Sediment deposition in the northern basins of the North Atlantic and characteristic variations in shelf sedimentation along the East Greenland margin

New seismic data off East Greenland were acquired in the summer of 2002, between 77°N and 81°N, north of the Greenland Fracture zone. The data were combined with results from the Greenland Basin and ODP site 909, and indicate a pronounced middle Miocene unconformity within the deep sea basins between 72°N and 81°N. Seismic unit NA-1 consists of sediments older than middle Miocene age and unit NA-2 contains sediments younger than the middle Miocene. Classification of a thinly bedded succession in the Molloy Basin resulted in a subdivision into four units (unit I, unit II, unit IIIA and unit IIIB). A comparison of volume estimations and sediment thickness maps between 72°N and 81°N indicates differences in sediment accumulation in the Greenland, Boreas and Molloy basins. Important controls on the variation of accumulation included different opening times of the basins, as well as tectonic conditions and varying sources of sediment transport.Due to prominent basement structures and the varying reflection character of the sediments along the entire East Greenland margin, we defined an age model of shelf sediments on the basis of similar sediment deposit geometry and known results from other regions. The seismic sequences on the shelf up to an age of middle Miocene are divided into three sub-units along the East Greenland margin: middle Miocene–middle late Miocene (SU-3), middle late Miocene–Pleistocene (SU-2), Pleistocene (SU-1). The differences in the geometry of the sequences show more ice stream related sedimentation between 72°N and 77°N and more ice sheet related sedimentation north of 78°N. The region south of 68°N is dominated by more aggradational sedimentary strata so that a glacio-fluvial drainage seems the main transport mechanism. Due to the Greenland Inland–ice borderlines, we assume the glaciers between the Scoresby Sund and 68°N did not reach the shelf break. A first comparison of the sediment structure of the Northeast Greenland margin with the Southeast Greenland margin made it possible to demonstrate significant differences in sedimentation along this margin.     

Synthesis of pyrope–grossular garnets: an experimental study at P = 2.5 GPa

Summary ?In order to evaluate the stability of Mg–Ca garnets at P = 2.5 GPa/T = 800–1500 °C, some experiments were performed using both natural and synthetic starting materials. Particular attention was paid to the investigation of the Ca rich side of the pyrope–grossular join and the maximum pyrope content in grossular was found to be about 10 mol.%. The addition of Cr to the system only slightly increases the observed pyrope solubility in grossular whereas Na stabilises melilite and merwinite. Clinopyroxene with a composition lying on the diopside – Ca Tschermak join appears to be the only stable crystalline phase in the middle part of the pyrope–grossular join. Received August 28, 2001; revised version accepted July 23, 2002 Published online February 24, 2003     

New insights into aggregation and conformational behaviour of humic substances: Application of high resolution ultrasonic spectroscopy

The potential of high resolution ultrasonic analysis (HRUS) in humic acid colloidal properties research has been demonstrated. Sodium salts of humic acids from soil and lignite showed similar behaviour, supporting the hypothesis that, at both neutral and alkaline pH, they aggregate from very low concentration. The same conclusion can be reached for solutions at high ionic strength. We tried to apply the same procedure as used for the study of micellization and determination of critical micelle concentration of common surfactants. As expected, our experiments did not show the same break as demonstrated on the HRUS records for sodium dodecyl sulfate, at least in the range of measured concentration (i.e. from 0.001 up to 10 g L⁻¹). The colloidal state of humic acids in aqueous solution is very sensitive to the presence of other, both charged and neutral, molecules. Aggregation of humic acids can be disturbed or promoted, depending on the concentration, by electrostatic or other weak interactions with extraneous molecules. Structures of varying mechanical strength (rigidity) can be formed in solutions of the same components but at different concentration. Such behaviour reflects mechanisms which occur during the sequestration of hydrophobic organic compounds and has several implications for the protection/transportation of labile structures and contaminants which are hypothesized to be encapsulated within hydrophobic pockets of soluble humic aggregates.     

Gradient in the climate change signal of European discharge predicted by a multi-model ensemble

In order to perform hydrological studies on the PRUDENCE regional climate model (RCM) simulations, a special focus was put on the discharge from large river catchments located in northern and central Europe. The discharge was simulated with a simplified land surface (SL) scheme and the Hydrological Discharge (HD) model. The daily fields of precipitation, 2 m temperature and evapotranspiration from the RCM simulations were used as forcing. Therefore the total catchment water balances are constrained by the hydrological cycle of the different RCMs. The validation of the simulated hydrological cycle from the control simulations shows that the multi-model ensemble mean is closer to the observations than each of the models, especially if different catchments and hydrological variables are considered. Therefore, the multi-model ensemble mean can be used to largely reduce the uncertainty that is introduced by a single RCM. This also provides more confidence in the future projections for the multi-model ensemble means. The scenario simulations predict a gradient in the climate change signal over Northern and Central Europe. Common features are the overall warming and the general increase of evapotranspiration. But while in the northern parts the warming will enhance the hydrological cycle leading to an increased discharge, the large warming, especially in the summer, will slow down the hydrological cycle caused by a drying in the central parts of Europe which is accompanied by a reduction of discharge. The comparison of the changes predicted by the multi-model ensemble mean to the changes predicted by the driving GCM indicates that the RCMs can compensate problems that a driving GCM may have with local scale processes or parameterizations.     

Morphological features of the Apennines foreland/accretionary-wedge boundary in the Ionian Sea

A detailed reconstruction of the morphology and recent tectonic activity of the Northern Ionian basin is provided on the basis of newly acquired high-resolution swath bathymetric and single and multichannel seismic profiles. The tectonic domains in this area are the Calabrian accretionary wedge and the Apulian foreland. The contact between the two domains, oriented NW–SE, morphologically coincides with a sea-bottom erosional channel (Taranto canyon) characterized on both sides by mass movements induced by slope instability. Along the accretionary wedge/Apulian foreland boundary three different morphological sectors have been recognized whose main characters are represented by a southward stepped increase of erosional canyon activity resulting in a pronounced slope acclivity and a superficial sediment instability. By means of seismic data we correlate the morphology of the sea-bottom to different contractional and flexural processes of the accretionary wedge/foreland system. The interaction between the different rheological domains in the subduction/collision processes could have also induced horizontal stress represented by areas of tectonic release. In an area like this, where very few detailed surveys have been carried out, this study represents the first attempt in correlating the recent tectonic activity to the morphological features and in locating possible slope instability that has to be evaluated for the positioning of offshore infrastructures.     

Mineralogical characterization of some basaltic asteroids in the neighborhood of (4) Vesta: first results

We present reflectance spectra of 19 V-type asteroids obtained at the 3.6 m Telescopio Nazionale Galileo covering 0.8 to 2.5 μm. For 8 of these asteroids we obtained also visible spectra in the same observational run. The range from 0.8 to 2.5 μm, encompassing the 1 and 2 μm pyroxene features, allows a precise mineralogical characterization of these asteroids. The obtained data suggests the possible coexistence of distinct mineralogical groups among the V-type asteroids, either probing different layers of (4) Vesta or coming from different bodies. No clear correlation was found between mineralogies and the objects being, or not, member of the Vesta dynamical family.     

First investigations on the quaternary system Na2O-K2O-CaO-SiO2: synthesis and crystal structure of the mixed alkali calcium silicate K1.08Na0.92Ca6Si4O15

Mineralogy and Petrology - In the course of an exploratory study on the quaternary system Na2O-K2O-CaO-SiO2 single crystals of the first anhydrous sodium potassium calcium silicate have been...     

Landslide susceptibility modeling assisted by Persistent Scatterers Interferometry (PSI): an example from the northwestern coast of Malta

Natural Hazards - Persistent Scatterers Interferometry (PSI) techniques are widely employed in geosciences to detect and monitor landslides with high accuracy over large areas, but they also suffer...