Sm–Nd isotopic mapping of lithospheric growth and stabilization in the eastern Kaapvaal craton

Whole-rock Sm–Nd isotope systematics of 79 Archean granitoids from the eastern Kaapvaal craton, southern Africa, are used to delineate lithospheric boundaries and to constrain the timescale of crustal growth, assembly and geochemical differentiation c. 3.66–2.70 Ga. Offsets in ε_Nd values for 3.2–3.3 Ga granitoids across the Barberton greenstone belt (BGB) are consistent with existing models for c. 3.23 Ga accretion of newly formed lithosphere north of the BGB onto pre-existing c. 3.66 Ga lithosphere south of the BGB along a doubly verging subduction margin. The Nd isotopic signature of c. 3.3–3.2 Ga magmatic rocks show that significant crustal growth occurred during subduction–accretion. After c. 3.2 Ga, however, the Nd signature of intrusive rocks c. 3.1 and 2.7 Ga is dominated by intracrustal recycling rather than by new additions from the mantle, signalling cratonic stability.     

Petrographic,fluid inclusion and isotopic study of the Dikulushi Cu–Ag deposit,Katanga (D.R.C.): implications for exploration

The Dikulushi Cu–Ag vein-type deposit is located on the Kundelungu Plateau, in the southeastern part of the Democratic Republic of Congo (D.R.C.). The Kundelungu Plateau is situated to the north of the Lufilian Arc that hosts the world-class stratiform Cu–Co deposits of the Central African Copperbelt. A combined petrographic, fluid inclusion and stable isotope study revealed that the mineralisation at Dikulushi developed during two spatially and temporally distinct mineralising episodes. An early Cu–Pb–Zn–Fe mineralisation took place during the Lufilian Orogeny in a zone of crosscutting EW- and NE-oriented faults and consists of a sequence of sulphides that precipitated from moderate-temperature, saline H₂O–NaCl–CaCl₂-rich fluids. These fluids interacted extensively with the country rocks. Sulphur was probably derived from thermochemical reduction of Neoproterozoic seawater sulphate. Undeformed, post-orogenic Cu–Ag mineralisation remobilised the upper part of the Cu–Pb–Zn–Fe mineralisation in an oxidising environment along reactivated and newly formed NE-oriented faults in the eastern part of the deposit. This mineralisation is dominated by massive Ag-rich chalcocite that precipitated from low-temperature H₂O–NaCl–KCl fluids, generated by mixing of moderate- and low-saline fluids. The same evolution in mineralisation assemblages and types of mineralising fluids is observed in three other Cu deposits on the Kundelungu Plateau. Therefore, the recognition of two distinct types of (vein-type) mineralisation in the study area has a profound impact on the exploration in the Kundelungu Plateau region. The identification of a Cu–Ag type mineralisation at the surface could imply the presence of a Cu–Pb–Zn–Fe mineralisation at depth.     

Methods and code for ‘classical’ age-modelling of radiocarbon sequences

Age–depth models form the backbone of most palaeoenvironmental studies. However, procedures for constructing chronologies vary between studies, they are usually not explained sufficiently, and some are inadequate for handling calibrated radiocarbon dates. An alternative method based on importance sampling through calibrated dates is proposed. Dedicated R code is presented which works with calibrated radiocarbon as well as other dates, and provides a simple, systematic, transparent, documented and customizable alternative. The code automatically produces age–depth models, enabling exploration of the impacts of different assumptions (e.g., model type, hiatuses, age offsets, outliers, and extrapolation).     

Efficiency of different mesh sizes for isolating fossil chironomids for stable isotope and radiocarbon analyses

We examined the effects of sieving with different mesh sizes on the efficiency of processing fossil chironomids from lake sediments for isotope analyses. Results obtained for three different sediments indicate that each of the studied sieve fractions (100–150, 150–200, 200–250, 250–300, >300 μm) contain a similar proportion of the overall mass of chironomid fossils in a sample. However, the sorting time needed to separate chironomids from other sieve residue is disproportionately large for smaller mesh sizes. Employing sieves with a 200-μm rather than the 100-μm mesh commonly used for standard palaeoecological analyses of fossil chironomids decreased processing time for a given mass of fossils by 30–58% in our study. For optimizing the efficiency of chironomid sample processing for stable isotope and radiocarbon analysis we therefore recommend a 200-μm mesh size sieve, although the sorting of all >100-μm fractions may be necessary in sediments with low chironomid abundances. Excluding certain small taxa from isotope analysis, may structurally bias isotope values of samples. Therefore, further studies on taxon-specific isotope analysis are required to quantify these effects.     

Phytoplankton,protozooplankton and nutrient dynamics in the Bornholm Basin (Baltic Sea) in 2002–2003 during the German GLOBEC Project

From March 2002 to until April 2003 we investigated the seasonal nutrient and phytoplankton dynamics in the central Bornholm Basin (Baltic Sea) within the framework of the German GLOBEC Project. We choose a nested approach consisting of vertical fluorescence profiles, phytoplankton counts and nutrient analyses. The Fluoroprobe (MultiProbe, BBE Moldaenke) is capable of distinguishing four algal groups (Cryptophyceae, Cyanophyceae, Chlorophyceae, Bacillariophyceae + Dinophyceae). Winter nutrient concentrations were about 5 μM NO₃ and 0.5 μM PO₄ in the central Basin. The spring phytoplankton bloom was dominated by the diatom Skeletonema sp. and reached a maximum of about 270 μg C/l before the onset of the seasonal stratification. Protozooplankton was dominated by the Mesodinium rubrum (a phototrophic ciliate = Myrionecta rubra) and reached a maximum biomass of about 200–300 μg C/l about 2 weeks after the demise of the diatom spring bloom. During summer, the water column was stratified and a subsurface maximum developed near the thermocline consisting of Bacillariophyceae, Cryptophycea and other phototrophic flagellates. Phytoplankton and protozooplankton biomass was generally low. Nutrient concentrations point towards a nitrogen limitation during this period. The stratification period ended during September and surface nutrient concentrations increased again. Protozooplankton reached a second maximum during September. With the Fluoroprobe small scale structures in the plankton community could be detected like a subsurface Cryptophyceae maximum near the thermocline that however, could not be confirmed by cell counts. The chlorophyll a estimate of the Fluoroprobe was in good agreement with the phytoplankton biomass estimated from counts. We conclude that only by combining modern sensing technology with microscopy, the small-scale dynamics and taxonomic spectrum of the plankton can be fully captured.     

可持续发展背景下区域旅游业竞争力评价研究

如何评价区域旅游业竞争力水平是区域旅游业进行旅游规划和提高竞争力水平的基础和出发点.在可持续发展背景下以竞争力理论、旅游系统理论等为依据,从旅游业基础竞争力、竞争业绩、竞争潜力3个层面构建了区域旅游业竞争力评价指标体系,运用层次分析法来确定指标权重,在此基础上以我国30个省级行政区为研究对象进行了应用,对我国区域旅游业竞争力水平进行了较为深入的分析.提出的指标体系和层次分析法可以为区域旅游业竞争力研究提供一定的借鉴.     

Immobilization of Ni by Al-modified montmorillonite: A novel uptake mechanism

The sorption capacity of montmorillonite clay minerals for small cations, such as Ni²⁺, can be greatly enhanced by modifying the clay mineral with Al(III). In this study, the mechanisms of Ni uptake by Al-modified montmorillonite were studied using extended x-ray absorption fine structure (EXAFS) spectroscopy of powders and polarized EXAFS spectroscopy of self-supporting clay films to delineate the binding structure of Ni formed as a function of the reaction conditions. Analysis of powder EXAFS spectra of wet pastes, collected from Ni-treated Al-modified montmorillonites reacted at pH 5-8, 25°C or 80°C (to accelerate the reaction process), and reaction times ranging from 1 month to 9 yrs, showed that Ni was surrounded on average by 6 O atoms at a distance of 2.05 Å and 6 Al atoms at 3.01 Å, suggesting the incorporation of Ni into a gibbsite-like structure. Only at pH 8, Ni-containing precipitates were congruently formed. Polarized EXAFS spectroscopy of self-supporting Ni-reacted Al-modified montmorillonite clay films showed a pronounced angular dependency of the spectra of the Ni-doped gibbsite, indicating that the orientation of this Ni-doped gibbsite coincided with the layering of the montmorillonite. Data analysis suggested that Ni is included slightly above and below the vacant octahedral sites of the postulated interstitial gibbsite monolayer. This newly identified mechanism of metal uptake by Al-modified montmorillonite provides a large metal sorption capacity and, because the metal is included in a monolayer gibbsite or gibbsite “islands” formed in the interstitial space of the clay mineral, it potentially leads to a permanent sequestration of the metal from the environment.     

Spatial scale and habitat-dependent diversity patterns in nematode communities in three seepage related sites along the Norwegian Sea margin

Assessing the relative contribution of local diversity to regional biodiversity may be the key to understanding large-scale and even global patterns in species diversity. Here, the contribution of habitat heterogeneity of cold seeps at three spatial scales [micro-scale (ms), macro-scale (10 to 100s of ms), and mega-scale (10 to 100s of km)] to the total nematode biodiversity (genus level) along the Norwegian continental margin is evaluated. Due to the development of higher resolution bathymetry and increased bottom sampling in recent years, continental margins, once regarded as monotonous landscapes, are now acknowledged to have a high degree of habitat complexity and diversity. By calculating the additive partitioning of gamma diversity in alpha and beta fractions, we examined to what extent habitat diversity of seep sites significantly increases the nematode genus composition and diversity at different spatial scales. Siboglinidae patches and control sediments yielded comparably high levels of nematode genus richness. They exhibited low turnover rates within and across the different seep sites. In contrast, the bacterial mats at Håkon Mosby Mud Volcano (HMMV) and the reduced sediments at the Nyegga pockmarks harboured genus-poor nematode communities with an equally high dominance of one or two species, which were different for each seep. Different habitats, in particular at the HMMV, contributed significantly to the seep nematode richness. This study demonstrates that the presence of distinct habitat types within multiple seep sites contributes to the high diversity of nematode communities inhabiting the seeps in the Norwegian deep sea.     

Water transport at subtidal frequencies in the Marsdiep inlet

Long-term time series of subtidal water transport in the 4-km wide Marsdiep tidal inlet in the western Dutch Wadden Sea have been analysed. Velocity data were obtained between 1998 and the end of 2002 with an acoustic Doppler current profiler that was mounted under the hull of the ferry ‘Schulpengat’. Velocities were integrated over the cross-section and low-pass filtered to yield subtidal water transport. A simple analytical model of the connected Marsdiep and Vlie tidal basins was extended to include wind stress and water-level and density gradients and applied to the time series of subtidal water transport. In accordance with the observations, the model calculates a mean throughflow from the Vlie to the Marsdiep basin. The mean water transport through the Marsdiep inlet consists of an export due to tidal stresses and freshwater discharge and an import due to southwesterly winds. In contrast, the variability in the subtidal water transport is mainly governed by wind stress. In particular, southwesterly winds that blow along the main axis of the Marsdiep basin force a throughflow from the Marsdiep to the Vlie basin, whereas northwesterly winds that blow along the main axis of the Vlie basin force a smaller mean water transport in the opposite direction. The contribution of remote sea-level change to the water transport, or coastal sea-level pumping, has been found to be much smaller than the contribution of local wind stress.     

Fast reconnaissance of carbonate dissolution based on the size distribution of calcareous ooze on Walvis Ridge, SE Atlantic Ocean

We present a new index of carbonate fragmentation based on the size distribution of bulk sediments in core MD962094 from Walvis Ridge (SE Atlantic Ocean). The carbonate fragmentation index is constructed by taking a ratio of the two coarsest fractions in the grain size distributions of the bulk calcareous ooze. The coarsest two fractions (25–90 μm and >90 μm) of the bulk sediments consist primarily of complete shells and fragments of adult foraminifera shells, and juvenile foraminifera shells and fragments, respectively. The ratio of the proportions of the two fractions is interpreted as a measure of fragmentation of the foraminifera shells caused by carbonate dissolution. Downcore changes in our carbonate fragmentation index compare very well with those in the coarse-carbonate fragmentation index in sediments from a nearby core on Walvis Ridge. The latter commonly used fragmentation index is defined as a ratio of foraminifera fragments over whole foraminifera in the >150-μm fraction as seen with a light microscope. Fragmentation is relatively high during glacial stages and relatively low during interglacial stages during the last 300 kyr, caused by the combined effect of wind-driven upwelling of corrosive water and increased production of organic matter, decreasing the preservation potential of carbonates both during and after deposition. The carbonate fragmentation index we present here provides a precise and fast method to establish a downcore fragmentation record. It can be applied to bulk sediments that are carbonate-rich (CaCO₃>68%) and to all other deep-marine sediments of which the grain size distribution of the carbonate-free fraction is available.