Quantitative Imaging of Stable Isotopes by Ion Microprobe

A new analytical procedure has been developed to measure oxygen isotopic ratios and, more generally, stable isotopic ratios in microparticles with a few % precision. This procedure uses ion microprobe quantitative imaging with a scanning microbeam. In this mode, ion images are acquired on the electron multiplier. Image processing allows extraction of areas of interest from the whole image and computation of isotopic ratios in the selected areas. The accuracy of this method has been tested for the analysis of the 18O/16O ratio in quartz and magnetite reference samples powdered to a grain size of 2-5 μm. A detailed study of the instrumental mass fractionation allowed an understanding of differences between classical spot analysis and scanning ion imaging, and showed that fractionation effects were related to grain topography for microparticle analysis, and to image processing or to secondary optical settings for ion imaging. The precision obtained for the measurement of ä18O was 3% for grains having a diameter of 2 μm.     

Experimental study of clinopyroxenite partial melting and the origin of ultra-calcic melt inclusions

Ultra-calcic melt inclusions (UCMI: CaO>13.5 wt% and/or CaO/Al₂O₃>0.9) are magnesian and near-primary liquids trapped in volcanic phenocrysts from mid-ocean ridges, arcs, back-arcs, and ocean islands. UCMI can be subdivided into two classes based on tectonic association and degree of silica saturation: those from arcs are nepheline normative and those from all other localities (silicic UCMI) are hypersthene normative. Silicic UCMI share a number of common features, including primitive host minerals, low alkali contents, and variable ratios of K₂O/TiO₂ ranging to high values. Their compositions are not easily derived by partial melting of mantle lherzolite. Accordingly, we have performed a series of partial melting experiments on three clinopyroxenite compositions at 1.0 to 2.0 GPa to investigate the role of partial melting of clinopyroxene-rich lithologies in silicic UCMI genesis. Estimated solidus temperatures for all three compositions are similar to those of normal peridotites, but 1.0 GPa isobaric melt productivities are higher for clinopyroxenite than for peridotite. High degree partial melts of the clinopyroxenites are ultra-calcic and have similarities to silicic UCMI, but the experiments produce ultra-calcic liquids only at melt fractions greater than 30% and temperatures higher than 1,350 °C at 1.0 GPa. Such temperatures are higher than those likely to be prevailing beneath normal mid-ocean ridges, which suggests that some or all silicic UCMI may originate by a process other than simple partial melting of clinopyroxene-rich lithologies. We consider a possible role for partial melting of depleted harzburgite in the genesis of silicic UCMI.     

The groundwater vulnerability map for the Flemish region: its principles and uses

Fobe, B. and Goossens, M., 1990. The groundwater vulnerability map for the Flemish region: its principles and uses. Eng. Geol., 29: 355–363.

The vulnerability map of the groundwater for the Flemish region demonstrates the possible risk for contamination of the groundwater in the upper aquifer of economical value. The map was ordered by the Flemish government and distributed among the people working in the environmental sector. The vulnerability map, in scale 1/100,000, is based on static factors, like the lithology of the aquifer and its possible coverlayers and the depth of the water table. The map will serve as a tool for proper management of the groundwater. Because of its smaller scale, the document will be used to determine areas where particular regulations and actions for the protection of groundwater are necessary.

Some of the data presented by the map suggest a safer situation than actually present. This is because the compilation followed strictly the principles of the legend. In the future, care should be taken to avoid such ambiguous situations on a map that is available for the public.

Plans exist to start with the compilation of dynamic vulnerability maps. One experimental project is already finished. This study and other recent scientific research gave experience about the influence of topography on the recharge of groundwater. It will be necessary to review the risk of groundwater contamination in some of the areas on the vulnerability map, especially in sandy hill ridges.     

Supergranular line profile variation of Mg i λ2852

The chromospheric network is barely visible in the Mg i 2852 line. Unlike in plages, where it shows well-defined self-reversed emission structure in the core, the line is an unreversed absorption feature in the network boundaries, exhibiting only a small blue asymmetry. In the network cell interiors, the line is unreversed and symmetrical.     

Changes in the volatile hydrocarbon content of Prudhoe Bay Crude Oil treated under different simulated weathering conditions

Changes have been determined in the concentrations of volatile saturate and aromatic hydrocarbons in Prudhoe Bay Crude Oil (PBC) weathered under three different simulated environmental conditions. A combination of light and water sprayed upon the surface of the oil produced the largest relative decreases in volatile saturate and most aromatic hydrocarbons. After 24 days, detectable amounts of monoaromatic hydrocarbons were absent in all three weathered oils, as were the saturate hydrocarbons from C₈ to C₁₀. Retention of aromatic hydrocarbons appeared to be related to molecular weight, as enrichments of triaromatics (phenanthrenes) were observed in weathered PBC relative to the original crude oil. These data are discussed with respect to effects resulting from spilled oil impacting benthic organisms residing in intertidal and shallow subtidal communities.     

Quantitative assessment of intertidal blue mussel (Mytilus edulis L.) stocks: combined methods of remote sensing, field investigation and sampling

The aim of this investigation was to develop appropriate methods for quantitative assessment of blue mussel beds. Combined methods of remote sensing, ground truth investigation and sampling in the field were applied to mature and young intertidal mussel beds. Three variables were measured to obtain reliable quantitative estimates of biomass and abundance: the total area covered by a bed; the cover, i.e. the area of mussel-covered patches in relation to the total mussel bed area; and the proportion, i.e. the area covered by mussels within the patches in relation to the total area of mussel patches. Cover and proportion of intertidal blue mussel beds were measured in the field by the transection method. Aerial photographs enabled the total area of the beds to be determined and large-scale surveys of mussel beds to be carried out synchronously. By examining large-scale aerial photographs it was possible also to determine the cover by remote sensing. The proportion could not be derived from aerial photographs, even from pictures at the largest scale tested during this investigation (scale 1:2500). By statistical methods it was estimated that 12 sub-samples (each covering 177 cm²) from mature beds, and 12 sub-samples (each covering 38 cm²) from young beds are needed to obtain reliable data on biomass and abundance.     

Role of particle size in till-fabric characteristics: systematic variation in till fabric from Vestari-Hagafellsjökull, Iceland

Till-fabric analysis has often been used to interpret glacier flow directions and subglacial dynamics using vector-based statistics, but recent data suggest that such analysis may also effectively indicate former glacier dynamics. The results of a fabric investigation of subglacially strained till deposited during a surge of Vestari-Hagafellsjökull, Iceland, are presented. Till fabric was collected at four sites within a limited area where ice-flow direction during deposition was known from subglacial bedforms at the site. Analysis was carried out on elongate grains (axial ratio <1.5:1) at seven size fractions, with the a-axis length ranging from 0.25 to 32 mm. The largest grains tend to be parallel to ice flow, whereas smaller grains reflect a mix of parallel and transverse orientations. The implications of these data for the role and validity of till-fabric analysis are discussed, with reference to vector analyses and the compilation of fabric shape envelopes. It is noted that, in contrast to laboratory experimental data, neither March nor Jeffery mechanisms explain the fabric configurations reported. It is concluded that a standardized approach is necessary for collecting fabric data, and in many situations analysis of data populations at a range of particle sizes is desirable.     

Evidence of NAO control on subsurface ice accumulation in a 1200 yr old cave-ice sequence, St. Livres ice cave, Switzerland

Mid-latitude ice caves are assumed to be highly sensitive to climatic changes and thus represent a potentially interesting environmental archive. Establishing a precise chronology is, however, a prerequisite for the understanding of processes driving the cave-ice mass balance and thus allows a paleoenvironmental interpretation. At St. Livres ice cave (Jura Mountains, Switzerland), subfossil trees and organic material are abundant in the cave-ice deposit, therefore allowing the dating of individual ice layers. The dendrochronological analysis of 45 subfossil samples of Norway spruce (Picea abies (L.) Karst.) from the overhanging front of the ice outcrop as well as the dating of seven wood samples with ¹⁴C dating allowed for a reconstruction of the St. Livres cave-ice sequence and for the determination of periods of ice accumulation and ablation. Results suggest a maximal age of 1200 ± 50 ¹⁴C yr BP for the observed ice sequence and indicate the presence of four major deposition gaps dated to the 14th, 15th, mid-19th and late 19th century, which can be related with periods of positive North Atlantic Oscillation anomalies (NAO+) over the winter half-year and/or anthropogenic cave-ice abstraction. Similarly, there is evidence that periods of cave-ice accumulation as observed between AD 1877-1900 and AD 1393-1415 would correspond with phases of negative NAO indices. Cave ice represents therefore an original climate archive for the winter half-year and is complementary to other continental proxies recording preferentially summer conditions (e.g., tree rings, varves).     

激光剥蚀-等离子体质谱技术及其在地球化学宇宙化学和环境研究中的应用

激光剥蚀-等离子体质谱(LA-ICPMS)已成为地球化学、宇宙化学和环境研究领域元素和同位素原位分析最重要的技术之一。文章介绍了多种类型的质谱仪及其使用的激光器。用途最广的LA-ICPMS仪器之一是单接收器扇形磁场质谱仪,配有Nd:YAG激光剥蚀系统(激光波长分为193 nm和213 nm两种),MPI Mainz实验室使用的就是这套系统,文章对此作一详细介绍。文中阐述了数据优化技术及其多种校正过程;介绍LA-ICPMS在痕量元素和同位素分析领域的一些应用,包括参考物质的研制,Hawaiian玄武岩、Martian陨石、生物骨针和珊瑚虫中痕量元素分析及熔融包裹体和富钙-铝碳质球粒陨石中的铅和锶同位素测量。