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  • 2020-2024  (167,818)
  • 2015-2019  (4,201,951)
  • 1980-1984  (1,016,749)
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  • 1
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    Ice sheet–free West Antarctica during peak early Oligocene glaciation (2024)
    American Association for the Advancement of Science (AAAS)
    In:  EPIC3Science, American Association for the Advancement of Science (AAAS), ISSN: 0036-8075
    Details
    Publication Date: 2024-07-08
    Description: One of Earth’s most fundamental climate shifts – the greenhouse-icehouse transition 34 Ma ago – initiated Antarctic ice-sheet build-up, influencing global climate until today. However, the extent of the ice sheet during the Early Oligocene Glacial Maximum (~33.7–33.2 Ma) that immediately followed this transition, a critical knowledge gap for assessing feedbacks between permanently glaciated areas and early Cenozoic global climate reorganization, is uncertain. Here, we present shallow-marine drilling data constraining earliest Oligocene environmental conditions on West Antarctica’s Pacific margin – a key region for understanding Antarctic ice sheet-evolution. These data indicate a cool-temperate environment, with mild ocean and air temperatures preventing West Antarctic Ice Sheet formation. Climate-ice sheet modeling corroborates a highly asymmetric Antarctic ice sheet, thereby revealing its differential regional response to past and future climatic change.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 2
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    SEISMONOISY: A Quasi-Real-Time Seismic Noise Network Monitoring System (2024)
    MDPI
    Details
    Publication Date: 2024-07-08
    Description: This paper introduces SEISMONOISY, an application designed for monitoring the spatiotemporal characteristic and variability of the seismic noise of an entire seismic network with a quasi-real-time monitoring approach. Actually, we have applied the developed system to monitor 12 seismic networks distributed throughout the Italian territory. These networks include the Rete Sismica Nazionale (RSN) as well as other regional networks with smaller coverage areas. Our noise monitoring system uses the methods of Spectral Power Density (PSD) and Probability Density Function (PDF) applied to 12 h long seismic traces in a 24 h cycle for each station, enabling the extrapolation of noise characteristics at seismic stations after a Seismic Noise Level Index (SNLI), which takes into account the global seismic noise model, is derived. The SNLI value can be used for different applications, including network performance evaluation, the identification of operational problems, site selection for new installations, and for scientific research applications (e.g., volcano monitoring, identification of active seismic sequences, etc.). Additionally, it aids in studying the main noise sources across different frequency bands and changes in the characteristics of background seismic noise over time.
    Description: Published
    Description: 3474
    Description: JCR Journal
    Keywords: background seismic noise level; real time monitoring; seismic noise; seismic noise trend; seismology
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 3
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    Transfer of Papua New Guinea’s Gleichenia hooglandii to Sticherus (Gleicheniaceae) (2018)
    In:  Blumea: Biodiversity, Evolution and Biogeography of Plants vol. 63, pp. 120-120
    Details
    Publication Date: 2024-07-08
    Description: Based on its morphology and in accordance with modern circumscriptions of genera among the Gleicheniaceae, a new combination in Sticherus is made for the Papua New Guinean fern originally described as Gleichenia hooglandii.
    Keywords: Gleichenia ; Gleicheniaceae ; Papua New Guinea ; Sticherus ; taxonomy
    Repository Name: National Museum of Natural History, Netherlands
    Type: info:eu-repo/semantics/article
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  • 4
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    Relating normal stiffness to permeability of a deformed self-affine rough fracture using its geometric properties (2024)
    In:  Journal of Rock Mechanics and Geotechnical Engineering
    Details
    Publication Date: 2024-07-08
    Description: In subsurface projects where the host rock is of low permeability, fractures play an important role in fluid circulation. Both the geometrical and mechanical properties of the fracture are relevant to the perme- ability of the fracture. To evaluate this relationship, we numerically generated self-affine fractures reproducing the scaling relationship of the power spectral density (PSD) of the measured fracture sur- faces. The fractures were then subjected to a uniform and stepwise increase in normal stress. A fast Fourier transform (FFT)-based elastic contact model was used to simulate the fracture closure. The evolution of fracture contact area, fracture closure, and fracture normal stiffness were determined throughout the whole process. In addition, the fracture permeability at each step was calculated by the local cubic law (LCL). The influences of roughness exponent and correlation length on the fracture hy- draulic and mechanical behaviors were investigated. Based on the power law of normal stiffness versus normal stress, the corrected cubic law and the linear relationship between fracture closure and me- chanical aperture were obtained from numerical modeling of a set of fractures. Then, we derived a fracture normal stiffness-permeability equation which incorporates fracture geometric parameters such as the root-mean-square (RMS), roughness exponent, and correlation length, which can describe the fracture flow under an effective medium regime and a percolation regime. Finally, we interpreted the flow transition behavior from the effective medium regime to the percolation regime during fracture closure with the established stiffness-permeability function.
    Type: info:eu-repo/semantics/article
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  • 5
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    Stability Of Magnesite In The Presence Of Hydrous Fluids Up To 12 Gpa: Insights Into Subduction Zone Processes And Carbon Cycling In The Earth’s Mantle (2024)
    In:  American Mineralogist
    Details
    Publication Date: 2024-07-08
    Description: Understanding the stability of magnesite in the presence of a hydrous fluid in the Earth’s upper mantle is crucial for modelling the carbon budget and cycle in the deep Earth. This study elucidates the behavior of magnesite in the presence of hydrous fluids. We examined the brucite magnesite (Mg(OH)2-MgCO3) system between 1 and 12 GPa by using synchrotron in situ energy dispersive X-ray diffraction experiments combined with textural observations from quenched experiments employing the falling sphere method. By subjecting magnesite to varying pressure-temperature conditions with controlled fluid proportion, we determined the stability limits of magnesite in the presence of a fluid and periclase. The observed liquidus provides insights into the fate of magnesite-bearing rocks in subduction zones. Our findings show that magnesite remains stable under typical subduction zone gradients even when infiltrated by hydrous fluids released from dehydration reactions during subduction. We conclude that magnesite can be subducted down to and beyond sub-arc depths. Consequently, our results have important implications for the carbon budget of the Earth’s mantle and its role in regulating atmospheric CO2 levels over geological timescales.
    Language: English
    Type: info:eu-repo/semantics/article
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  • 6
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    Climatic pacing of extreme Nile floods during the North African Humid Period (2024)
    In:  Nature Geoscience
    Details
    Publication Date: 2024-07-08
    Description: Understanding how large river systems will respond to an invigorated hydrological cycle as simulated under higher global temperatures is a pressing issue. Insights can be gained from studying past wetter-than-present intervals, such as the North African Humid Period during the early Holocene Epoch (~11–6 thousand years ago). Here we present a 1,500-year-long annually laminated (varved) offshore sediment record that tracks the seasonal discharge of the Nile River during the North African Humid Period. The record reveals mobilization of large amounts of sediments during strong summer floods that may have rendered the Nile valley uninhabitable. More frequent and rapid transitions between extremely strong and weak floods between 9.2 and 8.6 thousand years ago indicate highly instable fluvial dynamics. Climate simulations suggest flood variability was paced by El Niño/Southern Oscillation on interannual timescales, while multi-decadal oscillatory modes drove changes in extreme flood events. These pacemakers have also been identified in the Nile flow records from the Common Era, which implies their stationarity under contrasting hydroclimatic conditions.
    Type: info:eu-repo/semantics/article
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  • 7
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    Long-read based hybrid genome assembly and annotation of snow algal strain CCCryo 101-99 (cf. Sphaerocystis sp., Chlamydomonadales) (2024)
    In:  Genome Biology and Evolution
    Details
    Publication Date: 2024-07-08
    Description: Polar regions harbor a diversity of cold-adapted (cryophilic) algae, which can be categorized into psychrophilic (obligate cryophilic) and cryotrophic (non-obligate cryophilic) snow algae. Both can accumulate significant biomasses on glacier and snow habitats and play major roles in global climate dynamics. Despite their significance, genomic studies on these organisms remain scarce, hindering our understanding of their evolutionary history and adaptive mechanisms in the face of climate change. Here, we present the draft genome assembly and annotation of the psychrophilic snow algal strain CCCryo 101-99 (cf. Sphaerocystis sp.). The draft haploid genome assembly is 122.5 Mb in length and is represented by 664 contigs with an N50 of 0.86 Mb, a Benchmarking Universal Single-Copy Orthologs (BUSCO) completeness of 92.9% (n = 1519), a maximum contig length of 5.3 Mb, and a GC content of 53.1%. In total, 28.98% of the genome (35.5 Mb) contains repetitive elements. We identified 417 non-coding RNAs (ncRNAs) and annotated the chloroplast genome. The predicted proteome comprises 14,805 genes with a BUSCO completeness of 97.8%. Our preliminary analyses reveal a genome with a higher repeat content compared to mesophilic chlorophyte relatives, alongside enrichment in gene families associated with photosynthesis and flagella functions. Our current data will facilitate future comparative studies, improving our understanding of the likely response of polar algae to a warming climate as well as their evolutionary trajectories in permanently cold environments.
    Language: English
    Type: info:eu-repo/semantics/article
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  • 8
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    Performance of AI-Based Phase Picking and Event Association Methods after the Large 2023 Mw 7.8 and 7.6 Türkiye Doublet (2024)
    In:  Bulletin of the Seismological Society of America
    Details
    Publication Date: 2024-07-08
    Description: On 6 February 2023, a devastating earthquake doublet consisting of 7.8 and 7.6 events separated by about 9 hr struck the southeastern part of Türkiye. The developing aftershock sequence contained thousands of events during the first few days and overwhelmed the routine algorithms handling their detection and location. In addition, several stations temporarily lost real‐time contact and came online again later. At the same time the Omori decay of the aftershock event rate reduced the event frequency and allowed for inclusion of progressively smaller‐magnitude events with time. One possibility to help deal with such a complex situation is the use of machine learning (ML) methods to generate earthquake catalogs with a substantially higher number of events. Here, we present high‐resolution earthquake catalogs derived with two ML association methods for the first five days of the aftershock sequence of this doublet. In terms of the number of reliably located events, the event catalog created from PhaseNet picks and the GENIE phase association method outperforms both the routine regional catalog and the second ML‐derived catalog obtained from the GaMMA phase association method. Although both GaMMA and GENIE catalogs detect about 6 times more events than the routine catalog, GENIE associates on average about double the phases to a single event than GaMMA, which results in better constrained event locations. The spatiotemporal evolution of the event rates is sensitive to changes in the network geometry due to variable station availability. During the first few days, no decay of the event rate in the enhanced catalog is observed due to the inclusion of progressively smaller‐magnitude events with time and increased station availability. This study indicates that ML‐derived earthquake catalogs for challenging time periods like the early aftershock sequences of large earthquakes have the potential to significantly improve routine event catalogs.
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  • 9
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    Vibration Monitoring of the Rock Formation Above the Hatshepsut Temple (2024)
    In:  Proceedings - Special Issue of e-Journal of Nondestructive Testing (eJNDT)
    Details
    Publication Date: 2024-07-08
    Description: The Hatshepsut temple in Egypt is a masterpiece of ancient architecture. Just as distinct as the temple itself is the rock formation it is carved into, and recurring rock falls in the vicinity have raised concerns regarding the temple’s safety under progressing erosion and seismic activity. Due to the material characteristics (brittle carbonate rock), high stresses could lead to rapid crack propagation, and vibra-tion-based measures may be suitable precursors for imminent rock falls. This paper describes a two-day measurement campaign on the rock towers as a preliminary study prior to the implementation of a long-term seismic station. Next to operational modal analysis, horizontal-to-vertical spectral ratios, and standard spectral ratios are evaluated to cross-validate the resonance behaviour. To the author’s knowledge, this is the first study where stochastic subspace identification (SSI) is applied for the estimation and automated tracking of natural frequencies, mode shapes, and damping ratios in rock formations. One of the advantages of this method is the inherent uncertainty quantification, meaning for each vibration record, the mean values and the standard deviations are estimated for each modal parameter, giving deep insights into the reliability of the vibration-based monitoring of rock formations.
    Type: info:eu-repo/semantics/conferenceObject
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  • 10
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    Significance of conodont data for explaining geosystem perturbations during the Middle Devonian Kačák Episode (2023)
    In:  Marine Micropaleontology
    Details
    Publication Date: 2024-07-08
    Description: The present review of published data as well as the new results demonstrate the versatility of conodonts in documenting and explaining global environmental fluctuations related to the Kačák Episode (KE) in the latest Eifelian. Although the conodont zonation of the KE interval is ambiguous and requires revision, the compilation of conodont stratigraphic ranges shows their potential for a precise worldwide correlation of relevant marine strata. Conodont biofacies may serve to document environmental changes connected with KE, in particular the sealevel rise at its beginning, followed by a regressive trend. Nevertheless, the familiar Icriodus/Polygnathus ratio should be carefully applied as an indication of water depth and nearshore vs. offshore position, being controlled also by other factors, such as paleolatitude and/or climate. Oxygen isotopes in conodont apatite, studied using secondary ion mass spectrometry technique evidence a warming at the onset of KE, based on the new data from the open marine facies of the Prague Basin. At the same time, they indicated climate-controlled salinity fluctuations in the epeiric Belarusian Basin. The present investigations as well as previous results suggest caution when analyzing thermally altered conodonts which may result in biased oxygen isotope signatures. The present experience suggests the conodont colour alteration index CAI 3 as a boundary value above which the caution is necessary.
    Language: English
    Type: info:eu-repo/semantics/article
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