The distribution of neodymium isotopes in Arctic Ocean basins

Nd concentration and isotope data have been obtained for the Canada, Amundsen, and Makarov Basins of the Arctic Ocean. A pattern of high Nd concentrations (up to 58 pM) at shallow depths is seen throughout the Arctic, and is distinct from that generally seen in other oceans where surface waters are relatively depleted. A range of isotopic variations across the Arctic and within individual depth profiles reflects the different sources of waters. The dominant source of water, and so Nd, is the Atlantic Ocean, with lesser contributions from the Pacific and Arctic Rivers. Radiogenic isotope Nd signatures (up to ε_Nd = −6.5) can be traced in Pacific water flowing into the Canada Basin. Waters from rivers draining older terrains provide very unradiogenic Nd (down to ε_Nd = −14.2) that can be traced in surface waters across much of the Eurasian Basin. A distinct feature of the Arctic is the general influence of the shelves on the Nd concentrations of waters flowing into the basins, either from the Pacific across the Chukchi Sea, or from across the extensive Siberian shelves. Water-shelf interaction results in an increase in Nd concentration without significant changes in salinity in essentially all waters in the Arctic, through processes that are not yet well understood. In estuarine regions other processes modify the Nd signal of freshwater components supplied into the Arctic Basin, and possibly also contribute to sedimentary Nd that may be subsequently involved in sediment-water interactions. Mixing relationships indicate that in estuaries, Nd is removed from major river waters to different degrees. Deep waters in the Arctic are higher in Nd than the inflowing Atlantic waters, apparently through enrichments of waters on the shelves that are involved in ventilating the deep basins. These enrichments generally have not resulted in major shifts in the isotopic compositions of the deep waters in the Makarov Basin (ε_Nd ∼ −10.5), but have created distinctive Nd isotope signatures that were found near the margin of the Canada Basin (with ε_Nd ∼ −9.0). The deep waters of the Amundsen Basin are also distinct from the Atlantic waters (with ε_Nd = −12.3), indicating that there has been limited inflow from the adjacent Makarov Basin through the Lomonosov Ridge.     

Spectroscopic measurements of the pH in NaCl brines

Spectrophotometric measurements of the pH in natural waters such as seawater have been shown to yield precise results. In this paper, the sulfonephthalein indicator m-cresol purple (mCP, H₂I) has been used to determine the pH of NaCl brines. The indicator has been calibrated in NaCl solutions from 5 to 45 °C and ionic strengths from 0.03 to 5.5 m. The calibrations were made using TRIS buffers (0.03 m, TRIS/TRIS-HCl) with known dissociation constants pK_TRIS in NaCl solutions [Foti C., Rigano C. and Sammartano S. (1999) Analysis of thermodynamic data for complex formation: protonation of THAM and fluoride ion at different temperatures and ionic strength. Ann. Chim. 89, 1-12]. The values of pH were determined from

pH=pK_mCP+log{(R-e₁)/(e₂-Re₃)}     

Strain development in unconfined coals exposed to CO2, CH4 and Ar: Effect of moisture

Field experiments and laboratory studies have shown that swelling of coal takes place upon contact with carbon dioxide at underground pressure and temperature conditions. Understanding this swelling behavior is crucial for predicting the performance of future carbon dioxide sequestration operations in unminable coal seams conducted in association with methane production. Swelling is believed to be related to adsorption on the internal coal surface. Whereas it is well established that moisture influences the sorption capacity of coal, the influence of water on coal swelling is less well-defined. This paper presents the results of laboratory experiments to investigate the effect of moisture on coal swelling in the presence of carbon dioxide, methane and argon. Strain development of an unconfined sample of about 1.0–1.5 mm³ at 40 °C and 8 MPa (and at other pressures) was observed in an optical cell under a microscope as a function of time. Both air dried and moisturized samples were used. Results confirmed different swelling behaviors of coal with different substances: carbon dioxide leads to higher strain than methane, while exposure to argon leads to very little swelling. The experiments on moisturized samples seem to confirm the role of moisture as a competitor to gas molecules for adsorption sites. Adsorption of water could also explain the observed swelling due to water uptake at atmospheric pressure. A re-introduction of carbon dioxide, after intermediate gas release, results in higher strains which indicate a drying effect of the carbon dioxide on the coal. The results of this study show that the role of water cannot be ignored if one wants to understand the fundamental processes that are taking place in enhanced coalbed methane operations.     

Thermal diffusivity of natural and synthetic garnet solid solution series

Knowledge of heat transport properties as a function of mineral- and rock-composition and temperature is of major relevance to understand and model heat transfer in the Earth’s interior. A systematic study on 13 natural and 4 synthetic garnets was carried out in an attempt to obtain a better systematic understanding of the processes that affect the heat transport in minerals, especially the effect of chemical substitution in solid solution series. It is found that substitution significantly lowers the thermal diffusivity from end-member values for both synthetic and natural garnets with a minimum of thermal diffusivity at an intermediate composition. The thermal diffusivity as a function of the degree of substitution can be described by the approach of Padture and Klemens (J Am Ceram Soc 80 (4):1018–1020, 1997). With increasing temperature the thermal diffusivity decreases due to phonon-phonon-scattering effects. A quantitative analysis of the high-temperature behaviour was carried out by using the model of Roufosse and Klemens (J Geophys Res 79 (5):703–705, 1974), which takes a lower limit of thermal diffusivity at elevated temperatures into account. The model allows for an extrapolation of the deduced room temperature thermal diffusivities to higher temperatures. Furthermore, the model was modified to determine the high temperature limit of the thermal diffusivity for all investigated natural garnets D _min to be 0.64 ± 0.03 mm²/s.     

U–Pb dating, Hf-isotope characteristics and trace-REE-patterns of zircons from Medet porphyry copper deposit, Bulgaria: implications for timing, duration and sources of ore-bearing magmatism

Precise U–Pb geochronology, Hf isotope compositions and trace element distributions in zircons are combined in the present study to define the timing and sources of the magmatism forming the Medet porphyry copper deposit, Bulgaria. ID-TIMS U–Pb-zircon dating demonstrates that ore-bearing magmatism extended for less than 1.12 Ma. As inferred from the field relationships, it started with the intrusion of a quartz-monzodiorite at 90.59?±?0.29 Ma followed by granodiorite porphyries at 90.47?±?0.30 and 90.27?±?0.60 Ma and by crosscutting aplite dykes at 90.12?±?0.36 Ma. These units were overprinted by potassic alteration and host economic copper-(Mo–Au) mineralization. The main magmatic–hydrothermal activity ceased after that, and a later quartz-granodiorite porphyry dyke, dated at 89.26?±?0.32 Ma, only contains an uneconomic quartz–pyrite mineralization. Assimilation of Lower Paleozoic rocks with a mantle to mantle–crust signature is characteristic of the fertile magma in the Medet deposit, as defined by positive ?-Hf values of the inherited zircons. The positive Ce-anomalies and the higher Eu/Eu* ratios of the zircons in the mineralized Cretaceous rocks of Medet deposit argue for crystallization from a generally more oxidized magma compared to the later quartz-granodiorite porphyry dyke. A change in paleostress conditions occurred during the intrusion of the Medet pluton and its dykes. The initial stage reveals E–W extension associated with N–S compression, whereas the younger granodiorite dyke was emplaced during subsequent N–S extension. The large-scale switch of the extensional stress regime during the mineralization was favourable for ore deposition by channelling the fluids and increasing the effective permeability.     

Modelling phosphorus inputs from agricultural sources and urban areas in river basins

An area-differentiated model approach (MEPhos) for the quantification of mean annual P-inputs from point and diffuse sources is presented. The following pathways are considered: artificial drainage, wash-off, groundwater outflow, soil erosion, rainwater sewers, combined sewer overflows, municipal waste water treatment plants and industrial effluents. Two retention functions for rivers and reservoirs are included in order to model P-sinks within a river basin. This allows a complete record of P-loads in heterogeneous meso- and macroscale river basins and enables validation of modeling results with water quality data on a load basis. The model is applied to the River Ruhr basin (4,485 km²) in Germany, which includes contrasting natural conditions, land use patterns as well as population and industry densities. Based on validated modelling results sub-areas of high P-loads are localized and management options for the reduction of P-inputs to surface waters are proposed taking into account the site conditions of the sub-areas relevant for high P-inputs into surface waters.     

The Jiangnan orogenic belt between the Yangtze and Cathaysia blocks for Neoproterozoic context

In recent years, more high quality zircon U-Pb ages have been obtained from Neoproterozoic strata in the South China continental block. A refined chronostratigraphic framework is being set up on these data. A basis of the high quality chronostratigraphic system is fundamental for global Precambrian study and strata correlation. Our recent geological studies focus on systematic SHRIMP zircon dating. We will refine the chronostratigraphic framework of the Neoproterozoic and the start time of the cover beds of the Shuangqiaoshan Group basing on the new SHRIMP zircon ages from the volcanic ash beds in the Hengyong and Anlelin formations. Accordingly, we will also discuss Neoproterozoic tectonostratigraphy in South China     

K-bentonite,black-shale and flysch successions at the Ordovician–Silurian transition,South China: Possible sedimentary responses to the accretion of Cathaysia to the Yangtze Block and its implications for the evolution of Gondwana

The K-bentonite, black shale and flysch successions at the Ordovician–Silurian transition in South China have been the subject of comprehensive investigations relative to the probable accretion of the Yangtze Block and the questionable Cathaysia Block. First, the geochemical analyses of K-bentonites show that the parent magma originated in syn-collisional, volcanic-arc and within-plate tectonic settings, which produced mainly intermediate-to-felsic series magmas, associated with continuous collision and subduction of paleo-continental blocks/arcs. Further, the regional distribution of K-bentonite thickness indicates that voluminous explosive volcanism was located in the present southeastern shoreline provinces of China. Secondly, northwestwardly migrating, Ordovician–Silurian, transitional flysch successions, and the accompanying diachronous K-bentonite-bearing black-shale interval, as well as the related, overlying, shallowing-upward succession at the interior of the Yangtze Block, developed as an unconformity-bound sequence that mirrors foreland-basin tectophase cycles in the Appalachian basin. The above features suggest that the sequence accumulated in a similar foreland basin, which formed in response to adjacent deformational loading in a northwesterly migrating orogen located to the southeast. Geochemical and paleocurrent data from the turbiditic flyschoid sandstones also support these depositional settings. Accordingly, it seems that all criteria strongly support the presence of an Ordovician–Silurian, subduction-related orogen resulting from collision with a block to the southeast that must have been the original “Cathaysia Block” of Grabau and later workers. The K-bentonite, black-shale and flysch successions can be regarded as distal, foreland responses to the continuous northwestward collision and accretion of the Cathaysia Block to the Yangtze Block. Hence, we prefer to suggest that the suture zone with the sensu stricto Cathaysia Block probably developed along previously identified late Early Paleozoic suture relicts in the shoreline provinces of southeast China. On the other hand, although accretion of fragments with Cathaysian affinities to the Yangtze Block may have begun as early as Middle to Late Proterozoic time, the Ordovician–Silurian orogeny described above probably reflects the final phase of accretion between the two blocks. Moreover, when combined with similar peri-Iapetan orogenic events in other areas during the same period, this accretion event may have been part of a major stage of global tectonic reconstruction in the evolution of Gondwana.     

A Simulation of Historic Hydrology and Salinity in Everglades National Park: Coupling Paleoecologic Assemblage Data with Regression Models

Restoration of Florida’s Everglades requires scientifically supportable hydrologic targets. This study establishes a restoration baseline by developing a method to simulate hydrologic and salinity conditions prior to anthropogenic changes. The method couples paleoecologic data on long-term historic ecosystem conditions with statistical models derived from observed meteorologic and hydrologic data that provide seasonal and annual variation. Results indicate that pre-drainage freshwater levels and hydroperiods in major sloughs of the Everglades were about 0.15 m higher and two to four times greater, respectively, on average compared to today’s values. Pre-drainage freshwater delivered to the wetlands and estuaries is estimated to be 2.5 to four times greater than the modern-day flow, and the largest deficit is during the dry season. In Florida Bay, salinity has increased between 5.3 and 20.1 with the largest differences in the areas near freshwater outflow points. These results suggest that additional freshwater flows to the Everglades are needed for restoration of the freshwater marshes of the Everglades and estuarine environment of Florida Bay, particularly near the end of the dry season.     

Alfvénic Solitons in Ultrarelativistic Electron-Positron Plasmas

In electron-positron plasmas some of the plasma modes are decoupled due to the equal charge-to-mass ratio of both species. We derive the dispersion law for a low-frequency, generalized X-mode, which exists at all angles of propagation with respect to the static magnetic field. Its nonlinear evolution is governed by a Korteweg-de Vries equation, valid at all angles of propagation except strictly parallel propagation, for which a different approach leads to a vector form of the modified Korteweg-de Vries equation. The nonlinearity is strongest at perpendicular propagation. Ultrarelativistic effects are discussed. This revised version was published online in July 2006 with corrections to the Cover Date.