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  • CITATION GEO-LEO  (335)
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  • 1
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    The Global Seismic Moment Rate of Mars After Event S1222a (2023)
    Details
    Publication Date: 2023-07-20
    Description: The seismic activity of a planet can be described by the corner magnitude, events larger than which are extremely unlikely, and the seismic moment rate, the long‐term average of annual seismic moment release. Marsquake S1222a proves large enough to be representative of the global activity of Mars and places observational constraints on the moment rate. The magnitude‐frequency distribution of relevant Marsquakes indicates a $b$‐value of 1.06. The moment rate is likely between $1.55\times {10}^{15}\mathrm{N}\mathrm{m}/\mathrm{a}$ and $1.97\times {10}^{18}\mathrm{N}\mathrm{m}/\mathrm{a}$, with a marginal distribution peaking at $4.9\times {10}^{16}\mathrm{N}\mathrm{m}/\mathrm{a}$. Comparing this with pre‐InSight estimations shows that these tended to overestimate the moment rate, and that 30% or more of the tectonic deformation may occur silently, whereas the seismicity is probably restricted to localized centers rather than spread over the entire planet.
    Description: Plain Language Summary: The seismic moment rate is a measure for how fast quakes accumulate deformation of the planet's rigid outer layer, the lithosphere. In the past decades, several models for the deformation rate of Mars were developed either from the traces quakes leave on the surface, or from mathematical models of how quickly the planet's interior cools down and shrinks. The large marsquake that occurred on the 4th of May 2022 now allows a statistical estimation of the deformation accumulated on Mars per year, and thus to confront these models with reality. It turns out that, although there is a considerable overlap, the models published prior to InSight tend to overestimate the seismic moment rate, and hence the ongoing deformation on Mars. Possible explanations are that 30% or more of the deformation occurs silently, that is, without causing quakes, or that not the entire planet is seismically active but only specific regions.
    Description: Key Points: A single large marsquake suffices to constrain the global seismic moment rate. Pre‐InSight estimations tended to overestimate the moment rate. Either a significant part of the ongoing deformation occurs silent, or seismic activity is restricted to some activity centers, or both.
    Description: Eidgenössische Technische Hochschule Zürich http://dx.doi.org/10.13039/501100003006
    Description: National Aeronautics and Space Administration http://dx.doi.org/10.13039/100000104
    Description: UK Space Agency http://dx.doi.org/10.13039/100011690
    Description: Deutsches Zentrum für Luft‐ und Raumfahrt http://dx.doi.org/10.13039/501100002946
    Description: Insight SFI Research Centre for Data Analytics http://dx.doi.org/10.13039/501100021525
    Description: http://dx.doi.org/10.18715/SEIS.INSIGHT.XB_2016
    Description: http://doi.org/10.17189/1517570
    Keywords: ddc:523 ; Mars ; InSight ; seismic moment rate ; S1222a
    Language: English
    Type: doc-type:article
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  • 2
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    Novel experimental setup for megahertz X‐ray diffraction in a diamond anvil cell at the High Energy Density (HED) instrument of the European X‐ray Free‐Electron Laser (EuXFEL) (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2021-06-26
    Description: The high‐precision X‐ray diffraction setup for work with diamond anvil cells (DACs) in interaction chamber 2 (IC2) of the High Energy Density instrument of the European X‐ray Free‐Electron Laser is described. This includes beamline optics, sample positioning and detector systems located in the multipurpose vacuum chamber. Concepts for pump–probe X‐ray diffraction experiments in the DAC are described and their implementation demonstrated during the First User Community Assisted Commissioning experiment. X‐ray heating and diffraction of Bi under pressure, obtained using 20 fs X‐ray pulses at 17.8 keV and 2.2 MHz repetition, is illustrated through splitting of diffraction peaks, and interpreted employing finite element modeling of the sample chamber in the DAC.
    Description: The high‐precision X‐ray diffraction (XRD) setup for work with diamond anvil cells (DACs) in Interaction Chamber 2 of the High Energy Density (HED) instrument of the European X‐ray Free‐Electron Laser is described. image
    Keywords: 548 ; diamond anvil cells ; X‐ray free‐electron lasers ; high‐precision X‐ray diffraction ; finite element modeling
    Type: article
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  • 3
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    Climate Change and Weather Extremes in the Eastern Mediterranean and Middle East (2022)
    Details
    Publication Date: 2022-10-13
    Description: Observation‐based and modeling studies have identified the Eastern Mediterranean and Middle East (EMME) region as a prominent climate change hotspot. While several initiatives have addressed the impacts of climate change in parts of the EMME, here we present an updated assessment, covering a wide range of timescales, phenomena and future pathways. Our assessment is based on a revised analysis of recent observations and projections and an extensive overview of the recent scientific literature on the causes and effects of regional climate change. Greenhouse gas emissions in the EMME are growing rapidly, surpassing those of the European Union, hence contributing significantly to climate change. Over the past half‐century and especially during recent decades, the EMME has warmed significantly faster than other inhabited regions. At the same time, changes in the hydrological cycle have become evident. The observed recent temperature increase of about 0.45°C per decade is projected to continue, although strong global greenhouse gas emission reductions could moderate this trend. In addition to projected changes in mean climate conditions, we call attention to extreme weather events with potentially disruptive societal impacts. These include the strongly increasing severity and duration of heatwaves, droughts and dust storms, as well as torrential rain events that can trigger flash floods. Our review is complemented by a discussion of atmospheric pollution and land‐use change in the region, including urbanization, desertification and forest fires. Finally, we identify sectors that may be critically affected and formulate adaptation and research recommendations toward greater resilience of the EMME region to climate change.
    Description: Key Points: The Eastern Mediterranean and Middle East is warming almost two times faster than the global average and other inhabited parts of the world. Climate projections indicate a future warming, strongest in summers. Precipitation will likely decrease, particularly in the Mediterranean. Virtually all socio‐economic sectors will be critically affected by the projected changes.
    Description: European Union Horizon 2020
    Description: https://esg-dn1.nsc.liu.se/search/esgf-liu/
    Keywords: ddc:551.6
    Language: English
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  • 4
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    Studying the Global Spatial Randomness of Impact Craters on Mercury, Venus, and the Moon With Geodesic Neighborhood Relationships (2021)
    Details
    Publication Date: 2021-07-21
    Description: Impact crater records on planetary surfaces are often analyzed for their spatial randomness. Generalized approaches such as the mean second closest neighbor distance (M2CND) and standard deviation of adjacent area (SDAA) are available via a software tool but do not take the influence of the planetary curvature into account in the current implementation. As a result, the measurements are affected by map distortion effects and can lead to wrong interpretations. This is particularly critical for investigations of global data sets as the level of distortion typically increases with increasing distance from the map projection center. Therefore, we present geodesic solutions to the M2CND and SDAA statistics that can be implemented in future software tools. We apply the improved methods to conduct spatial randomness analyses on global crater data sets on Mercury, Venus, and the Moon and compare the results to known crater population variations and surface evolution scenarios. On Mercury, we find that the emplacement of smooth plain deposits strongly contributed to a global clustering of craters and that a random distribution of Mercury's basins is not rejected. On Venus, the randomness analyses show that craters are largely randomly distributed across all sizes but where local nonrandom distributions due to lower crater densities in regions of recent volcanic activity may appear. On the Moon, the global clustering of craters is more pronounced than on Mercury due to mare volcanism and the Orientale impact event. Furthermore, a random distribution of lunar basins is not rejected.
    Description: Plain Language Summary: The arrangement of craters on a planetary surface can be random or nonrandom. A nonrandom arrangement, such as clustered or ordered, can indicate geologic or cratering‐related processes. There are generalized approaches to quantify the arrangement of craters available via a software tool. The randomness calculations in this tool rely on the spatial relationships between craters and are determined in a two‐dimensional map projection. This is problematic because two‐dimensional representations do not take the influence of a curved planetary surface into account. Thus, measuring the spatial arrangement of craters is prone to errors. We revise the given approaches by implementing improved computations and measure the global spatial arrangement of craters on Mercury, Venus, and the Moon. On Mercury, we observe that the smooth plains' emplacement largely causes global clustering and that the distribution of basins cannot be distinguished from a random population. On Venus, craters across all sizes are largely in a random arrangement. However, nonrandomly distributed populations may occur due to local volcanic activity. On the Moon, we observe that the emplacement of lunar maria and the Orientale impact strongly influenced the global clustering of craters. Furthermore, the arrangement of lunar basins is similar to a random distribution.
    Description: Key Points: We improve approaches to quantify the spatial randomness of impact craters by applying geodesic methods. We apply these methods to analyze the global spatial randomness of impact crater populations on Mercury, Venus, and the Moon. We use the results to investigate known crater population variations and surface evolution scenarios on Mercury, Venus, and the Moon.
    Description: Deutsche Forschungsgemeinschaft (DFG) http://dx.doi.org/10.13039/501100001659
    Description: Deutsches Zentrum für Luft‐ und Raumfahrt (DLR) http://dx.doi.org/10.13039/501100002946
    Keywords: 523 ; cratering ; Mercury ; Moon ; planetary data ; spatial statistics ; Venus
    Type: article
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  • 5
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    Vesicle shrinkage in hydrous phonolitic melt during cooling (2020)
    Springer Berlin Heidelberg
    Details
    Publication Date: 2023-06-23
    Description: The ascent of hydrous magma prior to volcanic eruptions is largely driven by the formation of H2O vesicles and their subsequent growth upon further decompression. Porosity controls buoyancy as well as vesicle coalescence and percolation, and is important when identifying the differences between equilibrium or disequilibrium degassing from textural analysis of eruptive products. Decompression experiments are routinely used to simulate magma ascent. Samples exposed to high temperature (T) and pressure (P) are decompressed and rapidly cooled to ambient T for analysis. During cooling, fluid vesicles may shrink due to decrease of the molar volume of H2O and by resorption of H2O back into the melt driven by solubility increase with decreasing T at P 〈 300 MPa. Here, we quantify the extent to which vesicles shrink during cooling, using a series of decompression experiments with hydrous phonolitic melt (5.3–3.3 wt% H2O, T between 1323 and 1373 K, decompressed from 200 to 110–20 MPa). Most samples degassed at near-equilibrium conditions during decompression. However, the porosities of quenched samples are significantly lower than expected equilibrium porosities prior to cooling. At a cooling rate of 44 K·s−1, the fictive temperature Tf, where vesicle shrinkage stops, is up to 200 K above the glass transition temperature (Tg), Furthermore, decreasing cooling rate enhances vesicles shrinkage. We assess the implications of these findings on previous experimental degassing studies using phonolitic melt, and highlight the importance of correctly interpreting experimental porosity data, before any comparison to natural volcanic ejecta can be attempted.
    Description: German Science Foundation
    Keywords: ddc:550.78 ; Decompression experiments ; Vesiculation ; Vesicle shrinkage ; Quench effect ; H2O resorption ; Fictive temperature
    Language: English
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  • 6
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    Observing Earth’s magnetic environment with the GRACE-FO mission (2021)
    Stolle, C. ; Michaelis, I. ; Xiong, C. ; [et al.]
    Springer Berlin Heidelberg
    Details
    Publication Date: 2023-06-21
    Description: The Gravity Recovery and Climate Experiment Follow-On (GRACE-FO) mission carries magnetometers that are dedicated to enhance the satellite’s navigation. After appropriate calibration and characterisation of artificial magnetic disturbances, these observations are valuable assets to characterise the natural variability of Earth’s magnetic field. We describe the data pre-processing, the calibration, and characterisation strategy against a high-precision magnetic field model applied to the GRACE-FO magnetic data. During times of geomagnetic quiet conditions, the mean residual to the magnetic model is around 1 nT with standard deviations below 10 nT. The mean difference to data of ESA’s Swarm mission, which is dedicated to monitor the Earth’s magnetic field, is mainly within ± 10 nT during conjunctions. The performance of GRACE-FO magnetic data is further discussed on selected scientific examples. During a magnetic storm event in August 2018, GRACE-FO reveals the local time dependence of the magnetospheric ring current signature, which is in good agreement with results from a network of ground magnetic observations. Also, derived field-aligned currents (FACs) are applied to monitor auroral FACs that compare well in amplitude and statistical behaviour for local time, hemisphere, and solar wind conditions to approved earlier findings from other missions including Swarm. On a case event, it is demonstrated that the dual-satellite constellation of GRACE-FO is most suitable to derive the persistence of auroral FACs with scale lengths of 180 km or longer. Due to a relatively larger noise level compared to dedicated magnetic missions, GRACE-FO is especially suitable for high-amplitude event studies. However, GRACE-FO is also sensitive to ionospheric signatures even below the noise level within statistical approaches. The combination with data of dedicated magnetic field missions and other missions carrying non-dedicated magnetometers greatly enhances related scientific perspectives.
    Description: European Space Agency (FR)
    Description: HEIBRIDS
    Description: Projekt DEAL
    Description: ftp://isdcftp.gfz-potsdam.de/grace-fo/MAGNETIC_FIELD
    Keywords: ddc:538.7 ; Earth’s magnetic field ; Geomagnetism ; Ionospheric currents ; Magnetospheric ring current ; Satellite-based magnetometers ; Platform magnetometers ; GRACE-FO
    Language: English
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  • 7
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    The Sensitivity of Moisture Flux Partitioning in the Cold‐Point Tropopause to External Forcing (2023)
    Details
    Publication Date: 2023-07-20
    Description: 〈title xmlns:mml="http://www.w3.org/1998/Math/MathML"〉Abstract〈/title〉〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉The dryness of the stratosphere is the result of air entering through the cold tropical tropopause layer (TTL). However, our understanding of the moisture flux partitioning into water vapor and frozen hydrometeors is incomplete. This raises concerns regarding the ability of General Circulation Models to accurately predict changes in stratospheric water vapor following perturbations in the radiative budget due to volcanic aerosol or stratospheric geoengineering. We present the first results using a global storm‐resolving model investigating the sensitivity of moisture fluxes within the TTL to an additional heating source. We address the question how the partitioning of moisture fluxes into water vapor and frozen hydrometeors changes under perturbations. The analysis reveals the resilience of the TTL, keeping the flux partitioning constant even at an average cold‐point warming exceeding 8 K. In the control and perturbed simulations, water vapor contributes around 80% of the moisture entering the stratosphere.〈/p〉
    Description: Plain Language Summary: The stratosphere is a dry region since moisture entering it from below has to pass the cold‐point, a temperature minimum between troposphere and stratosphere. The low temperatures lead to ice formation and sedimentation of moisture. Frozen moisture within clouds rising above the cold‐point tropopause can pass this temperature barrier and be injected into the stratosphere, where temperatures increase again, promoting the melting and sublimation of ice crystals. However, little is known about the sensitivity of the split of moisture entering the stratosphere into frozen and non‐frozen moisture, especially under external influences, like heating by volcanic aerosol or stratospheric geoengineering efforts. Convective parameterizations in conventional simulations can lead to biases. The emerging km‐scale simulations, which explicitly resolve the physical processes, offer the unique possibility to study moisture fluxes under external forcing while circumventing the downsides of parameterizations. Here, the sensitivity of the moisture flux partitioning into non‐frozen and frozen components to an additional heating source is studied for the first time in global storm‐resolving simulations. The analysis reveals an unaltered flux partitioning even at an average cold‐point warming exceeding 8 K. In the control and perturbed simulations, water vapor contributes around 80% of the moisture entering the stratosphere.〈/p〉
    Description: Key Points:Water vapor dominates the stratospheric moisture budget with a contribution of around 80% in global storm‐resolving simulation. The partitioning of stratospheric moisture fluxes into vapor and frozen hydrometeors remains stable under large temperature perturbations.
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: Bundesministerium für Bildung und Forschung http://dx.doi.org/10.13039/501100002347
    Description: Fueglistaler Group
    Keywords: ddc:551.5 ; stratospheric water vapor ; tropopause ; perturbation ; moisture budget ; geoengineering ; volcano
    Language: English
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  • 8
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    Spontaneously Exsolved Free Gas During Major Storms as an Ephemeral Gas Source for Pockmark Formation (2022)
    Details
    Publication Date: 2023-01-27
    Description: Abrupt fluid emissions from shallow marine sediments pose a threat to seafloor installations like wind farms and offshore cables. Quantifying such fluid emissions and linking pockmarks, the seafloor manifestations of fluid escape, to flow in the sub‐seafloor remains notoriously difficult due to an incomplete understanding of the underlying physical processes. Here, using a compositional multi‐phase flow model, we test plausible gas sources for pockmarks in the south‐eastern North Sea, which recent observations suggest have formed in response to major storms. We find that the mobilization of pre‐existing gas pockets is unlikely because free gas, due to its high compressibility, damps the propagation of storm‐induced pressure changes deeper into the subsurface. Rather, our results point to spontaneous appearance of a free gas phase via storm‐induced gas exsolution from pore fluids. This mechanism is primarily driven by the pressure‐sensitivity of gas solubility, and the appearance of free gas is largely confined to sediments in the vicinity of the seafloor. We show that in highly permeable sediments containing gas‐rich pore fluids, wave‐induced pressure changes result in the appearance of a persistent gas phase. This suggests that seafloor fluid escape structures are not always proxies for overpressured shallow gas and that periodic seafloor pressure changes can induce persistent free gas phase to spontaneously appear.
    Description: Plain Language Summary: Thousands of pockmarks, circular depressions in the seafloor, were reported in North Sea, presumably formed in response to wave motions during major storms. It has been hypothesized that these pockmarks formed as pre‐existing shallow free‐gas pockets were mobilized by pressure changes of the waves. However, mechanisms that could have mobilized free‐gas are not yet constrained. Moreover, large scale free‐gas accumulations have not been reported in this region, and therefore, commonly invoked mechanisms like tensile failure and breaching of capillary seals are hard to justify as they rely on the presence of pre‐existing gas pockets. Here, through modeling studies, we tackle the question of the source of the observed free‐gas. Our study consists of two parts: First, assuming that some hitherto unknown shallow free‐gas pocket is indeed present, we test whether storm‐induced pressure changes could breach capillary seals. We find that free‐gas damps pressure changes due to its high compressibility, making the mobilization of pre‐existing gas unlikely. In the second part, we propose an alternative mechanism where free‐gas spontaneously appears due to exsolution from pore‐fluids. We test the feasibility of this mechanism and show how periodic pressure changes can lead to a persistent gas phase, that could explain the elusive gas source linked to these pockmarks.
    Description: Key Points: Storm‐induced pressure changes can lead to spontaneous appearance of free gas phase near the seafloor. This process is driven by pressure‐sensitive phase instabilities. This mechanism could help explain elusive gas sources in recently observed pockmarks in the North Sea.
    Description: Aker BP (AkerBP) http://dx.doi.org/10.13039/100016998
    Description: Deutsche Forschungsgemeinschaft, DFG
    Keywords: ddc:550 ; pockmarks ; storm related pockmarks ; spontaneous free gas ; gas source ; modeling
    Language: English
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  • 9
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    Lu–Hf geochronology of ultra-high-pressure eclogites from the Tromsø-Nappe, Scandinavian Caledonides: evidence for rapid subduction and exhumation (2020)
    Springer Berlin Heidelberg
    Details
    Publication Date: 2023-06-08
    Description: Geochronology of ultra-high-pressure metamorphic rocks is able to constrain the timing and rates of subduction-zone processes. Lu–Hf garnet dating has the potential to yield information about the timing of the prograde evolution of subducting rocks under increasing pressure. In combination with other methods, it thus allows constraining the complete P–T–t path with high precision. Ultra-high-pressure eclogites from the Tromsø Nappe, the structurally highest tectonic unit of the Scandinavian Caledonides in northern Norway, were dated using Lu–Hf geochronology on garnet. A sample from Tromsdalstind yielded an age of 448.3 ± 3.6 Ma, interpreted as dating prograde garnet growth due to preserved zoning in the major-element and Lu contents of garnet grains. A sample from the diamond-bearing locality Tønsvika yielded an identical age of 449.4 ± 3.3 Ma. Garnet from this sample shows a weak zoning in Ca content and near-homogeneous Lu content. These ages are identical within error among each other and with published U–Pb ages of peak-eclogite-facies zircon and rutile/titanite from exhumation-related leucosome veins. Consequently, the entire subduction–exhumation cycle leading to the ultra-high-pressure eclogites lasted only very few millions of years during the Late Ordovician.
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: Agentúra na Podporu Výskumu a Vývoja (SK)
    Keywords: ddc:552.4 ; Lu–Hf geochronology ; UHP metamorphism ; Garnet ; Scandinavian Caledonides ; Tromsø Nappe
    Language: English
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  • 10
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    Future-proofing hydrogeology by revising groundwater monitoring practice (2020)
    Rau, Gabriel C. ; Cuthbert, Mark O. ; Post, Vincent E. A. ; [et al.]
    Springer Berlin Heidelberg
    Details
    Publication Date: 2023-06-16
    Description: Groundwater is an important global resource and its sustainable use faces major challenges. New methods and advances in computational science could lead to much improved understanding of groundwater processes and subsurface properties. A closer look at current groundwater monitoring practice reveals the need for updates with a special focus on the benefits of high-frequency and high-resolution datasets. To future-proof hydrogeology, this technical note raises awareness about the necessity for improvement, provides initial recommendations and advocates for the development of universal guidelines.
    Description: European Commission http://dx.doi.org/10.13039/501100000780
    Keywords: ddc:551.49 ; Groundwater monitoring ; Equipment/field techniques ; High resolution ; High frequency ; Guidelines
    Language: English
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