Between the Neoarchean and the early Proterozoic, plate tectonics was gradually established on our planet. How this transition took place, and what kind of geodynamic paradigm dominated before, is a matter of debate, and systematic multidisciplinary studies help improving our understanding of such a transitional period of Earth's evolution. The Yilgarn Craton of Western Australia exposes upper-crustal granite-greenstone terranes that are juxtaposed along large-scale, Neoarchean shear zones, which mainly developed during the 2730 - 2660 Ma Yilgarn Orogeny. By combining structural, microstructural and geochemical data, we present here a systematic study of the main shear zones occurring in the best-exposed, northwestern half of the craton. Our structural data demonstrate that large granitic magma sheets were emplaced during shearing. Although these shear zones exhibit a variety of fabrics that developed over a wide range of temperatures, all preserve memory of at least one stage of shearing at near-solidus temperatures. Our results allow tracing a c. 100 Myr-long tectonomagmatic evolution of this portion of the Archean crust, with implications for lithosphere rheology, crustal evolution, and mineral systems. The major synorogenic structures can be interpreted as inclined transpressional shear zones, along which the bulk of the 3D deformation was efficiently partitioned between greenstones and crystallizing granitic sheets within the shear zones, with the latter accommodating large amounts of orogen-parallel strain through suprasolidus viscous flow. The positive feedback between protracted magmatism and transpression promoted the extraction and upward transfer of syntectonic magma originated between the uppermost mantle and the mid-crust, as demonstrated by our geochemical dataset. This synkinematic mode of granitic magma transfer contrasts fundamentally to the diapiric mode that was dominant during the lithospheric extension phase that pre-dated the Yilgarn orogeny. Our study suggests that the shear zone system studied here likely played a major role in controlling magma/fluid pathways throughout the late Archean lithosphere, therefore playing a critical role in controlling the development of near-surface mineral systems.

Lakes are rapidly losing ice under global warming, but little is known about ice structure changes. Ice structure is a key regulator of ice stability and thus safety, affecting activities on ice. Here, we analysed spatial and temporal variations in ice structure across 21 Swedish lakes, spanning from 55 to 69 °N, and over five decades. We found regional differences in ice structure, with fastest changes occurring in southern Sweden. The stable clear ice layer was particularly sensitive to warming, showing a rapid decline. The number of days when temperatures exceeded the freezing point during the ice cover period was identified as a strong driver for how ice was structured. Since there is a high risk for increased occurrences of unsafe ice conditions under predicted air temperature changes, we recommend re-establishing ice structure monitoring programmes, informing society on the increased risks of being on ice and including ice structure to safety guidelines.

AbstractMethods to document rock art in all three dimensions have become a standardized workflow. In this article, we discuss their advantages and disadvantages when compared to older reductive approaches to rock art documentation. Furthermore, some misunderstandings regarding 3D documentation are addressed. As the majority of the problems presented by the 3D documentation of rock art can be solved through advanced visualization workflows, recent developments in this area are described. The rock art documentation described in this contribution also serves wider research purposes, which will be discussed. Newly discovered images and newly developed machine learning algorithms will also be introduced.

In frozen cylinders composed of deuterium ice (Tm+3.8 ∘C) and 10 % water ice (Tm 0 ∘C), it is possible to track melt pathways produced by increasing the temperature during deformation. Raising the temperature to +2 ∘C produces water (H2O) which combines with the D2O ice to form mixtures of HDO. As a consequence of deformation, HDO and H2O meltwater are expelled along conjugate shear bands and as compactional melt segregations. Melt segregations are also associated with high-porosity networks related to the location of transient reaction fronts where the passage of melt-enriched fluids is controlled by the localized ductile yielding and lowering of the effective viscosity. Accompanying the softening, the meltwater also changes and weakens the crystallographic fabric development of the ice. Our observations suggest meltwater-enriched compaction and shear band initiation provide instabilities and the driving force for an enhancement of permeability in terrestrial ice sheets and glaciers.

Recent interest in microplastic pollution of natural environments has brought forth samples which confirm the pollutant's omnipresence in a variety of ecosystems. This includes locations furthest removed from human activity. Atmospheric transport and deposition are suspected as the primary transport pathway to these remote locations. The factors most influential on participation in atmospheric transport are yet to be determined. This meta-analysis aims to identify patterns that exist between physical characteristics of microplastic particles and their potential for atmospheric transport. Our review addresses the following questions: Which characteristics of microplastic particles promote atmospheric transport and deposition into remote regions, and how significant are these factors in determining distance transported from their sources? This article analyzes commonly reported physical attributes-- shape, polymer composition and color-- from studies in urban and remote areas. The analysis of 68 studies, composed of data from 2078 samples, shows higher occurrence of microplastic particles in remote samples with fiber shapes, polyester compositions, and red, blue, and transparent colors. This meta-analysis is the first to identify patterns between physical properties of microplastic particles and extent of their participation in atmospheric transport to global remote locations.

Figure 1.Schematic illustration showing workflow for 3D ice melting experiments.Involving sample preparation, deformation experiments on KOWARI, neutron tomography on DINGO, and followed by segmentation and visualization.

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AbstractThis chapter proposes a fieldtrip on NW of Portugal (Oporto metropolitan area), which is a sequence of thematic stops. The stops began on deep crustal level at a magmatic feeder zone—Leça da Palmeira Metamorphic Complex, and follows to a middle-upper crustal level with magmatic features associated with magmatic chamber dynamics of post-orogenic biotite granite (Bt-granites)—the Lavadores granite. Each theme is methodological divided into several sections: short introductory text about each feature highlighted on the outcrops; stop description supported with sketches and photos illustrating what can be really seen at the outcrops; field and/or drawing activity; discussion and conclusion section, focused on new approaches and interpretations of the geological results. On Leça Palmeira Metamorphic Complex the major issue is a granite-tonalite relationship on a deep shear zone, where a magmatic feeder zone was evolved as a gneissic complex. The Lavadores granite shows all a sequence of mesostructures related with the interaction between mafic microgranular enclaves and the host granite; a morphological potash feldspars (Kfs) classification is used; hybridization mechanism involving Kfs and enclaves motion and an Enclave Disruption Mechanism (EDM) is proposed; feldsphatic plume structure recorded the feeding process into the magmatic chamber.KeywordsGranitic rocksMetamorphic complexMagmatic structuresMagmatic chamber dynamicsMafic micogranular enclaves

The quality of lake ice is of uppermost importance for ice safety and under-ice ecology, but its temporal and spatial variability is largely unknown. Here we conducted a coordinated lake ice quality sampling campaign across the Northern Hemisphere during one of the warmest winters since 1880 and show that lake ice during 2020/2021 commonly consisted of unstable white ice, at times contributing up to 100% to the total ice thickness. We observed that white ice increased over the winter season, becoming thickest and constituting the largest proportion of the ice layer towards the end of the ice cover season when fatal winter drownings occur most often and light limits the growth and reproduction of primary producers. We attribute the dominance of white ice before ice-off to air temperatures varying around the freezing point, a condition which occurs more frequently during warmer winters. Thus, under continued global warming, the prevalence of white ice is likely to substantially increase during the critical period before ice-off, for which we adjusted commonly used equations for human ice safety and light transmittance through ice.

Current melting of glaciers has increased interest in understanding glacier hydrology and the interplay between subglacial meltwater, the glacier bed, and ice behavior. However, little is known about the sedimentology of subglacial meltwater deposits, and no sediment type or sequence has been identified as being unique to subglacial settings. Here, we analyze a repetitive, coarsening-upward, sorted-sediment sequence in a thick, diamicton section that we interpret to be seasonal, subglacial meltwater deposits. Over 20m of diamicton that we interpret to be subglacial traction till is exposed in a rock-cored drumlin at Dosebacka, Sweden, and the till contains multiple interbeds, 25-75 cm thick, of sorted sediment, each consisting of a coarsening-upward sequence of laminated clay, graded laminae of silt, and sand with pebbles. Based on sediment logs, grain-size, thin-section analysis, structural analysis, and field sedimentology, we investigate the genesis of these interbeds and conclude the interbeds to represent subglacial pond deposits. The coarsening-upward sequence represents cessation of till deposition due to hydrostatic bed separation followed by (1) suspension settling of clay in a subglacial blister/pond with drop-grains froman ice roof, (2) suspension settling of pulses of silt and very fine sand in still water coupled with occasional turbidites, (3) traction sedimentation (and loading) of sand and gravel from flowing water, and (4) renewed till deposition following reattachment. The interbeds also reveal deformation that is oriented parallel to the ice-flow direction and which we attribute to deformation during ice-bed reattachment. This sediment sequence parallels in character the seasonal behavior of supraglacial meltwater development on Greenland and moulin drainage, and we argue that the interbeds represent pond deposits during seasonal meltwater drainage. Drainage formed a subglacial blister/pond when the ice reached floatation point, and clay and, later, silt were deposited. With time, drainage became better integrated, and sand and pebbles were deposited by flowing water until reattachment when till deposition resumed. Additionally, based on our interpretation and the attitude of the beds in the drumlin, which parallel the drumlin slope, we argue the drumlin to have been formed by accretion rather than erosion. The anomalous thickness of the till and the numerous interbeds also imply a relatively rapid sedimentation rate, indicating the drumlin formed quickly (10's of years). This stoss-side environment allowed for preservation of the unique interbeds. (C) 2022 The Author(s). Published by Elsevier B.V.

The submarine tufa columns of Ikka Fjord in Southwest Greenland have been studied during multiple field campaigns since 1995. The fjord contains close to thousand columns previously shown to consist of the metastable carbonate mineral ikaite (CaCO3·6H2O), which requires near-freezing conditions to remain stable over longer periods of time. During a field campaign to Ikka Fjord in the summer of 2019, seawater temperatures of 6–9 °C and visual physical changes to the columns were observed. These are the highest recorded seawater temperatures measured in Ikka Fjord in over three decades of research. In response, three selected columns at three different locations were sampled at their bases, middle, and top sections for mineralogical analysis. These samples were supplemented by a four further column samples and an extensive hydrographical campaign during fieldwork in the summer 2021. Here, we report the results of the mineralogical analyses performed by X-ray diffraction and µ-Raman Spectroscopy on these column samples. The results show that the columns analysed now consist of the less hydrated carbonate minerals, monohydrocalcite (CaCO3·H2O), aragonite, and calcite (CaCO3). One of the columns has completely altered into monohydrocalcite, whereas the other columns have crusts of ikaite and cores of monohydrocalcite ± aragonite and calcite. This change is interpreted as a dehydration reaction and mineral alteration from ikaite to monohydrocalcite continuing to aragonite ± calcite in response to being bathed in warming seawater. Hydrographic profilers and static dataloggers recorded seawater temperatures of 4–8 °C in the column-containing fjord areas during June–August 2021. The upper parts of the columns are particularly exposed to temperatures > 6 °C, considered to be the long-term stability threshold of ikaite in Ikka Fjord. The mineral dehydration reactions are irreversible. It is therefore predicted in a warming Arctic, ikaite will only appear as new growth on the columns for a short period, and that with time, the columns of Ikka Fjord will change mineralogy into mainly monohydrocalcite.

To classify contaminated sites into different risk classes, many different methods exist in Europe and worldwide. However, no systematic comparison of European risk classification methods has been carried out so far to carve out the advantages and disadvantages of the methods and to homogenize them. To address this research gap, this study aims at comparing the Swedish Method for Inventories of Contaminated Sites (MIFO) with the German Individual Assessment of Contaminated Sites Method (EB) from the Hessian Agency for Nature Conservation, Environment and Geology (HLNUG) regarding the risk class categorization of 51 contaminated sites. The results revealed that with the MIFO 39% fewer contaminated sites are assigned to risk classes 1 and 2 and thus, subject to remediation compared to the EB. Moreover, in comparison to the EB, the MIFO showed a lower comparability, traceability, and a larger room for interpretation, which could be related to the lack of a quantitative approach such as a point or ranking system in the MIFO. Hence, we recommend providing the MIFO and other methods that lack a quantitative approach with a point and/or ranking system, similar to the EB, to increase their objectivity for the risk class categorization of contaminated sites.

The paper proposes a new method to quantify the flow of water and water accumulation zones on bedrock panels. This can be used to investigate how water influences the placement of rock art. The analysis is based on photogrammetric models on which water flows and accumulations were modelled using a NetLogo simulation and the SAGA hydrology package. To test the hypothesis that water was a structuring element in the creation of rock art, case studies of Bohus-granite panels from south-western Sweden were used. The described approach should be possible to use on most rock art placed on bedrock panels regardless of rock type, its state of cleaning, or present microfauna. The modelling of water flows and accumulations is a powerful tool to compare the image placement and image density in relation to water even on widely separated panels on which such observations cannot be made directly.

Today, it is widely accepted that typology is a biased and inconsistent attempt to classify archaeological material based on the similarity of a predefined set of features. In this respect, machine learning (ML) works similar to typology. ML approaches are often deployed because it is thought that they reduce biases. However, biases are introduced into the process at many points, e.g., feature selection. In a project applying ML to Scandinavian rock art data, it was noticed that the algorithm struggles with classifying certain motifs correctly. This contribution discusses the consistency in applying biases by ML in contrast to the inconsistency of human classification. It is argued that it is necessary to bring machines and humans into a meaningful dialogue attempting to understand why apparent “misclassifications” happen. This is important to inform us about the classification output, our biases, and the rock art data, which are in themself inconsistent, ambiguous, and biased because they are the outcomes of human creativity. The human inconsistency is a necessary component because in rock art not everything that looks similar has a similar meaning.

This data set includes the documents for risk classifying contaminated sites in Anderstorp, Sweden using the German Einzelfallbewertung Altlastenstandorte (EB) method from the Hessian Agency for Nature Conservation, Environment, and Geology (HLNUG).

It is vital to understand the mechanical properties of flowing ice to model the dynamics of ice sheets and ice shelves and to predict their behaviour in the future. We can increase our understanding of ice physical properties by performing deformation experiments on ice in laboratories and examining its mechanical and microstructural responses. However, natural conditions in ice sheets and ice shelves extend to low temperatures (≪-10 ∘C), and high octahedral strains (> 0.08), and emulating these conditions in laboratory experiments can take an impractically long time. It is possible to accelerate an experiment by running it at a higher temperature in the early stages and then lowering the temperature to meet the target conditions once the tertiary creep stage is reached. This can reduce total experiment run-time by > 1000 h; however it is not known whether this could affect the final strain rate or microstructure of the ice and potentially introduce a bias into the data. We deformed polycrystalline ice samples in uniaxial compression at −2 ∘C before lowering the temperature to either −7 or −10 ∘C, and we compared the results to constant-temperature experiments. Tertiary strain rates adjusted to the change in temperature very quickly (within 3 % of the total experiment run-time), with no significant deviation from strain rates measured in constant-temperature experiments. In experiments with a smaller temperature step (−2 to −7 ∘C) there is no observable difference in the final microstructure between changing-temperature and constant-temperature experiments which could introduce a bias into experimental results. For experiments with a larger temperature step (−2 to −10 ∘C), there are quantifiable differences in the microstructure. These differences are related to different recrystallisation mechanisms active at −10 ∘C, which are not as active when the first stages of the experiment are performed at −2 ∘C. For studies in which the main aim is obtaining tertiary strain rate data, we propose that a mid-experiment temperature change is a viable method for reducing the time taken to run low-stress and low-temperature experiments in the laboratory.

Microplastic particles, as a second-phase material in ice, may contribute to the effect such particles have on the melting and rheological behaviour of glaciers, and thus influence the future meltwater contribution to the oceans and rising sea levels. Hence, it is of the utmost importance to map and understand the presence and dispersal of microplastics on a global scale. In this work, we identified microplastic particles in snow cores collected in a remote and pristine location on the Vatnajökull ice cap in Iceland. Utilising optical microscopy and µ-Raman spectroscopy, we visualised and identified microplastic particles of various sizes and materials. Our findings support that atmospheric transport of microplastic particles is one of the important pathways for microplastic pollution.

Gneiss domes occur in a wide variety of orogenic and anorogenic domains of the continental crust, and play a major role in lithosphere dynamics by allowing upwards transfer of heat and mass. They commonly contain a core of granites and/or migmatites, overlain by a mantle of lower-grade rocks. Evolutionary models of many gneiss domes are controversial. Here we use new structural and zircon isotopic data to unravel the tectono-magmatic evolution of the Yalgoo dome and surroundings, at the margins of the Neoarchean Yilgarn Orogen, Western Australia. The study area includes at least seven granite-migmatite domes (5-70 km in average diameter), and several subdomes within the larger domes, all showing comparable structural features and age. In each dome, a concentric domal foliation is concordant with granite-greenstone contacts, bearing a radial, outward-plunging lineation. The bulk of the structures in each dome reflect magmatic flow, with pervasive subsolidus fabrics occurring only along the outer dome margins, and reflecting dome-up kinematics. Narrow greenstone keels pinched between domes and subdomes display vertical constriction, in an area regionally dominated by flattening along the steep sides of the deeply-eroded domes, and along the flat-laying dome roofs. The regional structural pattern and the kinematics of the high-strain zones are best explained by sequential emplacement of nested diapirs, which delivered large volumes of granitic magma in a c. 20 Myr time-span. The dome-and-keel regional architecture and the internal structures of each dome resulted therefore from multiscale polydiapirism. These diapirs were later weakly overprinted by a tectonic fabric that developed during the Neoarchean Yilgarn Orogeny. The contrast between the Yalgoo region and the rest of the craton, which was strongly reworked by this orogeny, highlights the dichotomy of tectonic styles in Archean terranes, demonstrating that diapirism dominated in times of tectonic quiescence.

Positive feedback mechanisms between magmatism and transpression allow efficient extraction, transfer, and delivery of synorogenic granitic magma. Although many Archean orogens are dominantly transpressional and record voluminous production of synorogenic granites, the role of crustal magmatism in Archean tectonics has been so far little explored. We detail here the structural evolution of the Ballard shear zone, a major synorogenic, inclined transpressional shear zone from the upper‐crustal granite‐greenstone system of the Neoarchean Yilgarn Orogen (Western Australia). We show that the bulk of the three‐dimensional deformation was efficiently partitioned between greenstones and crystallizing granitic sheets, with the latter accommodating large amounts of orogen‐parallel strain through hypersolidus viscous flow. Other large synorogenic Yilgarn shear zones show a similar structural evolution, allowing the formulation of a general tectonomagmatic model. The positive feedback between protracted magmatism and transpression promoted lower‐ to middle‐crustal extraction and upward transfer of syntectonic magma. In upper‐crustal sink regions, the rheological dichotomy between cold and strong greenstones and hot and weak sheets of crystallizing granite allowed efficient kinematic partitioning, resulting in the extrusion of the partially molten shear zone cores. This sequence of events occurred repeatedly throughout the orogeny, following magma pulses, with the bulk of the shearing along each shear zone waning with the cooling of each syntectonic pluton. Synorogenic magmatism played therefore a major role in promoting and localizing transpressional deformation, and ultimately in shaping the architecture of the whole Yilgarn orogen.