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  • Wiley  (88,664)
  • Wiley-Blackwell  (43,084)
  • American Geophysical Union  (26,228)
  • Blackwell Publishing Ltd  (20,455)
  • American Association for the Advancement of Science (AAAS)
  • International Union of Crystallography
  • 2020-2022  (55,137)
  • 1980-1984  (144,266)
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  • 1
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    Millimeter wave spectroscopic measurements over the South Pole: 5. Morphology and evolution of HNO3vertical distribution, 1993 versus 1995 (2020)
    American Geophysical Union
    Details
    Publication Date: 2020-09-21
    Description: We compare differences and similarities in the annual stratospheric HNO3 cycle derived from ground‐based measurements at the South Pole during 1993 and 1995, after correcting an error in earlier published profile retrievals for 1993 which led to under estimation of mixing ratios. The data series presented here provide profiling over the range ∼16–48 km, and cover the fall‐winter‐spring cycle in the behavior of HNO3 in the extreme Antarctic with a large degree of temporal overlap. With the exception of one gap of 20 days, the combined data sets cover a full annual cycle. The record shows an increase in HNO3 above 30 km occurring about 20 days before sunset, which appears to be the result of higher altitude heterogeneous conversion of NOx as photolysis diminishes. Both years show a strong increase in HNO3 beginning about polar sunset, in a layer peaking at about 25 km, as additional NOx is heterogeneously converted to nitric acid. When temperatures drop to the polar stratospheric cloud (PSC) formation range near the end of May, gas phase HNO3 is rapidly reduced in the lower stratosphere, although at least 2–3 weeks of temperatures ≤192 K appear to be required to complete most of the gas‐phase removal at the upper end of the depletion range (22–25 km). Despite a significant difference in residual sulfate loading from the explosion of Mount Pinatubo, there appears to be little gross difference in the timing and effects of PSC formation in removing gas phase HNO3 in these 2 years, though removal may be more rapid in 1995. Incorporation of gas phase HNO3 into PSCs appears to be nearly complete up to ∼25 km by midwinter. We also see a repeat of the formation of gas phase HNO3 in the middle stratosphere in early midwinter of 1995 with about the same timing as in 1993, suggesting that this phenomenon is driven by a repetition of dynamical transport and appropriate temperatures and pressures in the polar night, and not (as has been suggested) by ion‐based heterogeneous chemistry that requires triggering by large relativistic electron fluxes. High‐altitude HNO3 production peaks during a period of ∼20 days, but appears to persist for up to ∼40 days in the 40–45 km range, ceasing well before sunrise. This HNO3 descends rapidly throughout the production period, at a rate in good agreement with theoretically determined midwinter subsidence rates. As noted in earlier studies, later warming of this region above PSC evaporation temperatures does not cause reappearance of large amounts of HNO3, indicating that most PSCs gravitationally sink out of the stratosphere before early spring. We present evidence that smaller PSCs do evaporate to ∼1 to 3.5 ppbv of HNO3 in the lower stratosphere, however, working downward from ∼25 km as temperatures rise during the late winter. There is a delay of ∼15 days after sunrise before photolysis causes significant depletion in the altitude range below ∼30 km, where subsidence has carried virtually all higher‐altitude HNO3 by polar sunrise. Some continued subsidence and photolysis combine to keep mixing ratios less than ∼5 ppbv below 30 km until the final breakdown of the vortex in November brings larger amounts of HNO3 with air from lower latitudes.
    Description: Published
    Description: 17739-17750
    Description: 5A. Ricerche polari e paleoclima
    Description: JCR Journal
    Keywords: ozone depletion ; HNO3 ; Antarctic stratosphere ; 01.01. Atmosphere
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 2
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    Advances in understanding large-scale responses of the water cycle to climate change (2020)
    Wiley
    Details
    Publication Date: 2020-12-22
    Description: Globally, thermodynamics explains an increase in atmospheric water vapor with warming of around 7%/°C near to the surface. In contrast, global precipitation and evaporation are constrained by the Earth's energy balance to increase at ∼2-3%/°C. However, this rate of increase is suppressed by rapid atmospheric adjustments in response to greenhouse gases and absorbing aerosols that directly alter the atmospheric energy budget. Rapid adjustments to forcings, cooling effects from scattering aerosol, and observational uncertainty can explain why observed global precipitation responses are currently difficult to detect but are expected to emerge and accelerate as warming increases and aerosol forcing diminishes. Precipitation increases with warming are expected to be smaller over land than ocean due to limitations on moisture convergence, exacerbated by feedbacks and affected by rapid adjustments. Thermodynamic increases in atmospheric moisture fluxes amplify wet and dry events, driving an intensification of precipitation extremes. The rate of intensification can deviate from a simple thermodynamic response due to in-storm and larger-scale feedback processes, while changes in large-scale dynamics and catchment characteristics further modulate the frequency of flooding in response to precipitation increases. Changes in atmospheric circulation in response to radiative forcing and evolving surface temperature patterns are capable of dominating water cycle changes in some regions. Moreover, the direct impact of human activities on the water cycle through water abstraction, irrigation, and land use change is already a significant component of regional water cycle change and is expected to further increase in importance as water demand grows with global population.
    Description: Published
    Description: 49-75
    Description: 4A. Oceanografia e clima
    Description: JCR Journal
    Keywords: climate change; land surface; precipitation; radiative forcing; water cycle
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 3
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    Physical and geochemical record of an early Eocene carbon‐cycle perturbation on a turbiditic continental margin (2021)
    Wiley
    Details
    Publication Date: 2021-01-20
    Description: Multivariate analysis of the elemental composition of hemipelagic sedimentary successions has provided invaluable information about palaeoenvironmental evolution, including records of short-lived Eocene hyperthermal events. However, few studies have analyzed the sedimentary record of these climatic events in turbidite-rich continental margin successions. In order to test the usefulness of multivariate statistical techniques (factor and cluster analysis) in palaeonvironmental and palaeoclimatic research on turbiditic successions, the lowermost Eocene Solondota section, which accumulated on the North Iberian continental margin, was studied. A prominent negative carbon isotope excursion from Solondota was correlated with the Ypresian (early Eocene) hyperthermal event J, also known as C24n.2rH1. High-resolution sedimentological, geochemical (stable isotopes, major and trace elements) and mineralogical (bulk and clay mineralogy) data show that multivariate statistical analysis helps to manage large-sized quantitative datasets objectively, avoiding arbitrary choice of representative elements and identifying environmental factors (virtual variables) that may not be evident otherwise. Variations in major and minor elements from hemipelagic carbonates across the Solondota carbon isotope excursion suggest a temporarily more humid continental climate, which caused increased terrigenous material input into the marine environment. The finer grained fraction boosted hemipelagic carbonate dilution, whereas the coarser grained sediment was transported by temporarily more frequent and voluminous turbidity currents. Thus, the results from the Solondota carbon isotope excursion revealed similarities with deep marine records of other early Eocene minor hyperthermal events. This demonstrates the validity of deep-marine turbiditic successions for providing reliable sedimentological, mineralogical and geochemical records of global palaeoclimatic significance, complementing the information obtained from other sedimentary environments. Furthermore, the generally expanded nature of turbiditic successions can potentially provide palaeoclimatic information at very high resolution, enriching, and perhaps improving, the commonly condensed and sometimes discontinuous record of hemipelagic- only successions.
    Description: Published
    Description: 881-904
    Description: 1A. Geomagnetismo e Paleomagnetismo
    Description: JCR Journal
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 4
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    A minimum time control problem for aerobic degradation processes in biocell composting plants (2021)
    Wiley
    Details
    Publication Date: 2021-05-12
    Description: We introduce a mathematical model for the composting process in biocells. The model includes several phenomena, like the aerobic biodegradation of the soluble substrate by means of a bacterial population, the hydrolysis of insoluble substrate, and the biomass decay. We investigate the best strategies to reduce substrate components in minimal time by controlling the effects of cell oxygen concentration on the degradation phenomenon. It is shown that singular controls are not optimal for this model and the optimal control time profiles are of bang or bang-bang type. The occurrence of switching curves is discussed. In the case of a bang-bang control we prove that optimal control profiles have a unique switching time and the corresponding switching curve is determined.
    Description: Published
    Description: 1251-1266
    Description: 7A. Geofisica per il monitoraggio ambientale
    Description: JCR Journal
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 5
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    Integrated use of unmanned aerial vehicle photogrammetry and terrestrial laser scanning to support archaeological analysis: The Acropolis of Selinunte case (Sicily, Italy) (2021)
    Wiley
    Details
    Publication Date: 2021-06-14
    Description: Southwestern Sicily is an area of infrequent seismic activity; however, some studies carried out in the archaeological Selinunte site suggest that, between the fourth century BC and the early Middle Ages, probably at least two earthquakes strucked this area with enough energy to damage and cause the collapse and kinematics of much of the architecture of Selinunte. Take into account that, in 2008, a noninvasive archaeological prospection and traditional data gathering methods along the Acropolis north fortifications were carried out. Following these first studies, after about 10 years, a new geophysical campaign was carried out. This second campaign benefited from the application of modern technologies for the acquisition and processing of the point cloud data on the northern part of the Acropolis, like terrestrial laser scanning and unmanned aerial vehicle photogrammetry. In this paper, we present the application of these techniques and a strategy for their integration for the 3D modelling of buildings and cultural heritages. We show how the integration of data acquired independently by these two techniques is an added value able to overcome the intrinsic limits of the individual techniques. The application to Selinunte's Acropolis allowed it to highlight and measure with high accuracy fractures, dislocation, inclinations of walls, depressions of some areas and other interesting observations, which may be important starting points for future investigations.
    Description: Published
    Description: 153-165
    Description: 2IT. Laboratori analitici e sperimentali
    Description: JCR Journal
    Keywords: 3D reconstruction ; archaeological survey ; digital elevation model ; Selinunte Archaeological Park ; terrestrial laser scanning ; unmanned aerial vehicle photogrammetry ; 05.04. Instrumentation and techniques of general interest ; 04.02. Exploration geophysics ; 05.02. Data dissemination ; 05.06. Methods
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 6
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    Probabilistic Seismic Hazard Analysis at Regional and National Scales: State of the Art and Future Challenges (2020)
    American Geophysical Union
    Details
    Publication Date: 2020-09-01
    Description: Seismic hazard modeling is a multidisciplinary science that aims to forecast earthquake occurrence and its resultant ground shaking. Such models consist of a probabilistic framework that quantifies uncertainty across a complex system; typically, this includes at least two model components developed from Earth science: seismic source and ground motion models. Although there is no scientific prescription for the forecast length, the most common probabilistic seismic hazard analyses consider forecasting windows of 30 to 50 years, which are typically an engineering demand for building code purposes. These types of analyses are the topic of this review paper. Although the core methods and assumptions of seismic hazard modeling have largely remained unchanged for more than 50 years, we review the most recent initiatives, which face the difficult task of meeting both the increasingly sophisticated demands of society and keeping pace with advances in scientific understanding. A need for more accurate and spatially precise hazard forecasting must be balanced with increased quantification of uncertainty and new challenges such as moving from time‐independent hazard to forecasts that are time dependent and specific to the time period of interest. Meeting these challenges requires the development of science‐driven models, which integrate all information available, the adoption of proper mathematical frameworks to quantify the different types of uncertainties in the hazard model, and the development of a proper testing phase of the model to quantify its consistency and skill. We review the state of the art of the National Seismic Hazard Modeling and how the most innovative approaches try to address future challenges.
    Description: Published
    Description: e2019RG000653
    Description: 6T. Studi di pericolosità sismica e da maremoto
    Description: JCR Journal
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  • 7
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    Empirical nonergodic shaking scenarios based on spatial correlation models: An application to central Italy (2021)
    Wiley
    Details
    Publication Date: 2021-01-18
    Description: This paper provides a new methodological framework to generate empirical ground shaking scenarios, designed for engineering applications and civil protection planning. The methodology is useful both to reconstruct the ground motion pattern of past events and to generate future shaking scenarios, in regions where strong-motion datasets from multiple events and multiple stations are available. The proposed methodology combines (1) an ad-hoc nonergodic ground motion model (GMM) with (2) a spatial correlation model for the source region-, site-, and path-systematic residual terms, and (3) a model of the remaining aleatory error to take into account for directivity effects. The associated variability is a function of the type of scenario generated (bedrock or site, past or future event) and it is minimal for source areas where several events have occurred and for sites where recordings are available. In order to develop the region-specific fully nonergodic GMM and to compute robust estimation of the residual terms, the approach is calibrated on a highly dense dataset compiled for the area of central Italy. Example tests demonstrate the validity of the approach, which allows to simulate acceleration response spectra at unsampled sites, as well as to capture peculiar physical features of ground motion patterns in the region. The proposed approach could be usefully adopted for data-driven simulations of ground shaking maps, as alternative or complementary tool to physic-based and stochastic-based approaches.
    Description: Published
    Description: 60-80
    Description: 5T. Sismologia, geofisica e geologia per l'ingegneria sismica
    Description: JCR Journal
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 8
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    Geolithological and anthropogenic controls on the hydrochemistry of the Volturno river (Southern Italy) (2021)
    Wiley
    Details
    Publication Date: 2021-03-03
    Description: The present work aims to study the main chemical and physical water parameters in the upper and middle Volturno river catchment (southern Italy), between the Capo Volturno springs and the confluence with the Calore river. This study makes use of morphology, geolithology, tectonic, land use, and physico‐chemical (pH, electrical conductivity, redox potential, temperature, major ions, and 222Rn) data for the identification of the main sources of surface and groundwaters in the Volturno catchment and of their evolution and mixing both in base flow and peak flow conditions. The study was also performed to assess whether the alteration due to potential anthropogenic contamination may hamper the identification of natural “primitive” sources of surface waters, especially in the populated and farmed plains far from the river headwaters. Our data suggest that water chemistry of this stretch of the Volturno river is dominated mainly by lithology and, only marginally, by the intense exogenous activities and that this trend is appreciable in both base flow and peak flow conditions. The proposed simple geochemical approach based on easy‐to‐sample matrices and on cost‐effective standard methods is a valuable tool to address catchment functionality especially in upland areas, where complex geologic and structural settings, heterogeneous groundwater flow, and logistical issues are the rule rather than the exception. Because the upper and middle Volturno catchment is comparable with numerous valleys of the Mediterranean area, this study could be a reference for analogous applications.
    Description: Published
    Description: 627–638
    Description: 6A. Geochimica per l'ambiente e geologia medica
    Description: JCR Journal
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 9
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    Hydrogeochemical dynamics affecting steam-heated pools at El Chichón Crater (Chiapas - Mexico) (2021)
    Wiley
    Details
    Publication Date: 2021-03-02
    Description: El Chichon is an active volcano located in the north-western Chiapas, southern Mexico. The crater hosts a lake, a spring, named Soap Pool, emerging from the underlying volcanic aquifer and several mud pools/hot springs on the internal flanks of the crater which strongly interact with the current fumarolic system (steam-heated pools). Some of these pools, the crater lake and a cold spring emerging from the 1982 pumice deposits, have been sampled and analysed. Water–volcanic gas interactions determine the heating (43–99°C) and acidification (pH 2–4) of the springs, mainly by H2S oxidation. Significantly, in the study area, a significant NH3 partial pressure has been also detected. Such a geochemically aggressive environment enhances alteration of the rock in situ and strongly increases the mineralization of the waters (and therefore their electrical conductivity). Two different mineralization systems were detected for the crater waters: the soap pool-lake (Na+/Cl = 0.4, Na/Mg〉10) and the crater mud pools (Na+/Cl 〉 10, Na/Mg 〈 4). A deep boiling, Na+-K+-Cl -rich water reservoir generally influences the Soap Pool-lake, while the mud pool is mainly dominated by water-gas–rock interactions. In the latter case, conductivity of sampled water is directly proportional to the presence of reactive gases in solution. Therefore, chemical evolution proceeds through neutralization due to both rock alteration and bacterial oxidation of ammonium to nitrate. The chemical compositions show that El Chichon aqueous fluids, within the crater, interact with gases fed by a geothermal reservoir, without clear additions of deep magmatic fluids. This new geochemical dataset, together with previously published data, can be used as a base line with which to follow-up the activity of this deadly volcano.
    Description: Published
    Description: 331–343
    Description: 6A. Geochimica per l'ambiente e geologia medica
    Description: JCR Journal
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 10
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    Assessment of earthquake locations in 3D deterministic velocity models: a case study from the Altotiberina Near Fault Observatory (Italy) (2020)
    American Geophysical Union
    Details
    Publication Date: 2021-07-14
    Description: An edited version of this paper was published by AGU. Copyright (2016) American Geophysical Union.
    Description: The accuracy of earthquake locations and their correspondence with subsurface geology depends strongly on the accuracy of the available seismic velocity model. Most modern methods to construct a velocity model for earthquake location are based on the inversion of passive source seismological data. Another approach is the integration of high-resolution geological and geophysical data to construct deterministic velocity models in which earthquake locations can be directly correlated to the geological structures. Such models have to be kinematically consistent with independent seismological data in order to provide precise hypocenter solutions. We present the Altotiberina (AT) seismic model, a three-dimensional velocity model for the Upper Tiber Valley region (Northern Apennines, Italy), constructed by combining 300 km of seismic reflection profiles, 6 deep boreholes (down to 5 km depth), detailed data from geological surveys and direct measurements of P- and S-wave velocities performed in situ and in laboratory. We assess the robustness of the AT seismic model by locating 11,713 earthquakes with a non-linear, global-search inversion method and comparing the probabilistic hypocenter solutions to those calculated in three previously published velocity models, constructed by inverting passive seismological data only. Our results demonstrate that the AT seismic model is able to provide higher-quality hypocenter locations than the previous velocity models. Earthquake locations are consistent with the subsurface geological structures and show a high degree of spatial correlation with specific lithostratigraphic units, suggesting a lithological control on the seismic activity evolution.
    Description: Published
    Description: 8113-8135
    Description: 4T. Sismicità dell'Italia
    Description: JCR Journal
    Keywords: deterministic velocity model ; earthquakes ; nonlinear hypocenter location ; lithological control on seismicity ; 04. Solid Earth::04.06. Seismology::04.06.99. General or miscellaneous
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 11
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    Intercomparison of stratospheric HNO3measurements over Antarctica: Ground-based millimeter-wave versus UARS/MLS Version 5 retrievals (2020)
    American Geophysical Union
    Details
    Publication Date: 2020-09-21
    Description: [1] We present the first intercomparison between the two most comprehensive records of gas‐phase HNO3 profiles in the Antarctic stratosphere, covering the greater part of 1993 and 1995. We compare measurements by the Stony Brook Ground‐Based Millimeter‐wave Spectrometer (GBMS) at the South Pole with Version 5 HNO3 data from the Microwave Limb Sounder (MLS) aboard the Upper Atmospheric Research Satellite. Trajectory tracing was used to select MLS measurements in the 70°–80°S latitude band that sampled air observed by the GBMS during passage over the Pole. When temperatures were near the HNO3 condensation range, additional screening was performed to select MLS measurements that sampled air parcels within 1.5 K of the temperature they experienced over the Pole. Quantitative comparisons are given at 7 different potential temperature levels spanning the range ∼19–30 km. Agreement between the data sets is quite good between 465 and 655 K (∼20–25 km) during a large fraction of the year. Agreement is best during winter and spring, when seasonally averaged differences are generally within 1 ppbv below ∼25 km. At higher altitudes, and during summer and fall, the agreement becomes worse, and GBMS measurements can exceed MLS values by more than 3 ppbv. We provide evidence that differences occurring in the lower stratosphere during fall are due to lack of colocation between the two data sets during a period of strong poleward gradients in HNO3. Remaining discrepancies between GBMS and MLS V5 HNO3 measurements are thought to be due to instrumental or retrieval biases.
    Description: Published
    Description: id 4809
    Description: 5A. Ricerche polari e paleoclima
    Description: JCR Journal
    Keywords: MLS ; Nitric acid ; polar stratosphere ; 01.01. Atmosphere
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  • 12
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    New Applications in Gas Geochemistry (2021)
    Wiley
    Details
    Publication Date: 2021-02-03
    Description: Gases present in the Earth crust are important in various branches of human activities. Hydrocarbons are a significant energy resource, helium is applied in many high-tech instruments, and studies of crustal gas dynamics provide insight in the geodynamic processes and help monitor seismic and volcanic hazards. Quantitative analysis of methane and CO2 migration is important for climate change studies. Some of them are toxic (H2S, CO2, CO); radon is responsible for the major part of human radiation dose. The development of analytical techniques in gas geochemistry creates opportunities of applying this science in numerous fields. Noble gases, hydrocarbons, CO2, N2, H2, CO, and Hg vapor are measured by advanced methods in various environments and matrices including fluid inclusions. Following the “Geochemical Applications of Noble Gases”(2009), “Frontiers in Gas Geochemistry” (2013), and “Progress in the Application of Gas Geochemistry to Geothermal, Tectonic and Magmatic Studies” (2017) published as special issues of Chemical Geology and “Gas geochemistry: From conventional to unconventional domains” (2018) published as a special issue of Marine and Petroleum Geology, this volume continues the tradition of publishing papers reflecting the diversity in scope and application of gas geochemistry.
    Description: Published
    Description: 976190
    Description: 6A. Geochimica per l'ambiente e geologia medica
    Description: JCR Journal
    Keywords: geochemistry ; Atmosphere ; 03. Hydrosphere ; 04. Solid Earth
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  • 13
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    Sediment dynamics on the Northwest African continental margin (1982)
    Wiley
    In:  EPIC3The Ocean Floor : Bruce Heezen commemorative volume, (A Wiley-Interscience publication), Chichester, Wiley, pp. 147-163, ISBN: 0-471-10091-9
    Details
    Publication Date: 2014-05-12
    Description: The sedimentation regime off Northwest Africa is shaped by: (1) structur~al factors. which result in generallv low relief on land. shelf widths between 40 and more than 120 km. and av-erage sfope inclinations between 10 30' and 30; (2) land climates. which contral the delivery of terrigenous particles to the margin: (3) water movements including boundary currents and upwelling; and (4) the post- Pleistocene sea level rise. This chapter combines published and new results arising from research into the sedimentation processes off Northwest Africa. and emphasizes particularly the activities of the Kiel marine geological group during the past few years. Reviews of cruise activities and results were given in Closs et al. (1969) (Meteor cruise 8. 1967. off Morocco) . Seibold (1972) (Meteor cmise 25 . 1971. off Sahara to Central Senegal). Seibold and Hinz (1976) (Meteor cmise 39,1975 . and Valdivia cruise 10. 1975, from Morocco to South Senegal), and Waiden et al. (1974) (Meteor cmise 30, 1973, off Sierra Leone). Some of these cmises were used for pre- or post-site surveys for the Deep-Sea Drilling Project, or to add undisturbed Quaternary cores to the Glomar Challenger cores (leg 41, ] 975; Lancelot, et al .• 1978); leg 47 A, Arthur er al .• 1979; Lutze et al., 1979). We have concentrated our geological investigations on a number of standard profiles from the shelf to the upper continental rise as given in Figure 1. The manuscript was finished May 1979.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Inbook , peerRev
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  • 14
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    Tropical Rains Controlling Deposition of Saharan Dust Across the North Atlantic Ocean (2020)
    American Geophysical Union
    In:  EPIC3Geophysical Research Letters, American Geophysical Union, 47(5), ISSN: 0094-8276
    Details
    Publication Date: 2020-05-13
    Description: Mineral dust plays an important role in the atmospheric radiation budget as well as in the ocean carbon cycle through fertilization and by ballasting of settling organic matter. However, observational records of open‐ocean dust deposition are sparse. Here, we present the spatial and temporal evolution of Saharan dust deposition over 2 years from marine sediment traps across the North Atlantic, directly below the core of the Saharan dust plume, with highest dust fluxes observed in summer. We combined the observed deposition fluxes with model simulations and satellite observations and argue that dust deposition in the Atlantic is predominantly controlled by summer rains. The dominant depositional pathway changes from wet deposition in summer to dry deposition in winter. Wet deposition has previously been suggested to increase the release of dust‐derived nutrients and their bioavailability, which may be a key contributor to surface‐ocean productivity in remote and oligotrophic parts of the oceans.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev , info:eu-repo/semantics/article
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  • 15
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    Arctic Sea Ice in CMIP6 (2020)
    Wiley
    In:  EPIC3Geophysical Research Letters, Wiley, ISSN: 0094-8276
    Details
    Publication Date: 2020-05-04
    Description: We examine CMIP6 simulations of Arctic sea‐ice area and volume. We find that CMIP6 models produce a wide spread of mean Arctic sea‐ice area, capturing the observational estimate within the multi‐model ensemble spread. The CMIP6 multi‐model ensemble mean provides a more realistic estimate of the sensitivity of September Arctic sea‐ice area to a given amount of anthropogenic CO2 emissions and to a given amount of global warming, compared with earlier CMIP experiments. Still, most CMIP6 models fail to simulate at the same time a plausible evolution of sea‐ice area and of global mean surface temperature. In the vast majority of the available CMIP6 simulations, the Arctic Ocean becomes practically sea‐ice free (sea‐ice area 〈 1 million km2) in September for the first time before the year 2050 in each of the four emission scenarios SSP1‐1.9, SSP1‐2.6, SSP2‐4.5 and SSP5‐8.5 examined here.
    Repository Name: EPIC Alfred Wegener Institut
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  • 16
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    Circulation and Thermohaline Variability of the Hanna Shoal Region on the Northeastern Chukchi Sea Shelf (2020)
    Wiley
    In:  EPIC3Journal of Geophysical Research: Oceans, Wiley
    Details
    Publication Date: 2020-07-07
    Description: We analyzed velocity and hydrographic data from 23 moorings in the northeast Chukchi Sea from 2011 to 2014. In most years the eastern side of Hanna Shoal was strongly stratified year-round, while weakly stratified regions prevailed on the shelf south and west of the Shoal. Stratification differences cause differential vertical mixing rates, which in conjunction with advection of different bottom water properties resulted in seasonally-varying along-isobath density gradients. In agreement with numerical models, we find that bottom waters flow anticyclonically around the Shoal. Whereas most of the shelf responded barotropically to wind-forcing, there was a strong baroclinic component to the flow field northeast of Hanna Shoal, resulting in no net vertically-integrated transport on average. In contrast there is a net eastward transport from west of the Shoal, which implies convergence north of the Shoal. Convergence and along-isobath density gradients may foster cross-shelf exchange north of Hanna Shoal. Modal analyses indicate that the shelf south of the Shoal and Barrow Canyon responded coherently to local and remote winds, whereas the wind-current response around Hanna Shoal was less coherent. Barotropic topographic waves, of ~3-day period, were generated episodically northeast of the Shoal and propagate clockwise around Hanna Shoal, but are blocked from entering Barrow Canyon and are possibly scattered by the horizontally sheared flow and converging isobaths on the western side of the Shoal. Analysis of water properties on the western side of Hanna Shoal suggests that these include contributions from the western and southern portions of the Chukchi Sea.
    Repository Name: EPIC Alfred Wegener Institut
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  • 17
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    Limited Retreat of the Wilkes Basin Ice Sheet during the Last Interglacial (2020)
    Wiley
    In:  EPIC3Geophysical Research Letters, Wiley, 47(13), ISSN: 0094-8276
    Details
    Publication Date: 2020-07-20
    Description: The response of the East Antarctic Ice Sheet to global warming represents a major source of uncertainty in sea level projections. Thinning of the East Antarctic George V and Sabrina Coast ice‐cover is currently taking place, and regional ice‐sheet instability episodes might have been triggered in past warm climates. However, the magnitude of ice retreat in the past can not yet be quantitatively derived from paleo‐proxy records alone. We propose that a runaway retreat of the George V coast grounding line and subsequent instability of the Wilkes Basin ice‐sheet would either leave a clear imprint on the water isotope composition in the Talos Dome region or prohibit a Talos Dome ice‐core record from the Last Interglacial altogether. Testing this hypothesis our ice sheet model simulations suggest, that Wilkes Basin ice‐sheet retreat remained relatively limited during the Last Interglacial and provide a constraint on Last Interglacial East Antarctic grounding line stability.
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  • 18
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    Extent and cessation of the mid-Cretaceous Hikurangi Plateau underthrusting: Impact on global plate tectonics and the submarine Chatham Rise (2020)
    Wiley
    In:  EPIC3Journal of Geophysical Research-Solid Earth, Wiley, 125, ISSN: 0148-0227
    Details
    Publication Date: 2020-08-21
    Repository Name: EPIC Alfred Wegener Institut
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  • 19
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    Arctic Continental Margin Sediments as Possible Fe and Mn Sources to Seawater as Sea Ice Retreats: Insights From the Eurasian Margin (2020)
    American Geophysical Union
    In:  EPIC3Global Biogeochemical Cycles, American Geophysical Union, 34(8), ISSN: 0886-6236
    Details
    Publication Date: 2020-09-02
    Repository Name: EPIC Alfred Wegener Institut
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  • 20
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    Evolution of the Upper Ocean Stratification in the Japan Sea Since the Last Glacial (2020)
    Wiley
    In:  EPIC3Geophysical Research Letters, Wiley, 47(16), pp. e2020GL088255, ISSN: 0094-8276
    Details
    Publication Date: 2021-08-05
    Description: Paleoceanographic evidence commonly indicates that Last Glacial Maximum surface temperatures in the Japan Sea were comparable to modern conditions, in striking difference to colder neighboring regions. Here, based on a core from the central Japan Sea, our results show similar UK′37‐ and TEXL86‐derived temperatures between 24.7 and 16.3 ka BP, followed by an abrupt divergence at ~16.3 ka BP and a weakening of divergence after ~8.7 ka BP. We attribute this process to a highly stratified glacial upper ocean controlled by the East Asian Summer Monsoon, increasing thermal gradient between surface and subsurface layers during the deglaciation and the intrusion of Tsushima Warm Current since the mid‐Holocene, respectively. Therefore, we suggest that threshold‐like changes in upper‐ocean temperatures linked to sea level rise and monsoon dynamics, rather than just sea surface temperatures, play a critical role in shaping the thermal and ventilation history of this NW Pacific marginal sea.
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  • 21
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    AMOC recovery in a multi-centennial scenario using a coupled atmosphere-ocean-ice sheet model (2020)
    Wiley
    In:  EPIC3Geophysical Research Letters, Wiley, 47(16), pp. e2019GL086810, ISSN: 0094-8276
    Details
    Publication Date: 2020-09-14
    Description: We simulate the two Coupled Model Intercomparison Project scenarios RCP4.5 and RCP8.5, to assess the effects of melt‐induced fresh water on the Atlantic meridional overturning circulation (AMOC). We use a newly developed climate model with high resolution at the coasts, resolving the complex ocean dynamics. Our results show an AMOC recovery in simulations run with and without an included ice sheet model. We find that the ice sheet adds a strong decadal variability on the freshwater release, resulting in intervals in which it reduces the surface runoff by high accumulation rates. This compensating effect is missing in climate models without dynamic ice sheets. Therefore, we argue to assess those freshwater hosing experiments critically, which aim to parameterize Greenland's freshwater release. We assume the increasing net evaporation over the Atlantic and the resulting increase in ocean salinity, to be the main driver of the AMOC recovery.
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  • 22
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    Ocean Circulation and Variability Beneath Nioghalvfjerdsbræ (79 North Glacier) Ice Tongue (2020)
    Wiley
    In:  EPIC3Journal of Geophysical Research-Oceans, Wiley, 125(8), ISSN: 0148-0227
    Details
    Publication Date: 2020-11-30
    Repository Name: EPIC Alfred Wegener Institut
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  • 23
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    Spatial and Temporal variability of iodine in aerosol (2021)
    Wiley
    In:  EPIC3Journal of Geophysical Research-Atmospheres, Wiley, 126, pp. e2020JD034410, ISSN: 0148-0227
    Details
    Publication Date: 2021-05-10
    Description: In this work we describe the compilation and homogenization of an extensive dataset of aerosol iodine field observations in the period between 1963 and 2018 and we discuss the spatial and temporal dependences of total iodine in bulk aerosol by comparing the observations with CAM-Chem model imulations. Total iodine in aerosol shows a distinct latitudinal dependence, with an enhancement towards the northern hemisphere (NH) tropics and lower values towards the poles. This behavior, which has been predicted by atmospheric models to depend on the global distribution of the main ceanic iodine source (which in turn depends on the reaction of surface ozone with aqueous iodide on he sea water-air interface, generating gas-phase I2 and HOI), is confirmed here by field observations for the first time. Longitudinally, there is some indication of a wave-one profile in the Tropics, which peaks in the Atlantic and shows a minimum in the Pacific, following the wave-one longitudinal variation of tropical tropospheric ozone. New data from Antarctica show that the south polar seasonal variation of iodine in aerosol mirrors that observed previously in the Arctic, with two equinoctial maxima and the dominant maximum occurring in spring. While no clear seasonal variability is observed in NH middle latitudes, there is an indication of different seasonal cycles in the NH tropical Atlantic and Pacific. A weak positive long-term trend is observed in the tropical annual averages, which is consistent with an enhancement of the anthropogenic ozone-driven global oceanic source of iodine over the last 50 years.
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  • 24
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    Nonmonotonic Change of the Arctic Ocean Freshwater Storage Capability in a Warming Climate (2021)
    Wiley
    In:  EPIC3Geophysical Research Letters, Wiley, 48(10), pp. e2020GL090951, ISSN: 0094-8276
    Details
    Publication Date: 2021-07-01
    Description: Freshwater in the Arctic Ocean is one of the key climate components. It is not well understood how the capability of the Arctic Ocean to store freshwater will develop when freshwater supplies increase in a warming climate. By using numerical experiments, we find that this capability varies with the Arctic sea ice decline nonmonotonically, with the largest capability at intermediate strength of sea ice decline. Through enhancing the ocean surface stress, sea ice decline not only accumulates freshwater toward the Amerasian Basin but also tends to reduce the amount of freshwater in both the Eurasian and Amerasian basins by increasing the occupation of Atlantic-origin water in the upper ocean. An increase in river runoff modulates the counterbalance of the two competing effects, leading to the nonmonotonic changes of the Arctic freshwater storage capability in a warming climate.
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  • 25
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    On the Cause of the Mid‐Pleistocene Transition (2021)
    Wiley
    In:  EPIC3Reviews of Geophysics, Wiley, 59(2), pp. e2020RG000727, ISSN: 8755-1209
    Details
    Publication Date: 2021-06-17
    Description: The Mid-Pleistocene Transition (MPT), where the Pleistocene glacial cycles changed from 41 to ∼100 kyr periodicity, is one of the most intriguing unsolved issues in the field of paleoclimatology. Over the course of over four decades of research, several different physical mechanisms have been proposed to explain the MPT, involving non-linear feedbacks between ice sheets and the global climate, the solid Earth, ocean circulation, and the carbon cycle. Here, we review these different mechanisms, comparing how each of them relates to the others, and to the currently available observational evidence. Based on this discussion, we identify the most important gaps in our current understanding of the MPT. We discuss how new model experiments, which focus on the quantitative differences between the different physical mechanisms, could help fill these gaps. The results of those experiments could help interpret available proxy evidence, as well as new evidence that is expected to become available.
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  • 26
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    Dynamics of the African Plate 75 Ma: From Plate Kinematic Reconstructions to Intraplate Paleo-Stresses (2021)
    Wiley
    In:  EPIC3Tectonics, Wiley, 40(7), ISSN: 0278-7407
    Details
    Publication Date: 2021-07-26
    Description: Plate reconstruction studies show that the Neotethys Ocean was closing due to the convergence of Africa and Eurasia toward the end of the Cretaceous. The period around 75 Ma reflects the onset of continental collision between the two plates as convergence continued to be taken up mostly by subduction of the Neotethys slab beneath Eurasia. The Owen transform plate boundary in the northeast accommodated the fast northward motion of the Indian plate relative to the African plate. The rest of the plate was surrounded by mid-ocean ridges. Africa was experiencing continent-wide rifting related to northeast-southwest extension. We aim to quantify the forces and paleostresses that may have driven this continental extension. We use the latest plate kinematic reconstructions in a grid search to estimate horizontal gravitational stresses (HGSs), plate boundary forces, and the plate's interaction with the asthenosphere. The contribution of dynamic topography to HGSs is based on recent mantle convection studies. We model intraplate stresses and compare them with the strain observations. The fit to observations favors models where dynamic topography amplitudes are smaller than 300 m. The results also indicate that the net pull transmitted from slab to the surface African plate was low. To put this into context, we notice that available tectonic reconstructions show fragmented subduction zones and various colliding micro-continents along the northern margin of the African plate around this time. We therefore interpret a low net pull as resulting from either a small average slab length or from the micro-continents' resistance to subduction.
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  • 27
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    Global River Discharge and Floods in the Warmer Climate of the Last Interglacial (2020)
    Wiley
    In:  EPIC3Geophysical Research Letters, Wiley, 47(e2020G), ISSN: 0094-8276
    Details
    Publication Date: 2020-09-18
    Description: We investigate hydrology during a past climate slightly warmer than the present: the Last Interglacial (LIG). With daily output of pre‐industrial and LIG simulations from eight new climate models we force hydrological model PCR‐GLOBWB, and in turn hydrodynamic model CaMa‐Flood. Compared to pre‐industrial, annual mean LIG runoff, discharge, and 100‐year flood volume are considerably larger in the Northern Hemisphere, by 14%, 25% and 82%, respectively. Anomalies are negative in the Southern Hemisphere. In some boreal regions, LIG runoff and discharge are lower despite higher precipitation, due the higher temperatures and evaporation. LIG discharge is much higher for the Niger, Congo, Nile, Ganges, Irrawaddy, Pearl, and lower for the Mississippi, Saint Lawrence, Amazon, Paraná, Orange, Zambesi, Danube, Ob. Discharge is seasonally postponed in tropical rivers affected by monsoon changes. Results agree with published proxies on the sign of discharge anomaly in 15 of 23 sites where comparison is possible.
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  • 28
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    Travel Time and Source Variation Explain the Molecular Transformation of Dissolved Organic Matter in an Alpine Stream Network (2020)
    Wiley-Blackwell
    In:  EPIC3JGR Biogeosciences, Wiley-Blackwell, ISSN: 2169-8961
    Details
    Publication Date: 2020-09-21
    Description: Streams and rivers are important components of the carbon cycle as they transport and transform dissolved organic matter (DOM). Using high‐resolution Fourier‐transform ion cyclotron resonance mass spectrometry, we studied the spatial distribution of DOM at the molecular level at more than 100 sites across a stream network during summer and winter baseflow. We developed a model approximating the time DOM spent in the fluvial network, a key constraint on the biogeochemical processing of DOM. Discharge‐weighted travel time explained the compositional changes of DOM, which differed markedly in summer and winter. We attribute these seasonal differences to variation in source material, putatively reflecting the dynamics of freshly produced DOM in summer and DOM with an imprint of leaf litter in winter. Hydrological mixing was an important driver of the spatial dynamics of DOM. From the convergence rate of DOM compound intensities to the network‐wide average, we inferred the spatial distribution of sources within the catchment. Finally, we estimated network‐wide apparent mass transfer coefficients (vf app) of individual DOM compounds, which describe the vertical velocity at which DOM compounds are removed by biotic and abiotic processes. We identified the oxidative state of carbon as an important factor explaining vf app, which we consequently attribute to biological uptake of thermodynamically favorable DOM compounds. This work contributes to our understanding of the spatial processes, temporal constraints, and chemical properties of DOM that regulate the transformation and diagenesis of DOM at the fluvial network scale.
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  • 29
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    Ice flow and the conditions of the ice-bed interface at the onset of the Northeast Greenland Ice Stream (2020)
    American Geophysical Union
    In:  EPIC3AGU Fall Meeting 2020 - Online Everywhere, Online, 2020-12-01-2020-12-17American Geophysical Union
    Details
    Publication Date: 2020-12-15
    Description: The Northeast Greenland Ice Stream (NEGIS) is an important dynamic component contributing to the total mass balance of the Greenland ice sheet, as it reaches up to the central divide and drains 12% of the ice sheet. The ice stream geometry and surface velocities in the onset region of the NEGIS are not yet sufficiently well reproduced by ice sheet models. We present an assessment of the basal conditions of the onset region in a systematic analysis of airborne ultra-wideband radar data. Our data yield a new detailed model of ice-thickness distribution and basal topography in the upstream part of the ice stream. We observe a change from a smooth to a rougher bed where the ice stream widens from 10 to 60 km, and a distinct roughness anisotropy, indicating a preferred orientation of subglacial structures. The observation of off-nadir reflections that are symmetrical to the bed reflection in the radargrams suggests that these structures are elongated subglacial landforms, which in turn indicate potential streamlining of the bed. Together with basal water routing pathways, our observations hint to two different zones in this part of the NEGIS: an accelerating and smooth upstream region, which is collecting water, with reduced basal traction, and in the further downstream part, where the ice stream is slowing down and is widening, with a distribution of basal water towards the shear margins. Our findings support the hypothesis that the NEGIS is strongly interconnected to the subglacial water system in its onset region, but also to the subglacial substrate and morphology.
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    Necessary Conditions for Warm Inflow Toward the Filchner Ice Shelf, Weddell Sea (2020)
    Wiley
    In:  EPIC3Geophysical Research Letters, Wiley, 47(22), pp. 1-11, ISSN: 0094-8276
    Details
    Publication Date: 2020-11-18
    Description: Understanding changes in Antarctic ice shelf basal melting is a major challenge for predicting future sea level. Currently, warm Circumpolar Deep Water surrounding Antarctica has limited access to the Weddell Sea continental shelf; consequently, melt rates at Filchner‐Ronne Ice Shelf are low. However, large‐scale model projections suggest that changes to the Antarctic Slope Front and the coastal circulation may enhance warm inflows within this century. We use a regional high‐resolution ice shelf cavity and ocean circulation model to explore forcing changes that may trigger this regime shift. Our results suggest two necessary conditions for supporting a sustained warm inflow into the Filchner Ice Shelf cavity: (i) an extreme relaxation of the Antarctic Slope Front density gradient and (ii) substantial freshening of the dense shelf water. We also find that the on‐shelf transport over the western Weddell Sea shelf is sensitive to the Filchner Trough overflow characteristics.
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    A changing Arctic Ocean: How measured and modeled 129129I distributions indicate fundamental shifts in circulation between 1994 and 2015 (2021)
    Wiley
    In:  EPIC3Journal of Geophysical Research-Oceans, Wiley, 126(3), ISSN: 0148-0227
    Details
    Publication Date: 2021-03-11
    Description: 129I measurements on samples collected during GEOTRACES oceanographic missions in the Arctic Ocean in 2015 have provided the first detailed, synoptic 129I sections across the Eurasian, Canada and Makarov Basins. During the 1990s, increased discharges of 129I from European nuclear fuel reprocessing plants produced a large, tracer spike whose passage through the Arctic Ocean has been followed by 129I time series measurements over the past 25 years. Elevated 129I levels measured over the Lomonosov and Alpha-Mendeleyev Ridges in 2015 were associated with tracer labeled, Atlantic-origin water bathymetrically steered by the ridge systems through the central Arctic while lower 129I levels were evident in the more poorly ventilated basin interiors. 129I levels of 200-400 x 107 at/l measured in intermediate waters in 2015 had increased by a factor of 10 compared to results from the same locations in 1994-1996 owing to the circulation of the 1990s, 129I input spike mainly associated with enhanced discharges from the La Hague nuclear fuel reprocessing plant. Comparisons of the patterns of 129I distributions between the mid-1990s and 2015 delineate large scale circulation changes that occurred during the shift from a positive Arctic Oscillation and a cyclonic circulation regime in the mid-1990s to anticyclonic circulation in 2015. The latter is characterized by a broadened Beaufort Gyre in the upper ocean, a weakened boundary current and partial mid-depth, AW flow reversal in the southern Canada Basin. Tracer 129I simulations using the applied circulation model, NAOSIM agree with both historical 129I results and recent GEOTRACES data sets, thereby lending context and credibility to the interpretation of large scale changes in arctic circulation and their relationship to shifts in climate indices revealed by tracer 129I distributions. This paper reports measurements and simulation results for 129I for the 1990s and 2015, and interprets them in the context of ocean circulation responses to changing atmospheric forcing regimes.
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    New Magnetostratigraphic Insights From Iceberg Alley on the Rhythms of Antarctic Climate During the Plio-Pleistocene (2021)
    Wiley
    In:  EPIC3Paleoceanography and Paleoclimatology, Wiley, 36(2), pp. 1-27, ISSN: 0883-8305
    Details
    Publication Date: 2021-02-25
    Description: International Ocean Discovery Program (IODP) Expedition 382 in the Scotia Sea’s Iceberg Alley recovered among the most continuous and highest resolution stratigraphic records in the Southern Ocean near Antarctica spanning the last 3.3 Myr. Sites drilled in Dove Basin (U1536/U1537) have well‐resolved magnetostratigraphy and a strong imprint of orbital forcing in their lithostratigraphy. All magnetic reversals of the last 3.3 Myr are identified, providing a robust age model independent of orbital tuning. During the Pleistocene, alternation of terrigenous versus diatomaceous facies shows power in the eccentricity and obliquity frequencies comparable to the amplitude modulation of benthic δ18O records. This suggests that variations in Dove Basin lithostratigraphy during the Pleistocene reflect a similar history as globally integrated ice volume at these frequencies. However, power in the precession frequencies over the entire ∼3.3 Myr record does not match the amplitude modulation of benthic δ18O records, suggesting Dove Basin contains a unique record at these frequencies. Comparing the position of magnetic reversals relative to local facies changes in Dove Basin and the same magnetic reversals relative to benthic δ18O at North Atlantic IODP Site U1308, we demonstrate Dove Basin facies change at different times than benthic δ18O during intervals between ∼3 and 1 Ma. These differences are consistent with precession phase shifts and suggest climate signals with a Southern Hemisphere summer insolation phase were recorded around Antarctica. If Dove Basin lithology reflects local Antarctic ice volume changes, these signals could represent ice sheet precession‐paced variations not captured in benthic δ18O during the 41‐kyr world.
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    Climatically modulated dust inputs from New Zealand to the Southwest Pacific sector of the Southern Ocean over the last 410 kyr (2021)
    Wiley
    In:  EPIC3Paleoceanography and Paleoclimatology, Wiley, pp. e2020PA003949
    Details
    Publication Date: 2021-04-01
    Description: Eolian mineral dust is an active agent in the global climate system. It affects planetary albedo and can influence marine biological productivity and ocean‐atmosphere carbon dynamics. This makes understanding of the global dust cycle crucial for constraining the dust/climate relationship, which requires long‐term dust emission records for all major dust sources. Despite their importance, the sources of atmospheric dust deposited in the Southern Ocean remain poorly constrained. Eolian dust in the Pacific sector of the Southern Ocean is generally assumed to originate from Australia, with minor contributions from New Zealand. Here we present a high‐resolution elemental record of terrestrial inputs for the past ∼410 kyr from marine sediment core PS75/100‐4 recovered from east of South Island, New Zealand. Sediment grain size is slightly finer than that of loess deposits from South Island, New Zealand, and is coarser than that of marine sediments in the Tasman Sea to the west of New Zealand, which indicates that the dust originated mainly from New Zealand and not only from Australia. Core PS75/100‐4 records lithogenic mass accumulation rates ranging from ∼0.01 to 0.69 g/cm2/kyr (∼0.20 g/cm2/kyr average), with variations over a factor of ∼3‐4 over glacial versus interglacial timescales for the past 410 kyr. Our geochemical data correlate well with Southern Ocean and Antarctic eolian dust records and suggest a westerly wind‐supplied dust signal from New Zealand. Our findings, therefore, suggest that New Zealand should be considered an important long‐term regional dust source in global dust cycle models.
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    Evidence for a highly dynamic West Antarctic Ice Sheet during the Pliocene (2021)
    Wiley
    In:  EPIC3Geophysical Research Letters, Wiley, 48, ISSN: 0094-8276
    Details
    Publication Date: 2021-07-20
    Repository Name: EPIC Alfred Wegener Institut
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    Detailed Seismic Bathymetry Beneath Ekström Ice Shelf, Antarctica: Implications for Glacial History and Ice‐Ocean Interaction (2020)
    Wiley
    In:  EPIC3Geophysical Research Letters, Wiley, 47, pp. e2019G, ISSN: 0094-8276
    Details
    Publication Date: 2020-08-03
    Description: The shape of ice shelf cavities are a major source of uncertainty in understanding ice‐ocean interactions. This limits assessments of the response of the Antarctic ice sheets to climate change. Here we use vibroseis seismic reflection surveys to map the bathymetry beneath the Ekström Ice Shelf, Dronning Maud Land. The new bathymetry reveals an inland‐sloping trough, reaching depths of 1,100 m below sea level, near the current grounding line, which we attribute to erosion by palaeo‐ice streams. The trough does not cross‐cut the outer parts of the continental shelf. Conductivity‐temperature‐depth profiles within the ice shelf cavity reveal the presence of cold water at shallower depths and tidal mixing at the ice shelf margins. It is unknown if warm water can access the trough. The new bathymetry is thought to be representative of many ice shelves in Dronning Maud Land, which together regulate the ice loss from a substantial area of East Antarctica.
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  • 36
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    Wintertime Airborne Measurements of Ice Nucleating Particles in the High Arctic: A Hint to a Marine, Biogenic Source for Ice Nucleating Particles (2020)
    Wiley
    In:  EPIC3Geophysical Research Letters, Wiley, 47, pp. 1-11, ISSN: 0094-8276
    Details
    Publication Date: 2020-09-14
    Description: Ice nucleating particles (INPs) affect the radiative properties of cold clouds. Knowledge concerning their concentration above ground level and their potential sources is scarce. Here we present the first highly temperature resolved ice nucleation spectra of airborne samples from an aircraft campaign during late winter in 2018. Most INP spectra featured low concentration levels (〈3 · 10−4 L−1 at −15°C). −2 −1 However, we also found INP concentrations of up to 1.8·10 L at −15°C and freezing onsets as high as −7.5°C for samples mainly from the marine boundary layer. Shape and onset temperature of the ice nucleation spectra of those samples as well as heat sensitivity hint at biogenic INP. Colocated measurements additionally indicate a local marine influence rather than long‐range transport. Our results suggest that even in late winter above 80°N a local marine source for biogenic INP, which can efficiently nucleate ice at high temperatures, is present. Clouds are a key factor in the energy budget of the Arctic atmosphere. Ice nucleating particles (INPs) can modify the radiation properties and lifetime of clouds by affecting the relative abundance of liquid and frozen droplets in a cloud. Despite this important ability, knowledge about the INP concentration above ground level is limited as airborne INP measurements are very scarce in the Arctic. Here we present results from an aircraft campaign, which took place during the late winter of 2018 in latitudes above 80°N. We found INP concentrations at above −15°C, which are similar to those found in midlatitudes. These INPs also initiate freezing already at high temperatures. We found indications that the INPs are biogenic and originate from a local, marine source, rather than being transported from midlatitudes into the Arctic. Due to the presence of numerous cracks, open leads and polynyas in the sea ice in the investigation area, the ocean may provide a source for these biogenic INP in an environment, where sources on land are still shrouded in snow and ice. However, in a warming Arctic contributions from different sources might change, making the characterization of the current state important.
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    Simulated Thermohaline Fingerprints in Response to Different Greenland‐Scotland Ridge and Fram Strait Subsidence Histories (2020)
    American Geophysical Union
    In:  EPIC3Paleoceanography and Paleoclimatology, American Geophysical Union, 35, ISSN: 2572-4525
    Details
    Publication Date: 2021-02-16
    Description: Changes in ocean gateway configuration can induce basin‐scale rearrangements in ocean current characteristics. However, there is large uncertainty in the relative timing of the Oligocene/Miocene subsidence histories of the Greenland‐Scotland Ridge (GSR) and the Fram Strait (FS). By using a climate model, we investigate the temperature and salinity changes in response to the subsidence of these two key ocean gateways during early to middle Miocene. For a singular subsidence of the GSR, we detect warming and a salinity increase in the Nordic Seas and the Arctic Ocean. As convection sites shift to the north of Iceland, North Atlantic Deep Water (NADW) is formed at cooler temperatures. The associated deep ocean cooling and upwelling of deep waters to the Southern Ocean surface can cause a cooling in the southern high latitudes. These characteristic responses to the GSR deepening are independent of the FS being shallow or deep. An isolated subsidence of the FS gateway for a deep GSR shows less pronounced warming and salinity increase in the Nordic Seas. Arctic temperatures remain unaltered, but a stronger salinity increase is detected, which further increases the density of NADW. The increase in salinity enhances the contribution of NADW to the abyssal ocean at the expense of the colder southern source water component. These relative changes largely counteract each other and cause a negligible warming in the upwelling regions of the Southern Ocean.
    Repository Name: EPIC Alfred Wegener Institut
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    Deposition history and paleo-current activity on the southeastern Lomonosov Ridge and its Eurasian flank based on seismic data (2020)
    Wiley
    In:  EPIC3Geochemistry, Geophysics, Geosystems, Wiley, 21, pp. #e2020GC009133
    Details
    Publication Date: 2020-11-01
    Description: A regional seismic survey on the southeastern Lomonosov Ridge and adjacent basins provides constraints on the coupled evolution of ocean circulations, depositional regime and tectonic processes. First, Mesozoic strata on the Lomonosov Ridge, its faulted flanks and the initial Amundsen Basin were covered with syn-rift sediments of Paleocene to early Eocene age. Numerous vertical faults indicate differential compaction of possibly anoxic sediments deposited in the young, still isolated Eurasian Basin. The second stage, as indicated by a prominent high-amplitude-reflector sequence (HARS) covering the ridge, was a time of widespread changes in deposition conditions, likely controlled by the ongoing subsidence of the Lomonosov Ridge and gradual opening of the Fram Strait. Episodic incursions of water masses from the North Atlantic probably were the consequences, and led to the deposition of thin sedimentary layers of different lithology. The third stage is marked by continuous deposition since the early Miocene (20 Ma). At that time, the ridge no longer posed an obstacle between the Amerasia and Eurasia Basins and pelagic sedimentation was established. Drift bodies, sediment waves, and erosional structures indicate the onset of circulation. Faulting on the ridge slope has led to a series of terraces where sediment drifts have accumulated since the early Miocene. It is suggested that ongoing sagging of the ridge and currents may have shaped the steep sediment free flanks of the terraces. Lastly, a sequence of high-amplitude reflectors marks the transition to the early Pliocene large-scale Northern Hemisphere glaciations.
    Repository Name: EPIC Alfred Wegener Institut
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    Amplified Arctic Surface Warming and Sea Ice Loss Due to Phytoplankton and Colored Dissolved Material (2020)
    Wiley
    In:  EPIC3Geophysical Research Letters, Wiley, 47, pp. e2020GL088795, ISSN: 0094-8276
    Details
    Publication Date: 2020-11-16
    Description: Optically active water constituents attenuate solar radiation and hence affect the vertical distribution of energy in the upper ocean. To understand their implications, we operate an ocean biogeochemical model coupled to a general circulation model with sea ice. Incorporating the effect of phytoplankton and colored dissolved organic matter (CDOM) on light attenuation in the model increases the sea surface temperature in summer and decreases sea ice concentration in the Arctic Ocean. Locally, the sea ice season is reduced by up to one month. CDOM drives a significant part of these changes, suggesting that an increase of this material will amplify the observed Arctic surface warming through its direct thermal effect. Indirectly, changing advective processes in the Nordic Seas may further intensify this effect. Our results emphasize the phytoplankton and CDOM feedbacks on the Arctic ocean and sea ice system and underline the need to consider these effects in future modeling studies to enhance their plausibility.
    Repository Name: EPIC Alfred Wegener Institut
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    COVID-19 crisis reduces free tropospheric ozone across the northern hemisphere (2021)
    Wiley
    In:  EPIC3Geophysical Research Letters, Wiley, 48(5), ISSN: 0094-8276
    Details
    Publication Date: 2021-03-04
    Description: Throughout spring and summer 2020, ozone stations in the northern extratropics recorded unusually low ozone in the free troposphere. From April to August, and from 1 to 8 kilometers altitude, ozone was on average 7% (≈4 nmol/mol) below the 2000 to 2020 climatological mean. Such low ozone, over several months, and at so many stations, has not been observed in any previous year since at least 2000. Atmospheric composition analyses from the Copernicus Atmosphere Monitoring Service and simulations from the NASA GMI model indicate that the large 2020 springtime ozone depletion in the Arctic stratosphere contributed less than one quarter of the observed tropospheric anomaly. The observed anomaly is consistent with recent chemistry-climate model simulations, which assume emissions reductions similar to those caused by the COVID-19 crisis. COVID-19 related emissions reductions appear to be the major cause for the observed reduced free tropospheric ozone in 2020.
    Repository Name: EPIC Alfred Wegener Institut
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    Evolution of (Bio-)geochemical Processes and Diagenetic Alteration of Sediments Along the Tectonic Migration of Ocean Floor in the Shikoku Basin off Japan (2021)
    Wiley
    In:  EPIC3Geochemistry, Geophysics, Geosystems, Wiley
    Details
    Publication Date: 2021-06-30
    Description: Biogeochemical processes in subseafloor sediments are closely coupled to global element cycles. To improve the understanding of changes in biogeochemical conditions on geological timescales, we investigate sediment cores from a 1180 m deep hole in the Nankai Trough offshore Japan (Site C0023) drilled during International Ocean Discovery Program Expedition 370. During its tectonic migration from the Shikoku Basin to the Nankai Trough over the past 15 Ma, Site C0023 has experienced significant changes in depositional, thermal, and geochemical conditions. By combining pore-water, solid-phase, and rock magnetic data, we demonstrate that a transition from organic carbon-starved conditions with predominantly aerobic respiration to an elevated carbon burial environment with increased sedimentation occurred at ∼2.5 Ma. Higher rates of organic carbon burial in consequence of increased nutrient supply and productivity likely stimulated the onset of anaerobic electron-accepting processes during organic carbon degradation. A significant temperature increase by ∼50°C across the sediment column associated with trench-style sedimentation since ∼0.5 Ma could increase the bioavailability of organic matter and enhance biogenic methanogenesis. The resulting shifts in reaction fronts led to diagenetic transformation of iron (oxyhydr)oxides into pyrite in the organic carbon-starved sediments several millions of years after burial. We also show that high amounts of reducible iron(III) which can serve as electron acceptor for microbial iron(III) reduction are preserved and still available as phyllosilicate-bound Fe. This is the first study that shows the evolution of long-term variations of (bio-)geochemical processes along tectonic migration of ocean floor, thereby altering the primary sediment composition long after deposition.
    Repository Name: EPIC Alfred Wegener Institut
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  • 42
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    Planet Microbe: An Ontology-Enriched Cyberinfrastructure System for FAIR Marine ‘Omics Data (2020)
    American Geophysical Union
    In:  EPIC3Ocean Sciences Meeting 2020, 2020-02-16-2020-02-21American Geophysical Union
    Details
    Publication Date: 2020-02-12
    Repository Name: EPIC Alfred Wegener Institut
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  • 43
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    Bathymetry beneath ice shelves of western Dronning Maud Land, East Antarctica, and implications on ice shelf stability (2020)
    Wiley
    In:  EPIC3Geophysical Research Letters, Wiley, 47(12), pp. e2019GL086724, ISSN: 0094-8276
    Details
    Publication Date: 2020-09-06
    Description: Antarctica's ice shelves play a key role in stabilizing the ice streams that feed them. Since basal melting largely depends on ice‐ocean interactions, it is vital to attain consistent bathymetry models to estimate water and heat exchange beneath ice shelves. We have constructed bathymetry models beneath the ice shelves of western Dronning Maud Land by inverting airborne gravity data, and incorporating seismic, multibeam and radar depth references. Our models reveal deep glacial troughs beneath the ice shelves and terminal moraines close to the continental shelf breaks, which currently limit the entry of Warm Deep Water from the Southern Ocean. The ice shelves buttress a catchment that comprises an ice volume equivalent to nearly 1 meter of eustatic sea level rise, partly susceptible to ocean forcing. Changes in water temperature and thermocline depth may accelerate marine based ice sheet drainage and constitute an underestimated contribution to future global sea level rise.
    Repository Name: EPIC Alfred Wegener Institut
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    Antarctic Sea Ice Area in CMIP6 (2020)
    Wiley
    In:  EPIC3Geophysical Research Letters, Wiley, 47(9), ISSN: 0094-8276
    Details
    Publication Date: 2020-06-02
    Repository Name: EPIC Alfred Wegener Institut
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  • 45
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    Regionally coupled atmosphere - ocean - marine biogeochemistry model ROM: 2. Studying the climate change signal in the North Atlantic and Europe (2020)
    Wiley
    In:  EPIC3Journal of Advances in Modeling Earth Systems, Wiley, n/a(n/a), pp. e2019MS001646, ISSN: 1942-2466
    Details
    Publication Date: 2020-07-06
    Description: Climate simulations for the North Atlantic and Europe for recent and future conditions simulated with the regionally coupled ROM model are analyzed and compared to the results from the MPI‐ESM. The ROM simulations also include a biogeochemistry and ocean tides. For recent climate conditions, ROM generally improves the simulations compared to the driving model MPI‐ESM. Reduced oceanic biases in the Northern Atlantic are found, as well as a better simulation of the atmospheric circulation, notably storm tracks and blocking. Regarding future climate projections for the 21st century following the RCP 4.5 and 8.5 scenarios, MPI‐ESM and ROM largely agree qualitatively on the climate change signal over Europe. However, many important differences are identified. For example, ROM shows an SST cooling in the Subpolar Gyre which is not present in MPI‐ESM. Under the RCP8.5 scenario, ROM Arctic sea ice cover is thinner and reaches the seasonally ice‐free state by 2055, well before MPI‐ESM. This shows the decisive importance of higher ocean resolution and regional coupling for determining the regional responses to global warming trends. Regarding biogeochemistry, both ROM and MPI‐ESM simulate a widespread decline in winter nutrient concentration in the North Atlantic of up to ~35%. On the other hand, the phytoplankton spring bloom in the Arctic and in the North‐Western Atlantic starts earlier and the yearly primary production is enhanced in the Arctic in the late 21st century. These results clearly demonstrate the added value of ROM to determine more detailed and more reliable climate projections at the regional scale.
    Repository Name: EPIC Alfred Wegener Institut
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    Antarctic Circumpolar Current Dynamics at the Pacific Entrance to the Drake Passage Over the Past 1.3 Million Years (2020)
    American Geophysical Union
    In:  EPIC3Paleoceanography and Paleoclimatology, American Geophysical Union, 35(7), pp. e2019PA003773, ISSN: 2572-4525
    Details
    Publication Date: 2021-02-01
    Description: The Antarctic Circumpolar Current (ACC) is the world's largest current system connecting all three major basins of the global ocean. Our knowledge of glacial‐interglacial changes in ACC dynamics in the southeast Pacific is not well constrained and presently only based on reconstructions covering the last glacial cycle. Here we use a combination of mean sortable silt grain size of the terrigenous sediment fraction (10–63 μm, "Sortable Silt") and X‐ray fluorescence scanner‐derived Zr/Rb ratios as flow strength proxies to examine ACC variations at the Pacific entrance to the Drake Passage (DP) in the vicinity of the Subantarctic Front. Our results indicate that at the DP entrance, ACC strength varied by ~6–16% on glacial‐interglacial time scales, yielding higher current speeds during interglacial times and reduced current speeds during glacials. We provide evidence that previous observations of a reduction in DP throughflow during the last glacial period are part of a consistent pattern extending for at least the last 1.3 Ma. The orbital‐scale cyclicity follows well‐known global climate changes from prevailing ca. 41‐kyr cycles in the early part of the record (1.3 Ma to 850 ka; marine isotope stage 21) across the mid‐Pleistocene transition into the middle and late Pleistocene 100‐kyr world. A comparison to a bottom water flow record from the deep western boundary current off New Zealand (Ocean Drilling Program Site 1123) reveals anti‐phased changes between the two sites. The enhanced supply of deep water along the DP and into the Atlantic Ocean during interglacials corresponds to a weakened flow of the SW Pacific deep western boundary current.
    Repository Name: EPIC Alfred Wegener Institut
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    Eddy Kinetic Energy in the Arctic Ocean From a Global Simulation With a 1‐km Arctic (2020)
    Wiley
    In:  EPIC3Geophysical Research Letters, Wiley, 47(14), ISSN: 0094-8276
    Details
    Publication Date: 2020-07-28
    Description: Simulating Arctic Ocean mesoscale eddies in ocean circulation models presents a great challenge because of their small size. This study employs an unstructured‐mesh ocean‐sea ice model to conduct a decadal‐scale global simulation with a 1‐km Arctic. It provides a basinwide overview of Arctic eddy energetics. Increasing model resolution from 4 to 1 km increases Arctic eddy kinetic energy (EKE) and total kinetic energy (TKE) by about 40% and 15%, respectively. EKE is the highest along main currents over topography slopes, where strong conversion from available potential energy to EKE takes place. It is high in halocline with a maximum typically centered in the depth range of 70–110 m, and in the Atlantic Water layer of the Eurasian Basin as well. The seasonal variability of EKE along the continental slopes of southern Canada and eastern Eurasian basins is similar, stronger in fall and weaker in spring.
    Repository Name: EPIC Alfred Wegener Institut
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    Meta-analysis of multiple driver effects on marine phytoplankton highlights modulating role of pCO2 (2020)
    Wiley
    In:  EPIC3Global Change Biology, Wiley, 26(12), pp. 6787-6804
    Details
    Publication Date: 2020-11-23
    Description: Responses of marine primary production to a changing climate are determined by a concert of multiple environmental changes, for example in temperature, light, pCO2, nutrients, and grazing. To make robust projections of future global marine primary production, it is crucial to understand multiple driver effects on phytoplankton. This meta-analysis quantifies individual and interactive effects of dual driver combinations on marine phytoplankton growth rates. Almost 50% of the single-species laboratory studies were excluded because central data and metadata (growth rates, carbonate system, experimental treatments) were insufficiently reported. The remaining data (42 studies) allowed for the analysis of interactions of pCO2 with temperature, light, and nutrients, respectively. Growth rates mostly respond non-additively, whereby the interaction with increased pCO2 profusely dampens growth-enhancing effects of high temperature and high light. Multiple and single driver effects on coccolithophores differ from other phytoplankton groups, especially in their high sensitivity to increasing pCO2. Polar species decrease their growth rate in response to high pCO2, while temperate and tropical species benefit under these conditions. Based on the observed interactions and projected changes, we anticipate primary productivity to: (a) first increase but eventually decrease in the Arctic Ocean once nutrient limitation outweighs the benefits of higher light availability; (b) decrease in the tropics and mid-latitudes due to intensifying nutrient limitation, possibly amplified by elevated pCO2; and (c) increase in the Southern Ocean in view of higher nutrient availability and synergistic interaction with increasing pCO2. Growth-enhancing effect of high light and warming to coccolithophores, mainly Emiliania huxleyi, might increase their relative abundance as long as not offset by acidification. Dinoflagellates are expected to increase their relative abundance due to their positive growth response to increasing pCO2 and light levels. Our analysis reveals gaps in the knowledge on multiple driver responses and provides recommendations for future work on phytoplankton.
    Repository Name: EPIC Alfred Wegener Institut
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    Dropstones in the Mar del Plata Canyon Area (SW Atlantic): Evidence for Provenance, Transport, Distribution, and Oceanographic Implications (2020)
    Wiley
    In:  EPIC3Geochemistry Geophysics Geosystems, Wiley, 22, ISSN: 1525-2027
    Details
    Publication Date: 2021-01-28
    Repository Name: EPIC Alfred Wegener Institut
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  • 50
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    Ammonium in Antarctic aerosol: Marine biological activity versus long-range transport of biomass burning (2021)
    Wiley
    In:  EPIC3Geophysical Research Letters, Wiley, 48, pp. e2021GL092826, ISSN: 0094-8276
    Details
    Publication Date: 2021-06-14
    Description: Year-round records of the ionic composition of Antarctic aerosol were obtained at the inland Dome C (DC) and coastal Neumayer (NM) sites, with additional observations of black carbon at NM. Discussions focus on the origin of ammonium in Antarctica. This first Antarctic atmospheric study of several species emitted by biomass burning indicates that black carbon, oxalate, and fine potassium reach a maximum in October in relation to biomass burning activity in the southern hemisphere. Ammonium reaches a maximum two months later, suggesting that biomass burning remains a minor ammonium source there. The ammonium maximum in December coincides with the occurrence of diatom blooms in the austral ocean, suggesting that oceanic ammonia emissions are the main source of ammonium in Antarctica. The ammonium to sulfur-derived biogenic species molar ratio of 0.15 in summer suggests far lower ammonia emissions from the Antarctic oceans than mid-latitude southern oceans.
    Repository Name: EPIC Alfred Wegener Institut
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    Seasonality in Saharan Dust Across the Atlantic Ocean: From Atmospheric Transport to Seafloor Deposition (2021)
    Wiley
    In:  EPIC3Journal of Geophysical Research-Atmospheres, Wiley, 126, ISSN: 0148-0227
    Details
    Publication Date: 2021-06-25
    Description: Saharan dust is transported in great quantities from the North African continent every year, most of which is deposited across the North Atlantic Ocean. This dust impacts regional and global climate by affecting the atmospheric radiation balance and altering ocean carbon budgets. However, little research has been carried out on time series of Saharan dust collected in situ across the open Atlantic. Here, we present a unique three-year time series of Saharan dust along a trans-Atlantic transect, sampled by moored surface buoys and subsurface sediment traps. Results show a good correlation between the particle-size distributions of atmospheric dust and the lithogenic particles settling to the deep ocean floor, confirming the aeolian origin of the lithogenic particles intercepted by the subsurface sediment traps, even in the distal western part of the Atlantic Ocean. Dust from both dry and wet deposition as collected by the sediment traps, shows increased deposition fluxes and coarser grain size in summer and/or autumn that coincides with increased precipitation at the sampling sites as derived from satellite data. In contrast, both buoys that sampled dust during transport at sea level show little seasonal variation in both concentration and particle size, as the large amounts of dust transported in summer and early autumn at high altitudes are far above their sampling range. This implies that wet deposition in summer and autumn defines the typical seasonal trends of both the dust deposition flux and its particle-size distribution observed in the sediment traps.
    Repository Name: EPIC Alfred Wegener Institut
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    New Developments in the PuffinPlot Paleomagnetic Data Analysis Program (2020)
    Wiley
    Details
    Publication Date: 2020-03-06
    Description: PuffinPlot is a program for paleomagnetic data analysis and plotting, first released in 2012 and under continuous development since then. It is free, cross‐platform software and provides both a graphical desktop interface for interactive use and an application‐programmer interface for scripting. We present a major new release of the program, describe significant new features added since the first release, and demonstrate their application to real‐world data. New features include automatic magnetic declination realignment, relative paleointensity calculation, virtual geomagnetic pole determination, calculation of inclination‐only statistics, support for reproducible research via the export of self‐contained data bundles, and support for reading a number of popular paleomagnetic file formats. We also discuss the application of unit tests in ensuring PuffinPlot's long‐term reliability and outline directions for future development of the software.
    Description: Published
    Description: 5578-5587
    Description: 1A. Geomagnetismo e Paleomagnetismo
    Description: JCR Journal
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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    Fine‐Scale Structure of the 2016–2017 Central Italy Seismic Sequence From Data Recorded at the Italian National Network (2020)
    Wiley
    Details
    Publication Date: 2020-05-25
    Description: We explore the three‐dimensional structure of the 2016–2017 Central Italy sequence using ~34,000 ML ≥ 1.5 earthquakes that occurred between August 2016 and January 2018. We applied cross‐correlation and double‐difference location methods to waveform and parametric data routinely produced at the Italian National Institute of Geophysics and Volcanology. The sequence activated an 80 km long system of normal faults and near‐horizontal detachment faults through the MW 6.0 Amatrice, the MW 5.9 Visso, and the MW 6.5 Norcia mainshocks and aftershocks. The system has an average strike of N155°E and dips 38°–55° southwestward and is segmented into 15–30 km long faults individually activated by the cascade of MW ≥ 5.0 shocks. The two main normal fault segments, Mt. Vettore‐Mt. Bove to the North and Mt. della Laga to the South, are separated by an NNE‐SSW‐trending lateral ramp of the Sibillini thrust, a regional structure inherited from the previous compressional tectonic phase putting into contact diverse lithologies with different seismicity patterns. Space‐time reconstruction of the fault system supports a composite rupture scenario previously proposed for the MW 6.5 Norcia earthquake, where the rupture possibly propagated also along an oblique portion of the Sibillini thrust. This dissected set of normal fault segments is bounded at 8–10 km depth by a continuous 2 km thick seismicity layer of extensional nature slightly dipping eastward and interpreted as a shear zone. All three mainshocks in the sequence nucleated along the high‐angle planes at significant distance from the shear zone, thus complicating the interpretation of the mechanisms driving strain partitioning between these structures.
    Description: Published
    Description: e2019JB018440
    Description: 3T. Sorgente sismica
    Description: JCR Journal
    Keywords: normal fault ; shear zone ; fault segmentation ; apennines ; 04.06. Seismology
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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    Active Extension in a Foreland Trapped Between Two Contractional Chains: The South Apulia Fault System (SAFS) (2020)
    Wiley
    Details
    Publication Date: 2020-07-08
    Description: The response of continental forelands to subduction and collision is a widely investigated topic in geodynamics. The deformation occurring within a foreland shared by two opposite‐verging chains, however, is uncommon and poorly understood. The Apulia Swell in the southern end of the Adria microplate (Africa‐Europe plate boundary, central Mediterranean Sea) represents one of these cases, as it is the common foreland of the SW verging Albanides‐Hellenides and the NE verging Southern Apennines merging into the SSE verging Calabrian Arc. We investigated the internal deformation of the Apulia Swell using multiscale geophysical data: multichannel seismic profiles recording up to 12‐s two‐way time (TWT) for a consistent image of the upper crust; high‐resolution multichannel seismic profiles, high‐resolution multibeam bathymetry, and CHIRP profiles acquired by R/V OGS Explora to constrain the Quaternary geological record. The results of our analyses characterize the geometry of the South Apulia Fault System (SAFS), a 100‐km‐long and 12‐km‐wide structure attesting an extensional (and possibly transtensional) response of the foreland to the two contractional fronts. The SAFS consists of two NW‐SE right‐stepping master faults and several secondary structures. The SAFS activity spans from the Early Pleistocene through the Holocene, as testified by the bathymetric and high‐resolution seismic data, with long‐term slip rates in the range of 0.2–0.4 mm/yr. Considering the position within an area with few or none other active faults in the surroundings, the dimension, and the activity rates, the SAFS can be a candidate causative fault of the 20 February 1743, M 6.7, earthquake.
    Description: Italian Ministry for Education, University, and Research (MIUR), Premiale 2014 D. M. 291 03/05/2016.
    Description: Published
    Description: e2020TC006116
    Description: 2T. Deformazione crostale attiva
    Description: 2TR. Ricostruzione e modellazione della struttura crostale
    Description: JCR Journal
    Keywords: active tectonics ; apulia ; south apulia fault system ; 1743 earthquake ; marine geology ; stable continental region ; ionian sea ; active faults ; subsurface geology ; seismic interpretation ; 04.04. Geology ; 04.07. Tectonophysics ; 04.02. Exploration geophysics
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  • 55
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    Evaluating learning spaces in flood risk management in Germany: Lessons for governance research (2021)
    Blackwell Publishing Ltd | Oxford, UK
    Details
    Publication Date: 2021-06-28
    Description: Efforts to collaboratively manage the risk of flooding are ultimately based on individuals learning about risks, the decision process, and the effectiveness of decisions made in prior situations. This article argues that much can be learned about a governance setting by explicitly evaluating the relationships through which influential individuals and their immediate contacts receive and send information to one another. We define these individuals as “brokers,” and the networks that emerge from their interactions as “learning spaces.” The aim of this article is to develop strategies to identify and evaluate the properties of a broker's learning space that are indicative of a collaborative flood risk management arrangement. The first part of this article introduces a set of indicators, and presents strategies to employ this list so as to systematically identify brokers, and compare their learning spaces. The second part outlines the lessons from an evaluation that explored cases in two distinct flood risk management settings in Germany. The results show differences in the observed brokers' learning spaces. The contacts and interactions of the broker in Baden‐Württemberg imply a collaborative setting. In contrast, learning space of the broker in North Rhine‐Westphalia lacks the same level of diversity and polycentricity.
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: MWK Baden‐Württemberg
    Keywords: 333.91 ; brokerage ; collaborative water governance ; comanagement ; comparative analysis ; social networks
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    Facilitated crystal handling using a simple device for evaporation reduction in microtiter plates (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2021-03-30
    Description: In the past two decades, most of the steps in a macromolecular crystallography experiment have undergone tremendous development with respect to speed, feasibility and increase of throughput. The part of the experimental workflow that is still a bottleneck, despite significant efforts, involves the manipulation and harvesting of the crystals for the diffraction experiment. Here, a novel low‐cost device is presented that functions as a cover for 96‐well crystallization plates. This device enables access to the individual experiments one at a time by its movable parts, while minimizing evaporation of all other experiments of the plate. In initial tests, drops of many typically used crystallization cocktails could be successfully protected for up to 6 h. Therefore, the manipulation and harvesting of crystals is straightforward for the experimenter, enabling significantly higher throughput. This is useful for many macromolecular crystallography experiments, especially multi‐crystal screening campaigns.
    Description: A simple and low‐cost device has been developed to minimize evaporation in microtiter plates for easy crystal handling and harvesting. image
    Keywords: 548 ; evaporation reduction ; crystal handling ; crystal harvesting ; crystallographic fragment screening
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    Cation distribution in Cu2ZnSnSe4, Cu2FeSnS4 and Cu2ZnSiSe4 by multiple‐edge anomalous diffraction (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2021-03-30
    Description: Multiple‐Edge Anomalous Diffraction (MEAD) has been applied to various quaternary sulfosalts belonging to the adamantine compound family in order to validate the distribution of copper, zinc and iron cations in the structure. Semiconductors from this group of materials are promising candidates for photovoltaic applications. Their properties strongly depend on point defects, in particular related to cation order–disorder. However, Cu+, Zn2+ and Fe2+ have very similar scattering factors and are all but indistinguishable in usual X‐ray diffraction experiments. Anomalous diffraction utilizes the dependency of the atomic scattering factors f′ and f′′ of the energy of the radiation, especially close to the element‐specific absorption edges. In the MEAD technique, individual Bragg peaks are tracked over an absorption edge. The intensity changes depending on the structure factor can be highly characteristic for Miller indices selected for a specific structural problem, but require very exact measurements. Beamline KMC‐2 at synchrotron BESSY II, Berlin, has been recently upgraded for this technique. Anomalous X‐ray powder diffraction and XAFS compliment the data. Application of this technique confirmed established cation distribution in Cu2ZnSnSe4 (CZTSe) and Cu2FeSnS4 (CFTS). In contrast to the literature, cation distribution in Cu2ZnSiSe4 (CZSiSe) is shown to adopt a highly ordered wurtz‐kesterite structure type.
    Description: Multiple‐Edge Anomalous Diffraction (MEAD) has been applied to various quaternary sulfosalts belonging to the adamantine compound family in order to validate the distribution of copper, zinc and iron cations in the structure. Application of this technique confirms established cation distribution in Cu2ZnSnSe4 (CZTSe) and Cu2FeSnS4 (CFTS), but in Cu2ZnSiSe4 (CZSiSe) the cation distribution is shown to adopt a highly ordered wurtz‐kesterite structure type in contrast to the literature. image
    Keywords: 548 ; synchrotron ; anomalous diffraction ; semiconductor ; MEAD
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    The copper(II)‐binding tripeptide GHK, a valuable crystallization and phasing tag for macromolecular crystallography (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2021-03-27
    Description: The growth of diffraction‐quality crystals and experimental phasing remain two of the main bottlenecks in protein crystallography. Here, the high‐affinity copper(II)‐binding tripeptide GHK was fused to the N‐terminus of a GFP variant and an MBP‐FG peptide fusion. The GHK tag promoted crystallization, with various residues (His, Asp, His/Pro) from symmetry molecules completing the copper(II) square‐pyramidal coordination sphere. Rapid structure determination by copper SAD phasing could be achieved, even at a very low Bijvoet ratio or after significant radiation damage. When collecting highly redundant data at a wavelength close to the copper absorption edge, residual S‐atom positions could also be located in log‐likelihood‐gradient maps and used to improve the phases. The GHK copper SAD method provides a convenient way of both crystallizing and phasing macromolecular structures, and will complement the current trend towards native sulfur SAD and MR‐SAD phasing.
    Description: A novel three‐residue tag containing the residues GHK that can be used to promote crystallization and in SAD phasing experiments using its tightly bound copper ion is described. image
    Keywords: 548 ; phasing ; crystallization ; GHK ; SAD
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    Determining paracrystallinity in mixed‐tacticity polyhydroxybutyrates (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2021-03-30
    Description: Recently, the authors reported on the development of crystallinity in mixed‐tacticity polyhydroxybutyrates. Comparable values reported in the literature vary depending on the manner of determination, the discrepancies being partially attributable to scattering from paracrystalline portions of the material. These portions can be qualified by peak profile fitting or quantified by allocation of scattered X‐ray intensities. However, the latter requires a good quality of the former, which in turn must additionally account for peak broadening inherent in the measurement setup, and due to limited crystallite sizes and the possible presence of microstrain. Since broadening due to microstrain and paracrystalline order both scale with scattering vector, they are easily confounded. In this work, a method to directionally discern these two influences on the peak shape in a Rietveld refinement is presented. Allocating intensities to amorphous, bulk and paracrystalline portions with changing tactic disturbance provided internal validations of the obtained directional numbers. In addition, the correlation between obtained thermal factors and Young's moduli, determined in earlier work, is discussed.
    Description: A method to robustly determine paracrystalline contents from Rietveld‐refined powder X‐ray data is presented and discussed for the example of mixed‐tacticity polyhydroxybutyrates. image
    Keywords: 548 ; polyhydroxybutyrates ; mixed tacticity ; paracrystallinity ; Rietveld refinement ; thermal factors
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    Concepts for nondestructive and depth‐resolved X‐ray residual stress analysis in the near‐surface region of nearly single crystalline materials with mosaic structure (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2021-03-27
    Description: Two evaluation concepts for nondestructive depth‐resolved X‐ray residual stress analysis in the near‐surface region of materials with cubic symmetry and nearly single crystalline structure are introduced by simulated examples. Both concepts are based on the same data acquisition strategy, which consists in the determination of lattice‐spacing depth profiles along the ⟨hkl⟩ poles by stepwise sample rotation around the scattering vector. Segmentation of these profiles parallel to the sample surface provides the lattice strain state as a function of depth. The first evaluation concept extends the crystallite group method developed for materials with pronounced crystallographic texture by the feature of depth resolution and can be applied to samples with arbitrary orientation. The second evaluation concept, which adapts the linear regression approach of the sin2ψ method for the case of single crystalline materials, is restricted to samples with (001) orientation. The influence of the strain‐free lattice parameter a0 on residual stress analysis using both evaluation concepts is discussed on the basis of explicitly derived relations.
    Description: Two data evaluation concepts are proposed for nondestructive and depth‐resolved X‐ray residual stress analysis by means of energy‐dispersive diffraction on materials featuring cubic symmetry and a nearly single crystalline structure. image
    Keywords: 548 ; residual stress ; X‐ray diffraction ; depth‐resolved analysis ; mosaic crystals
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    X‐ray dichroism in polyimide caused by non‐resonant scattering (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
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    Publication Date: 2021-03-30
    Description: Dichroism is one of the most important optical effects in both the visible and the X‐ray range. Besides absorption, scattering can also contribute to dichroism. This paper demonstrates that, based on the example of polyimide, materials can show tiny dichroism even far from electronic resonances due to scattering. Although the effect is small, it can lead to a measurable polarization change and might have influence on highly sensitive polarimetric experiments.
    Description: Aligned molecules, for example in polyimide foils, lead to small dichroism even far from resonances, which can be revealed by high‐precision X‐ray polarimetry. image
    Keywords: 548 ; polyimide ; polarization ; X‐ray polarimetry ; wide‐angle scattering ; X‐ray dichroism
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    Elastic stiffness coefficients of thiourea from thermal diffuse scattering (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2021-03-27
    Description: The complete elastic stiffness tensor of thiourea has been determined from thermal diffuse scattering (TDS) using high‐energy photons (100 keV). Comparison with earlier data confirms a very good agreement of the tensor coefficients. In contrast with established methods to obtain elastic stiffness coefficients (e.g. Brillouin spectroscopy, inelastic X‐ray or neutron scattering, ultrasound spectroscopy), their determination from TDS is faster, does not require large samples or intricate sample preparation, and is applicable to opaque crystals. Using high‐energy photons extends the applicability of the TDS‐based approach to organic compounds which would suffer from radiation damage at lower photon energies.
    Description: The elastic stiffness coefficients of thiourea are determined from thermal diffuse scattering. image
    Keywords: 548 ; thermal diffuse scattering ; elastic stiffness ; thiourea
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    Fast fitting of reflectivity data of growing thin films using neural networks (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2021-07-03
    Description: X‐ray reflectivity (XRR) is a powerful and popular scattering technique that can give valuable insight into the growth behavior of thin films. This study shows how a simple artificial neural network model can be used to determine the thickness, roughness and density of thin films of different organic semiconductors [diindenoperylene, copper(II) phthalocyanine and α‐sexithiophene] on silica from their XRR data with millisecond computation time and with minimal user input or a priori knowledge. For a large experimental data set of 372 XRR curves, it is shown that a simple fully connected model can provide good results with a mean absolute percentage error of 8–18% when compared with the results obtained by a genetic least mean squares fit using the classical Parratt formalism. Furthermore, current drawbacks and prospects for improvement are discussed.
    Description: Artificial neural networks trained with simulated data are shown to correctly and quickly determine film parameters from experimental X‐ray reflectivity curves.
    Keywords: 548 ; X‐ray reflectivity ; machine learning ; organic semi‐conductors ; neural networks
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    Numerically stable form factor of any polygon and polyhedron (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2021-06-05
    Description: Coordinate‐free expressions for the form factors of arbitrary polygons and polyhedra are derived using the divergence theorem and Stokes's theorem. Apparent singularities, all removable, are discussed in detail. Cancellation near the singularities causes a loss of precision that can be avoided by using series expansions. An important application domain is small‐angle scattering by nanocrystals.
    Description: Coordinate‐free expressions for the form factors of arbitrary polygons and polyhedra are derived using the divergence theorem and Stokes's theorem. Series expansions are used to ensure numeric precision close to apparent singularities. image
    Keywords: 548 ; form factors ; polyhedra ; Fourier shape transform
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    ROBL‐II at ESRF: a synchrotron toolbox for actinide research (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2021-06-30
    Description: ROBL‐II provides four different experimental stations to investigate actinide and other alpha‐ and beta‐emitting radionuclides at the new EBS storage ring of ESRF within an energy range of 3 to 35 keV. The XAFS station consists of a highly automatized, high sample throughput installation in a glovebox, to measure EXAFS and conventional XANES of samples routinely at temperatures down to 10 K, and with a detection limit in the sub‐p.p.m. range. The XES station with its five bent‐crystal analyzer, Johann‐type setup with Rowland circles of 1.0 and 0.5 m radii provides high‐energy resolution fluorescence detection (HERFD) for XANES, XES, and RIXS measurements, covering both actinide L and M edges together with other elements accessible in the 3 to 20 keV energy range. The six‐circle heavy duty goniometer of XRD‐1 is equipped for both high‐resolution powder diffraction as well as surface‐sensitive CTR and RAXR techniques. Single crystal diffraction, powder diffraction with high temporal resolution, as well as X‐ray tomography experiments can be performed at a Pilatus 2M detector stage (XRD‐2). Elaborate radioprotection features enable a safe and easy exchange of samples between the four different stations to allow the combination of several methods for an unprecedented level of information on radioactive samples for both fundamental and applied actinide and environmental research.
    Description: ROBL‐II at ESRF provides four experimental stations to investigate actinides with X‐ray absorption and emission spectroscopy, and with surface, high‐resolution powder, and single‐crystal X‐ray diffractometry.
    Keywords: 549 ; actinides ; EXAFS ; XANES ; HERFD‐XANES ; XAS ; XES ; RIXS ; XRD ; CTR ; RAXR ; surface diffraction
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    ATSAS 3.0: expanded functionality and new tools for small‐angle scattering data analysis (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2021-03-30
    Description: The ATSAS software suite encompasses a number of programs for the processing, visualization, analysis and modelling of small‐angle scattering data, with a focus on the data measured from biological macromolecules. Here, new developments in the ATSAS 3.0 package are described. They include IMSIM, for simulating isotropic 2D scattering patterns; IMOP, to perform operations on 2D images and masks; DATRESAMPLE, a method for variance estimation of structural invariants through parametric resampling; DATFT, which computes the pair distance distribution function by a direct Fourier transform of the scattering data; PDDFFIT, to compute the scattering data from a pair distance distribution function, allowing comparison with the experimental data; a new module in DATMW for Bayesian consensus‐based concentration‐independent molecular weight estimation; DATMIF, an ab initio shape analysis method that optimizes the search model directly against the scattering data; DAMEMB, an application to set up the initial search volume for multiphase modelling of membrane proteins; ELLLIP, to perform quasi‐atomistic modelling of liposomes with elliptical shapes; NMATOR, which models conformational changes in nucleic acid structures through normal mode analysis in torsion angle space; DAMMIX, which reconstructs the shape of an unknown intermediate in an evolving system; and LIPMIX and BILMIX, for modelling multilamellar and asymmetric lipid vesicles, respectively. In addition, technical updates were deployed to facilitate maintainability of the package, which include porting the PRIMUS graphical interface to Qt5, updating SASpy – a PyMOL plugin to run a subset of ATSAS tools – to be both Python 2 and 3 compatible, and adding utilities to facilitate mmCIF compatibility in future ATSAS releases. All these features are implemented in ATSAS 3.0, freely available for academic users at https://www.embl‐hamburg.de/biosaxs/software.html.
    Description: ATSAS is a comprehensive software suite for the processing, visualization, analysis and modelling of small‐angle scattering data. This article describes developments in the ATSAS 3.0 release, including new programs for data simulation and for the structural modelling of lipids, nucleic acids and polydisperse systems. image
    Keywords: 548 ; small‐angle scattering ; data analysis ; biological macromolecules ; structural modelling ; ATSAS
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    Synthetic resampling strategies and machine learning for digital soil mapping in Iran (2021)
    Blackwell Publishing Ltd | Oxford, UK
    Details
    Publication Date: 2021-07-04
    Description: Most common machine learning (ML) algorithms usually work well on balanced training sets, that is, datasets in which all classes are approximately represented equally. Otherwise, the accuracy estimates may be unreliable and classes with only a few values are often misclassified or neglected. This is known as a class imbalance problem in machine learning and datasets that do not meet this criterion are referred to as imbalanced data. Most datasets of soil classes are, therefore, imbalanced data. One of our main objectives is to compare eight resampling strategies that have been developed to counteract the imbalanced data problem. We compared the performance of five of the most common ML algorithms with the resampling approaches. The highest increase in prediction accuracy was achieved with SMOTE (the synthetic minority oversampling technique). In comparison to the baseline prediction on the original dataset, we achieved an increase of about 10, 20 and 10% in the overall accuracy, kappa index and F‐score, respectively. Regarding the ML approaches, random forest (RF) showed the best performance with an overall accuracy, kappa index and F‐score of 66, 60 and 57%, respectively. Moreover, the combination of RF and SMOTE improved the accuracy of the individual soil classes, compared to RF trained on the original dataset and allowed better prediction of soil classes with a low number of samples in the corresponding soil profile database, in our case for Chernozems. Our results show that balancing existing soil legacy data using synthetic sampling strategies can significantly improve the prediction accuracy in digital soil mapping (DSM). Highlights Spatial distribution of soil classes in Iran can be predicted using machine learning (ML) algorithms. The synthetic minority oversampling technique overcomes the drawback of imbalanced and highly biased soil legacy data. When combining a random forest model with synthetic sampling strategies the prediction accuracy of the soil model improves significantly. The resulting new soil map of Iran has a much higher spatial resolution compared to existing maps and displays new soil classes that have not yet been mapped in Iran.
    Description: Alexander von Humboldt‐Stiftung http://dx.doi.org/10.13039/100005156
    Description: German Research Foundation http://dx.doi.org/10.13039/501100001659
    Description: Soil and Water Research Institute, Agricultural Research, Education and Extension Organization, Karaj, Iran
    Keywords: 631.4 ; covariates ; imbalanced data ; machine learning ; random forest ; soil legacy data
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    XGANDALF – extended gradient descent algorithm for lattice finding (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2021-03-27
    Description: Serial crystallography records still diffraction patterns from single, randomly oriented crystals, then merges data from hundreds or thousands of them to form a complete data set. To process the data, the diffraction patterns must first be indexed, equivalent to determining the orientation of each crystal. A novel automatic indexing algorithm is presented, which in tests usually gives significantly higher indexing rates than alternative programs currently available for this task. The algorithm does not require prior knowledge of the lattice parameters but can make use of that information if provided, and also allows indexing of diffraction patterns generated by several crystals in the beam. Cases with a small number of Bragg spots per pattern appear to particularly benefit from the new approach. The algorithm has been implemented and optimized for fast execution, making it suitable for real‐time feedback during serial crystallography experiments. It is implemented in an open‐source C++ library and distributed under the LGPLv3 licence. An interface to it has been added to the CrystFEL software suite.
    Description: A description and evaluation are given of XGANDALF, extended gradient descent algorithm for lattice finding, an algorithm developed for fast and accurate indexing of snapshot diffraction patterns. image
    Keywords: 548 ; indexing ; XGANDALF ; CrystFEL ; multiple lattices ; serial crystallography
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    pinkIndexer – a universal indexer for pink‐beam X‐ray and electron diffraction snapshots (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2021-03-27
    Description: A crystallographic indexing algorithm, pinkIndexer, is presented for the analysis of snapshot diffraction patterns. It can be used in a variety of contexts including measurements made with a monochromatic radiation source, a polychromatic source or with radiation of very short wavelength. As such, the algorithm is particularly suited to automated data processing for two emerging measurement techniques for macromolecular structure determination: serial pink‐beam X‐ray crystallography and serial electron crystallography, which until now lacked reliable programs for analyzing many individual diffraction patterns from crystals of uncorrelated orientation. The algorithm requires approximate knowledge of the unit‐cell parameters of the crystal, but not the wavelengths associated with each Bragg spot. The use of pinkIndexer is demonstrated by obtaining 1005 lattices from a published pink‐beam serial crystallography data set that had previously yielded 140 indexed lattices. Additionally, in tests on experimental serial crystallography diffraction data recorded with quasi‐monochromatic X‐rays and with electrons the algorithm indexed more patterns than other programs tested.
    Description: pinkIndexer, an algorithm developed for indexing of snapshot diffraction patterns recorded with pink‐beam X‐rays, monochromatic X‐rays and electrons, is described and its use evaluated. image
    Keywords: 548 ; indexing ; pinkIndexer ; CrystFEL ; pink X‐ray beam ; serial electron diffraction
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    Crystal structure of human CRM1, covalently modified by 2‐mercaptoethanol on Cys528, in complex with RanGTP (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2021-06-17
    Description: CRM1 is a nuclear export receptor that has been intensively targeted over the last decade for the development of antitumor and antiviral drugs. Structural analysis of several inhibitor compounds bound to CRM1 revealed that their mechanism of action relies on the covalent modification of a critical cysteine residue (Cys528 in the human receptor) located in the nuclear export signal‐binding cleft. This study presents the crystal structure of human CRM1, covalently modified by 2‐mercaptoethanol on Cys528, in complex with RanGTP at 2.58 Å resolution. The results demonstrate that buffer components can interfere with the characterization of cysteine‐dependent inhibitor compounds.
    Description: The covalent modification of human CRM1 by 2‐mercaptoethanol interferes with the characterization of cysteine‐dependent inhibitor compounds. image
    Keywords: 548 ; nuclear export ; cancer ; exportin 1 ; cysteine modification
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    Impact of biochar on nutrient supply, crop yield and microbial respiration on sandy soils of northern Germany (2021)
    Blackwell Publishing Ltd | Oxford, UK
    Details
    Publication Date: 2021-06-16
    Description: The application of biochar to agricultural soils to increase nutrient availability, crop production and carbon sequestration has gained increasing interest but data from field experiments on temperate, marginal soils are still under‐represented. In the current study, biochar, produced from organic residues (digestates) from a biogas plant, was applied with and without digestates at low (3.4 t ha−1) and intermediate (17.1 t ha−1) rates to two acidic and sandy soils in northern Germany that are used for corn (Zea mays L.) production. Soil nutrient availability, crop yields, microbial biomass and carbon dioxide (CO2) emissions from heterotrophic respiration were measured over two consecutive years. The effects of biochar application depended on the intrinsic properties of the two tested soils and the biochar application rates. Although the soils at the fallow site, with initially low nutrient concentrations, showed a significant increase in pH, soil nutrients and crop yield after low biochar application rates, a similar response was found at the cornfield site only after application of substantially larger amounts of biochar. The effect of a single dose of biochar at the beginning of the experiment diminished over time but was still detectable after 2 years. Whereas plant available nutrient concentrations increased after biochar application, the availability of potentially phytotoxic trace elements (Zn, Pb, Cd, Cr) decreased significantly, and although slight increases in microbial biomass carbon and heterotrophic CO2 fluxes were observed after biochar application, they were mostly not significant. The results indicate that the application of relatively small amounts of biochar could have positive effects on plant available nutrients and crop yields of marginal arable soils and may decrease the need for mineral fertilizers while simultaneously increasing the sequestration of soil organic carbon. Highlights A low rate of biochar increased plant available nutrients and crop yield on marginal soils. Biochar application reduced the availability of potentially harmful trace elements. Heterotrophic respiration showed no clear response to biochar application. Biochar application may reduce fertilizer need and increase carbon sequestration on marginal soils.
    Description: German Academic Exchange Service http://dx.doi.org/10.13039/501100001655
    Description: Institute Strategic Programme grants, “Soils to Nutrition”
    Keywords: 631.4 ; black carbon ; carbon sequestration ; corn ; digestate ; heterotrophic respiration ; marginal soils ; microbial biomass
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    Staircase array of inclined refractive multi‐lenses for large field of view pixel super‐resolution scanning transmission hard X‐ray microscopy (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2021-06-26
    Description: Owing to the development of X‐ray focusing optics during the past decades, synchrotron‐based X‐ray microscopy techniques allow the study of specimens with unprecedented spatial resolution, down to 10 nm, using soft and medium X‐ray photon energies, though at the expense of the field of view (FOV). One of the approaches to increase the FOV to square millimetres is raster‐scanning of the specimen using a single nanoprobe; however, this results in a long data acquisition time. This work employs an array of inclined biconcave parabolic refractive multi‐lenses (RMLs), fabricated by deep X‐ray lithography and electroplating to generate a large number of long X‐ray foci. Since the FOV is limited by the pattern height if a single RML is used by impinging X‐rays parallel to the substrate, many RMLs at regular intervals in the orthogonal direction were fabricated by tilted exposure. By inclining the substrate correspondingly to the tilted exposure, 378000 X‐ray line foci were generated with a length in the centimetre range and constant intervals in the sub‐micrometre range. The capability of this new X‐ray focusing device was first confirmed using ray‐tracing simulations and then using synchrotron radiation at BL20B2 of SPring‐8, Japan. Taking account of the fact that the refractive lens is effective for focusing high‐energy X‐rays, the experiment was performed with 35 keV X‐rays. Next, by scanning a specimen through the line foci, this device was used to perform large FOV pixel super‐resolution scanning transmission hard X‐ray microscopy (PSR‐STHXM) with a 780 ± 40 nm spatial resolution within an FOV of 1.64 cm × 1.64 cm (limited by the detector area) and a total scanning time of 4 min. Biomedical implant abutments fabricated via selective laser melting using Ti–6Al–4V medical alloy were measured by PSR‐STHXM, suggesting its unique potential for studying extended and thick specimens. Although the super‐resolution function was realized in one dimension in this study, it can be expanded to two dimensions by aligning a pair of presented devices orthogonally.
    Description: A new X‐ray focusing device generates hundreds of thousands of line foci, periodically spaced in the sub‐micrometre range, with centimetre length. It enables to achieve large FOV pixel super‐resolution scanning transmission hard X‐ray microscopy. image
    Keywords: 502.82 ; inclined refractive X‐ray multi‐lens array ; pixel super‐resolution ; scanning transmission hard X‐ray microscopy ; deep X‐ray lithography and electroplating
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    A new concept for temporal gating of synchrotron X‐ray pulses (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2021-07-02
    Description: A new concept for temporal gating of synchrotron X‐ray pulses based on laser‐induced thermal transient gratings is presented. First experimental tests of the concept yield a diffraction efficiency of 0.18%; however, the calculations indicate a theoretical efficiency and contrast of 〉30% and 10−5, respectively. The full efficiency of the pulse picker has not been reached yet due to a long‐range thermal deformation of the sample after absorption of the excitation laser. This method can be implemented in a broad spectral range (100 eV to 20 keV) and is only minimally invasive to an existing setup.
    Description: A new concept for temporal gating of synchrotron X‐ray pulses based on laser‐induced thermal transient gratings is presented.
    Keywords: 548 ; synchrotron ; time‐resolved ; thermal deformation ; transient grating ; pulse picking
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    The time‐resolved hard X‐ray diffraction endstation KMC‐3 XPP at BESSY II (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
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    Publication Date: 2021-06-06
    Description: The time‐resolved hard X‐ray diffraction endstation KMC‐3 XPP for optical pump/X‐ray probe experiments at the electron storage ring BESSY II is dedicated to investigating the structural response of thin film samples and heterostructures after their excitation with ultrashort laser pulses and/or electric field pulses. It enables experiments with access to symmetric and asymmetric Bragg reflections via a four‐circle diffractometer and it is possible to keep the sample in high vacuum and vary the sample temperature between ∼15 K and 350 K. The femtosecond laser system permanently installed at the beamline allows for optical excitation of the sample at 1028 nm. A non‐linear optical setup enables the sample excitation also at 514 nm and 343 nm. A time‐resolution of 17 ps is achieved with the `low‐α' operation mode of the storage ring and an electronic variation of the delay between optical pump and hard X‐ray probe pulse conveniently accesses picosecond to microsecond timescales. Direct time‐resolved detection of the diffracted hard X‐ray synchrotron pulses use a gated area pixel detector or a fast point detector in single photon counting mode. The range of experiments that are reliably conducted at the endstation and that detect structural dynamics of samples excited by laser pulses or electric fields are presented.
    Description: The KMC‐3 XPP endstation of the synchrotron BESSY II is dedicated to time‐resolved studies of structural dynamics of matter upon optical and/or electrical excitation using hard X‐ray diffraction with an accessible time range from 17 ps to several microseconds. image
    Keywords: 548 ; beamline instrumentation ; time‐resolved X‐ray diffraction ; optical excitation ; thermal transport ; ferroelectric switching
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    Self‐stated recovery from flooding: Empirical results from a survey in Central Vietnam (2021)
    Blackwell Publishing Ltd | Oxford, UK
    Details
    Publication Date: 2021-06-27
    Description: Social inequalities lead to flood resilience inequalities across social groups, a topic that requires improved documentation and understanding. The objective of this paper is to attend to these differences by investigating self‐stated flood recovery across genders in Vietnam as a conceptual replication of earlier results from Germany. This study employs a regression‐based analysis of 1,010 respondents divided between a rural coastal and an urban community in Thua Thien‐Hue province. The results highlight an important set of recovery process‐related variables. The set of relevant variables is similar across genders in terms of inclusion and influence, and includes age, social capital, internal and external support after a flood, perceived severity of previous flood impacts, and the perception of stress‐resilience. However, women were affected more heavily by flooding in terms of longer recovery times, which should be accounted for in risk management. Overall, the studied variables perform similarly in Vietnam and Germany. This study, therefore, conceptually replicates previous results suggesting that women display slightly slower recovery levels as well as that psychological variables influence recovery rates more than adverse flood impacts. This provides an indication of the results' potentially robust nature due to the different socio‐environmental contexts in Germany and Vietnam.
    Keywords: 333.7 ; flood recovery ; resilience ; societal equity ; vulnerability
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  • 76
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    Disordered sodium alkoxides from powder data: crystal structures of sodium ethoxide, propoxide, butoxide and pentoxide, and some of their solvates (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2021-03-27
    Description: The crystal structures of sodium ethoxide (sodium ethanolate, NaOEt), sodium n‐propoxide (sodium n‐propanolate, NaOnPr), sodium n‐butoxide (sodium n‐butanolate, NaOnBu) and sodium n‐pentoxide (sodium n‐amylate, NaOnAm) were determined from powder X‐ray diffraction data. NaOEt crystallizes in space group P421m, with Z = 2, and the other alkoxides crystallize in P4/nmm, with Z = 2. To resolve space‐group ambiguities, a Bärnighausen tree was set up, and Rietveld refinements were performed with different models. In all structures, the Na and O atoms form a quadratic net, with the alkyl groups pointing outwards on both sides (anti‐PbO type). The alkyl groups are disordered. The disorder becomes even more pronounced with increasing chain length. Recrystallization from the corresponding alcohols yielded four sodium alkoxide solvates: sodium ethoxide ethanol disolvate (NaOEt·2EtOH), sodium n‐propoxide n‐propanol disolvate (NaOnPr·2nPrOH), sodium isopropoxide isopropanol pentasolvate (NaOiPr·5iPrOH) and sodium tert‐amylate tert‐amyl alcohol monosolvate (NaOtAm·tAmOH, tAm = 2‐methyl‐2‐butyl). Their crystal structures were determined by single‐crystal X‐ray diffraction. All these solvates form chain structures consisting of Na+, –O− and –OH groups, encased by alkyl groups. The hydrogen‐bond networks diverge widely among the solvate structures. The hydrogen‐bond topology of the iPrOH network in NaOiPr·5iPrOH shows branched hydrogen bonds and differs considerably from the networks in pure crystalline iPrOH.
    Description: The crystal structures of NaOEt, NaOPr, NaOBu and NaOAm (Am = amyl = pentyl) were determined from powder data. These compounds crystallize in an anti‐PbO structure in the space groups P21m and P4/nmm. Additionally, solvates with the composition NaOEt·2EtOH, NaOPr·2PrOH, NaOiPr·5iPrOH and NaOtAm·tAmOH were synthesized, and their structures were determined from single crystals. They form interesting chain structures of different compositions and topologies. image
    Keywords: 548 ; sodium alkoxide ; powder data ; solvate ; isopropanol ; Bärnighausen tree ; PXRD
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  • 77
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    The potential of ryegrass as cover crop to reduce soil N2O emissions and increase the population size of denitrifying bacteria (2021)
    Blackwell Publishing Ltd | Oxford, UK
    Details
    Publication Date: 2021-07-05
    Description: Nitrogen (N) fertilization is the major contributor to nitrous oxide (N2O) emissions from agricultural soil, especially in post‐harvest seasons. This study was carried out to investigate whether ryegrass serving as cover crop affects soil N2O emissions and denitrifier community size. A microcosm experiment was conducted with soil planted with perennial ryegrass (Lolium perenne L.) and bare soil, each with four levels of N fertilizer (0, 5, 10 and 20 g N m−2; applied as calcium ammonium nitrate). The closed‐chamber approach was used to measure soil N2O fluxes. Real‐time PCR was used to estimate the biomass of bacteria and fungi and the abundance of genes involved in denitrification in soil. The results showed that the presence of ryegrass decreased the nitrate content in soil. Cumulative N2O emissions of soil with grass were lower than in bare soil at 5 and 10 g N m−2. Fertilization levels did not affect the abundance of soil bacteria and fungi. Soil with grass showed greater abundances of bacteria and fungi, as well as microorganisms carrying narG, napA, nirK, nirS and nosZ clade I genes. It is concluded that ryegrass serving as a cover crop holds the potential to mitigate soil N2O emissions in soils with moderate or high NO3− concentrations. This highlights the importance of cover crops for the reduction of N2O emissions from soil, particularly following N fertilization. Future research should explore the full potential of ryegrass to reduce soil N2O emissions under field conditions as well as in different soils. Highlights This study was to investigate whether ryegrass serving as cover crop affects soil N2O emissions and denitrifier community size; Plant reduced soil N substrates on one side, but their root exudates stimulated denitrification on the other side; N2O emissions were lower in soil with grass than bare soil at medium fertilizer levels, and growing grass stimulated the proliferation of almost all the denitrifying bacteria except nosZ clade II; Ryegrass serving as a cover crop holds the potential to mitigate soil N2O emissions.
    Description: China Scholarship Council http://dx.doi.org/10.13039/501100004543
    Description: The National Science Project for University of Anhui Province
    Keywords: 551.9 ; 631.4 ; denitrification ; perennial ryegrass (Lolium perenne L.) ; soil bacteria ; soil CO2 emissions ; soil N2O emissions
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  • 78
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    Small‐angle X‐ray scattering from GaN nanowires on Si(111): facet truncation rods, facet roughness and Porod's law (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2021-03-27
    Description: Small‐angle X‐ray scattering from GaN nanowires grown on Si(111) is measured in the grazing‐incidence geometry and modelled by means of a Monte Carlo simulation that takes into account the orientational distribution of the faceted nanowires and the roughness of their side facets. It is found that the scattering intensity at large wavevectors does not follow Porod's law I(q) ∝ q−4. The intensity depends on the orientation of the side facets with respect to the incident X‐ray beam. It is maximum when the scattering vector is directed along a facet normal, reminiscent of surface truncation rod scattering. At large wavevectors q, the scattering intensity is reduced by surface roughness. A root‐mean‐square roughness of 0.9 nm, which is the height of just 3–4 atomic steps per micrometre‐long facet, already gives rise to a strong intensity reduction.
    Description: The intensity of small‐angle X‐ray scattering from GaN nanowires on Si(111) depends on the orientation of the side facets with respect to the incident beam. This reminiscence of truncation rod scattering gives rise to a deviation from Porod's law. A roughness of just 3–4 atomic steps per micrometre‐long side facet notably changes the intensity curves. image
    Keywords: 548 ; nanowires ; Porod's law ; facet truncation rods ; small‐angle X‐ray scattering ; SAXS ; grazing‐incidence small‐angle X‐ray scattering ; GISAXS
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  • 79
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    The accuracy of protein models automatically built into cryo‐EM maps with ARP/wARP (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2021-06-28
    Description: Recent developments in cryogenic electron microscopy (cryo‐EM) have enabled structural studies of large macromolecular complexes at resolutions previously only attainable using macromolecular crystallography. Although a number of methods can already assist in de novo building of models into high‐resolution cryo‐EM maps, automated and reliable map interpretation remains a challenge. Presented here is a systematic study of the accuracy of models built into cryo‐EM maps using ARP/wARP. It is demonstrated that the local resolution is a good indicator of map interpretability, and for the majority of the test cases ARP/wARP correctly builds 90% of main‐chain fragments in regions where the local resolution is 4.0 Å or better. It is also demonstrated that the coordinate accuracy for models built into cryo‐EM maps is comparable to that of X‐ray crystallographic models at similar local cryo‐EM and crystallographic resolutions. The model accuracy also correlates with the refined atomic displacement parameters.
    Keywords: 548 ; ARP/wARP ; model building ; cryo‐EM ; model accuracy ; sequence assignment
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  • 80
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    Synthesis, crystal structure and structure–property relations of strontium orthocarbonate, Sr2CO4 (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2021-06-05
    Description: Carbonates containing CO4 groups as building blocks have recently been discovered. A new orthocarbonate, Sr2CO4 is synthesized at 92 GPa and at a temperature of 2500 K. Its crystal structure was determined by in situ synchrotron single‐crystal X‐ray diffraction, selecting a grain from a polycrystalline sample. Strontium orthocarbonate crystallizes in the orthorhombic crystal system (space group Pnma) with CO4, SrO9 and SrO11 polyhedra as the main building blocks. It is isostructural to Ca2CO4. DFT calculations reproduce the experimental findings very well and have, therefore, been used to predict the equation of state, Raman and IR spectra, and to assist in the discussion of bonding in this compound.
    Description: A new orthocarbonate, Sr2CO4, was synthesized under extreme pressure and temperature conditions of 92 GPa and 2500 K, respectively. The crystal structure of the compound s fully characterized in situ by synchrotron single‐crystal X‐ray diffraction and DFT calculations were employed to provide insight into its equation of state, Raman and IR spectra, and bonding. image
    Keywords: 548 ; orthocarbonates ; crystal structure ; single‐crystal X‐ray diffraction ; high pressure ; Sr2CO4
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  • 81
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    Anomalous SAXS at P12 beamline EMBL Hamburg: instrumentation and applications (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2021-06-28
    Description: Small‐angle X‐ray scattering (SAXS) is an established method for studying nanostructured systems and in particular biological macromolecules in solution. To obtain element‐specific information about the sample, anomalous SAXS (ASAXS) exploits changes of the scattering properties of selected atoms when the energy of the incident X‐rays is close to the binding energy of their electrons. While ASAXS is widely applied to condensed matter and inorganic systems, its use for biological macromolecules is challenging because of the weak anomalous effect. Biological objects are often only available in small quantities and are prone to radiation damage, which makes biological ASAXS measurements very challenging. The BioSAXS beamline P12 operated by the European Molecular Biology Laboratory (EMBL) at the PETRA III storage ring (DESY, Hamburg) is dedicated to studies of weakly scattering objects. Here, recent developments at P12 allowing for ASAXS measurements are presented. The beamline control, data acquisition and data reduction pipeline of the beamline were adapted to conduct ASAXS experiments. Modelling tools were developed to compute ASAXS patterns from atomic models, which can be used to analyze the data and to help designing appropriate data collection strategies. These developments are illustrated with ASAXS experiments on different model systems performed at the P12 beamline.
    Keywords: 548 ; ASAXS ; biological SAXS ; metalloproteins ; gold nanoparticles ; anomalous scattering ; beamline development
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  • 82
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    Reservoir Structure and Hydraulic Properties of the Campi Flegrei Geothermal System Inferred by Audiomagnetotelluric, Geochemical, and Seismicity Study (2020)
    Wiley
    Details
    Publication Date: 2020-01-23
    Description: The Campi Flegrei caldera is a large volcanic complex lying in the Campanian Plain, Southern Italy. During its history the caldera experienced episodes of bradyseism and intense swarm seismicity. The mechanism leading to unrest episodes is still debated, and great efforts are ongoing to improve the knowledge of this structure and its evolution due to the high volcanic risk in such a densely populated area. Here we present a resistivity model from a two‐dimensional inversion of audiomagnetotelluric data acquired along an approximately 5.6‐km long profile crosscutting the Solfatara‐Pisciarelli district and the Agnano plain. The resistivity model shows (1) very low resistivity values confined in the first 500 m of depth both in correspondence of the Solfatara‐Pisciarelli districts and the Agnano depression; (2) a resistive plume that extends underneath the Solfatara crater down to 2,000‐ to 3,000‐m depth, and (3) an adjoining relative conductive unit eastward. We discuss the resistivity structures in a multidisciplinary framework integrating inedited geochemical and seismological observations with existing surface geology and subsurface information. The Solfatara‐Pisciarelli district and the Agnano plain, both being expression of intense hydrothermal activity, show different characteristics. Below the Solfatara‐Pisciarelli area, the shallow conductive zone is interpreted as a faulted clay cap that overlies a highly active vapor‐dominated reservoir characterized by a convective mechanism. Conversely, below the Agnano plain, a liquid phase seems to prevail in the reservoir. The spatiotemporal variations of seismicity imply a combined action of preexisting tectonic lineaments and fluid interaction between the gas/steam reservoir and the outflow zone.
    Description: Published
    Description: 5336-5356
    Description: 2V. Struttura e sistema di alimentazione dei vulcani
    Description: JCR Journal
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 83
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    Insight Into Campi Flegrei Caldera Unrest Through Seismic Tremor Measurements at Pisciarelli Fumarolic Field (2020)
    Wiley
    Details
    Publication Date: 2020-01-23
    Description: Within a general volcanic unrest in the densely urbanized area of Campi Flegrei caldera (Italy) an increase in the activity of Pisciarelli hydrothermal area is occurring. The seismic amplitude of Pisciarelli fumarolic tremor is a proxy for the fluid emission rate of the entire Solfatara‐Pisciarelli hydrothermal system. The long‐term analysis indicates a significant increase, by a factor of ~3 of the fumarolic tremor amplitude since May 2017. This increment matches with the trend of geochemical and seismic parameters observed in Campi Flegrei, therefore highlighting that Pisciarelli is a key site to monitor the volcanic unrest underway in this high‐risk caldera. The analysis of data from three closely spaced seismic stations provided new clues about the source mechanism of the tremor. Analyzing the fumarolic tremor amplitude we could also identify an episode of enlargement of the emission area close to the main fumarole of Pisciarelli. We propose a monitoring system based on the fumarolic tremor analysis, which provides real‐time information on the Pisciarelli hydrothermal activity and therefore on the current unrest in Campi Flegrei caldera.
    Description: Published
    Description: 5544-5555
    Description: 4V. Processi pre-eruttivi
    Description: JCR Journal
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 84
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    Water Availability and Deformation Processes in Smectite‐Rich Gouges During Seismic Slip (2020)
    Wiley
    Details
    Publication Date: 2020-02-10
    Description: Smectite clays occur in subduction zone fault cores at shallow depth (approximately 1 km; e.g., Japan Trench) and landslide décollements (e.g., Vajont, Italy, 1963). The availability of pore fluids affects the likelihood that seismic slip propagates from deeper to shallow fault depths or that a landslide accelerates to its final collapse. To investigate the deformation processes active during seismic faulting we performed friction experiments with a rotary machine on 2‐mm‐thick smectite‐rich gouge layers (70/30 wt % Ca‐montmorillonite/opal) sheared at 5‐MPa normal stress, at slip rates of 0.001, 0.01, 0.1, and 1.3 m/s, and total displacement of 3 m. Experiments were performed on predried gouges under vacuum, under room humidity and under partly saturated conditions. The fault shear strength measured in the experiments was included in a one‐dimensional numerical model incorporating frictional heating, thermal, and thermochemical pressurization. Quantitative X‐ray powder diffraction and scanning electron microscopy investigations were performed on pristine and deformed smectite‐rich gouges. Under dry conditions, cataclasis and amorphization dominated at slip rates of 0.001–0.1 m/s, whereas grain size sensitive flow and, under vacuum, frictional melting occurred at fast slip rates (1.3 m/s). Under partly saturated conditions, frictional slip in a smectite foliation occurred in combination with pressurization of water by shear‐enhanced compaction and, for V = 0.01–1.3 m/s, with thermal pressurization. Pseudotachylytes, the only reliable microstructural markers for seismic slip, formed only with large frictional power (〉2 MW/m2), which could be achieved at shallow depth with high slip rates, or, at depth, with high shear stress in dehydrated smectites.
    Description: Published
    Description: 10855-10876
    Description: 3T. Sorgente sismica
    Description: JCR Journal
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 85
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    Symmetry relations in wurtzite nitrides and oxide nitrides and the curious case of Pmc21 (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2021-06-27
    Description: Binary III–V nitrides such as AlN, GaN and InN in the wurtzite‐type structure have long been considered as potent semiconducting materials because of their optoelectronic properties, amongst others. With rising concerns over the utilization of scarce elements, a replacement of the trivalent cations by others in ternary and multinary nitrides has led to the development of different variants of nitrides and oxide nitrides crystallizing in lower‐symmetry variants of wurtzite. This work presents the symmetry relationships between these structural types specific to nitrides and oxide nitrides and updates some prior work on this matter. The non‐existence of compounds crystallizing in Pmc21, formally the highest subgroup of the wurtzite type fulfilling Pauling's rules for 1:1:2 stoichiometries, has been puzzling scientists for a while; a rationalization is given, from a crystallographic basis, of why this space group is unlikely to be adopted.
    Keywords: 548 ; group–subgroup relationships ; nitride materials ; wurtzite type
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  • 86
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    Comparison and evaluation of pair distribution functions, using a similarity measure based on cross‐correlation functions (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2021-06-20
    Description: An approach for the comparison of pair distribution functions (PDFs) has been developed using a similarity measure based on cross‐correlation functions. The PDF is very sensitive to changes in the local structure, i.e. small deviations in the structure can cause large signal shifts and significant discrepancies between the PDFs. Therefore, a comparison based on pointwise differences (e.g. R values and difference curves) may lead to the assumption that the investigated PDFs as well as the corresponding structural models are not in agreement at all, whereas a careful visual inspection of the investigated structural models and corresponding PDFs may reveal a relatively good match. To quantify the agreement of different PDFs for those cases an alternative approach is introduced: the similarity measure based on cross‐correlation functions. In this paper, the power of this application of the similarity measure to the analysis of PDFs is highlighted. The similarity measure is compared with the classical Rwp values as representative of the comparison based on pointwise differences as well as with the Pearson product‐moment correlation coefficient, using polymorph IV of barbituric acid as an example.
    Description: A novel approach to the quantification of the agreement between pair distribution functions by a similarity measure based on cross‐correlation functions is introduced and evaluated. image
    Keywords: 548 ; pair distribution functions ; similarity measures ; total scattering techniques ; cross‐correlation functions ; R values
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  • 87
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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
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  • 88
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    The anisotropy in the optical constants of quartz crystals for soft X‐rays (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2021-06-26
    Description: The refractive index of a y‐cut SiO2 crystal surface is reconstructed from orientation‐dependent soft X‐ray reflectometry measurements in the energy range from 45 to 620 eV. Owing to the anisotropy of the crystal structure in the (100) and (001) directions, a significant deviation of the measured reflectance at the Si L2,3 and O K absorption edges is observed. The anisotropy in the optical constants reconstructed from these data is also confirmed by ab initio Bethe–Salpeter equation calculations for the O K edge. This new experimental data set expands the existing literature data for quartz crystal optical constants significantly, particularly in the near‐edge regions.
    Description: The refractive index of a y‐cut SiO2 crystal surface is reconstructed from polarization‐dependent soft X‐ray reflectometry measurements in the energy range from 45 to 620 eV. The reconstructed anisotropy in the optical constants is also confirmed by ab initio Bethe–Salpeter equation calculations of the O K edge. image
    Keywords: 548 ; optical constants ; quartz ; anisotropy ; soft X‐ray reflectometry
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  • 89
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    Unravelling the crystal structure of Nd5.8WO12−δ and Nd5.7W0.75Mo0.25O12−δ mixed ionic electronic conductors (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2021-07-05
    Description: Mixed ionic electronic conducting ceramics Nd6−yWO12−δ (δ is the oxygen deficiency) provide excellent stability in harsh environments containing strongly reactive gases such as CO2, CO, H2, H2O or H2S. Due to this chemical stability, they are promising and cost‐efficient candidate materials for gas separation, catalytic membrane reactors and protonic ceramic fuel cell technologies. As in La6−yWO12−δ, the ionic/electronic transport mechanism in Nd6−yWO12−δ is expected to be largely controlled by the crystal structure, the conclusive determination of which is still lacking. This work presents a crystallographic study of Nd5.8WO12−δ and molybdenum‐substituted Nd5.7W0.75Mo0.25O12−δ prepared by the citrate complexation route. High‐resolution synchrotron and neutron powder diffraction data were used in combined Rietveld refinements to unravel the crystal structure of Nd5.8WO12−δ and Nd5.7W0.75Mo0.25O12−δ. Both investigated samples crystallize in a defect fluorite crystal structure with space group Fm3m and doubled unit‐cell parameter due to cation ordering. Mo replaces W at both Wyckoff sites 4a and 48h and is evenly distributed, in contrast with La6−yWO12−δ. X‐ray absorption spectroscopy as a function of partial pressure pO2 in the near‐edge regions excludes oxidation state changes of Nd (Nd3+) and W (W6+) in reducing conditions: the enhanced hydrogen permeation, i.e. ambipolar conduction, observed in Mo‐substituted Nd6−yWO12−δ is therefore explained by the higher Mo reducibility and the creation of additional – disordered – oxygen vacancies.
    Description: The crystal structures of non‐substituted and Mo‐substituted neodymium tungstates are described in detail through neutron diffraction and high‐resolution X‐ray diffraction. Combined X‐ray and neutron diffraction refinements and electron probe micro‐analysis were employed to locate Mo atoms in the crystal structure of Nd6−yW1−zMozO12−δ (z = 0, 0.25), while X‐ray absorption spectroscopy in the near‐edge regions confirmed no changes in the oxidation states of Nd and W.
    Keywords: 548 ; powder diffraction ; mixed conductors ; X‐ray absorption spectroscopy (XAS) ; Nd6−yWO12−δ
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  • 90
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    ogs5py: A Python‐API for the OpenGeoSys 5 Scientific Modeling Package (2021)
    Blackwell Publishing Ltd | Malden, US
    Details
    Publication Date: 2021-07-04
    Description: High‐performance numerical codes are an indispensable tool for hydrogeologists when modeling subsurface flow and transport systems. But as they are written in compiled languages, like C/C++ or Fortran, established software packages are rarely user‐friendly, limiting a wider adoption of such tools. OpenGeoSys (OGS), an open‐source, finite‐element solver for thermo‐hydro‐mechanical–chemical processes in porous and fractured media, is no exception. Graphical user interfaces may increase usability, but do so at a dramatic reduction of flexibility and are difficult or impossible to integrate into a larger workflow. Python offers an optimal trade‐off between these goals by providing a highly flexible, yet comparatively user‐friendly environment for software applications. Hence, we introduce ogs5py, a Python‐API for the OpenGeoSys 5 scientific modeling package. It provides a fully Python‐based representation of an OGS project, a large array of convenience functions for users to interact with OGS and connects OGS to the scientific and computational environment of Python.
    Description: German Federal Environmental Foundation http://dx.doi.org/10.13039/100007636
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Keywords: 551.49 ; hydrogeology ; subsurface flow ; modeling ; software
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  • 91
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    High‐temperature treatments of niobium under high vacuum, dilute air‐ and nitrogen‐atmospheres as investigated by in situ X‐ray absorption spectroscopy (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2021-06-30
    Description: Niobium metal foils were heat‐treated at 900°C under different conditions and in situ investigated with time‐resolved X‐ray absorption fine‐structure (EXAFS and XANES) measurements. The present study aims to mimic the conditions usually applied for heat treatments of Nb materials used for superconducting radiofrequency cavities, in order to better understand the evolving processes during vacuum annealing as well as for heat treatments in controlled dilute gases. Annealing in vacuum in a commercially available cell showed a substantial amount of oxidation, so that a designated new cell was designed and realized, allowing treatments under clean high‐vacuum conditions as well as under well controllable gas atmospheres. The experiments performed under vacuum demonstrated that the original structure of the Nb foils is preserved, while a detailed evaluation of the X‐ray absorption fine‐structure data acquired during treatments in dilute air atmospheres (10−5 mbar to 10−3 mbar) revealed a linear oxidation with the time of the treatment, and an oxidation rate proportional to the oxygen (air) pressure. The structure of the oxide appears to be very similar to that of polycrystalline NbO. The cell also permits controlled exposures to other reactive gases at elevated temperatures; here the Nb foils were exposed to dilute nitrogen atmospheres after a pre‐conditioning of the studied Nb material for one hour under high‐vacuum conditions, in order to imitate typical conditions used for nitrogen doping of cavity materials. Clear structural changes induced by the N2 exposure were found; however, no evidence for the formation of niobium nitride could be derived from the EXAFS and XANES experiments. The presented results establish the feasibility to study the structural changes of the Nb materials in situ during heat treatments in reactive gases with temporal resolution, which are important to better understand the underlaying mechanisms and the dynamics of phase formation during those heat treatments in more detail.
    Keywords: 548 ; in situ EXAFS ; high temperature ; time‐resolved EXAFS ; niobium
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  • 92
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    High‐Resolution Integrated Transport Model for Studying Surface Water–Groundwater Interaction (2021)
    Blackwell Publishing Ltd | Malden, US
    Details
    Publication Date: 2021-06-27
    Description: Transport processes that lead to exchange of mass between surface water and groundwater play a significant role for the ecological functioning of aquatic systems, for hydrological processes and for biogeochemical transformations. In this study, we present a novel integral modeling approach for flow and transport at the sediment–water interface. The model allows us to simultaneously simulate turbulent surface and subsurface flow and transport with the same conceptual approach. For this purpose, a conservative transport equation was implemented to an existing approach that uses an extended version of the Navier–Stokes equations. Based on previous flume studies which investigated the spreading of a dye tracer under neutral, losing and gaining flow conditions the new solver is validated. Tracer distributions of the experiments are in close agreement with the simulations. The simulated flow paths are significantly affected by in‐ and outflowing groundwater flow. The highest velocities within the sediment are found for losing condition, which leads to shorter residence times compared to neutral and gaining conditions. The largest extent of the hyporheic exchange flow is observed under neutral condition. The new solver can be used for further examinations of cases that are not suitable for the conventional coupled models, for example, if Reynolds numbers are larger than 10. Moreover, results gained with the integral solver provide high‐resolution information on pressure and velocity distributions at the rippled streambed, which can be used to improve flow predictions. This includes the extent of hyporheic exchange under varying ambient groundwater flow conditions.
    Description: Technische Universität Berlin, Germany
    Description: German Research Foundation http://dx.doi.org/10.13039/501100001659
    Keywords: 551.4 ; aquatic systems ; sediment-water interface ; transport model
    Type: article
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  • 93
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    Pressure‐induced Pb–Pb bonding and phase transition in Pb2SnO4 (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2021-03-27
    Description: High‐pressure single‐crystal to 20 GPa and powder diffraction measurements to 50 GPa, show that the structure of Pb2SnO4 strongly distorts on compression with an elongation of one axis. A structural phase transition occurs between 10 GPa and 12 GPa, with a change of space group from Pbam to Pnam. The resistivity decreases by more than six orders of magnitude when pressure is increased from ambient conditions to 50 GPa. This insulator‐to‐semiconductor transition is accompanied by a reversible appearance change from transparent to opaque. Density functional theory‐based calculations show that at ambient conditions the channels in the structure host the stereochemically‐active Pb 6s2 lone electron pairs. On compression the lone electron pairs form bonds between Pb2+ ions. Also provided is an assignment of irreducible representations to the experimentally observed Raman bands.
    Description: The structure of Pb2SnO4 is found to strongly distort on compression and a structural phase transition with a change of space group from Pbam to Pnam occurs at ∼11 GPa. Our complementary DFT‐based calculations show that at ambient conditions, the channels in the structure host the stereochemically active Pb 6s2 lone electron pairs which form bonds between the Pb2+ ions with increasing pressure. image
    Keywords: 548 ; lead stannate (Pb2SnO4) ; density functional theory ; high‐pressure X‐ray diffraction ; pressure‐induced phase transition ; insulator–semiconductor transition
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  • 94
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    Iron isotope fractionation in soil and graminaceous crops after 100 years of liming in the long‐term agricultural experimental site at Berlin‐Dahlem, Germany (2021)
    Blackwell Publishing Ltd | Oxford, UK
    Details
    Publication Date: 2021-07-05
    Description: Sustainable arable cropping relies on repeated liming. Yet, the associated increase in soil pH can reduce the availability of iron (Fe) to plants. We hypothesized that repeated liming, but not pedogenic processes such as lessivage (i.e., translocation of clay particles), alters the Fe cycle in Luvisol soil, thereby affecting Fe isotope composition in soils and crops. Hence, we analysed Fe concentrations and isotope compositions in soil profiles and winter rye from the long‐term agricultural experimental site in Berlin‐Dahlem, Germany, where a controlled liming trial with three field replicates per treatment has been conducted on Albic Luvisols since 1923. Heterogeneity in subsoil was observed at this site for Fe concentration but not for Fe isotope composition. Lessivage had not affected Fe isotope composition in the soil profiles. The results also showed that almost 100 years of liming lowered the concentration of the HCl‐extractable Fe that was potentially available for plant uptake in the surface soil (0–15 cm) from 1.03 (standard error (SE) 0.03) to 0.94 (SE 0.01) g kg−1. This HCl‐extractable Fe pool contained isotopically lighter Fe (δ56Fe = −0.05 to −0.29‰) than the bulk soil (δ56Fe = −0.08 to 0.08‰). However, its Fe isotope composition was not altered by the long‐term lime application. Liming resulted in relatively lower Fe concentrations in the roots of winter rye. In addition, liming led to a heavier Fe isotope composition of the whole plants compared with those grown in the non‐limed plots (δ56FeWholePlant_ + Lime = −0.12‰, SE 0.03 vs. δ56FeWholePlant_‐Lime = −0.21‰, SE 0.01). This suggests that the elevated soil pH (increased by one unit due to liming) promoted the Fe uptake strategy through complexation of Fe(III) from the rhizosphere, which favoured heavier Fe isotopes. Overall, the present study showed that liming and a related increase in pH did not affect the Fe isotope compositions of the soil, but may influence the Fe isotope composition of plants grown in the soil if they alter their Fe uptake strategy upon the change of Fe availability. Highlights Fe concentrations and stocks, but not Fe isotope compositions, were more heterogeneous in subsoil than in topsoil. Translocation of clay minerals did not result in Fe isotope fractionation in the soil profile of a Luvisol. Liming decreased Fe availability in topsoil, but did not affect its δ56Fe values. Uptake of heavier Fe isotopes by graminaceous crops was more pronounced at elevated pH.
    Description: Bundesministerium für Bildung und Forschung http://dx.doi.org/10.13039/501100002347
    Keywords: 551.9 ; liming ; plant‐available Fe pool in soil ; winter rye ; δ56Fe
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  • 95
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    A discussion on `Domain formation and phase transitions in the wurtzite‐based heterovalent ternaries: a Landau theory analysis' (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2021-06-05
    Description: Heterovalent ternary nitrides are considered one of the promising classes of materials for photovoltaics, combining attractive physical properties with low toxicity and element abundance. One of the front‐runner systems under consideration is ZnSnN2. Although it is nominally a ternary compound, no clear crystallographic evidence for cation ordering has been observed so far. An attempt to elucidate this discrepancy [Quayle (2020). Acta Cryst. A76, 410–420] was the trigger for an intensive discussion between the authors, and an agreement was reached to elaborate on some points in order to set things in perspective. Rather than using a conventional comment–answer scheme, this is published in the form of a joint discussion to celebrate constructive criticism and collegiality.
    Description: A scientific exchange on an earlier paper [Quayle (2020). Acta Cryst. A76, 410–420] has led to the clarification of some of the points. image
    Keywords: 548 ; group–subgroup relationships ; nitride materials ; wurtzite type
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  • 96
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    X‐SPEC: a 70 eV to 15 keV undulator beamline for X‐ray and electron spectroscopies (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2021-06-26
    Description: X‐SPEC is a high‐flux spectroscopy beamline at the KIT (Karlsruhe Institute of Technology) Synchrotron for electron and X‐ray spectroscopy featuring a wide photon energy range. The beamline is equipped with a permanent magnet undulator with two magnetic structures of different period lengths, a focusing variable‐line‐space plane‐grating monochromator, a double‐crystal monochromator and three Kirkpatrick–Baez mirror pairs. By selectively moving these elements in or out of the beam, X‐SPEC is capable of covering an energy range from 70 eV up to 15 keV. The flux of the beamline is maximized by optimizing the magnetic design of the undulator, minimizing the number of optical elements and optimizing their parameters. The beam can be focused into two experimental stations while maintaining the same spot position throughout the entire energy range. The first experimental station is optimized for measuring solid samples under ultra‐high‐vacuum conditions, while the second experimental station allows in situ and operando studies under ambient conditions. Measurement techniques include X‐ray absorption spectroscopy (XAS), extended X‐ray absorption fine structure (EXAFS), photoelectron spectroscopy (PES) and hard X‐ray PES (HAXPES), as well as X‐ray emission spectroscopy (XES) and resonant inelastic X‐ray scattering (RIXS).
    Description: X‐SPEC is a high‐flux undulator beamline for electron and X‐ray spectroscopy with an energy range from 70 eV to 15 keV. It offers X‐ray absorption spectroscopy (XAS), extended X‐ray absorption fine structure (EXAFS), photoelectron spectroscopy (PES) and hard X‐ray PES (HAXPES), as well as X‐ray emission spectroscopy (XES) and resonant inelastic X‐ray scattering (RIXS) for in vacuo, in situ and operando sample environments. image
    Keywords: 548 ; undulator beamline ; soft X‐ray ; tender X‐ray ; hard X‐ray ; in situ ; operando ; HAXPES ; RIXS ; XAS ; XES
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  • 97
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    Sediment dynamics on the Northwest African continental margin (1982)
    Wiley
    In:  EPIC3The Ocean Floor, The Ocean Floor, Wiley, pp. 147-163
    Details
    Publication Date: 2016-03-17
    Repository Name: EPIC Alfred Wegener Institut
    Type: Inbook , peerRev
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  • 98
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    The evolving paleobathymetry of the circum-Antarctic Southern Ocean since 34 Ma – A key to understanding past cryosphere-ocean developments (2020)
    Wiley
    In:  EPIC3Geochemistry Geophysics Geosystems, Wiley, 21, ISSN: 1525-2027
    Details
    Publication Date: 2021-07-19
    Description: The Southern Ocean is a key player in the climate, ocean and atmospheric system. As the only direct connection between all three major oceans since the opening of the Southern Ocean gateways, the development of the Southern Ocean and its relationship with the Antarctic cryosphere has influenced the climate of the entire planet. Although the depths of the ocean floor have been recognized as an important factor in climate and paleoclimate models, appropriate paleobathymetric models including a detailed analysis of the sediment cover are not available. Here, we utilize more than 40 years of seismic reflection data acquisition along the margins of Antarctica and its conjugate margins, along with multiple drilling campaigns by the International Ocean Discovery Program (IODP) and its predecessor programs. We combine and update the seismic stratigraphy across the regions of the Southern Ocean and calculate ocean-wide paleobathymetry grids via a backstripping method. We present a suite of high-resolution paleobathymetric grids from the Eocene-Oligocene Boundary to modern times. The grids reveal the development of the Southern Ocean from isolated basins to an interconnected ocean affected by the onset and vigor of an Antarctic Circumpolar Current, as well as the glacial sedimentation and erosion of the Antarctic continent. The ocean-wide comparison through time exposes patterns of ice sheet development such as switching of glacial outlets and the change from wet-based to dry-based ice sheets. Ocean currents and bottom-water production interact with the sedimentation along the continental shelf and slope and profit from the opening of the ocean gateways.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 99
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    Structure determination of organic compounds by a fit to the pair distribution function from scratch without prior indexing (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2021-06-26
    Description: A method for the ab initio crystal structure determination of organic compounds by a fit to the pair distribution function (PDF), without prior knowledge of lattice parameters and space group, has been developed. The method is called `PDF‐Global‐Fit' and is implemented by extension of the program FIDEL (fit with deviating lattice parameters). The structure solution is based on a global optimization approach starting from random structural models in selected space groups. No prior indexing of the powder data is needed. The new method requires only the molecular geometry and a carefully determined PDF. The generated random structures are compared with the experimental PDF and ranked by a similarity measure based on cross‐correlation functions. The most promising structure candidates are fitted to the experimental PDF data using a restricted simulated annealing structure solution approach within the program TOPAS, followed by a structure refinement against the PDF to identify the correct crystal structure. With the PDF‐Global‐Fit it is possible to determine the local structure of crystalline and disordered organic materials, as well as to determine the local structure of unindexable powder patterns, such as nanocrystalline samples, by a fit to the PDF. The success of the method is demonstrated using barbituric acid as an example. The crystal structure of barbituric acid form IV solved and refined by the PDF‐Global‐Fit is in excellent agreement with the published crystal structure data.
    Keywords: 548 ; pair distribution function analysis ; structure determination ; total scattering technique ; similarity measures ; PDF‐Global‐Fit
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  • 100
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    Structural basis of chitin utilization by a GH20 β‐N‐acetylglucosaminidase from Vibrio campbellii strain ATCC BAA‐1116 (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2021-07-01
    Description: Vibrio species play a crucial role in maintaining the carbon and nitrogen balance between the oceans and the land through their ability to employ chitin as a sole source of energy. This study describes the structural basis for the action of the GH20 β‐N‐acetylglucosaminidase (VhGlcNAcase) in chitin metabolism by Vibrio campbellii (formerly V. harveyi) strain ATCC BAA‐1116. Crystal structures of wild‐type VhGlcNAcase in the absence and presence of the sugar ligand, and of the unliganded D437A mutant, were determined. VhGlcNAcase contains three distinct domains: an N‐terminal carbohydrate‐binding domain linked to a small α+β domain and a C‐terminal (β/α)8 catalytic domain. The active site of VhGlcNAcase has a narrow, shallow pocket that is suitable for accommodating a small chitooligosaccharide. VhGlcNAcase is a monomeric enzyme of 74 kDa, but its crystal structures show two molecules of enzyme per asymmetric unit, in which Gln16 at the dimeric interface of the first molecule partially blocks the entrance to the active site of the neighboring molecule. The GlcNAc unit observed in subsite −1 makes exclusive hydrogen bonds to the conserved residues Arg274, Tyr530, Asp532 and Glu584, while Trp487, Trp546, Trp582 and Trp505 form a hydrophobic wall around the −1 GlcNAc. The catalytic mutants D437A/N and E438A/Q exhibited a drastic loss of GlcNAcase activity, confirming the catalytic role of the acidic pair (Asp437–Glu438).
    Description: Crystal structures of a GH20 β‐N‐acetylglucosaminidase from V. campbellii reveal substrate specificity in chitin utilization.
    Keywords: 577.14 ; GH20 β‐N‐acetylglucosaminidase ; chitin recycling ; Vibrio spp ; marine bacteria
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