Pleistocene stratigraphy in the Devils Hole Area,Central North Sea: Foraminiferal and amino-acid evidence

A detailed study of the foraminiferal assemblages from the 229.1-m-deep core 81/34 in the central North Sea has been combined with a series of measurements of the isoleucine epimerisation of foraminiferal tests. A total of 17 foraminiferal zones have been established and both the faunal compositions and the amino-acid values suggest that a major part of the sequence represents deposits of early and middle Pleistocene age. Only the uppermost zone is referred to the late Pleistocene. The sequence mainly comprises a series of marine zones from cold periods, but with some barren, possibly non-marine intervals in between. Only two of the foraminiferal zones can be referred to interglacial periods. The oldest one of these, defined here as the Devils Hole Interglacial, may belong to the latter part of the Cromerian Complex, while the upper warm interval is correlated with the Holsteinian of northwest Europe on the basis of its amino-acid values. A detailed stratigraphical correlation between core 81/34 and the neighbouring core 81/29 is suggested on the basis of their foraminiferal content, palaeomagnetic evidence and amino-acid measurements from both cores. A characteristic feature of both sequences is that most of the Quaternary record is missing. Similar episodic patterns of deposition and erosion have been reported previously from the North Sea area.     

Petrogenesis and significance of late Caledonian granitoid magmatism in western Norway

Obduction of the late Ordovician Solund-Stavfjord Ophiolite Complex (443±3 Ma), west Norwegian Caledonides, involved generation and high-level emplacement of granitic and granodioritic dikes and plutons. Initial ⁸⁷Sr/⁸⁶Sr ratios in the granites are low (0.7042–0.7059), suggesting either a mantle component or a Rb-poor crustal source. Initial Nd (Nd(t)) ranges from-0.8 to-8.8, indicating that the granites represent recycling of old crustal rocks, which is supported by Precambrian inheritance in zircons from two of the studied granites. I argue that the Rb-Sr and the Sm-Nd isotope systems are decoupled in the sense that the Sr-and the Nd-isotopes derive their dominant signals from two different sources, a mantle source and a crustal source respectively. The granites are metaluminous to peraluminous and typically have high Sr, Ba and Na₂O/K₂O ratios. SiO₂ contents range from 66 to 74 wt%. REE abundances are highly variable; the La contents range from 80 to 200 times chondrite, and are inversely correlated with the contents of SiO₂. The concentration of Nd in the granites decreases asymptotically with decreasing Nd(t) suggesting fractional crystallization of accessory phases and assimilation of continental crust. This argument is supported by the presence of partly dismembered xenoliths in the granites with Nd(t)-values that are significantly lower than Nd(t)-values in the host granite. The following models are suggested for the granites. When the ophiolite complex obducted, an outboard subduction zone approached the continental margin, and subduction-related magmas accumulated beneath the continental margin, and probably intruded the overlying eugeosynclinal deposits. The mantle-derived magmas most likely evolved to granitoid composition by assimilation of these eugeosynclinal sediments and by fractional crystallization of amphibole, feldspar, sphene, and allanite. Alternatively, but less likely, the heat content of the mantle-derived magmas caused extensive melting of immature graywackes and calc-alkaline volcaniclastic rocks in the deepest portions of the eugeosyncline. Either way, during ascent, the compositions of the granitic melts were modified by fractional crystallization of LREE-rich phases and by assimilation of continental metasediments.     

The Trænadjupet Slide: a large slope failure affecting the continental margin of Norway 4,000 years ago

¹⁴C AMS-dated gravity cores reveal that the Trænadjupet Slide offshore Norway occurred about 4,000 ¹⁴C years B.P. (ca. 4,000 cal. years ago). From 4,000 to 3,000 years B.P., minor areas of the newly formed slide scar were probably eroded, the result of smaller episodes of mass wasting caused by delayed collapse of part of the western, upper sidewall or by bottom currents. From about 3,000 years B.P. to the present, sediments were derived from alongslope-flowing, north-eastward-oriented ocean currents carrying sediments in suspension. These results demonstrate that large-scale mass wasting during sea-level highstand is rather common on passive continental margins.     

Equilibrium and structural studies of silicon(IV) and aluminium(III) in aqueous solution. II. Formation constants for the monosilicate ions SiO(OH)3 and SiO2(OH)2. A precision study at 25°C in a simplified seawater medium

The hydrolysis of silicic acid, Si(OH)₄, was studied in a simplified seawater medium (0.6 M Na(Cl)) at 25°C. The measurements were performed as potentiometric titrations (hydrogen electrode) in which OH⁻ was generated coulometrically. The total concentration of Si(OH)₄, B, and log[H⁺] were varied within the limits 0.00075 B 0.008 M and 2.5 -log[H⁺] 11.7, respectively. Within these ranges the formation of SiO(OH)₃⁻ and SiO₂(OH)₂²⁻ with formation constants log β₋₁₁(Si(OH)₄ SiO(OH)₃⁻ + H⁺) = −9.472 ±0.002 and log β₋₂₁(Si(OH)₄ SiO₂(OH)₂²⁻ + 2H⁺) = −22.07 ± 0.01 was established. With B > 0.003 M polysilicate complexes are formed, however, with -log[H⁺] 10.7 their formation does not significantly affect the evaluated formation constants. Data were analyzed with the least squares computer program LETAGROPVRID.     

Centrifuge tests on installation of suction anchors in soft clay

Three centrifuge model tests were performed in normally consolidated Speswhite Kaolin to study the penetration of suction anchors in soft clay. The suction anchors could be penetrated by means of underpressure to a depth of about 12.4 to a little more than 14.5 times the diameter. When the anchors were penetrated by underpressure, all clay displaced by the skirt moved into the anchor. At a penetration depth of about half the maximum penetration depth, the volume of the soil heave inside the anchor actually increased more than the volume of the displaced clay. When a material coefficient of 1.5 against plug failure was mobilized, more than the clay displaced by the skirts had accumulated inside the anchor. The penetration resistance increased by 42 and 26% during rest periods of 4.5 and 0.8 days prototype time, respectively. Some uncertainty in the shear strength of the clay beds gave some uncertainty with respect to the interpretation, but the observed behaviour generally confirmed the theoretical analyses.     

Environmental responses to Lateglacial climatic fluctuations recorded in the sediments of pre‐Alpine Lake Mondsee (northeastern Alps)

Investigation of the sedimentary record of pre‐Alpine Lake Mondsee (Upper Austria) focused on the environmental reaction to rapid Lateglacial climatic changes. Results of this study reveal complex proxy responses that are variable in time and influenced by the long‐term evolution of the lake and its catchment. A new field sampling approach facilitated continuous and precisely controlled parallel sampling at decadal to sub‐annual resolution for µ‐XRF element scanning, carbon geochemistry, stable isotope measurements on ostracods, pollen analyses and large‐scale thin sections for microfacies analysis. The Holocene chronology is established through microscopic varve counting and supported by accelerator mass spectrometry ¹⁴C dating of terrestrial plant macrofossils, whereas the Lateglacial age model is based on δ¹⁸O wiggle matching with the Greenland NGRIP record, using the GICC05 chronology. Microfacies analysis enables the detection of subtle sedimentological changes, proving that depositional processes even in rather large lake systems are highly sensitive to climate forcing. Comparing periods of major warming at the onset of the Lateglacial and Holocene and of major cooling at the onset of the Younger Dryas reveals differences in proxy responses, reflecting threshold effects and ecosystem inertia. Temperature increase, vegetation recovery, decrease of detrital flux and intensification of biochemical calcite precipitation at the onset of the Holocene took place with only decadal leads and lags over a ca. 100 a period, whereas the spread of woodlands and the reduction of detrital flux lagged the warming at the onset of the Lateglacial Interstadial by ca. 500–750 a. Cooling at the onset of the Younger Dryas is reflected by the simultaneous reaction of δ¹⁸O and vegetation, but sedimentological changes (reduction of endogenic calcite content, increase in detrital flux) were delayed by about 150–300 a. Three short‐term Lateglacial cold intervals, corresponding to Greenland isotope substages GI‐1d, GI‐1c2 and GI‐1b, also show complex proxy responses that vary in time. Copyright © 2011 John Wiley & Sons, Ltd.     

The geochemical composition of the terrestrial surface (without soils) and comparison with the upper continental crust

The terrestrial surface, the “skin of the earth”, is an important interface for global (geochemical) material fluxes between major reservoirs of the Earth system: continental and oceanic crust, ocean and atmosphere. Because of a lack in knowledge of the geochemical composition of the terrestrial surface, it is not well understood how the geochemical evolution of the Earth’s crust is impacted by its properties. Therefore, here a first estimate of the geochemical composition of the terrestrial surface is provided, which can be used for further analysis. The geochemical average compositions of distinct lithological classes are calculated based on a literature review and applied to a global lithological map. Comparison with the bulk composition of the upper continental crust shows that the geochemical composition of the terrestrial surface (below the soil horizons) is significantly different from the assumed average of the upper continental crust. Specifically, the elements Ca, S, C, Cl and Mg are enriched at the terrestrial surface, while Na is depleted (and probably K). Analysis of these results provide further evidence that chemical weathering, chemical alteration of minerals in marine settings, biogeochemical processes (e.g. sulphate reduction in sediments and biomineralization) and evaporite deposition are important for the geochemical composition of the terrestrial surface on geological time scales. The movement of significant amounts of carbonate to the terrestrial surface is identified as the major process for observed Ca-differences. Because abrupt and significant changes of the carbonate abundance on the terrestrial surface are likely influencing CO₂-consumption rates by chemical weathering on geological time scales and thus the carbon cycle, refined, spatially resolved analysis is suggested. This should include the recognition of the geochemical composition of the shelf areas, now being below sea level.     

Comparative study to evaluate three ground-based optical remote sensing techniques under field conditions by a gas tracer experiment

Today, ground-based optical remote sensing (ORS) has become an intensively used method for quantifying pollutant or greenhouse gas emissions from point or area sources, and for the validation of airborne or satellite remote sensing data. In this study, we present the results of a release experiment using acetylene (C₂H₂) as a tracer gas, where three ORS techniques were simultaneously tested for two main purposes: (1) the detection of emission sources and (2) the quantification of release rates. Therefore, passive and active open-path Fourier transform infrared spectroscopy (OP-FTIR) and open-path tunable diode laser absorption spectroscopy (TDLAS) were applied and evaluated. The concentration results of the active ORS methods are compared to those estimated by a Lagrangian stochastic atmospheric dispersion model. Our results reveal that passive OP-FTIR is a valuable tool for the rapid detection and imaging of emission sources and the spatial tracer gas distribution; while with active OP-FTIR and TDLAS, C₂H₂ concentrations in the sub-ppm range could be quantified that correlated well with the concentration data obtained by our modeling approach.     

Visualizing the temporal development of thermo-radiative features on ground-based thermographs

In urban microclimate research, ground-based thermography is used to gain insight into the spatial distribution of surface temperatures of various materials. Taking snapshots over a certain time span helps experts to observe the temporal thermo-radiative behavior of the monitored surface elements and therefore supports decisions on possible optimizations, e.g., improving the thermal comfort in a neighborhood. Appropriate visualization techniques facilitate decision-making and are thus crucial in the optimization process. In this study, we present a tool that eases the extraction of thermo-radiative features from multi-temporal thermographs taken from a monitored scene. Assisted by our tool, users can identify, choose, and register thermo-radiative features for each time step according to their individual research needs. The features’ temporal development is then visualized using a directed graph that encodes topological events as well as each feature’s size and summarizing statistics. To enhance this summary, a comprehensive animated sequence emphasizes the spatiotemporal behavior of the most significant thermo-radiative features. Salient developments are visually embedded and highlighted in the original infrared images, which are blended in an animation from time step to time step. Since we enable the user to interact with the data in a flexible way, noisy and low resolution image data sets can also be processed.