preserved sediments as well as on physical parameters that may yield evidence of the postdepositional history of the sediments now at the surface. Only if the burial and exhumation history of the basins can be deciphered is it possible to infer the geological development in the Scandinavian hinterland where Cenozoic sediments are rarely preserved. We have identified four Mesozoic–Cenozoic palaeothermal phases related to burial and subsequent exhumation, and one phase reflecting climate change during the Eocene. This is based on new apatite fission-track analyses (AFTA) and vitrinite reflectance data from eight Danish wells (Japsen et al. 2007a). The study combined thermal history reconstruction with exhumation studies based on palaeoburial (sonic velo city), stratigraphic and seismic data (cf. Japsen & Bidstrup 1999; Green et al. 2002; Nielsen 2003; Rasmussen 2004; Japsen et al. 2007b). Two of the exhumation phases occurred during the mid-Jurassic and the mid-Cretaceous. In this study we focus on the Cenozoic development and on the early and late Neogene exhumation phases during which up to 1 km of sediments were removed across most of the Danish region (Fig. 1).

A review of early gadiform evolution and diversification: first record of a rattail fish skull (Gadiformes, Macrouridae) from the Eocene of Antarctica, with otoliths preserved in situ

Codfishes, the Gadiformes, are quite abundant in modern temperate and polar waters with a fossil record ranging back into the Palaeogene. The oldest records are from the Danian and Selandian of Europe and South Australia. The bipolar distribution early in their evolutionary history implies that their origin must have occurred quite early in the Palaeocene, or even in the Late Cretaceous with subsequent rapid diversification. By the Eocene, gadiforms were highly abundant and widespread. With the exception of gadiforms, no Eocene Antarctic teleostean group is present in the modern Antarctic fauna. Here, we review the early evolution and diversification of gadiforms in general and of macrouroids in particular. We also describe the undoubtedly oldest skeletal macrourid specimen with otoliths preserved in situ. It is the first definitive record of this group from the Eocene of Antarctica filling a gap in its stratigraphic distribution. The fossil record of gadiforms in general and macrouroids in particular indicates that the origin of both was in shallow shelf environments but with adaptations to deep-water settings early in their evolution. While gadoids seemingly originated in the earliest Palaeogene and rapidly experienced a first major radiation event in the eastern North Atlantic and/or North Sea Basin, macrouroids evolved in the Southern Ocean and migrated northwards into the South Atlantic before the establishment of the circum-Antarctic current and subsequent isolation of the Antarctic fish fauna. These two timely and regional separated adaptive radiation events in the Palaeogene gave rise to their modern taxonomic diversity and global distribution.

The Black Sea halacarid fauna (Halacaridae, Acari): Faunal comparison with the Mediterranean, Eastern North Atlantic, North Sea, and Baltic and reflection on its origin

Forty-one halacarid species are recorded from the Black Sea basin, adjacent limans, deltas and river inlets. The genera and the number of species (in parentheses) are: Acarochelopodia (1), Actacarus (2), Agaue (1), Agauopsis (3), Anomalohalacarus (2), Arhodeoporus (1), Caspihalacarus (1), Copidognathides (1), Copidognathus (9), Halacarellus (6), Isobactrus (2), Lohmannella (1), Porohalacarus (1), Porolohmannella (1), Rhombognathides (1), Rhombognathus (6), Soldanellonyx (1), and Thalassarachna (1). The list includes both marine and limnic genera and species. The epibenthic and algae-inhabiting Black Sea halacarid fauna is a reduced Mediterranean one. Most of these species are assumed to have colonized the Black Sea within the last 9000 years, following the flooding of the Black Sea by Mediterranean water. The Black Sea mesopsammal fauna is distinct from that of the Mediterranean and dominated by the genus Halacarellus. Three of the Halacarellus species are not known from the Mediterranean but from the North Atlantic. Scenarios for the origin and development of the Black Sea fauna are discussed. Aus dem Schwarzen Meer, einschlieslich der angrenzenden Kustenseen und Flussmundungen, sind 41 Halacariden-Arten genannt. Die Gattungen und, in Klammern, Zahl der Arten sind: Acarochelopodia (1), Actacarus (2), Agaue (1), Agauopsis (3), Anomalohalacarus (2), Arhodeoporus (1), Caspihalacarus (1), Copidognathides (1), Copidognathus (9), Halacarellus (6), Isobactrus (2), Lohmannella (1), Porohalacarus (1), Porolohmannella (1), Rhombognathides (1), Rhombognathus (6), Soldanellonyx (1) und Thalassarachna (1). Aufgefuhrt in dieser Liste sind Arten sowohl mariner als auch limnischer Gattungen. Zum Vergleich, 90 Arten mariner Gattungen sind aus dem Mittelmeer genannt, 120 aus dem Flachwasser des Nordostatlantiks und 30 aus der Ostsee. Hinsichtlich der Algen- und Tierkolonien-besiedelnden Halacariden-Arten entspricht die Schwarzmeerfauna weitgehend einer reduzierten Mittelmeerfauna. Es ist anzunehmen, dass die einstige Fauna des heutigen Schwarzmeerbeckens die Umweltanderungen im spaten Miozaen, oder die im Pleistozaen, nicht uberlebt hat und die heutigen Arten entweder im Laufe des Pliozaens oder erst nach der Eiszeit das Schwarze Meer besiedelten. Die Herkunft der Schwarzmeerpopulation von Rhombognathides pascens last sich nicht klaren. Die Sandluckensystemfauna des Schwarzen Meeres unterscheidet sich von der des Mittelmeeres. Die in Stranden des Schwarzen Meeres mit mehreren Arten vertretene Gattung Halacarellus ist im Mittelmeer selten, im Nordatlantik aber verbreitet. Es ist nicht auszuschliesen, dass einige Arten Relikte einer einst weit verbreiteten Halacariden-Fauna sind, somit die vergangenen Jahrmillionen unverandert uberstanden haben. Ein Vergleich der Artenzusammensetzung in den vier Seegebieten Schwarzes Meer, Mittelmeer, Nordostatlantik und Ostsee ergab, dass im Mittelmeer die Copidognathinen, vor allem die Gattung Copidognathus, die meisten Arten stellt, in der Ostsee die Rhombognathinen dominieren. Die Gattung Halacarellus ist im Mittelmeer selten, reich vertreten aber in den anderen drei Seegebieten.

Future wind, wave and storm surge climate in the Northern Seas: a revisit

We consider possible changes in the future climate of wind speed (WS), significant wave height (SWH) and storm surge residual (SSR) for a region covering the Northern Seas. Our results are based on an analysis of changes in the response derived with regional atmosphere, wave, and storm surge models run for two time periods 1961–1990 and 2071–2100. Available for the study were atmospheric downscalings of the Hadley Centre’s SRES A2 and B2 scenarios, the Max-Planck Institute’s SRES B2 scenario and the Bjerknes Centre’s SRES A1B scenario. The most important statistically significant findings are, first, a decrease in WS south of Iceland accompanied by a decrease of about 4–6% in SWH. Secondly, there is an increase in the eastern North Sea that continues into the Skagerrak. Along the North Sea east coast and in the Skagerrak the annual 99-percentiles of SWH and SSR increase 6–8% and 8–10%, respectively, and these results are robust across the various choices in global models and emission scenarios. Finally, there is an increase in the annual 99-percentiles of all variables west of the British Isles.

Structural, Sedimentologic, and Sea-Level Controls on Sand Distribution in a Steep-Clinoform Asymmetric Wave-Influenced Delta: Miocene Billund Sand, Eastern Danish North Sea and Jylland

Abstract The lower Miocene Billund sand of Jylland, Denmark, provides an excellent opportunity to study the distribution of sands and the types of clinoform generated by a wave-dominated delta prograding into a deep shelf environment. In particular seismic sections, the sand-rich parts correlate with parallel clinoformal seismic facies, in which the clinoforms dip 7° to 10°. The stacking pattern of this seismic facies also indicates whether the progradation occurred during rising or falling sea level by displaying an ascending or descending shoreline trajectory, respectively. The Billund delta was deposited in the eastern North Sea Basin during the early Miocene and is on the available data recognized as a NW to SE trending feature. It forms a wave-dominated delta with thick sand bodies deposited in relatively deep waters (> 100 m) at the river mouth and in the up-drift area of newly formed delta lobes. Sands and muds associated with a spit complex or a lagoonal complex dominated the down-drift area. In the distal delta-front area, alternating sands and muds were laid down, the sands associated mainly with storm events. Progradation of the studied part of the delta occurred during high sea level and a subsequent fall in sea level that was caused by a eustatic fall during the mid Aquitanian (early Miocene). Although sand intervals 10 to 20 m thick are common throughout the delta complex, the thickest (up to 100 m) and cleanest sand is found in units deposited in narrow bands within structural lows and during periods of forced regression. The Billund delta may be an excellent analogue for hydrocarbon-bearing, wave-dominated deltas, and seems to exhibit similarities to Jurassic deposits in the North Sea area.

Future wind, wave and storm surge climate in the Northern Seas: a revisit

We consider possible changes in the future climate of wind speed (WS), significant wave height (SWH) and storm surge residual (SSR) for a region covering the Northern Seas. Our results are based on an analysis of changes in the response derived with regional atmosphere, wave, and storm surge models run for two time periods 1961–1990 and 2071–2100. Available for the study were atmospheric downscalings of the Hadley Centre’s SRES A2 and B2 scenarios, the Max-Planck Institute’s SRES B2 scenario and the Bjerknes Centre’s SRES A1B scenario.The most important statistically significant findings are, first, a decrease in WS south of Iceland accompanied by a decrease of about 4–6% in SWH. Secondly, there is an increase in the eastern North Sea that continues into the Skagerrak. Along the North Sea east coast and in the Skagerrak the annual 99-percentiles of SWH and SSR increase 6–8% and 8–10%, respectively, and these results are robust across the various choices in global models and emission scenarios. Finally, there is an increase in the annual 99-percentiles of all variables west of the British Isles.

Regional and annual variation in black-legged kittiwake breeding productivity is related to sea surface temperature

Spatiotemporal variation in seabird demographic parameters is often pronounced and may be an important source of information on the state of marine ecosystems. Black-legged kittiwakes Rissa tridactyla in Britain and Ireland show strong regional structure in breeding productivity, and both temporal and spatial variation are probably related to abundance of the principal prey of breeding kittiwakes, the lesser sandeel Ammodytes marinus. Annual regional estimates of sandeel abundance do not exist, prohibiting direct tests of this hypothesis. We examined relationships between kittiwake breeding productivity and 2 potential proxies of sandeel abundance, winter sea surface temperature (SST) and abundance of Calanus copepods, within and among 6 regions in Britain and Ireland from 1986 to 2004. Means and trends in winter SST differed among regions, with higher means and less pronounced increasing trends in western (Atlantic) regions than in eastern (North Sea) regions. A negative relationship between breeding productivity and winter SST in the previous year was found within 2 regions (East Scotland and Orkney), as well as in a cross-regional analysis. Results were inconclusive for Calanus abundance, with a positive relationship in East Scotland and negative in Orkney. These results demonstrate that although a single environmental driver (SST) is related to both within- and between-region variation in a key demographic parameter, regional heterogeneity in SST trends as well as the importance of other factors may lead to highly variable responses. Understanding this heterogeneity is critical for predicting long-term effects of climate change or other anthropogenic drivers on marine ecosystems.

Mudflat biota since the 1930s: change beyond return?

Where, since the 1980s, patchy and variable green algal mats are prevailing, distinct belts of an amphipod (Corophium volutator) and seagrass (Zostera spp.) had dominated in the 1930s. The zonation between tide marks has been mapped in a sheltered sedimentary bay in the Wadden Sea near the island of Sylt (coastal eastern North Sea). Maps on vegetation from 1924 and on selected macrobenthos from 1932 and 1934 are compared with biannual surveys conducted from 1988 to 2006. Rising high water levels and eutrophication are suggested to be major causes of the observed long-term changes. In front of a saltmarsh, a sandy beach developed and partly displaced former cyanobacterial mats. Advancing sandiness may have inhibited C. volutator and facilitated lugworms, Arenicola marina, in the upper tidal zone. A variable occurrence of green algal mats arising in the 1980s affected infauna and seagrass by smothering the biota underneath. This dissolved a coherent belt of Zostera noltii. In the lower tidal zone, natural disturbances had lasting effects on the occurrence of mussels with attached fucoid algae. The spectrum of species became enriched by alien species (13% of macrobenthic taxa). A reversal to habitat structure and biotic zonation of the 1920–1930s does not seem possible. Aliens, in combination with climate change, are expected to further divert the ecological pattern to new configurations.

Seagrass recovery in the Northern Wadden Sea?

Aerial surveys on seagrass (Zostera spp.) indicate a three to fourfold increase in bed area from 1994 to 2006 with up to 100 km2 or 11% of intertidal flats in the Northfrisian Wadden Sea (coastal eastern North Sea), observed at seasonal maximum in August when flying during low tide exposure 300 to 500 m above ground. When viewed from the air, difficulties in distinguishing between seagrass and green algae and a lack of contrast on dark-coloured mudflats are sources of error in areal estimates. Particularly the positioning of beds remote from shores was imprecise. However, the consistency in method over time gives confidence to the inferred positive trend which is opposite to the global pattern. Both, the spatial pattern and a recent decrease in storminess suggest that sediment stability is the key factor for seagrass dynamics in this tidal area. On exposed sand flats, high sediment mobility may be limiting and along the sheltered mainland shore land claim activities with high accretion rates may cause a scarcity of seagrass. The potential area of seagrass beds may be twice as large as the realized maximum in 2006 but eventually the rising sea level will reverse the observed seagrass expansion.

A morphometric analysis of tunnel valleys in the eastern North Sea based on 3D seismic data

AbstractA 1250 km2 3D seismic volume is used to provide a detailed spatial and geometrical analysis of fifteen Pleistocene tunnel valleys in the Danish North Sea. All the valleys are buried; they are up to 39 km long, 3–4 km wide and up to 350 m deep. The valleys are part of a vast tunnel valley province covering an area of some 0.5 million km2 of the formerly glaciated lowland areas of North West Europe. The valleys consist of non‐branching, non‐anastomosing troughs; they exhibit strongly undulating bottom profiles with numerous sub‐basins and thresholds, and are characterised by adverse end slopes. Cross‐cutting relationships and theoretical considerations suggest the occurrence of seven major episodes of valley incision attributed to ice marginal oscillations within a few glacials. Calculations considering the valley end gradients and theoretical ice‐surface profiles suggest that the valleys were formed by pressurised subglacial meltwater erosion. Given a range of theoretical ice‐surface profiles, the adverse end slopes are well beyond the supercooling threshold, which suggests that the water was not in thermal equilibrium with the basal ice and that flow was concentrated in substantial conduits with sufficient mass and flux to maintain water temperature well above the freezing point. Copyright © 2007 John Wiley & Sons, Ltd.

Chalk depth structure maps, Central to Eastern North Sea, Denmark

The Upper Cretaceous – Danian chalk may be considered to be the economically most important rock type in Denmark. Onshore it constitutes an important groundwater aquifer and it is also quarried for e.g. building materials and paper production. Offshore the chalk reservoirs contain more than 80% of the oil and gas produced in Denmark (Fig. 1). During the last few years efforts have therefore been made to map this important succession in the Danish and adjoining areas (Vejbæk et al. 2003). The stratigraphic interval mapped comprises the Chalk Group of Cenomanian to Danian ages and its stratigraphically equivalent units (Fig. 2). The north-eastern limit of the Chalk Group is determined by Neogene erosion. The limits of the map to the west and south were mainly determined by the amount of available data.