Mixing and chemical interdiffusion of trachytic and latitic magma in a subvolcanic complex of the Tertiary Westerwald (Germany)

A special kind of magma mixing is extraordinarily well exposed in the Bittersberg subvolcanic complex in the Tertiary volcanic field of the German Westerwald: A trachytic melt has been penetrated by a latitic dyke which has been dispersed within the host magma as small spherical enclaves (globules). Whole rock analyses of the globules show a change in composition that cannot be explained by a simple mechanical mixing between the endmembers. The most evolved globules have a phonolitic composition. Microprobe measurements in the microlithic matrix of the host rock and the guest indicate a diffusive motion of the alkalis from the host into the globules. On the other hand, an opposite trend can be observed for Ca, Mg, Fe and Ti, which are impoverished in the globules. The trace elements and the middle rare earth elements (MREE) has also been involved in the diffusive exchange. The REE-pattern of the most evolved (phonolitic) globules shows a characteristic trough in the area of the MREE which is almost identical to the REE-pattern of many phonolites. The phonolites and the alkali-rich trachytes of the Westerwald show similar globular textures as the Bittersberg volcanics. Therefore, generation of these rocks involving diffusive element exchange during mixing processes in a magma reservoir situated on a deeper crustal level may be possible.     

Optimizing a layered and laterally constrained 2D inversion of resistivity data using Broyden's update and 1D derivatives

Dense profile-oriented resistivity data allows for 2D and 3D inversions. However, huge amounts of data make it practically impossible to do full 2D or 3D inversions on a routine basis. Therefore, a number of approximations have been suggested over the years to speed up computations. We suggest using a combination of Broyden's update on the Jacobian matrix with derivatives calculated using a 1D formulation on a parameterized 2D model of locally 1D layered models. The approximations bring down the effective number of 2D forward responses to a minimum, which again gives us the ability to invert very large sections. Broyden's update is not as useful with a parameterized problem as is the case with a smooth minimum structure problem that has been the usual application. 1D derivatives, however, seem to be very effective when initiating a full 2D solution with Broyden's update. We compare the different methods using two different kinds of data on two synthetic models and on two field examples. The most effective and reliable optimization combines 1D derivatives with a full 2D solution and Broyden's update. When using Broyden's update the Jacobian matrix needs to be reset every once in a while. We do this whenever the difference in data residual from the previous iteration is less than 5%. This combined inversion method reduces the computation time approximately a factor of 3 without losing model resolution.     

Chemical fractionations in meteorites—IX. C3 chondrites

Four C3V chondrites (Grosnaja, Kaba, Mokoia, Vigarano) and three C3O chondrites (Felix, Kainsaz, and Lancé) were analyzed by radiochemical neutron activation for 17 trace elements. Both classes show a typical chondritic step pattern, reflecting loss of volatiles during chondrule formation. Elements condensing above 1300 K (U, Re, Ir, Ni) are present in essentially Cl chondrite proportions, while moderately volatile elements condensing between 1300 K and 800 K (Ge, Rb, Ag) are depleted by a factor of 0.44. However, elements condensing below 700 K (S, Cs, Bi, Tl, Br, Se, Te, In, Cd) are depleted to a still greater degree, and more so in the Ornans subclass (factor of 0.24, except Cd 0.007) than in the Vigarano subclass (factor of 0.29). This additional depletion may be due to a slight (less than 3-fold) dust-gas fractionation, by settling of dust to the median plane of the solar nebula. Among other chondrite classes, ordinary chondrites show a similar depletion, but C2 chondrites do not. Possibly the undepleted meteorites formed in one of the convection zones of the nebula predicted by Cameron and Pine, whereas the depleted meteorites formed in a quiescent region.The condensation of chalocophile elements as a function of H₂S partial pressure is discussed, in an attempt to explain the drastic difference in Cd abundance between the two subclasses. It appears that the $\text{H}{}_2\text{S}\text{H}{}_2$ ratio is the key variable. C3O's seem to have condensed in a region where enough metallic Fe was present to buffer the H₂S pressure, while C3V's condensed in a more oxidized region, where H₂S was in excess. Accretion temperatures, for an assumed nebular pressure of 10^?5 atm, were between 415 and 430 K for C3O's and less than 440 K for C3V's.Two slightly volatile elements, Sb and Au, show variable depletion, presumably reflecting variable loss during chondrule formation. Indeed, their depletion correlates with the abundance of iron-poor olivine, a measure of the peak temperature and time during chondrule formation.     

Methods for locating the proper position of a planned fishway entrance near a hydropower tailrace

The spatial distribution of upstream migrating Atlantic salmon (Salmo salar) spawners was studied in 2008 and 2009 in the surroundings of the tailrace from a hydropower station in the River Umeälven. This area is problematic because the fish have difficulties finding their way into the original riverbed, which prompted an investigation on the feasibility of adding a fishway in the area. Echo sounding was used in 2008 to investigate the spatial use of fish in the tailrace channel during the time of salmon migration. Presence of other fish species was so low that all echo sounding detections were assumed to be salmon. In 2009, data on wild radio-tagged salmon (n = 94) was collected in the same tailrace by an array of underwater antennas with a detection radius of approximately 10 m, to validate the results from the echo sounding. Both types of surveys showed aggregations of fish in one part of the tailrace. As a final step, Computational Fluid Dynamics (CFD) modeling was performed to analyze hydrodynamics. This CFD modeling showed a coincidence of fish detections in areas with turbulence intensities between 0.6 and 0.8, which may be an indication that the fish are holding in these areas to reduce energy expenditure during migration. A high proportion of the radio-tagged salmon were observed in the tailrace area (a median of 21 days between their first and last detection), indicating that the salmon are delayed in their upstream migration by the attraction to the tailrace in this area. The overall data on fish behavior in the tailrace led us to suggest a location for a new fishway where the fish aggregation was most pronounced. The number of detections from either technology had similar distributions over the tailrace, suggesting that the results are comparable. Thus, the split beam echo sounder can preferably be used to investigate which location is most appropriate for locations of entrances to new fishways since many more individual fishes are covered by this method compared to telemetry. Furthermore, there is no need to handle the fish in the echo sounding studies as is required in telemetry studies.     

A network theory approach for a better understanding of overland flow connectivity

Hydrological connectivity describes the physical coupling (linkages) of different elements within a landscape regarding (sub‐) surface flows. A firm understanding of hydrological connectivity is important for catchment management applications, for example, habitat and species protection, and for flood resistance and resilience improvement. Thinking about (geomorphological) systems as networks can lead to new insights, which has also been recognized within the scientific community, seeing the recent increase in the use of network (graph) theory within the geosciences. Network theory supports the analysis and understanding of complex systems by providing data structures for modelling objects and their linkages, and a versatile toolbox to quantitatively appraise network structure and properties. The objective of this study was to characterize and quantify overland flow connectivity dynamics on hillslopes in a humid sub‐Mediterranean environment by using a combination of high‐resolution digital‐terrain models, overland flow sensors and a network approach. Results showed that there are significant differences between overland flow connectivity on agricultural areas and semi‐natural shrubs areas. Significant positive correlations between connectivity and precipitation characteristics were found. Significant negative correlations between connectivity and soil moisture were found, most likely because of soil water repellency and/or soil surface crusting. The combination of structural networks and dynamic networks for determining potential connectivity and actual connectivity proved a powerful tool for analysing overland flow connectivity. Copyright © 2016 John Wiley & Sons, Ltd.     

Land cover in Norway based on an area frame survey of vegetation types

The Norwegian area frame survey of land cover and outfield land resources (AR18X18), completed in 2014, provided unbiased statistics of land cover in Norway. The article reports the new statistics, discusses implications of the data set, and provides potential value in terms of research, management, and monitoring. A gridded sampling design for 1081 primary statistical units of 0.9 km² at 18?km intervals was implemented in the survey. The plots were mapped in situ, aided by aerial photos, and all areas were coded following a vegetation type system. The results provide new insights into the cover and distribution of vegetation and land cover types. The statistic for mire and wetlands, which previously covered 5.8%, has since been corrected to 8.9%. The survey results can be used for environmental and agricultural management, and the data can be stratified for regional analyses. The survey data can also serve as training data for remote sensing and distribution modelling. Finally, the survey data can be used to calibrate vegetation perturbations in climate change research that focuses on atmospheric–vegetation feedback. The survey documented novel land cover statistics and revealed that the national cover of wetlands had previously been underestimated.     

Sediment flux from a fjord during glacial periods, Isfjorden, Spitsbergen

Sediment has accumulated in Isfjorden, a deep fjord in Spitsbergen, at a rate of 1.7 km³/k.y. during the past 13 k.y. Between 200 ka and 13 ka the fjord was free of ice for 120 k.y. Assuming a similar sediment delivery rate during this ice-free time, 200 km³ of sediment would have accumulated in the fjord. An alternative calculation based on erosion rates suggests that 400 km³ could have been delivered to Isfjorden during this 120 k.y.Seismic studies have identified a 330 km³ package of sediment on the continental shelf and slope west of Isfjorden. This sediment is believed to have accumulated between 200 ka and 13 ka. Herein we argue that this is sediment that was originally deposited in the fjord, and that it was transferred to the shelf by glaciers in the 70 ka during which the fjord was occupied by ice. Calculations using a steady-state numerical model suggest that the sediment could have been moved in a deforming layer of subglacial till and in subglacial melt streams at rates of 7.6 × 10⁶ m³ a⁻¹ and 0.3 × 10⁶ m³ a⁻¹, respectively, resulting in a total flux of 7.9 × 10⁶ m³ a⁻¹. It is unlikely that much sediment was moved in a basal layer of dirty ice, as intense basal melting would have inhibited sediment entrainment.Of the time that glaciers occupied the fjord, 60% would have been required to evacuate the accumulated sediment. During the remaining time, the ice could have been deepening the fjord.     

Land acquisition: a means to mitigate water scarcity and reduce conflict?

ABSTRACT

In recent years there has been a surge in land investments, primarily in the African continent, but also in Asia and Latin America. This increase in land investment was driven by the food pricing crisis of 2007–2008. Land investors can be identified from a variety of sectors, with actors ranging from hedge funds to national companies. Many water-scarce countries in the Middle East and North Africa (MENA) are among these financiers, and primarily invest in Africa. Recognizing the potential for “outsourcing” their food security (and thereby also partly their water security), Middle Eastern countries such as Jordan, Qatar and the United Arab Emirates have invested in land for food production in Africa. The extent to which this is happening is still unclear, as many contracts are not yet official and the extent of the leases is vague. This paper investigates the land investments and acquisitions by Middle Eastern countries. It also seeks to analyse what effect, if any, these investments can have on the potential for conflict reduction and subsequent peacebuilding in the Middle East region as the activity removes pressure from transboundary water resources.

EDITOR D. Koutsoyiannis ASSOCIATE EDITOR K. Aggestam     

PCB-containing paint and plaster caused extreme PCB-concentrations in biota from the Sørfjord (Western Norway)--a case study

The Sørfjord (Western Norway) has a long history of industry and pollution, and has been monitored for several decades. The environmental monitoring has comprised analyses of different contaminants in sea water, mussel, fish, seaweed and sediments. Measurements of polychlorinated biphenyls (PCBs) in blue mussels (Mytilus edulis) some 17 years ago indicated a local source. In 2001 severe concentrations were measured in blue mussels and further investigations disclosed the primary source of PCBs in the Sørfjord. In 2002, extreme PCB-concentrations were found in cod (Gadus morhua) from the same area. However, no induction of EROD activity was detected, indicating the limitations of this assay as marker for PCB contamination. A future scientific challenge will be to understand the specific mechanisms and effects of such PCB accumulation in fish.