Experimentally-controlled carbon and oxygen isotope exchange between bioapatites and water under inorganic and microbially-mediated conditions

Modern bone and enamel powders have reacted at 301 K with ¹³C- and ¹⁸O-labelled waters under inorganic and microbial conditions. The aim of the study is to investigate the resistance of stable isotope compositions of bioapatite carbonate (δ¹³C, δ¹⁸Oc) and phosphate (δ¹⁸Op) to isotopic alteration during early diagenesis. Rapid and significant carbon and oxygen isotope changes were observed in the carbonate and phosphate fractions of bone apatite before any detectable change occurred in the crystallinity or organic matter content. These observations indicate that chemical alterations of bone apatite are likely to start within days of death. Enamel crystallites are much more resistant than bone crystallites, but are not exempt of alteration. Non removable carbon and oxygen isotope enrichments were measured in the carbonate phase of bone (50-90%) and enamel (40%) after the acetic acid treatment. This result indicates that a significant part of ¹³C and ¹⁸O-labelled coming from the aqueous fluid has been durably incorporated into the apatite structure, probably through isotopic exchange or secondary carbonate apatite precipitation. As a result, acetic acid pre-treatments that are currently used to remove exogenous material by selective dissolution, are not adequate to restore pristine δ¹³C and δ¹⁸Oc values of fossil apatites. Under inorganic conditions, kinetics of oxygen isotope exchange are 10 times faster in carbonate than in phosphate. On the opposite, during biologically-mediated reactions, the kinetics of oxygen isotope exchange between phosphate and water is, at least, from 2 to 15 times faster than between carbonate and water. Enamel is a more suitable material than bone for paleoenvironmental or paleoclimatical reconstructions, but interpretations of δ¹⁸Op or δ¹³C values must be restricted to specimens for which no or very limited trace of microbial activity can be detected.     

Following tracer through the unsaturated zone using a multiple interacting pathways model: Implications from laboratory experiments

Models must effectively represent velocities and celerities if they are to address the old water paradox. Celerity information is recorded indirectly in hydrograph observations, whereas velocity information is more difficult to measure and simulate effectively, requiring additional assumptions and parameters. Velocity information can be obtained from tracer experiments, but we often lack information on the influence of soil properties on tracer mobility. This study features a combined experimental and modelling approach geared towards the evaluation of different structures in the multiple interacting pathways (MIPs) model and validates the representation of velocities with laboratory tracer experiments using an undisturbed soil column. Results indicate that the soil microstructure was modified during the experiment. Soil water velocities were represented using MIPs, testing how the (a) shape of the velocity distribution, (b) transition probability matrices (TPMs), (c) presence of immobile storage, and (d) nonstationary field capacity influence the model's performance. In MIPs, the TPM controls exhanges of water between pathways. In our experiment, MIPs were able to provide a good representation of the pattern of outflow. The results show that the connectedness of the faster pathways is important for controlling the percolation of water and tracer through the soil. The best model performance was obtained with the inclusion of immobile storage, but simulations were poor under the assumption of stationary parameters. The entire experiment was adequately simulated once a time‐variable field capacity parameter was introduced, supporting the need for including the effects of soil microstructure changes observed during the experiment.     

News Items

The process of reading a topographic map requires users to recognize and learn the cartographic symbols of the key (or legend) while interpreting the territory as depicted on the map at a given level of abstraction (the form and nature of features, their saliency and relationships). We present the results of an empirical user study that aims to identify and assess the main graphical characteristics that are used by map users to recognize the design principles which constitute the topographic mapping style adopted by IGN (Institut National de l'Information Géographique et Forestière), France. Our results suggest that 91% of the participants were able to recognize an IGN-France topographic map amongst other topographic map products. We also determine which graphical characteristics play a role in the recognition of this cartographic style, either by visual memory or by visual perception, and identify the representation of relief, including contour lines and shaded relief, as one of the major graphical characteristics of the topographic mapping style of IGN-France. Moreover, the participants of our study considered the representation of touristic POI (points of interest), toponymy, typography, the main roads network, the individual buildings and the forests, to be essential for stylistic recognition.     

Persistent organic pollutants (POPs) in killer whales (Orcinus orca) from the Crozet Archipelago, southern Indian Ocean

Persistent organic pollutants (POPs), including polychlorinated biphenyls (PCBs), polychlorinated dibenzo-p-dioxins (PCDDs), and dibenzofurans (PCDFs), are ubiquitous environmental contaminants of which significant concentrations are reported in upper trophic level animals. In 1998, we collected blubber biopsy samples (n = 11) from killer whales (Orcinus orca) inhabiting the coastal waters around Possession Island, Crozet Archipelago, southern Indian Ocean, for contaminant analyses. Despite inhabiting an isolated region far removed from industrial activities, these killer whales can presently be considered among the most PCB-contaminated cetaceans in the southern hemisphere, with concentrations ranging from 4.4 to 20.5 mg/kg lipid weight (lw). PCDD levels ranged from below the detection limit (5 ng/kg) to 77.1 ng/kg lw and PCDF levels from below the detection limit (7 ng/kg) to 36.1 ng/kg lw. Over 70% of our study animals had PCB concentrations which exceeded a 1.3 mg/kg PCB threshold established for endocrine disruption and immunotoxicity in free-ranging harbour seals, suggesting that organic contaminants cannot be ruled out as an additional threat to this declining population.     

A new interpretation of Stephanian deformation in the Decazeville basin (Massif Central, France): consequences on late Variscan tectonism

Five stages of faulting were observed in and around the Stephanian Decazeville basin, in the SW French Massif Central, at the southern edge of the Sillon houiller fault. The older stage ends during middle Stephanian time, and corresponds to a strike-slip regime with N–S shortening and E–W extension. Before the end of the middle Stephanian, three other stages were recorded: two strike-slip regimes with NW–SE, then E–W compression and NE–SW, then N–S extension; and finally a NNE–SSW extensional regime during the main subsidence of the basin from the end of the middle Stephanian to late Stephanian. Based on mining documents, a new interpretation of the N–S striking folds of the Decazeville basin is proposed. Folding may not be associated with E–W compression but with diapirism of coal seams along syn-sedimentary normal faults during the extensional phase. A last strike-slip regime with N–S compression and E–W extension may be related to Cainozoic Pyrenean orogeny. At a regional scale, it is suggested that from the end of the middle Stephanian to the late Stephanian, the main faults in the Decazeville basin may represent a horsetail splay structure at the southern termination of the Sillon houiller fault.     

Soil erosion assessment using RUSLE model in the Congo Nile Ridge region of Rwanda

This research assessed the soil erosion threat in the Congo Nile Ridge Region of Rwanda. The study forecasted erosion by applying the Revised Universal Soil Erosion (RUSLE) with five factors (rainfall, soil, topography, cover management, and support practices) and spatial data. About 85.5% of the area under investigation was predisposed to erosion with unsustainable average soil loss rates of > 1 t/ha/yr. The outcomes of the research highlighted that the average rate of estimated soil loss in the region prone to erosion was > 63.62 t/ha/yr, resulting in an overall annual predicted soil loss of approximately 44 × 10⁶ t in 2016. All of the districts studied have steep slope gradients (30.4%–36.1%) and high annual rainfall totals (1199–1484 mm/yr), except Rubavu district. More than 88.8% of croplands had unsustainable average soil loss rates of > 1 t/ha/yr. The analysis indicated that both terracing and strip cropping have the potential to reduce rates of soil loss in the farmland, by 64.4% and 10.4%, respectively. The results of this study will serve as a baseline for soil erosion mitigation and land-use planning in the study area and Rwanda at large.     

Cadmium isotopic constraints on metal sources in the Huize Zn-Pb deposit,SW China

The Sichuan-Yunnan-Guizhou(SYG)Zn-Pb metallogenic zone in SW China contains＞400 carbonate-hosted hydrothermal Zn-Pb deposits.Some of these,such as the Huize,Tianbaoshan,and Daliangzi deposits,are super-large deposits with significant reserves of Cd,Ge,and Ag.However,the sources of these metals remain controversial.This study investigated the Cd isotopic geochemistry of the Huize deposit,the largest Zn-Pb deposit in the SYG area.Sphalerites formed at three stages in the deposit have different colors:black or dark brown(Stage Ⅰ),red(Stage Ⅱ),and light-yellow(Stage Ⅲ).The δ114/110Cd values of the sphalerites are in the order Stage Ⅲ＜Stage Ⅰ＜Stage Ⅱ.Kinetic isotopic fractionation is likely the key factor causing the lower δ114/110Cd values in the early formed Stage Ⅰ sphalerites than in later-formed Stage Ⅱ sphalerites,with cooling of ore-forming fluids being responsible for the still lower values of the Stage Ⅲ sphalerites.In galena,the δ114/110Cd values are inversely correlated with Cd contents and tend to be higher in high-Zn galena.We speculate that Cd isotopic fractionation was significant during the precipitation of sphalerite and galena,with light Cd isotopes being enriched in galena rather than sphalerite.Comparison of the Cd isotopic signatures and Zn/Cd ratios of different endmembers suggests that the δ114/110Cd values and Zn/Cd ratios of sphalerite from the Huize deposit,as well as other large-scale deposits from the SYG area,are lie in those range of Emeishan basalts and sedimentary rocks and the mean δ114/110Cd values of these deposits show good negative correlation with 1/Cd,suggesting that the ore-forming materials of these deposits were derived from the mixing of Emeishan basalts and sed-imentary rocks.This study demonstrates that Cd isotopes can be useful proxies in elucidating ore genesis in large Zn-Pb deposits.     

Ocean feedback to tropical cyclones: climatology and processes

This study presents the first multidecadal and coupled regional simulation of cyclonic activity in the South Pacific. The long-term integration of state-of the art models provides reliable statistics, missing in usual event studies, of air–sea coupling processes controlling tropical cyclone (TC) intensity. The coupling effect is analyzed through comparison of the coupled model with a companion forced experiment. Cyclogenesis patterns in the coupled model are closer to observations with reduced cyclogenesis in the Coral Sea. This provides novel evidence of air–sea coupling impacting not only intensity but also spatial cyclogenesis distribution. Storm-induced cooling and consequent negative feedback is stronger for regions of shallow mixed layers and thin or absent barrier layers as in the Coral Sea. The statistical effect of oceanic mesoscale eddies on TC intensity (crossing over them 20 % of the time) is also evidenced. Anticyclonic eddies provide an insulating effect against storm-induced upwelling and mixing and appear to reduce sea surface temperature (SST) cooling. Cyclonic eddies on the contrary tend to promote strong cooling, particularly through storm-induced upwelling. Air–sea coupling is shown to have a significant role on the intensification process but the sensitivity of TCs to SST cooling is nonlinear and generally lower than predicted by thermodynamic theories: about 15 rather than over 30 hPa °C^?1 and only for strong cooling. The reason is that the cooling effect is not instantaneous but accumulated over time within the TC inner-core. These results thus contradict the classical evaporation-wind feedback process as being essential to intensification and rather emphasize the role of macro-scale dynamics.     

Type I eclogites from Roberts Victor kimberlites: Products of extensive mantle metasomatism

Type I and Type II eclogite xenoliths from the Roberts Victor kimberlite (South Africa) show marked differences in terms of microstructures, mineralogy, major- and trace-element compositions and oxygen-isotope compositions. The unequilibrated microstructures of Type I eclogites, their typical accessory assemblages (phologopite, diamond, sulphides, fluid inclusions) and the ubiquitous presence of “melt pockets” in garnets provide strong evidence of metasomatism. Type II eclogites systematically lack such features and are microstructurally more equilibrated. Type I eclogites are more magnesium-rich than most Type II (mean Mg# = 0.56 vs. 0.46), while Type II eclogites are generally more Ca-rich (mean CaO = 9 vs. 12 wt%) and Fe-rich (mean FeO = 10 vs. 12 wt%). Type I eclogites are systematically enriched in LREE, Sr, Ba, alkali elements, HFSE, Th and U compared to the more depleted Type II eclogites. Calculated trace-element patterns of fluids in equilibrium with Type I eclogites are closely similar to those of volatile-rich small-volume mantle melts in the carbonatite-kimberlite spectrum commonly inferred to be responsible for mantle metasomatism. Although oxygen isotopes are often used to argue for a subduction origin of mantle eclogites, correlations between δ¹⁸O of garnet and typical metasomatic tracers suggest that the metasomatic process also has shifted the oxygen-isotope compositions of the Type I eclogites toward heavier values. Roberts Victor Type I eclogites thus carry the imprint of a metasomatic process that strongly modified their major-element, trace-element and isotopic compositions, while the more pristine Type II eclogites escaped this modification. Therefore, attempts to constrain the origin of Roberts Victor eclogites should not be based on the much more abundant Type I eclogites, which retain little geochemical memory of their protoliths. The most suitable materials for such investigations may be the less metasomatised, but more rare, Type II eclogites.