Description: Das Europäische Nordmeer, wie die kontinentale Eisbedeckung der angrenzenden Gebiete zeigen eine starke gegenseitige Beeinflussung. Die Wassermassen in den hohen Breiten reagieren sehr empfindlich auf quartäre Klimaschwankungen. Als Folge der Klimaschwankungen führen Veränderung der Strömungssysteme zu einer Anderung in der Sedimentation. Glaziale Verhältnisse im Europäischen Nordmeer wurden modellhaft von KELLOGG (1975, 1976, 1977, 1980), KELLOGG et al. (1978), BELANGER (1982), STREETER et al. (1982) und HENRICH et al. (1989) aufgrund sedimentologischer Untersuchungen und mit Hilfe von Isotopendaten rekonstruiert. Anhand der Arbeiten läßt sich zeigen, daß der Einfluß des warmen Atlantikwassers große Auswirkung auf die Sedimentationsverhältnisse im Europäischen Nordmeer hat. Während der quartären Warmphasen besitzen diese Wassermassen eine große Verbreitung und drängen damit die Polarfront weit nach Nordwesten zurück. Der kalte, zum Teil eisbedeckte Ostgrönland-Strom zeigt dagegen größte Ausbreitungen während der Kaltphasen. Der untersuchte Kern stammt aus der Islandsee (Abb.1) und liegt damit im Einflußbereich des Ostgrönland-Stromes. Die vorliegende Arbeit dient als weitere Ergänzung der sedimentologischen Daten in diesem Gebiet. Es wurde eine genaue Analyse der Grobfraktion, sowie der lithologischen und geochemischen Daten des Sediments vorgenommen, um aufgrund dieser Ergebnisse eine möglichst genaue Rekonstruktion dieses Zeitabschnittes zu erhalten. Von besonderer Bedeutung ist hierbei, wie stark die Ausprägung der Glaziale und Interglaziale war, und was für eine Auswirkung dies auf die Sedimentation hatte. Wichtig hierfür sind die Isotpenwerte und Karbonatgehalte, sowie die Intensität der Produktivität und der Eintrag an eistransportiertem Material. Daneben lassen sich auch Aussagen über die Ausbreitung des Ostgrönland-Stromes machen. Für einen methodischen Vergleich zwischen Siebanalyse und Sedimentationswaage wurde der gesamte GKG, sowie die ersten 350 cm des Kerns mit der Sedimentationswaage untersucht. Anschließend wurde eine Komponentenanalyse mit Hilfe des Separators durchgeführt. Die Ergebnisse sollen zeigen wo eine gute Übereinstimmung und wo Abweichungen zwischen beiden Analyseverfahren bestehen. Dabei wurde versucht, die Ergebnisse der Sedimentationswaage einzelnen Sedimenttypen zu zuordnen. Weiter stellte sich die Frage auf welcher Basis sich die Ergebnisse des Separators mit den lithologischen und geochemischen Daten vergleichen lassen.

Description: Some basic characteristics of ridge axis topography are related to spreading rate and distance from neighboring transform faults. For example, the presence of an axial depression coincides in most cases with slow spreading rates, and the overall depth of the ridge axis increases toward ridge-transform intersections (RTIs). On the other hand, it is also well known that the relief and width of the axial valley on, say, the Mid-Atlantic Ridge (MAR) vary along strike in an unpredictable manner. The purpose of the present study is to quantify how much of the observed variation in the first-order topography at the axis is related to changes in other parameters, such as spreading rate and distance from RTIs. To carry out this test, the zero-age depth and the relief and width of the axial valley have been estimated on 46 profiles that cross the axis of the MAR between the equator and 50°N (full spreading rates 22–36 km/Ma). Zero-age depth is here defined to be the depth at age zero of the best fit thermal subsidence trend. Axial valley relief and width have been measured with respect to the ridge flanks by the least squares fit of a Gaussian bell. The measured axial valley relief varies between 600 and 2100 m (average ∼1300 m), while the valley width varies between 16 and 62 km (average ∼35 km). The correlation between zero-age depth, axial valley relief and width, latitude of axial crossing, spreading rate, distance from nearest RTT, and offset on the nearby transforms has been investigated using linear regression techniques. The main results of the present study are that (1) zero-age depth significantly correlates with latitude of crossing, distance from nearest RTI, and offset on the nearby transforms; and (2) the variation in axial valley relief and width is essentially uncorrelated with spreading rate, zero-age depth, distance from nearest RTT, and offset on nearby transforms. The preferred explanation for the observed spatial variation in axial valley geometry is that it reflects a temporal variation. In fact, if the rough abyssal hill topography typical of the MAR flanks is created within the axial valley, the shape of the axial valley cannot be steady state (although the existence of an axial valley may be a steady state phenomenon). This hypothesis is supported by the observation that the variability in axial valley relief is similar to the overall amplitude of abyssal hill topography, measured as the residual on the thermal subsidence trend.

Description: This paper describes the large-scale distribution of laminated sediments and the deposition of nutrients in the Baltic offshore accumulation region. The area of laminated surficial sediments in the Baltic proper, excluding the Gulf of Finland and the Gulf of Riga, has been estimated to cover approximately one third of the total area. Accumulation of autochthonous and allochthonous material accounts for only a minor part of the total amount of nutrients sequestered in these deep offshore accumulation bottoms; most of the nutrients may originate from shallow sediments that are eroded as a result of the isostatic land uplift.

Description: A seismic refraction profile across Langeland (Denmark) obtained from land stations recording airgun shots allowed to resolve upper crustal velocities to a depth of 8 km. The profile traverses the proposed Caledonian Deformation Front and the Ringkoebing-Fyn High. The Ringkoebing-Fyn High is about 10 km wide and the top basement lies less than 2 km below the surface. Basement velocities as high as 6.4 km/s, at depths between 6 and 8 km, can be best explained by compositional changes between adjoining basement units to the north and south. South of the Ringkoebing-Fyn High another high velocity basement unit is encountered and most probably represents a basement affected by the Caledonian orogeny. Along this profile on Langeland the positions of the Caledonian Deformation Front and the northern limit of the Zechstein deposits coincide.

Description: A deep Seismic reflection profile collected by DEKORP and BELCORP in the western Rhenish Massif was supplemented by wide-angle measurements. Signals from a vibrator source were successfully recorded to a distance of 60 km. A passive recording array was operated that recorded all shots along the profile. The wide-angle and near-vertical data were used to construct a velocity model for the profile. Most of the wide-angle reflections coincide with strong near-vertical reflections or bands of high reflectivity. The North Variscan Deformation Front, seen as a prominent shallow reflection on many profiles in this region, separates an upper crust with rather nigh velocities from a layer with lower velocities underneath. At a depth of 20–22 km a thin (2–3 km thick) layer of high velocities is found. The Moho is not reflective either in the near-vertical or in the wide-angle data, suggesting the presence of a thick crust-mantle transition zone.

Description: The isotopic composition of dissolved O2 in seawater, expressed as the δ18O of O2, is unique among the bioactive tracers of the aphotic zone in that it is not linearly related to oxygen utilization via the stoichiometry of organic matter decomposition. In fact, δ18O of O2 depends on the history of water mixing and O2 consumption in the sample studied (Craig and Kroopnick, 1970; Kroopnick and Craig, 1976). For this reason, the variation of δ18O of O2 with O2 concentration depends on regional circulation patterns and oxygen utilization rates. The δ18O of O2 can be used to chartacterize these processes by decoupling their effects. As an example of this assertion, we interpret the covariation between the concentration of O2 and its isotopic composition in the Pacific Ocean as reported by Kroopnick (1987), using four simple representations of seawater mixing and respiration. Kroopnick's data are in general accord with an elementary model of isopycnal mixing represented by diffusive exchange and oxygen utilization in the ocean's interior, coupled with atmospheric equilibrium at the point where the isopycnals outcrop at the sea surface. This specific result illustrates the general point that δ18O of O2 in seawater can serve as an important constraint on more extensive and sophisticated physical models used to estimate rates of oxygen utilization in the deep sea.

Description: The Quaternary Herchenberg composite tephra cone (East Eifel, FR Germany) with an original bulk volume of 1.17·107 m3 (DRE of 8.2·106 m3) and dimensions of ca. 900·600·90 m (length·width·height) erupted in three main stages: (a) Initial eruptions along a NW-trending, 500-m-long fissure were dominantly Vulcanian in the northwest and Strombolian in the southeast. Removal of the unstable, underlying 20-m-thick Tertiary clays resulted in major collapse and repeated lateral caving of the crater. The northwestern Lower Cone 1 (LC1) was constructed by alternating Vulcanian and Strombolian eruptions. (b) Cone-building, mainly Strombolian eruptions resulted in two major scoria cones beginning initially in the northwest (Cone 1) and terminating in the southeast (Cones 2 and 3) following a period of simultaneous activity of cones 1 and 2. Lapilli deposits are subdivided by thin phreatomagmatic marker beds rich in Tertiary clays in the early stages and Devonian clasts in the later stages. Three dikes intruded radially into the flanks of cone 1. (c) The eruption and deposition of fine-grained uppermost layers (phreatomagmatic tuffs, accretionary lapilli, and Strombolian fallout lapilli) presumably from the northwestern center (cone 1) terminated the activity of Herchenberg volcano. The Herchenberg volcano is distinguished from most Strombolian scoria cones in the Eifel by (1) small volume of agglutinates in central craters, (2) scarcity of scoria bomb breccias, (3) well-bedded tephra deposits even in the proximal facies, (4) moderate fragmentation of tephra (small proportions of both ash and coarse lapilli/bomb-size fraction), (5) abundance of dense ellipsoidal juvenile lapilli, and (6) characteristic depositional cycles in the early eruptive stages beginning with laterally emplaced, fine-grained, xenolith-rich tephra and ending with fallout scoria lapilli. Herchenberg tephra is distinguished from maar deposits by (1) paucity of xenoliths, (2) higher depositional temperatures, (3) coarser grain size and thicker bedding, (4) absence of glassy quenched clasts except in the initial stages and late phreatomagmatic marker beds, and (5) predominance of Strombolian, cone-building activity. The characteristics of Herchenberg deposits are interpreted as due to a high proportion of magmatic volatiles (dominantly CO2) relative to low-viscosity magma during most of the eruptive activity.

Description: Cylindrical samples of sand consolidated with tetrahydrofuran hydrate were tested for their compressive strength and creep behavior under uniaxial compression. The samples were 15 cm in length and 7.5 cm in diameter and were tested at −10 °C. The results, when combined with our previous measurements on similar samples at −6 °C, show that the material becomes stronger by about 10% with decrease in temperature; otherwise, the slopes of the peak stress – strain rate curves are the same. These results are similar to those of sand consolidated with ice, except that in the latter case the increase in strength over the same temperature range is about 30%. Furthermore, the slope of the peak stress – strain rate curve for the hydrate-consolidated sand is almost zero, whereas for the ice-consolidated sand it is quite steep. Consequently, at strain rates below 10−5 s−1 the hydrate-consolidated sand is stronger, whereas at strain rates above 10−5 s−1 the ice-consolidated sand is the stronger material. Noticeable differences were also observed in the creep behavior of the hydrate- and ice-consolidated sands. At −10 °C, ice-consolidated sand failed in about 15 h under a stress of about 7 MPa, whereas hydrate-consolidated sand failed after 52.3 h under a stress of 12.2 MPa and some samples did not fail even after 540 h when subjected to a stress of 9.3 MPa.

Description: A 30 km2 diapiric field has been identified near 13°50′N up to 12 km seaward of the deformation front of the Barbados accretionary complex. Using a deep‐towed side scan sonar with a 3.5‐kHz profiler, we identified 31 different diapiric structures. Based on seismic stratigraphy, we show that this field has been active for 200,000 years and that it is a transient feature triggered by the seaward propagation of the high pore fluid pressure associated with the décollement beneath the accretionary complex. Both basement and décollement in this area are anomalously shallow due to the presence of a N110° basement ridge. The height of the diapirs above seafloor does not exceed 40–50 m and can be related to the pressure head of the mud below the décollement. Two types of structures are identified: mud volcanoes and massively emplaced diapirs and ridges on the one hand, enigmatic circular very flat mud pies and conical mounds on the other hand. The second type of structures has steeper slopes and appears to be associated with very active venting, as confirmed by a submersible exploration reported in a companion paper (Le Pichon et al., this issue (b)). The venting results in the formation of a stiff carbonate crust and of large subsiding basins around the mud pies. Continuous active fluid expulsion through these structures indicates that an efficient piping system still connects them to the zone of anomalously high pore pressure below the protodécollement.