Search publications of the members of the Royal Belgian institute of natural Sciences
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Joseph Charles Hippolyte Crosse (1826-1898), 1: biography, bibliography and new taxa introduced
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The transition between coastal and offshore areas in the North Sea unraveled by suspended particle composition
- Identifying the mechanisms that contribute to the variability of suspended particulate matter concentrations in coastal areas is important but difficult, especially due to the complexity of physical and biogeochemical interactions involved. Our study addresses this complexity and investigates changes in the horizontal spread and composition of particles, focusing on cross-coastal gradients in the southern North Sea and the English Channel. A semi-empirical model is applied on in situ data of SPM and its organic fraction to resolve the relationship between organic and inorganic suspended particles. The derived equations are applied onto remote sensing products of SPM concentration, which provide monthly synoptic maps of particulate organic matter concentrations (here, particulate organic nitrogen) at the surface together with their labile and less reactive fractions. Comparing these fractions of particulate organic matter reveals their characteristic features along the coastal-offshore gradient, with an area of increased settling rate for particles generally observed between 5 and 30 km from the coast. We identify this area as the transition zone between coastal and offshore waters with respect to particle dynamics. Presumably, in that area, the turbulence range and particle composition favor particle settling, while hydrodynamic processes tend to transport particles of the seabed back towards the coast. Bathymetry plays an important role in controlling the range of turbulent dissipation energy values in the water column, and we observe that the transition zone in the southern North Sea is generally confined to water depths below 20 m. Seasonal variations in suspended particle dynamics are linked to biological processes enhancing particle flocculation, which do not affect the location of the transition zone. We identify the criteria that allow a transition zone and discuss the cases where it is not observed in the domain. The impact of these particle dynamics on coastal carbon storage and export is discussed.
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Lessons from the calibration and sensitivity analysis of a fish larval transport model
- ABSTRACT: Numerous fish populations show strong year-to-year variations in recruitment. The early life stages play a crucial role in determining recruitment and dispersal patterns. A helpful tool to understand recruitment and dispersal involves simulations with a Lagrangian transport model, which results from the coupling between a hydrodynamic model and an individual-based model. Larval transport models require sound knowledge of the biological processes governing larval dispersal, and they may be highly sensitive to the parameters selected. Various assumptions about larval traits, behaviour and other model parameters can be tested by comparing simulation results with field data to identify the most sensitive parameters and to improve model calibration. This study shows that biological parameterization is more important than inter-annual variability in explaining the year-to-year differences in larval recruitment of common sole in the North Sea and the eastern English Channel. In contrast, year-to-year variability of connectivity leads to higher variability than changes in the biological parameters. The most influential parameters are pelagic larval duration, spawning period and mortality. Calibration over a 12 yr recruitment survey shows that a scenario with low mortality associated with a long larval duration and behaviour involving nycthemeral and tidal migration best reproduces the observations. This research provides insights into factors influencing fish dispersal and recruitment, suggesting a strategy for enhancing the accuracy of models in upcoming studies. The study supports the improvement of larval dispersal modelling by incorporating an easily applicable sensitivity analysis for both calibration and validation. Incorporating sensitivity analyses enhances larval dispersal models, providing performing tools that can contribute to informed fisheries management and understanding of recruitment variability.
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Discovery-defense strategy as a mechanism of social foraging of ants in tropical rainforest canopies
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Distance–decay patterns differ between canopy and ground ant assemblages in a tropical rainforest
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Spatial and functional structure of an entire ant assemblage in a lowland Panamanian rainforest
- ABSTRACT Ants are a major ecological group in tropical rainforests. Few studies in the Neotropics have documented the distribution of ants from the ground to the canopy, and none have included the understorey. A previous analysis of an intensive arthropod study in Panama, involving 11 sampling methods, showed that the factors influencing ant beta diversity (i.e., changes in assemblage composition) were, in decreasing order of importance, the vertical (height), temporal (season), and horizontal (geographic distance) dimensions. In the present study, we went one step further and aimed (1) to identify the best sampling methods to study the entire ant assemblage across the three strata, (2) to test if all strata show a similar horizontal beta diversity and (3) to analyze the functional structure of the entire ant assemblage. We identified 405 ant species from 11 subfamilies and 68 genera. Slightly more species were sampled in the canopy than on the ground; they belonged to distinct sub-assemblages. The understorey fauna was mainly a mixture of species found in the other two strata. The horizontal beta diversity between sites was similar for the three strata. About half of the ant species foraged in two (29%) or three (25%) strata. A single method, aerial flight interception traps placed alongside tree trunks, acting as arboreal pitfall traps, collected half of the species and reflected the vertical stratification. Using the functional traits approach, we observed that generalist species with mid-sized colonies were by far the most numerous (31%), followed by ground- or litter-dwelling species, either specialists (20%), or generalists (16%), and arboreal species, either generalists (19%) or territorially dominant (8%), and finally army ants (5%). Our results reinforce the idea that a proper understanding of the functioning of ant assemblages requires the inclusion of arboreal ants in survey programs.
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Inter‐specific aggression generates ant mosaics in canopies of primary tropical rainforest
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Rapid assessment of the three‐dimensional distribution of dominant arboreal ants in tropical forests
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Rapid assessment of the three‐dimensional distribution of dominant arboreal ants in tropical forests
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Neolithic fishing in the South Caucasus as seen from Aruchlo I, Georgia
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Optimal geodata centralization and disclosure as support for subsurface exploration
- It is widely known that the subsurface will play a crucial role in the transition towards a carbon-neutral society, with the aid of technologies like geothermal energy, CO2-storage, .... Nevertheless, still a lot of aspects concerning the subsurface, its structure and characteristics remain to be investigated to facilitate the use of underground space in an efficient and safe way. In-depth investigation of the subsurface with conventional techniques such as seismic campaigns or drillings requires high investments, and it is not always straightforward to determine the success-rate upfront. This leads to geodata collections typically displaying a large variety and scatter, both concerning data (type) availability and in spatial distribution. Additionally, incorporating subsurface knowledge from neighboring countries often is challenging, but at the same time indispensable to increase understanding of the own subsurface, not least because some projects may display cross-border influences. It is clear that subsurface exploration benefits from a cross-border and cross-thematic data collection and interpretation approach. One way to organize such data centralization was explored in the framework of the European Horizon2020-project GeoConnect³d, by means of constructing a Structural Framework (SF) and a database of Geomanifestations (GM) for several pilot study areas. The Structural Framework defines geological units by its limits (e.g., faults, terrane boundaries, ...). All known limits and associated parameters are structured in a uniform and inter-connected way. Furthermore, the SF is designed on multiple zoom-levels, hence it can serve as a real backbone to integrate multiple other subsurface models of various scale and resolution together. Geomanifestations are anomalous observations covering a wide range of geo-disciplines, including —but not limited to— temperature, geochemistry, mineralogy and even geophysics data. Such irregularities are too often excluded or ignored in view of the larger cloud of ‘normal’ datapoints. Nevertheless, precisely these anomalies can be of great value for identifying subsurface processes and serve as an excellent pathway for communication to non-experts, and also as guideline for further research. In addition to GIS- and attribute-information, Factsheets summarize the relations between individual geomanifestations, and, if applicable, their connection to the Structural Framework. Especially the latter, the combination of the (independent) elements SF and GM, gives a powerful tool that allows exploring the subsurface in an original and cost-efficient way. The newly gained insights can be directly linked and are extremely relevant to the use of the subsurface, either as storage space or as renewable/green energy-source. But it goes further than that. The overall usability of the SF and GM database is far more fundamental, as it gives innovative clues about characteristics and processes at play in the subsurface, such as fault permeability and connectivity, the presence of advection cells in the upper crust, or gas origin and migration pathways. To quote just one example; in the area of Spa, Belgium, elevated 3He/4He-ratios were analyzed (Griesshaber et al., 1992), a parameter that can highlight mantle gas contribution in gas seeps (White, 2013). This observation was unexpected given the far distance from any volcanic activity, but suggests the presence of deep-seated, transcrustal faults and/or a large-distance connectivity till the Eifel area where mantle-derived magma was involved in recent volcanism. When indirect indications like this are not considered further, such valuable subsurface knowledge is easily overlooked and not at all taken into account for investigating in more detail in the future. Even when limited resources or funding is available, the above-illustrated SF+GM approach can shed new light on properties and processes of the subsurface, given its novel and multidisciplinary approach. An inherent drawback, however, is that such a database is never complete and includes information from a variety of sources. Not only does this demands careful consideration on which data is included (or not), it also has to be taken into account for future database expansion as well as for data interpretation. Simple visualizations on a map without further (geological) background, e.g., combining both surface and at depth data as is the case for Wiesbaden, Germany (Mittelbach & Siebert, 2014), may lead to false conclusions. However, the provided Factsheets and metadata can help in this. Furthermore, at this moment, a large proportion of the entries depends on the availability of literature data, which implies some data source bias is unavoidable. For example, CO2-data typically is measured for springs and streams, while dry CO2-seeps easier remain unnoticed and therefore are reported less consistently. New data collection campaigns, possibly including bio-indicators like plants or ants (e.g., Berberich & Schreiber, 2013), can provide a good starting point for this. The uniform and well-designed structure of the database allows very easy expansion, be it for newly discovered faults, additional geomanifestation types, or parameter updates of either part. In addition, as demonstrated in the GeoConnect³d project, the SF+GM approach is fully transferable to other study areas. This clears the way for a cost-efficient cross-border exploration of the subsurface with wins for both the academic world and common public (geoheritage, education, ...), and significantly contributes to a more data-supported outline for subsurface management. This project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 731166. References Berberich, G., & Schreiber, U., 2013. GeoBioScience: Red Wood Ants as Bioindicators for Active Tectonic Fault Systems in the West Eifel (Germany). Animals, 3, 475-498. Griesshaber, E., O'Nions, R.K. & Oxburg, E.R., 1992. Helium and carbon isotope systematics in crustal fluids from the Eifel, the Rhine Graben and Black Forest, F.R.G. Chemical Geology, 99, 213-235. Mittelbach, G. & Siebert, S., 2014. Gutachten zur Festsetzung eines Heilquellenschutzgebietes für die Heilquellen (Große und Kleine Adlerquelle, Schützenhofquelle, Kochbrunnen, Salmquelle und Faulbrunnen) von Wiesbaden, Stadt Wiesbaden (WSG-ID 414-005), Wiesbaden, pp. 1-52. White, W.M., 2013. Chapter 12: Noble Gas Isotope Geochemistry, Isotope Geochemistry course notes. Cornell University.
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GeoConnect³d: transforming geological data into a knowledge system in support of the clean energy transition
- The transition towards a clean and low carbon energy system in Europe will increasingly rely on the use of the subsurface. Despite the vastness of subsurface space, only a fraction of it is suitable for the exploitation of geo-resources. The distribution and fitting combination of required conditions is determined by geological processes. We are, therefore, constrained in where we can develop resources and capacities. Moreover, increased subsurface use in a restricted area will inevitably lead to high chances of interferences and conflicts of interest. This means that sound geological information is essential to optimise the subsurface contribution to a safe and efficient energy transition. Within this scope, the main goal of the GeoConnect³d project is to convert existing geological data into an information system that can be used for various geo-applications, decision-making, and subsurface spatial planning. This is being accomplished through the innovative structural framework model, which reorganises, contextualises, and adds value to geological data. The model is primarily focused on geological limits, or broadly planar structures that separate a given geological unit from its neighbouring units. It also includes geomanifestations, highlighting any distinct local expression of ongoing or past geological processes. These manifestations, or anomalies, often point to specific geologic conditions and, therefore, can be important sources of information to improve geological understanding of an area. Geological data in this model are composed of spatial data at different scales, with a one-to-one link between geometries and their specific attributes (including uncertainties), and of semantic data, with data organised conceptually and categorised and/or linked using SKOS hierarchical and generic schemes. Concepts and geometries are linked by a one-to-many relationship. The combination of these elements then results in a multi-scale, harmonised and robust model. The structural framework-geomanifestations methodology has now been applied to different areas in Europe. The focus on geological limits brings various advantages, such as displaying geological information in an explicit, and therefore more understandable, way, and simplifying harmonisation efforts in large-scale geological structures crossing national borders. The link between spatial and semantic data is the essential step adding conceptual definitions and interpretations to geometries. Additionally, geomanifestation data successfully validates or points to inconsistencies in specific areas of the model, which can then be further investigated. The model demonstrates it is possible to gather existing geological data into a comprehensive knowledge system. We consider this as the way forward towards pan-European integration and harmonisation of geological information. Moreover, we identify the great potential of the structural framework model as a toolbox to communicate geosciences beyond our specialised community. This is an important step to support subsurface spatial planning towards a clean energy transition by making geological information available to all stakeholders involved. This project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 731166.
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Reading Minerals: Rare Element Enrichment, the Magmatic-Hydrothermal Transition, and Geochemical Exploration of Lithium Pegmatites in Ireland
- The battery market for electric vehicles and renewable energy storage is dominated by rechargeable lithium-ion batteries, making lithium supply essential to climate action through decarbonization. In 2019, more than half of the world's lithium was sourced from lithium pegmatites of the Li-Cs-Ta (LCT) family, predominantly from Australia. Current global lithium supply involves long diesel-fueled maritime transport routes, which counteracts lithium's role in climate action. Responsible consumption and production require shorter supply chains from deposit to battery. Reading the mineralogical record of LCT pegmatite deposits can help address the challenge of reducing the climate impact of lithium production, by informing deposit models, mineral exploration, and geometallurgy, therefore promoting local supply. Our research focuses on a belt of LCT pegmatites, which is located along the eastern margin of the late-Caledonian S-type Leinster Batholith, southeast Ireland. The LCT pegmatites are hosted by a major regional shear zone and are part of a tin-lithium province that stretches subparallel to the Iapetus suture from Europe through Nova Scotia to North and South Carolina. We investigated crystal chemical zoning in muscovite, cassiterite, and columbite-tantalite using petrography, scanning electron microscopy, and LA-ICP-MS chemical mapping. The zoning patterns record that pegmatite rare element mineralization resulted from an interplay of magmatic crystallization, metasomatism, and hydrothermal processes. Late-stage metasomatic alteration led to partial resorption of early minerals including the lithium ore-mineral spodumene, followed by dispersion of lithium and other rare elements into country rocks, mostly within dark mica. Dispersion led to formation of geochemical halos around the LCT pegmatites with the potential to use country-rock lithogeochemistry and mica composition as geochemical vectoring tools. Geochemistry of mica in the granite host analyzed by handheld LIBS has been found to exhibit coherent spatial patterns occurring adjacent to and above LCT pegmatites known at depth from drilling. These channels of mineral-specific geochemical information are distinct from soil geochemical patterns and are not influenced by the same secondary, surface processes such as dilution. As outcrop is virtually absent in the study area, regional stream sediment geochemistry data (Geological Survey Ireland) was assessed as an LCT pegmatite exploration tool. After correcting for geologic background using a linear regression approach, catchments containing LCT pegmatites show high residuals for concentrations of both tantalum and tin. The mineralogy of stream sediment samples from a subsample of these catchments was subsequently analyzed to characterize the host minerals of tin and tantalum. Cassiterite and columbite-tantalite were identified, and both show geochemical and textural signatures that correspond to the zoning patterns mentioned above, which indicates that these minerals were derived from the local LCT pegmatites. These results suggest that, when regional geology and tectonic setting are prospective, lithium pegmatite prospectivity can be further assessed for tin-tantalum associations in (often publicly available) regional stream sediment data. Following geospatial analysis, stream sediment samples could be obtained from individual prospective catchments and their mineralogy analyzed. Local-scale geochemical surveys could follow where stream sediments of prospective catchments contain tin and tantalum oxides with chemistries and textures indicative of a lithium pegmatite source.
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A decomposition approach to cyclostratigraphic signal processing
- Sedimentary rocks can record signals produced by highly complex processes. These signals are generated by a progressive deposition of sediments which can be affected, mainly through the climate system, by regular astronomical cycles (i.e. Milankovitch cycles), and by irregular oscillations like the El Niño-Southern Oscillation. Also, usually through biological, chemical and/or physical post-depositional processes, the sedimentary records can be affected by pattern-creating heterogeneous processes. The noise in the signals further complicates the records, and the deposition rate (or sedimentation rate) can fluctuate, which greatly reduces the effectiveness of the classical stationary time-series analysis methods commonly used in cyclostratigraphy (i.e. the study of the cycles found in the sedimentary records). Faced with this multiplicity of processes, a common approach used in cyclostratigraphy is to reduce each signal to more manageable sub-signals, either over a given range of frequencies (e.g., by filtering), or by considering a continuum of constant frequencies (e.g., using transforms). This makes it possible to focus on the features of interest, commonly astronomical cycles. However, working with sub-signals is not trivial. Firstly, sub-signals have a certain amount of cross-cancellation when they are summed back to reconstruct the initial signal. This means that in filters and in transforms, wiggles that are not present in the initial signal can appear in the sub-signals. Secondly, the sub-signals considered often cannot be summed to reconstruct the initial signal: this means that there are processes affecting the signal which remain unstudied. It is possible to take cross-cancellation into account and to consider the entire content of a signal by dividing the signal into a decomposition: a set of sub-signals that can be added back together to reconstruct the original signal. We discuss here how to reframe commonly used time-series analysis techniques in the context of decomposition, how they are affected by cross-cancellation, and how adequate they are for comprehending the whole signals. We also show that decomposition can be carried out by non-stationary time-series methods, which can minimise cross-cancellation, and have now reached sufficient maturity to tackle sedimentary records signals. We present novel tools to adapt non-stationary decomposition for cyclostratigraphic purposes, based on the concepts of Empirical Mode Decomposition (EMD) and Instantaneous Frequency (IF), mainly: (1) a fast Ensemble Empirical Mode Decomposition (EEMD) algorithm, (2) quality metrics for decomposition, and (3) plots to visualise instantaneous frequency, amplitude and frequency ratio. We illustrate the use of these tools by applying them on a greyscale signal from the site 926 of the Ocean Drilling Program, at Ceara Rise (western equatorial Atlantic), especially to identify and characterise the expression of astronomical cycles. The main goal is to show that by minimising cross-cancellation, we can apply in real signals what we call the wiggle-in-signal approach: making the sub-signals in the decomposition more representative of the expression, wiggle by wiggle, of all the processes affecting the signal (e.g., astronomical cycles). We finally argue that decomposition could be used as a practical standard output for time-series analysis interpretation of cyclostratigraphic signals.
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StratigrapheR: Concepts for Litholog Generation in R
- The StratigrapheR package proposes new concepts for the generation of lithological logs, or lithologs, in R. The generation of lithologs in a scripting environment opens new opportunities for the processing and analysis of stratified geological data. Among the new concepts presented: new plotting and data processing methodologies, new general R functions, and computer-oriented data conventions are provided. The package structure allows for these new concepts to be further improved, which can be done independently by any R user. The current limitations of the package are highlighted, along with the limitations in R for geological data processing, to help identify the best paths for improvements.
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Optimizing multiple non-invasive techniques (PXRF, pMS, IA) to characterize coarse-grained igneous rocks used as building stones.
- We present a workflow to conduct a full characterization of medium to coarse-grained igneous rocks, using portable, non-invasive, and reproducible approaches. This includes: (i) Image Analysis (IA) to quantify mineral phase proportions, grain size distribution using the Weka trainable machine learning algorithm. (ii) Portable X-ray fluorescence spectrometer (PXRF, Bruker Tracer IV) to quantify the whole-rock's chemical composition. For this purpose, a specific calibration method dedicated to igneous rocks using the open-source CloudCal app was developed. It was then validated for several key elements (Si, Al, K, Ti, Ca, Fe, Mn, Sr, Ga, Ba, Rb, Zn, Nb, Zr, and Y) by analyzing certified standard reference igneous rocks. (iii) Portable Magnetic Susceptibilimeter (pMS, Bartington MS2K system) to constrain the mineralogical contribution of the samples. The operational conditions for these three methods were tested and optimized by analyzing five unprepared surfaces of igneous rocks ranging from a coarse-grained alkaline granite to a fine-grained porphyric diorite and hence, covering variable grain sizes, mineralogical contents, and whole-rock geochemical compositions. For pMS and PXRF tools, one hundred analyses were conducted as a 10 cm × 10 cm square grid on each sample. Bootstrap analysis was implemented to establish the best grid size sampling to reach an optimized reproducibility of the whole-rock signature. For PXRF analysis, averaged compositions were compared to PXRF analysis on press-pellets and laboratory WD-XRF analysis on fused disk and solution ICP-OES (for major) and solution-ICPMS (for trace element concentrations). Ultimately, this workflow was applied in the field on granitoids from three Roman quarrying sites in the Lavezzi archipelago (southern Corsica) and tested against the Bonifacio granitic War Memorial, for which its provenance is established. Our results confirm this information and open the door to geoarchaeological provenance studies with a high spatial resolution.
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Brussels’ bedrock paleorelief from borehole-controlled power laws linking polarised H/V resonance frequencies and sediment thickness
- The empirical power law relation (PR) between resonance frequency (f0), obtained from H/V spectral ratio analysis of ambient noise, and sediment thickness (h), obtained from boreholes, is frequently used in microzonation studies to predict bedrock depth. In this study, we demonstrate (i) how to optimally construct a PR by including the error on the picked f0 in the regression, and (ii) how to evaluate a regression quality by identifying the under- or overestimation of the sediment thickness prediction. We apply this methodology on f0 data derived from 74 ambient noise recordings acquired above boreholes that reach the Brabant Massif bedrock below Brussels (Belgium). Separating the f0 data into different subset based on the cover geology does not significantly improve the bedrock depth prediction because the cover geology in Brussels has common base layers. In Brussels, the PR relation h = 88.631.f0−1.683 is the best candidate to convert f0 to depth, with a prediction error of 10%. The Brussels PR was subsequently applied on a local survey (404 measurements; 25 km2) in southern Brussels with the aim to study Brussels’ Brabant Massif bedrock paleorelief. By linking the obtained paleorelief, Bouguer gravity data and aeromagnetic data, a NNW-SSE oriented, 20 m-high subsurface ridge could be identified. This ridge stands out because of differential erosion between less-resistant and hard quartzitic rock formations of the Brabant Massif. This subsurface ridge deflects the local radiation of seismic energy resulting in an anomaly in the otherwise regional consistent azimuthal dependency of the resonance frequency. We conclude that adding a polarisation analysis to a microzonation survey analysis allows detecting anomalous features in the paleorelief.
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Arguments (Ostracodes) pour une régression culminant à proximité de la limite Frasnien-Famennien, à Sinsin (bord sud du Bassin de Dinant)
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Les Ostracodes du Frasnien terminal ("Kellwasser" supérieur) de Coumiac (Montagne Noire, France)
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Ostracods and the upper Devonian mass extinction in the southern border of the Dinant Basin (Belgium)
