The rotation of Italy: Preliminary palaeomagnetic data from the Umbrian sequence,Northern Apennines

A preliminary collection of 43 palaeomagnetic samples (10 sites) from the miogeosynclinal and supposedly autochthonous Umbrian sequence in the Northern Apennines, Italy, was analysed by means of alternating magnetic fields and thermal demagnetization studies. The older group of samples, taken from the upper part of the Calcari Diasprini (Malm), the Fucoid Marls (Albian/Cenomanian) and from the basal part of the Scaglia Bianca (Early Late Cretaceous), all showed normal polarity directions and resulted in a mean site direction:D = 290.5°,I = +51.5°,α₉₅ = 11°,k = 74,N = 4.The younger group of samples, taken throughout the Scaglia Rossa sequence (Latest Cretaceous/Middle Eocene) showed normal and reversed polarity directions. In contrast to the older group, the magnetic analysis of these samples resulted in a considerably less dense grouping of site mean directions. This presumably is due to inaccuracies introduced with the very large bedding tilt corrections that had to be applied to the samples of some sites. A tentative mean site direction for these Scaglia Rossa samples was computed as:D = 351°,I = +52.5°,α₉₅ = 23.5°,k = 11.5,N = 5.Despite the low precision of the Scaglia Rossa result, the significant deviation between this Latest Cretaceous/Early Tertiary direction and the Late Jurassic/Early Late Cretaceous direction indicates a counterclockwise rotation of more than forty degrees. This rotation can be dated as Late Cretaceous.How far these data from the Northern Apennines apply to other parts of the Italian Peninsula has yet to be established. The timing of this rotation is not at variance with the data from other parts of Mediterranean Europe (Southern Alps, Iberian Peninsula) and from Africa. However, taking into account the preliminary nature of the results, the amount of rotation of the Northern Apennines seems to surpass the rotation angle which is deduced from the palaeomagnetic data for Africa.     

Seismic velocities of granulite-facies xenoliths from Central Ireland: Implications for lower crustal composition and anisotropy

V_p and V_s values have been measured experimentally and calculated for granulite-facies lower crustal xenoliths from central Ireland close to the Caledonian Iapetus suture zone. The xenoliths are predominantly foliated and lineated metapelitic (garnet–sillimanite–K-feldspar) granulites. Their metapelitic composition is unusual compared with the mostly mafic composition of lower crustal xenoliths world-wide. Based on thermobarometry, the metapelitic xenoliths were entrained from depths of c. 20–25 ± 3.5 km and rare mafic granulites from depths of 31–33 ± 3.4 km. The xenoliths were emplaced during Lower Carboniferous volcanism and are considered to represent samples of the present day lower crust.V_p values for the metapelitic granulites range between 6.26 and 7.99 km s^{− 1} with a mean value of 7.09 ± 0.4 km s^{− 1}. Psammite and granitic orthogneiss samples have calculated V_p values of 6.51 and 6.23 km s^{− 1}, respectively. V_s values for the metapelites are between 3.86 and 4.34 km s^{− 1}, with a mean value of 4.1 ± 0.15 km s^{− 1}. The psammite and orthogneiss have calculated V_s values of 3.95 and 3.97 km s^{− 1}, respectively.The measured seismic velocities correlate with density and with modal mineralogy, especially the high content of sillimanite and garnet. V_p anisotropy is between 0.15% and 13.97%, and a clear compositional control is evident, mainly in relation to sillimanite abundance. Overall V_s anisotropy ranges from 1% to 11%. Poisson's ratio (σ) lies between 0.25 and 0.35 for the metapelitic granulites, mainly reflecting a high V_p value due to abundant sillimanite in the sample with the highest σ. Anisotropy is probably a function of deformation associated with the closure of the Iapetus ocean in the Silurian as well as later extension in the Devonian. The orientation of the bulk strain ellipsoid in the lower crust is difficult to constrain, but lineation is likely to be NE–SW, given the strike-slip nature of the late Caledonian and subsequent Acadian deformation.When corrected for present-day lower crustal temperature, the experimentally determined V_p values correspond well with velocities from the ICSSP, COOLE I and VARNET seismic refraction lines. Near the xenolith localities, the COOLE I line displays two lower crustal layers with in situ V_p values of 6.85–6.9 and 6.9–8.0 km s^{− 1}, respectively. The upper (lower velocity) layer corresponds well with the metapelitic granulite xenoliths while the lower (higher velocity) layer matches that of the basic granulite xenoliths, though their metamorphic pressures suggest derivation from depths corresponding to the present-day upper mantle.     

Relative stress variations as determined by b-values from earthquakes in circum-pacific subduction zones

Assuming a relation of “b” to stress state, the possibility of globe-wide stress variation and transmission was investigated. The NOAA earthquake data file served to determine the temporal change in “b” of log N = a − bM from 1963 to 1975.Periods of six to eight years are observed in the b-values (stress pattern) for most circum-Pacific areas (South America, Tonga, Kermadec, New Hebrides, Kamchatka and Eastern Aleutians).In the Kurils, fore- and aftershock sequences of large earthquakes seem to mask any characteristic global pattern that might exist. These sequences exhibit low b-values (high stress) through the time of foreshocks and early stages of aftershocks, followed by rapid increase in b-values (decrease in stress).Use of a worldwide earthquake data file clearly yields less resolution of the temporal “b” variation than the use of local network studies published by other authors.Incidental to the study, 1124 earthquakes of the NOAA data file yield the M_s − m_b relations: M_s = 1.16m_b − 0.835 for 4.5 m_b 6 and: log₁₀M_s = 0.1432m_b − 0.0629 form_b > 6 with correlative coefficients of 0.994 and 0.992 respectively.     

Lucinid clam influence on the biogeochemistry of the seagrass<Emphasis Type="Italic">Thalassia testudinum</Emphasis> sediments

Lucinid bivalves dominate the infauna of tropical seagrass sediments. While the effect of seagrass on lucinids has been studied, the reverse effect has largely been ignored. Lucinids can alter porewater chemistry (i.e., increase porewater nutrients by suspension feeding and decrease porewater sulfides by oxygen introduction and bacterial oxidation), which can potentially change seagrass productivity and growth morphology. To observe correlations between porewater chemistry and lucinid presence, a field survey and laboratory microcosm experiment were conducted. Survey sampling sites with lucinids had significantly lower sulfide and higher ammonium concentrations than sampling sites without lucinids. There was no difference in phosphate concentration among sampling sites. Both lucinid species used in the microcosm experiment (Ctena orbiculata andLucinesca nassula) significantly lowered sulfide concentrations in the sediment porewater. Microcosm and field survey results were incorporated into a sulfide budget. In seagrass sediments, lucinids remove 2–16% of the total sulfide produced. Sulfide is a major stressor to both plants and animals in Florida Bay sediments; this removal may be important to maintaining seagrass productivity and health. Oxygen introduction into sediments byC. orbiculata was estimated in a dye experiment.C. orbiculata were added to small tubes containing sieved mud and incubated in a bath of seawater with a Rhodamine WT. Rhodamine WT accumulation in the sediment was measured. A first order estimate showed that oxygen introduction can account for less than 5% ofC. orbiculata sulfide removal.     

Transient release of Ni,Mn and Fe from mixed metal sulphides under oxidising and reducing conditions

The potential release of metals from anoxic sediments exposed to oxygen was investigated by using a synthetic preparation of metal sulphides dominated by solid phase FeS. The technique of DGT (diffusive gradients in thin-films) was used to measure sulphide and Fe, Mn and Ni in the anoxic metal-sulphide slurry, which had a pH of 6.4. Speciation calculations based on these data showed there was moderate supersaturation with respect to amorphous FeS in the solution phase. Measurements made using DGT with a range of diffusion layer thicknesses showed that when Fe, Mn and Ni are removed from solution there is fairly rapid (minutes) release from the solid phase, that is reasonably well sustained. This presumed desorptive release will be responsible for elevated concentrations of some metals in solution when sediments are resuspended. Oxidation of the slurry by bubbling with air rapidly (hours) removed Fe, Mn and Ni from the pore water solution. While Fe concentrations in solution remained low after the removal, Mn and Ni were transiently released. These results were consistent with initial rapid oxidation of Fe(II) to oxyhydroxides, which remove Mn(II) and Ni by adsorption. The slower oxidation of FeS then releases Mn and Ni, but these too are eventually removed by adsorption to iron oxyhydroxides. These data suggest that oxidation of metal sulphides will contribute to the release of metals from sediment disturbed by dredging or remedial aeration, but it is likely to be short lived, with complete removal within a day.     

High resolution regional climate model simulations for Germany: Part II—projected climate changes

The projected climate change signals of a five-member high resolution ensemble, based on two global climate models (GCMs: ECHAM5 and CCCma3) and two regional climate models (RCMs: CLM and WRF) are analysed in this paper (Part II of a two part paper). In Part I the performance of the models for the control period are presented. The RCMs use a two nest procedure over Europe and Germany with a final spatial resolution of 7 km to downscale the GCM simulations for the present (1971–2000) and future A1B scenario (2021–2050) time periods. The ensemble was extended by earlier simulations with the RCM REMO (driven by ECHAM5, two realisations) at a slightly coarser resolution. The climate change signals are evaluated and tested for significance for mean values and the seasonal cycles of temperature and precipitation, as well as for the intensity distribution of precipitation and the numbers of dry days and dry periods. All GCMs project a significant warming over Europe on seasonal and annual scales and the projected warming of the GCMs is retained in both nests of the RCMs, however, with added small variations. The mean warming over Germany of all ensemble members for the fine nest is in the range of 0.8 and 1.3 K with an average of 1.1 K. For mean annual precipitation the climate change signal varies in the range of ?2 to 9 % over Germany within the ensemble. Changes in the number of wet days are projected in the range of ±4 % on the annual scale for the future time period. For the probability distribution of precipitation intensity, a decrease of lower intensities and an increase of moderate and higher intensities is projected by most ensemble members. For the mean values, the results indicate that the projected temperature change signal is caused mainly by the GCM and its initial condition (realisation), with little impact from the RCM. For precipitation, in addition, the RCM affects the climate change signal significantly.     

River channel and bar patterns explained and predicted by an empirical and a physics‐based method

Our objective is to understand general causes of different river channel patterns. In this paper we compare an empirical stream power‐based classification and a physics‐based bar pattern predictor. We present a careful selection of data from the literature that contains rivers with discharge and median bed particle size ranging over several orders of magnitude with various channel patterns and bar types, but no obvious eroding or aggrading tendency. Empirically a continuum is found for increasing specific stream power, here calculated with pattern‐independent variables: mean annual flood, valley gradient and channel width predicted with a hydraulic geometry relation. ‘Thresholds’, above which certain patterns emerge, were identified as a function of bed sediment size. Bar theory predicts nature and presence of bars and bar mode, here converted to active braiding index (B_i). The most important variables are actual width–depth ratio and nonlinearity of bed sediment transport. Results agree reasonably well with data. Empirical predictions are somewhat better than bar theory predictions, because the bank strength is indirectly included in the empirical prediction. In combination, empirical and theoretical prediction provide partial explanations for bar and channel patterns. Increasing potential‐specific stream power implies more energy to erode banks and indeed correlates to channels with high width–depth ratio. Bar theory predicts that such rivers develop more bars across the width (higher B_i). At the transition from meandering to braiding, weakly braided rivers and meandering rivers with chutes are found. Rivers with extremely low stream power and width–depth ratios hardly develop bars or dynamic meandering and may be straight or sinuous or, in case of disequilibrium sediment feed, anastomosing. Copyright © 2010 John Wiley & Sons, Ltd.     

Towards non-linear inversion for characterization of time-lapse phenomena through numerical modelling

We compare two geophysical survey measurements of the same type made at different times in order to characterize the change in the geological medium during the elapsed time. The aim of this study is to develop a strategy using a full non-linear inversion algorithm as the interpretation tool. In this way, not only the location and the form of the changes are recovered, but also the changes in the material parameters of the geological medium can be estimated. In order to solve this fully non-linear problem, the so-called ‘multiplicative regularized contrast source inversion’ (MR-CSI) method is employed. The unique property of this iterative method is that it does not solve the forward problem at each iterative step. This makes it possible to use the non-linear inversion algorithm for large-scale computation problems. The numerical results show that by taking into account the non-linear nature of the problem, interpretation of the time-lapse data can be significantly improved, compared with that obtained using linear inversion.     

Comparison of arsenic concentrations in simultaneously-collected groundwater and aquifer particles from Bangladesh,India, Vietnam,and Nepal

One of the reasons the processes resulting in As release to groundwater in southern Asia remain poorly understood is the high degree of spatial variability of physical and chemical properties in shallow aquifers. In an attempt to overcome this difficulty, a simple device that collects groundwater and sediment as a slurry from precisely the same interval was developed in Bangladesh. Recently published results from Bangladesh and India relying on the needle-sampler are augmented here with new data from 37 intervals of grey aquifer material of likely Holocene age in Vietnam and Nepal. A total of 145 samples of filtered groundwater ranging in depth from 3 to 36 m that were analyzed for As (1–1000 μg/L), Fe (0.01–40 mg/L), Mn (0.2–4 mg/L) and S (0.04–14 mg/L) are compared. The P-extractable (0.01–36 mg/kg) and HCl-extractable As (0.04–36 mg/kg) content of the particulate phase was determined in the same suite of samples, in addition to Fe(II)/Fe ratios (0.2–1.0) in the acid-leachable fraction of the particulate phase. Needle-sampler data from Bangladesh indicated a relationship between dissolved As in groundwater and P-extractable As in the particulate phase that was interpreted as an indication of adsorptive equilibrium, under sufficiently reducing conditions, across 3 orders of magnitude in concentrations according to a distribution coefficient of 4 mL/g. The more recent observations from India, Vietnam and Nepal show groundwater As concentrations that are often an order of magnitude lower at a given level of P-extractable As compared to Bangladesh, even if only the subset of particularly reducing intervals characterized by leachable Fe(II)/Fe >0.5 and dissolved Fe >0.2 mg/L are considered. Without attempting to explain why As appears to be particularly mobile in reducing aquifers of Bangladesh compared to the other regions, the consequences of increasing the distribution coefficient for As between the particulate and dissolved phase to 40 mL/g for the flushing of shallow aquifers of their initial As content are explored.