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  • Cell Press  (51,126)
  • International Union of Crystallography  (49,833)
  • American Geophysical Union (AGU)
  • Annual Reviews
  • 2020-2024  (466)
  • 2020-2023  (15)
  • 2005-2009  (65,738)
  • 1990-1994  (28,096)
  • 1980-1984  (19,535)
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  • 1
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    On incoherent diffractive imaging (2021)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2022-04-07
    Description: Incoherent diffractive imaging (IDI) promises structural analysis with atomic resolution based on intensity interferometry of pulsed X‐ray fluorescence emission. However, its experimental realization is still pending and a comprehensive theory of contrast formation has not been established to date. Explicit expressions are derived for the equal‐pulse two‐point intensity correlations, as the principal measured quantity of IDI, with full control of the prefactors, based on a simple model of stochastic fluorescence emission. The model considers the photon detection statistics, the finite temporal coherence of the individual emissions, as well as the geometry of the scattering volume. The implications are interpreted in view of the most relevant quantities, including the fluorescence lifetime, the excitation pulse, as well as the extent of the scattering volume and pixel size. Importantly, the spatiotemporal overlap between any two emissions in the sample can be identified as a crucial factor limiting the contrast and its dependency on the sample size can be derived. The paper gives rigorous estimates for the optimum sample size, the maximum photon yield and the expected signal‐to‐noise ratio under optimal conditions. Based on these estimates, the feasibility of IDI experiments for plausible experimental parameters is discussed. It is shown in particular that the mean number of photons per detector pixel which can be achieved with X‐ray fluorescence is severely limited and as a consequence imposes restrictive constraints on possible applications.
    Description: Starting from a simple model of stochastic fluorescence emission, a theory is derived of contrast formation and signal‐to‐noise ratio for incoherent diffractive imaging; its feasibility for plausible experimental parameters is discussed. image
    Keywords: ddc:548
    Language: English
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  • 2
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    Role of carbon cycle observations and knowledge in carbon management (2005)
    Annual Reviews
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © Annual Reviews, 2003. This article is posted here by permission of Annual Reviews for personal use, not for redistribution. The definitive version was published in Annual Review of Environment and Resources 28 (2003): 521-558, doi:10.1146/annurev.energy.28.011503.163443.
    Description: Agriculture and industrial development have led to inadvertent changes in the natural carbon cycle. As a consequence, concentrations of carbon dioxide and other greenhouse gases have increased in the atmosphere and may lead to changes in climate. The current challenge facing society is to develop options for future management of the carbon cycle. A variety of approaches has been suggested: direct reduction of emissions, deliberate manipulation of the natural carbon cycle to enhance sequestration, and capture and isolation of carbon from fossil fuel use. Policy development to date has laid out some of the general principles to which carbon management should adhere. These are summarized as: how much carbon is stored, by what means, and for how long. To successfully manage carbon for climate purposes requires increased understanding of carbon cycle dynamics and improvement in the scientific capabilities available for measurement as well as for policy needs. The specific needs for scientific information to underpin carbon cycle management decisions are not yet broadly known. A stronger dialogue between decision makers and scientists must be developed to foster improved application of scientific knowledge to decisions. This review focuses on the current knowledge of the carbon cycle, carbon measurement capabilities (with an emphasis on the continental scale) and the relevance of carbon cycle science to carbon sequestration goals.
    Description: The National Center for Atmospheric Research is supported by the National Science Foundation.
    Keywords: Carbon sequestration ; Measurement techniques ; Climate ; Kyoto protocol
    Repository Name: Woods Hole Open Access Server
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  • 3
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    Long nonlinear internal waves (2006)
    Annual Reviews
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © Annual Reviews, 2006. This article is posted here by permission of Annual Reviews for personal use, not for redistribution. The definitive version was published in Annual Review of Fluid Mechanics 38 (2006): 395-425, doi:10.1146/annurev.fluid.38.050304.092129.
    Description: Over the past four decades, the combination of in situ and remote sensing observations has demonstrated that long nonlinear internal solitary-like waves are ubiquitous features of coastal oceans. The following provides an overview of the properties of steady internal solitary waves and the transient processes of wave generation and evolution, primarily from the point of view of weakly nonlinear theory, of which the Korteweg-de Vries equation is the most frequently used example. However, the oceanographically important processes of wave instability and breaking, generally inaccessible with these models, are also discussed. Furthermore, observations often show strongly nonlinear waves whose properties can only be explained with fully nonlinear models.
    Description: KRH acknowledges support from NSF and ONR and an Independent Study Award from the Woods Hole Oceanographic Institution. WKM acknowledges support from NSF and ONR, which has made his work in this area possible, in close collaboration with former graduate students at Scripps Institution of Oceanography and MIT.
    Keywords: Solitary waves ; Nonlinear waves ; Stratified flow ; Physical Oceanography
    Repository Name: Woods Hole Open Access Server
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  • 4
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    Design and function of superfast muscles : new insights into the physiology of skeletal muscle (2005)
    Annual Reviews
    Details
    Publication Date: 2022-05-25
    Description: First published online as a Review in Advance on October 24, 2005. (Some corrections may occur before final publication online and in print)
    Description: Author Posting. © Annual Reviews, 2005. This article is posted here by permission of Annual Reviews for personal use, not for redistribution. The definitive version was published in Annual Review of Physiology 68 (2006): 22.1-22.29, doi:10.1146/annurev.physiol.68.040104.105418.
    Description: Superfast muscles of vertebrates power sound production. The fastest, the swimbladder muscle of toadfish, generates mechanical power at frequencies in excess of 200 Hz. To operate at these frequencies, the speed of relaxation has had to increase approximately 50-fold. This increase is accomplished by modifications of three kinetic traits: (a) a fast calcium transient due to extremely high concentration of sarcoplasmic reticulum (SR)-Ca2+ pumps and parvalbumin, (b) fast off-rate of Ca2+ from troponin C due to an alteration in troponin, and (c) fast cross-bridge detachment rate constant (g, 50 times faster than that in rabbit fast-twitch muscle) due to an alteration in myosin. Although these three modifications permit swimbladder muscle to generate mechanical work at high frequencies (where locomotor muscles cannot), it comes with a cost: The high g causes a large reduction in attached force-generating cross-bridges, making the swimbladder incapable of powering low-frequency locomotory movements. Hence the locomotory and sound-producing muscles have mutually exclusive designs.
    Description: This work was made possible by support from NIH grants AR38404 and AR46125 as well as the University of Pennsylvania Research Foundation.
    Keywords: Parvalbumin ; Ca2+ release ; Ca2+ uptake ; Cross-bridges ; Adaptation ; Sound production ; Whitman Center
    Repository Name: Woods Hole Open Access Server
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  • 5
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    Sub‐micrometer focusing setup for high‐pressure crystallography at the Extreme Conditions beamline at PETRA III (2022)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2022-06-24
    Description: Scientific tasks aimed at decoding and characterizing complex systems and processes at high pressures set new challenges for modern X‐ray diffraction instrumentation in terms of X‐ray flux, focal spot size and sample positioning. Presented here are new developments at the Extreme Conditions beamline (P02.2, PETRA III, DESY, Germany) that enable considerable improvements in data collection at very high pressures and small scattering volumes. In particular, the focusing of the X‐ray beam to the sub‐micrometer level is described, and control of the aberrations of the focusing compound refractive lenses is made possible with the implementation of a correcting phase plate. This device provides a significant enhancement of the signal‐to‐noise ratio by conditioning the beam shape profile at the focal spot. A new sample alignment system with a small sphere of confusion enables single‐crystal data collection from grains of micrometer to sub‐micrometer dimensions subjected to pressures as high as 200 GPa. The combination of the technical development of the optical path and the sample alignment system contributes to research and gives benefits on various levels, including rapid and accurate diffraction mapping of samples with sub‐micrometer resolution at multimegabar pressures.
    Description: Facing the challenges of X‐ray diffraction from tiny samples subjected to multimegabar pressures, instrumentation developments are presented that enable, among other studies, single‐crystal data collection from micrometer‐ to sub‐micrometer‐sized grains. The developments are based on a sub‐micrometer beam capability employing compound refractive lenses operating with a phase correcting plate and a precise motorization solution.
    Keywords: ddc:548
    Language: English
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  • 6
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    A pushing mechanism for microtubule aster positioning in a large cell type (2020)
    Cell Press
    Details
    Publication Date: 2022-10-27
    Description: © The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Meaders, J. L., de Matos, S. N., & Burgess, D. R. A pushing mechanism for microtubule aster positioning in a large cell type. Cell Reports, 33(1), (2020): 108213, doi:10.1016/j.celrep.2020.108213.
    Description: After fertilization, microtubule (MT) sperm asters undergo long-range migration to accurately position pronuclei. Due to the large sizes of zygotes, the forces driving aster migration are considered to be from pulling on the astral MTs by dynein, with no significant contribution from pushing forces. Here, we re-investigate the forces responsible for sperm aster centration in sea urchin zygotes. Our quantifications of aster geometry and MT density preclude a pulling mechanism. Manipulation of aster radial lengths and growth rates, combined with quantitative tracking of aster migration dynamics, indicates that aster migration is equal to the length of rear aster radii, supporting a pushing model for centration. We find that dynein inhibition causes an increase in aster migration rates. Finally, ablation of rear astral MTs halts migration, whereas front and side ablations do not. Collectively, our data indicate that a pushing mechanism can drive the migration of asters in a large cell type.
    Description: We would like to thank Dr. Jesse Gatlin for sending us the Tau-mCherry fusion protein for imaging live MTs. We would also like to thank Dr. Timothy Mitchison, Dr. Christine Field, and Dr. James Pelletier for supplying us with CA4, p150-CC1, and EB1-GFP peptides, as well as for fruitful discussions. Finally, we would like to thank Dr. Charles Shuster and Leslie Toledo-Jacobo for constructive feedback when preparing the manuscript. We thank Bret Judson and the Boston College Imaging Core for infrastructure and support. This material is based upon work supported by NSF grant no. 124425 to D.R.B.
    Keywords: Dynein ; Aster ; Microtubule ; Centrosome ; Pronucleus ; Fertilization ; Aster position
    Repository Name: Woods Hole Open Access Server
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  • 7
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    Yeast cell death pathway requiring AP-3 vesicle trafficking leads to vacuole/lysosome membrane permeabilization (2022)
    Cell Press
    Details
    Publication Date: 2022-10-27
    Description: © The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Stolp, Z. D., Kulkarni, M., Liu, Y., Zhu, C., Jalisi, A., Lin, S., Casadevall, A., Cunningham, K. W., Pineda, F. J., Teng, X., & Hardwick, J. M. Yeast cell death pathway requiring AP-3 vesicle trafficking leads to vacuole/lysosome membrane permeabilization. Cell Reports, 39(2), (2022): 110647, https://doi.org/10.1016/j.celrep.2022.110647.
    Description: Unicellular eukaryotes have been suggested as undergoing self-inflicted destruction. However, molecular details are sparse compared with the mechanisms of programmed/regulated cell death known for human cells and animal models. Here, we report a molecular cell death pathway in Saccharomyces cerevisiae leading to vacuole/lysosome membrane permeabilization. Following a transient cell death stimulus, yeast cells die slowly over several hours, consistent with an ongoing molecular dying process. A genome-wide screen for death-promoting factors identified all subunits of the AP-3 complex, a vesicle trafficking adapter known to transport and install newly synthesized proteins on the vacuole/lysosome membrane. To promote cell death, AP-3 requires its Arf1-GTPase-dependent vesicle trafficking function and the kinase Yck3, which is selectively transported to the vacuole membrane by AP-3. Video microscopy revealed a sequence of events where vacuole permeability precedes the loss of plasma membrane integrity. AP-3-dependent death appears to be conserved in the human pathogenic yeast Cryptococcus neoformans.
    Description: Funding sources: National Institutes of Health, United States grants AI144373 and NS127076 (J.M.H.), AI115016 and AI153414 (K.W.C.), and AI052733, AI152078, and HL059842 (A.C.); National Natural Science Foundation of China 31970550; and the Priority Academic Program Development of the Jiangsu Higher Education Institutes (X.T.).
    Keywords: Yeast ; Programmed cell death ; Vesicle trafficking ; AP-3 ; Vacuole ; Cryptococcus ; Yck3 ; Regulated cell death ; Lysosome ; Vacuolar membrane permeabilization
    Repository Name: Woods Hole Open Access Server
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  • 8
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    Modeling the morphodynamics of coastal responses to extreme events: what shape are we in? (2022)
    Annual Reviews
    Details
    Publication Date: 2022-10-27
    Description: This paper is not subject to U.S. copyright. The definitive version was published in Sherwood, C. R., van Dongeren, A., Doyle, J., Hegermiller, C. A., Hsu, T.-J., Kalra, T. S., Olabarrieta, M., Penko, A. M., Rafati, Y., Roelvink, D., van der Lugt, M., Veeramony, J., & Warner, J. C. Modeling the morphodynamics of coastal responses to extreme events: what shape are we in? Annual Review of Marine Science, 14, (2022): 457–492, https://doi.org/10.1146/annurev-marine-032221-090215.
    Description: This review focuses on recent advances in process-based numerical models of the impact of extreme storms on sandy coasts. Driven by larger-scale models of meteorology and hydrodynamics, these models simulate morphodynamics across the Sallenger storm-impact scale, including swash,collision, overwash, and inundation. Models are becoming both wider (as more processes are added) and deeper (as detailed physics replaces earlier parameterizations). Algorithms for wave-induced flows and sediment transport under shoaling waves are among the recent developments. Community and open-source models have become the norm. Observations of initial conditions (topography, land cover, and sediment characteristics) have become more detailed, and improvements in tropical cyclone and wave models provide forcing (winds, waves, surge, and upland flow) that is better resolved and more accurate, yielding commensurate improvements in model skill. We foresee that future storm-impact models will increasingly resolve individual waves, apply data assimilation, and be used in ensemble modeling modes to predict uncertainties.
    Description: All authors except D.R. were partially supported by the IFMSIP project, funded by US Office of Naval Research grant PE 0601153N under contracts N00014-17-1-2459 (Deltares), N00014-18-1-2785 (University of Delaware), N0001419WX00733 (US Naval Research Laboratory, Monterey), N0001418WX01447 (US Naval Research Laboratory, Stennis Space Center), and N0001418IP00016 (US Geological Survey). C.R.S., C.A.H., T.S.K., and J.C.W. were supported by the US Geological Survey Coastal/Marine Hazards and Resources Program. A.v.D. and M.v.d.L. were supported by the Deltares Strategic Research project Quantifying Flood Hazards and Impacts. M.O. acknowledges support from National Science Foundation project OCE-1554892.
    Keywords: Coastal morphodynamics ; Extreme storms ; Coastal modeling ; Sandy coasts ; Waves ; Sediment transport
    Repository Name: Woods Hole Open Access Server
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  • 9
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    Robust approaches for model‐free small‐angle scattering data analysis (2022)
    Bender, Philipp ; Honecker, Dirk ; Bersweiler, Mathias ; [et al.]
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2022-10-04
    Description: The small‐angle neutron scattering data of nanostructured magnetic samples contain information regarding their chemical and magnetic properties. Often, the first step to access characteristic magnetic and structural length scales is a model‐free investigation. However, due to measurement uncertainties and a restricted q range, a direct Fourier transform usually fails and results in ambiguous distributions. To circumvent these problems, different methods have been introduced to derive regularized, more stable correlation functions, with the indirect Fourier transform being the most prominent approach. Here, the indirect Fourier transform is compared with the singular value decomposition and an iterative algorithm. These approaches are used to determine the correlation function from magnetic small‐angle neutron scattering data of a powder sample of iron oxide nanoparticles; it is shown that with all three methods, in principle, the same correlation function can be derived. Each method has certain advantages and disadvantages, and thus the recommendation is to combine these three approaches to obtain robust results.
    Description: Three different approaches are compared for determination of the correlation function from the small‐angle neutron scattering data of a powder sample of iron oxide nanoparticles.
    Keywords: ddc:548
    Language: English
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  • 10
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    Ciliary flows in corals ventilate target areas of high photosynthetic oxygen production (2022)
    Cell Press
    In:  EPIC3Current Biology, Cell Press, ISSN: 09609822
    Details
    Publication Date: 2022-08-30
    Description: Most tropical corals live in symbiosis with Symbiodiniaceae algae whose photosynthetic production of oxygen (O2) may lead to excess O2 in the diffusive boundary layer (DBL) above the coral surface. When flow is low, cilia-induced mixing of the coral DBL is vital to remove excess O2 and prevent oxidative stress that may lead to coral bleaching and mortality. Here, we combined particle image velocimetry using O2-sensitive nanoparticles (sensPIV) with chlorophyll (Chla)-sensitive hyperspectral imaging to visualize the microscale distribution and dynamics of ciliary flows and O2 in the coral DBL in relation to the distribution of Symbiodiniaceae Chla in the tissue of the reef building coral, Porites lutea. Curiously, we found an inverse relation between O2 in the DBL and Chla in the underlying tissue, with patches of high O2 in the DBL above low Chla in the underlying tissue surrounding the polyp mouth areas and pockets of low O2 concentrations in the DBL above high Chla in the coenosarc tissue connecting neighboring polyps. The spatial segregation of Chla and O2 is related to ciliary-induced flows, causing a lateral redistribution of O2 in the DBL. In a 2D transport-reaction model of the coral DBL, we show that the enhanced O2 transport allocates parts of the O2 surplus to areas containing less chla, which minimizes oxidative stress. Cilary flows thus confer a spatially complex mass transfer in the coral DBL, which may play an important role in mitigating oxidative stress and bleaching in corals.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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  • 11
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    Structure determination from unindexed powder data from scratch by a global optimization approach using pattern comparison based on cross‐correlation functions (2022)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2022-06-16
    Description: A method of ab initio crystal structure determination from powder diffraction data for organic and metal–organic compounds, which does not require prior indexing of the powder pattern, has been developed. Only a reasonable molecular geometry is required, needing knowledge of neither unit‐cell parameters nor space group. The structures are solved from scratch by a global fit to the powder data using the new program FIDEL‐GO (`FIt with DEviating Lattice parameters ‐ Global Optimization'). FIDEL‐GO uses a similarity measure based on cross‐correlation functions, which allows the comparison of simulated and experimental powder data even if the unit‐cell parameters deviate strongly. The optimization starts from large sets of random structures in various space groups. The unit‐cell parameters, molecular position and orientation, and selected internal degrees of freedom are fitted simultaneously to the powder pattern. The optimization proceeds in an elaborate multi‐step procedure with built‐in clustering of duplicate structures and iterative adaptation of parameter ranges. The best structures are selected for an automatic Rietveld refinement. Finally, a user‐controlled Rietveld refinement is performed. The procedure aims for the analysis of a wide range of `problematic' powder patterns, in particular powders of low crystallinity. The method can also be used for the clustering and screening of a large number of possible structure candidates and other application scenarios. Examples are presented for structure determination from unindexed powder data of the previously unknown structures of the nanocrystalline phases of 4,11‐difluoro‐, 2,9‐dichloro‐ and 2,9‐dichloro‐6,13‐dihydro‐quinacridone, which were solved from powder patterns with 14–20 peaks only, and of the coordination polymer dichloro‐bis(pyridine‐N)copper(II).
    Description: A new method for the structure determination of molecular crystals from unindexed powder data has been developed and successfully applied. The method performs a global optimization using pattern comparison based on cross‐correlation functions.
    Keywords: ddc:548
    Language: English
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  • 12
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    Affinity purification of label-free tubulins from xenopus egg extracts (2021)
    Cell Press
    Details
    Publication Date: 2022-05-26
    Description: © The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Reusch, S., Biswas, A., Hirst, W. G., & Reber, S. Affinity purification of label-free tubulins from xenopus egg extracts. STAR Protocols, 1(3), (2020): 100151, doi:10.1016/j.xpro.2020.100151.
    Description: Cytoplasmic extracts from unfertilized Xenopus eggs have made important contributions to our understanding of microtubule dynamics, spindle assembly, and scaling. Until recently, these in vitro studies relied on the use of heterologous tubulin. This protocol allows for the purification of physiologically relevant Xenopus tubulins in milligram yield, which are a complex mixture of isoforms with various post-translational modifications. The protocol is applicable to any cell or tissue of interest. For complete details on the use and execution of this protocol, please refer to Hirst et al. (2020).
    Description: This article was prompted by our stay at the Marine Biological Laboratory (MBL), Woods Hole, MA, in the summer of 2016 funded by the Princeton-Humboldt Strategic Partnership Grant together with the lab of Sabine Petry (Princeton University). We are grateful to the National Xenopus Resource (NXR) for supplying frogs. For mass spectrometry, we would like to acknowledge the assistance of Benno Kuropka and Chris Weise from the Core Facility BioSupraMol supported by the Deutsche Forschungsgemeinschaft (DFG). We thank the Protein Expression Purification and Characterization (PEPC) facility at the MPI-CBG; in particular, we thank Aliona Bogdanova and Barbara Borgonovo. We thank all former and current members of the Reber lab for discussions and helpful advice, in particular Christoph Hentschel and Soma Zsoter for technical assistance. S.R. acknowledges funding from the IRI Life Sciences (Humboldt-Universität zu Berlin, Excellence Initiative/DFG). W.H. was supported by the Alliance Berlin Canberra co-funded by a grant from the Deutsche Forschungsgemeinschaft (DFG) for the International Research Training Group (IRTG) 2290 and the Australian National University.
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  • 13
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    Site dependence of the magnetocaloric effect in Mn5−xFexSi3 (2022)
    Ait Haddouch, Mohammed ; Abboushi, Nour ; Sharma, Neetika ; [et al.]
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2022-12-06
    Description: The nuclear and magnetic structures of Mn3Fe2Si3 are investigated in the temperature range from 20 to 300 K. The magnetic properties of Mn3Fe2Si3 were measured on a single crystal. The compound undergoes a paramagnetic to antiferromagnetic transition at TN2 ≃ 120 K and an antiferromagnetic to antiferromagnetic transition at TN1 ≃ 69 K. A similar sequence of magnetic phase transitions is found for the parent compound Mn5Si3 upon temperature variation, but the field‐driven transition observed in Mn5Si3 is not found in Mn3Fe2Si3, resulting in a strongly reduced magnetocaloric effect. Structurally, the hexagonal symmetry found for both compounds under ambient conditions is preserved in Mn3Fe2Si3 through both magnetic transitions, indicating that the crystal structure is only weakly affected by the magnetic phase transition, in contrast to Mn5Si3 where both transitions distort the nuclear structure. Both compounds feature a collinear high‐temperature magnetic phase AF2 and transfer into a non‐collinear phase AF1 at low temperature. While one of the distinct crystallographic sites remains disordered in the AF2 phase in the parent compound, the magnetic structure in the AF2 phase involves all magnetic atoms in Mn3Fe2Si3. These observations imply that the distinct sites occupied by the magnetic atoms play an important role in the magnetocaloric behaviour of the family.
    Description: The nuclear and magnetic structures of Mn3Fe2Si3 are determined and the magnetic properties are compared with those of the parent compound Mn5Si3. The results imply that the distinct magnetic sites play an important role in the magnetocaloric behaviour of the family. image
    Keywords: ddc:548 ; magnetocaloric effect ; magnetic structure ; neutron diffraction ; synchrotron diffraction ; site dependence
    Language: English
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  • 14
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    Arctic Ocean Freshwater in CMIP6 Coupled Models (2022)
    American Geophysical Union (AGU)
    In:  EPIC3Earth's Future, American Geophysical Union (AGU), 10(9), ISSN: 2328-4277
    Details
    Publication Date: 2022-11-06
    Description: In this study we assessed the representation of the sea surface salinity (SSS) and liquid freshwater content (LFWC) of the Arctic Ocean in the historical simulation of 31 CMIP6 models with comparison to 39 Coupled Model Intercomparison Project phase 5 (CMIP5) models, and investigated the projected changes in Arctic liquid and solid freshwater content and freshwater budget in scenarios with two different shared socioeconomic pathways (SSP2-4.5 and SSP5-8.5). No significant improvement was found in the SSS and LFWC simulation from CMIP5 to CMIP6, given the large model spreads in both CMIP phases. The overestimation of LFWC continues to be a common bias in CMIP6. In the historical simulation, the multi-model mean river runoff, net precipitation, Bering Strait and Barents Sea Opening (BSO) freshwater transports are 2,928 ± 1,068, 1,839 ± 3,424, 2,538 ± 1,009, and −636 ± 553 km3/year, respectively. In the last decade of the 21st century, CMIP6 MMM projects these budget terms to rise to 4,346 ± 1,484 km3/year (3,678 ± 1,255 km3/year), 3,866 ± 2,935 km3/year (3,145 ± 2,651 km3/year), 2,631 ± 1,119 km3/year (2,649 ± 1,141 km3/year) and 1,033 ± 1,496 km3/year (449 ± 1,222 km3/year) under SSP5-8.5 (SSP2-4.5). Arctic sea ice is expected to continue declining in the future, and sea ice meltwater flux is likely to decrease to about zero in the mid-21st century under both SSP2-4.5 and SSP5-8.5 scenarios. Liquid freshwater exiting Fram and Davis straits will be higher in the future, and the Fram Strait export will remain larger. The Arctic Ocean is projected to hold a total of 160,300 ± 62,330 km3 (141,590 ± 50,310 km3) liquid freshwater under SSP5-8.5 (SSP2-4.5) by 2100, about 60% (40%) more than its historical climatology.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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  • 15
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    In Vitro reconstitution and imaging of microtubule dynamics by fluorescence and label-free microscopy (2021)
    Cell Press
    Details
    Publication Date: 2022-05-26
    Description: © The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Hirst, W. G., Kiefer, C., Abdosamadi, M. K., Schäffer, E., & Reber, S. In Vitro reconstitution and imaging of microtubule dynamics by fluorescence and label-free microscopy. STAR Protocols, 1(3), (2020): 100177, doi:10.1016/j.xpro.2020.100177.
    Description: Dynamic microtubules are essential for many processes in the lives of eukaryotic cells. To study and understand the mechanisms of microtubule dynamics and regulation, in vitro reconstitution with purified components has proven a vital approach. Imaging microtubule dynamics can be instructive for a given species, isoform composition, or biochemical modification. Here, we describe two methods that visualize microtubule dynamics at high speed and high contrast: (1) total internal reflection fluorescence microscopy and (2) label-free interference reflection microscopy.
    Description: We thank the AMBIO imaging facility (Charité, Berlin) and Nikon at MBL for imaging support. We thank all former and current members of the Reber lab for discussion and helpful advice, in particular Christoph Hentschel and Soma Zsoter for technical assistance. S.R. acknowledges funding by the IRI Life Sciences (Humboldt-Universität zu Berlin, Excellence Initiative/DFG). W.H. was supported by the Alliance Berlin Canberra co-funded by a grant from the Deutsche Forschungsgemeinschaft (DFG) for the International Research Training Group (IRTG) 2290 and the Australian National University. C.K. thanks the Deutsche Forschungsgesellschaft (DFG, JA 2589/1-1). C.K. and M.A. thank Steve Simmert and Tobias Jachowski former and current members of the Schäffer lab.
    Keywords: Biophysics ; Cell Biology ; Microscopy
    Repository Name: Woods Hole Open Access Server
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    Microfluidic encapsulation of Xenopus laevis cell-free extracts using hydrogel photolithography (2021)
    Cell Press
    Details
    Publication Date: 2022-05-26
    Description: © The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Geisterfer, Z. M., Oakey, J., & Gatlin, J. C. . Microfluidic encapsulation of Xenopus laevis cell-free extracts using hydrogel photolithography. STAR Protocols, 1(3), (2020): 100221, doi:10.1016/j.xpro.2020.100221.
    Description: Cell-free extract derived from the eggs of the African clawed frog Xenopus laevis is a well-established model system that has been used historically in bulk aliquots. Here, we describe a microfluidic approach for isolating discrete, biologically relevant volumes of cell-free extract, with more expansive and precise control of extract shape compared with extract-oil emulsions. This approach is useful for investigating the mechanics of intracellular processes affected by cell geometry or cytoplasmic volume, including organelle scaling and positioning mechanisms. For complete details on the use and execution of this protocol, please refer to Geisterfer et al. (2020).
    Description: This work was made possible by an Institutional Development Award (IDeA) from the National Institute of General Medical Sciences of the National Institutes of Health under grant no. 2P20GM103432. It was also supported by additional funding provided by the NIGMS under grant no. R01GM113028, the NSF Faculty CAREER Program under award no. BBBE 1254608, Whitman Center fellowships at the Marine Biological Laboratory, and the Biomedical Scholars program of the Pew Charitable Trusts. We thank Drs. Aaron Groen and Tim Mitchison for their intellectual contributions and involvement in some of the pioneering experiments that set the foundation for this approach.
    Keywords: Biophysics ; Cell Biology ; Cell isolation ; Microscopy ; Model Organisms
    Repository Name: Woods Hole Open Access Server
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    Widely rhythmic transcriptome in Calanus finmarchicus during the high Arctic summer solstice period (2021)
    Cell Press
    In:  EPIC3iScience, Cell Press, (101927)
    Details
    Publication Date: 2023-06-21
    Description: Solar light/dark cycles and seasonal photoperiods underpin daily and annual rhythms of life on Earth. Yet, the Arctic is characterized by severalmonths of permanent illumination (‘‘midnight sun’’). To determine the persistence of 24h rhythms during the midnight sun, we investigated transcriptomic dynamics in the copepod Calanus finmarchicus during the summer solstice period in the Arctic, with the lowest diel oscillation and the highest altitude of the sun’s position. Here we reveal that in these extreme photic conditions, a widely rhythmic daily transcriptome exists, showing that very weak solar cues are sufficient to entrain organisms. Furthermore, at extremely high latitudes and under sea-ice, gene oscillations become re-organized to include 〈24h rhythms. Environmental synchronization may therefore be modulated to include non-photic signals (i.e. tidal cycles). The ability of zooplankton to be synchronized by extremely weak diel and potentially tidal cycles, may confer an adaptive temporal reorganization of biological processes at high latitudes.
    Repository Name: EPIC Alfred Wegener Institut
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    On the Damping Time Scale of EVP Sea Ice Dynamics (2021)
    American Geophysical Union (AGU)
    In:  EPIC3Journal of Advances in Modeling Earth Systems, American Geophysical Union (AGU), 13(10), ISSN: 1942-2466
    Details
    Publication Date: 2023-06-21
    Description: We propose to make the damping time scale, which governs the decay of pseudo-elastic waves in the Elastic Viscous Plastic (EVP) sea-ice solvers, independent of the external time step and large enough to warrant numerical stability for a moderate number of internal time steps. A necessary condition is that the forcing on sea ice varies slowly on the damping time scale, in which case an EVP solution may still approach a Viscous Plastic one, but on a time scale longer than a single external time step. In this case, the EVP method becomes very close to the recently proposed modified EVP (mEVP) method in terms of stability and simulated behavior. In a simple test case dealing with sea ice breaking under the forcing of a moving cyclone, the EVP method with an enlarged damping time scale can simulate linear kinematic features which are very similar to those from the traditional EVP implementation, although a much smaller number of internal time steps is used. There is more difference in sea-ice thickness and linear kinematic features simulated in a realistic Arctic configuration between using the traditional and our suggested choices of EVP damping time scales, but it is minor considering model uncertainties associated with choices of many other parameters in sea-ice models.
    Repository Name: EPIC Alfred Wegener Institut
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    The Role of Zooplankton Grazing and Nutrient Recycling for Global Ocean Biogeochemistry and Phytoplankton Phenology (2022)
    American Geophysical Union (AGU)
    In:  EPIC3Journal of Geophysical Research Biogeosciences, American Geophysical Union (AGU), 127(10), ISSN: 2169-8953
    Details
    Publication Date: 2023-06-21
    Description: Zooplankton plays a notable role in ocean biogeochemical cycles. However, it is often simulated as one generic group and top closure term in ocean biogeochemical models. This study presents the description of three zooplankton functional types (zPFTs, micro-, meso- and macrozooplankton) in the ocean biogeochemical model FESOM-REcoM. In the presented model, microzooplankton is a fast-growing herbivore group, mesozooplankton is another major consumer of phytoplankton, and macrozooplankton is a slow-growing group with a low temperature optimum. Meso- and macrozooplankton produce fast-sinking fecal pellets. With three zPFTs, the annual mean zooplankton biomass increases threefold to 210 Tg C. The new food web structure leads to a 25% increase in net primary production and a 10% decrease in export production globally. Consequently, the export ratio decreases from 17% to 12% in the model. The description of three zPFTs reduces model mismatches with observed dissolved inorganic nitrogen and chlorophyll concentrations in the South Pacific and the Arctic Ocean, respectively. Representation of three zPFTs also strongly affects phytoplankton phenology: Fast nutrient recycling by zooplankton sustains higher chlorophyll concentrations in summer and autumn. Additional zooplankton grazing delays the start of the phytoplankton bloom by 3 weeks and controls the magnitude of the bloom peak in the Southern Ocean. As a result, the system switches from a light-controlled Sverdrup system to a dilution-controlled Behrenfeld system. Overall, the results suggest that representation of multiple zPFTs is important to capture underlying processes that may shape the response of ecosystems and ecosystem services to on-going and future environmental change in model projections.
    Repository Name: EPIC Alfred Wegener Institut
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    A Kinematic Kinetic Energy Backscatter Parametrization: From Implementation to Global Ocean Simulations (2020)
    American Geophysical Union (AGU)
    In:  EPIC3Journal of Advances in Modeling Earth Systems, American Geophysical Union (AGU), 12(12), ISSN: 1942-2466
    Details
    Publication Date: 2023-06-21
    Description: Ocean models at eddy-permitting resolution are generally overdissipative, damping the intensity of the mesoscale eddy field. To reduce overdissipation, we propose a simplified, kinematic energy backscatter parametrization built into the viscosity operator in conjunction with a new flow-dependent coefficient of viscosity based on nearest neighbor velocity differences. The new scheme mitigates excessive dissipation of energy and improves global ocean simulations at eddy-permitting resolution. We find that kinematic backscatter substantially raises simulated eddy kinetic energy, similar to an alternative, previously proposed dynamic backscatter parametrization. While dynamic backscatter is scale aware and energetically more consistent, its implementation is more complex. Furthermore, it turns out to be computationally more expensive, as it applies, among other things, an additional prognostic subgrid energy equation. The kinematic backscatter proposed here, by contrast, comes at no additional computational cost, following the principle of simplicity. Our primary focus is the discretization on triangular unstructured meshes with cell placement of velocities (an analog of B-grids), as employed by the Finite-volumE Sea ice-Ocean Model (FESOM2). The kinematic backscatter scheme with the new viscosity coefficient is implemented in FESOM2 and tested in the simplified geometry of a zonally reentrant channel as well as in a global ocean simulation on a 1/4° mesh. This first version of the new kinematic backscatter needs to be tuned to the specific resolution regime of the simulation. However, the tuning relies on a single parameter, emphasizing the overall practicality of the approach.
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    Digitization of imaging plates from Guinier powder X‐ray diffraction cameras (2022)
    Nasir, Jamal ; Steinbrück, Nils ; Xu, Ke ; [et al.]
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2023-01-15
    Description: A Guinier camera equipped with an imaging plate is used to investigate and eliminate the sources of instrumental errors affecting the quality of the obtained scanned Guinier data. A program with a graphical user interface is presented which converts the data of the scanned images into different standard file formats for powder X‐ray patterns containing intensities, their standard deviations and the diffraction angles. The program also allows for manual and automatic correction of the 2gθ scale against a known reference material. It is shown using LaB6 that the exported X‐ray diffraction patterns provide a 2gθ scale reproducible enough to allow for averaging diffractograms obtained from different exposures of the imaging plate for the same sample. As shown on a mixture of NaCl and sodalite, the quality of the produced data is sufficient for Rietveld refinement. The software including source code is made available under a free software license.
    Description: A program for the digitization of Guinier powder diffraction images is described, which works with images from both optical and laser scanners. Thus, processing of data from storage‐phosphor‐based imaging plates and Ag‐based photographic films is possible.
    Keywords: ddc:548 ; IPreader software ; Guinier cameras ; imaging plates (IPs) ; diffraction pattern conversion into data columns ; powder X‐ray diffraction ; data processing ; Guinier method
    Language: English
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    Crystal diffraction prediction and partiality estimation using Gaussian basis functions (2023)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2023-07-04
    Description: The recent diversification of macromolecular crystallographic experiments including the use of pink beams, convergent electron diffraction and serial snapshot crystallography has shown the limitations of using the Laue equations for diffraction prediction. This article gives a computationally efficient way of calculating approximate crystal diffraction patterns given varying distributions of the incoming beam, crystal shapes and other potentially hidden parameters. This approach models each pixel of a diffraction pattern and improves data processing of integrated peak intensities by enabling the correction of partially recorded reflections. The fundamental idea is to express the distributions as weighted sums of Gaussian functions. The approach is demonstrated on serial femtosecond crystallography data sets, showing a significant decrease in the required number of patterns to refine a structure to a given error.
    Description: Reflection position, size and shape prediction and partiality estimation of crystal diffraction by integrating using a Gaussian basis are described.
    Keywords: ddc:548 ; partiality estimation ; diffraction prediction ; merging ; serial snapshot crystallography
    Language: English
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    Small‐angle neutron scattering of long‐wavelength magnetic modulations in reduced sample dimensions (2022)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2023-07-04
    Description: Magnetic small‐angle neutron scattering (SANS) is ideally suited to providing direct reciprocal‐space information on long‐wavelength magnetic modulations, such as helicoids, solitons, merons or skyrmions. SANS of such structures in thin films or micro‐structured bulk materials is strongly limited by the tiny scattering volume vis a vis the prohibitively high background scattering by the substrate and support structures. Considering near‐surface scattering just above the critical angle of reflection, where unwanted signal contributions due to substrate or support structures become very small, it is established that the scattering patterns of the helical, conical, skyrmion lattice and fluctuation‐disordered phases in a polished bulk sample of MnSi are equivalent for conventional transmission and near‐surface SANS geometries. This motivates the prediction of a complete repository of scattering patterns expected for thin films in the near‐surface SANS geometry for each orientation of the magnetic order with respect to the scattering plane.
    Description: Near‐surface SANS is discussed for its potential as a probe of long‐wavelength magnetic modulations in specimens with reduced sample dimensions.
    Keywords: ddc:548 ; small‐angle neutron scattering ; near‐surface SANS ; magnetism ; non‐collinear magnetism ; thin films ; skyrmions ; MnSi
    Language: English
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    Future Arctic Climate Change in CMIP6 Strikingly Intensified by NEMO‐Family Climate Models (2023)
    American Geophysical Union (AGU)
    In:  EPIC3Geophysical Research Letters, American Geophysical Union (AGU), 50(4), ISSN: 0094-8276
    Details
    Publication Date: 2023-06-23
    Description: Climate change in the Arctic has substantial impacts on human life and ecosystems both within and beyond the Arctic. Our analysis of CMIP6 simulations shows that some climate models project much larger Arctic climate change than other models, including changes in sea ice, ocean mixed layer, air-sea heat flux, and surface air temperature in wintertime. In particular, dramatic enhancement of Arctic Ocean convection down to a few hundred meters is projected in these models but not in others. Interestingly, these models employ the same ocean model family (NEMO) while the choice of models for the atmosphere and sea ice varies. The magnitude of Arctic climate change is proportional to the strength of the increase in poleward ocean heat transport, which is considerably higher in this group of models. Establishing the plausibility of this group of models with high Arctic climate sensitivity to anthropogenic forcing is imperative given the implied ramifications.
    Repository Name: EPIC Alfred Wegener Institut
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    Sea‐Ice Forecasts With an Upgraded AWI Coupled Prediction System (2022)
    American Geophysical Union (AGU)
    In:  EPIC3Journal of Advances in Modeling Earth Systems, American Geophysical Union (AGU), 14(12), ISSN: 1942-2466
    Details
    Publication Date: 2023-06-23
    Description: A new version of the AWI Coupled Prediction System is developed based on the Alfred Wegener Institute Climate Model v3.0. Both the ocean and the atmosphere models are upgraded or replaced, reducing the computation time by a factor of 5 at a given resolution. This allowed us to increase the ensemble size from 12 to 30, maintaining a similar resolution in both model components. The online coupled data assimilation scheme now additionally utilizes sea-surface salinity and sea-level anomaly as well as temperature and salinity profile observations. Results from the data assimilation demonstrate that the sea-ice and ocean states are reasonably constrained. In particular, the temperature and salinity profile assimilation has mitigated systematic errors in the deeper ocean, although issues remain over polar regions where strong atmosphere-ocean-ice interaction occurs. One-year-long sea-ice forecasts initialized on 1 January, 1 April, 1 July and 1 October from 2003 to 2019 are described. To correct systematic forecast errors, sea-ice concentration from 2011 to 2019 is calibrated by trend-adjusted quantile mapping using the preceding forecasts from 2003 to 2010. The sea-ice edge raw forecast skill is within the range of operational global subseasonal-to-seasonal forecast systems, outperforming a climatological benchmark for about 2 weeks in the Arctic and about 3 weeks in the Antarctic. The calibration is much more effective in the Arctic: Calibrated sea-ice edge forecasts outperform climatology for about 45 days in the Arctic but only 27 days in the Antarctic. Both the raw and the calibrated forecast skill exhibit strong seasonal variations.
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  • 26
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    Turbulent heat exchange over polar leads revisited: A large eddy simulation study (2023)
    American Geophysical Union (AGU)
    In:  EPIC3Journal of Geophysical Research: Atmospheres, American Geophysical Union (AGU), ISSN: 2169-897X
    Details
    Publication Date: 2023-06-23
    Description: Sea ice leads play an important role in energy exchange between the ocean and atmosphere in polar regions, and therefore must be considered in weather and climate models. As sea ice leads are not explicitly resolved in such models, lead-averaged surface heat flux is of considerable interest for the parameterization of energy exchange. Measurements and numerical studies have established that the lead-averaged surface heat flux depends not only on meteorological parameters, but also on lead width. Nonetheless, few studies to date have investigated the dependency of surface heat flux on lead width. Most findings on that dependency are based on observations with lead widths smaller than a few hundred meters, but leads can have widths from a few meters to several kilometers. In this parameter study, we present the results of three series of large-eddy simulations of turbulent exchange processes above leads. We varied the lead width and air temperature, as well as the roughness length. As this study focused on conditions without background wind, ice-breeze circulation occurred, and was the main driver of the adjustment of surface heat flux. A previous large-eddy simulation study with uncommonly large roughness length found that lead-averaged surface heat flux exhibited a distinct maximum at lead widths of about 3 km, while our results show the largest heat fluxes for the smallest leads simulated (lead width of 50 m). At more realistic roughness lengths, we observed monotonously increasing heat fluxes with increasing lead width. Further, new scaling laws for the ice-breeze circulation are proposed.
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    Impact of Cyclonic Wind Anomalies Caused by Massive Winter Sea Ice Retreat in the Barents Sea on Atlantic Water Transport Toward the Arctic: A Model Study (2023)
    American Geophysical Union (AGU)
    In:  EPIC3Journal of Geophysical Research - Oceans, American Geophysical Union (AGU), 128(3), ISSN: 2169-9275
    Details
    Publication Date: 2023-06-23
    Description: The Arctic is warming much faster than the global average. This is known as Arctic Amplification and is caused by feedbacks in the local climate system. In this study, we explore a previously proposed hypothesis that an associated wind feedback in the Barents Sea could play an important role by increasing the warm water inflow into the Barents Sea. We find that the strong recent decrease in Barents Sea winter sea ice cover causes enhanced ocean-atmosphere heat flux and a local air temperature increase, thus a reduction in sea level pressure and a local cyclonic wind anomaly with eastward winds in the Barents Sea Opening. By investigating various reanalysis products and performing high-resolution perturbation experiments with the ocean and sea ice model FESOM2.1, we studied the impact of cyclonic atmospheric circulation changes on the warm Atlantic Water import into the Arctic via the Barents Sea and Fram Strait. We found that the observed wind changes do not significantly affect the warm water transport into the Barents Sea, which rejects the wind-feedback hypothesis. At the same time, the cyclonic wind anomalies in the Barents Sea increase the amount of Atlantic Water recirculating westwards in Fram Strait by a downslope shift of the West Spitsbergen Current, and thus reduce Atlantic Water reaching the Arctic basin via Fram Strait. The resulting warm-water anomaly in the Greenland Sea Gyre drives a local anticyclonic circulation anomaly.
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  • 28
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    In situ neutron diffraction for analysing complex coarse‐grained functional materials (2023)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2023-10-24
    Description: 〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉Complex functional materials play a crucial role in a broad range of energy‐related applications and in general for materials science. Revealing the structural mechanisms is challenging due to highly correlated coexisting phases and microstructures, especially for 〈italic〉in situ〈/italic〉 or 〈italic〉operando〈/italic〉 investigations. Since the grain sizes influence the properties, these microstructural features further complicate investigations at synchrotrons due to the limitations of illuminated sample volumes. In this study, it is demonstrated that such complex functional materials with highly correlated coexisting phases can be investigated under 〈italic〉in situ〈/italic〉 conditions with neutron diffraction. For large grain sizes, these experiments are valuable methods to reveal the structural mechanisms. For an example of 〈italic〉in situ〈/italic〉 experiments on barium titanate with an applied electric field, details of the electric‐field‐induced phase transformation depending on grain size and frequency are revealed. The results uncover the strain mechanisms in barium titanate and elucidate the complex interplay of stresses in relation to grain sizes as well as domain‐wall densities and mobilities.〈/p〉
    Description: 〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉This work reports 〈italic〉in situ〈/italic〉 neutron diffraction experiments on a broad range of grain sizes of barium titanate. The study reveals the grain‐size‐dependent strain mechanisms and shows the competitiveness of neutron diffraction with high‐resolution synchrotron diffraction.〈boxed-text position="anchor" content-type="graphic" xml:lang="en"〉〈graphic position="anchor" id="jats-graphic-1" xlink:href="urn:x-wiley:16005767:jcr2vb5054:jcr2vb5054-fig-0001"〉 〈alt-text〉image〈/alt-text〉 〈/graphic〉〈/boxed-text〉〈/p〉
    Keywords: ddc:550.724 ; ddc:548 ; neutron diffraction ; in situ ; applied electric fields ; barium titanate ; strain mechanisms ; grain sizes ; complex functional materials ; microstructures ; coexisting phases
    Language: English
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    The Impacts of Optimizing Model‐Dependent Parameters on the Antarctic Sea Ice Data Assimilation (2023)
    American Geophysical Union (AGU)
    In:  EPIC3Geophysical Research Letters, American Geophysical Union (AGU), 50(22), ISSN: 0094-8276
    Details
    Publication Date: 2023-11-25
    Description: Given the role played by the historical and extensive coverage of sea ice concentration (SIC) observations in reconstructing the long‐term variability of Antarctic sea ice, and the limited attention given to model‐dependent parameters in current sea ice data assimilation studies, this study focuses on enhancing the performance of the Data Assimilation System for the Southern Ocean in assimilating SIC through optimizing the localization and observation error estimate, and two assimilation experiments were conducted from 1979 to 2018. By comparing the results with the sea ice extent of the Southern Ocean and the sea ice thickness in the Weddell Sea, it becomes evident that the experiment with optimizations outperforms that without optimizations due to achieving more reasonable error estimates. Investigating uncertainties of the sea ice volume anomaly modeling reveals the importance of the sea ice‐ocean interaction in the SIC assimilation, implying the necessity of assimilating more oceanic and sea‐ice observations.
    Repository Name: EPIC Alfred Wegener Institut
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  • 30
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    Using diffraction losses of X‐rays in a single crystal for determination of its lattice parameters as well as for monochromator calibration (2022)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2023-12-04
    Description: 〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉A way has been developed to measure the unit‐cell parameters of a single crystal just from an energy scan with X‐rays, even when the exact energy of the X‐rays is not well defined due to an error in the pitch angle of the monochromator. The precision of this measurement reaches 〈italic〉da〈/italic〉/〈italic〉a〈/italic〉 ∼ 1 × 10〈sup〉−5〈/sup〉. The method is based on the analysis of diffraction losses of the beam, transmitted through a single crystal (the so‐called `glitch effect'). This method can be easily applied to any transmissive X‐ray optical element made of single crystals (for example, X‐ray lenses). The only requirements are the possibility to change the energy of the generated X‐ray beam and some intensity monitor to measure the transmitted intensity. The method is agnostic to the error in the monochromator tuning and it can even be used for determination of the absolute pitch (or 2gθ) angle of the monochromator. Applying the same method to a crystal with well known lattice parameters allows determination of the exact cell parameters of the monochromator at any energy.〈/p〉
    Description: 〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉Diffraction losses (glitches) at certain energies of the X‐ray beam, transmitted through a single crystal, can be used for lattice parameters determination as well as for calibrating the monochromator (absolute pitch angle and the unit‐cell parameter).〈boxed-text position="anchor" content-type="graphic" xml:lang="en"〉〈graphic position="anchor" id="jats-graphic-1" xlink:href="urn:x-wiley:16005775:jsy2ay5590:jsy2ay5590-fig-0001"〉 〈alt-text〉image〈/alt-text〉 〈/graphic〉〈/boxed-text〉〈/p〉
    Keywords: ddc:548 ; X‐ray glitches ; diffraction losses ; unit‐cell parameter ; single‐crystal X‐ray optics ; monochromator calibration
    Language: English
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    Snow‐Atmosphere Humidity Exchange at the Ice Sheet Surface Alters Annual Mean Climate Signals in Ice Core Records (2023)
    American Geophysical Union (AGU)
    In:  EPIC3Geophysical Research Letters, American Geophysical Union (AGU), 50(20), ISSN: 0094-8276
    Details
    Publication Date: 2023-11-20
    Description: Surface processes alter the water stable isotope signal of the surface snow after deposition. However, it remains an open question to which extent surface post-depositional processes should be considered when inferring past climate information from ice core records. Here, we present simulations for the Greenland Ice Sheet, combining outputs from two climate models with an isotope-enabled snowpack model. We show that surface vapor exchange and associated fractionation imprint a climate signal into the firn, resulting in an increase in the annual mean value of δ18O by +2.3‰ and a reduction in d-excess by −6.3‰. Further, implementing isotopic fractionation during surface vapor exchange improves the representation of the observed seasonal amplitude in δ18O from 65.0% to 100.2%. Our results stress that surface vapor exchange is important in the climate proxy signal formation and needs consideration when interpreting ice core climate records.
    Repository Name: EPIC Alfred Wegener Institut
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    Preconditioning of Summer Melt Ponds From Winter Sea Ice Surface Temperature (2023)
    American Geophysical Union (AGU)
    In:  EPIC3Geophysical Research Letters, American Geophysical Union (AGU), 50(4), ISSN: 0094-8276
    Details
    Publication Date: 2023-02-23
    Description: Comparing helicopter-borne surface temperature maps in winter and optical orthomosaics in summer from the year-long Multidisciplinary drifting Observatory for the Study of Arctic Climate expedition, we find a strong geometric correlation between warm anomalies in winter and melt pond location the following summer. Warm anomalies are associated with thinner snow and ice, that is, surface depression and refrozen leads, that allow for water accumulation during melt. Warm surface temperature anomalies in January were 0.3–2.5 K warmer on sea ice that later formed melt ponds. A one-dimensional steady-state thermodynamic model shows that the observed surface temperature differences are in line with the observed ice thickness and snow depth. We demonstrate the potential of seasonal prediction of summer melt pond location and coverage from winter surface temperature observations. A threshold-based classification achieves a correct classification for 41% of the melt ponds.
    Repository Name: EPIC Alfred Wegener Institut
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  • 33
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    Atmospheric CO2 concentration based on boron isotopes versus simulations of the global carbon cycle during the Plio‐Pleistocene (2023)
    American Geophysical Union (AGU)
    In:  EPIC3Paleoceanography and Paleoclimatology, American Geophysical Union (AGU), 38, 22 p., pp. e2022PA004439-e2022PA004439, ISSN: 2572-4517
    Details
    Publication Date: 2023-08-30
    Description: Atmospheric carbon dioxide concentrations (pCO2) beyond ice core records have been reconstructed from δ11B derived from planktic foraminifera found in equatorial sediment cores. Here, I applied a carbon cycle model over the Plio-Pleistocene to evaluate the assumptions leading to these numbers. During glacials times, simulated atmospheric pCO2 was unequilibrated with pCO2 in the equatorial surface ocean by up to 35 ppm while the δ11B-based approaches assume unchanged (quasi)equilibrium between both. In the Pliocene, δ11B-based estimates of surface ocean pH are lower in the Pacific than in the Atlantic resulting in higher calculated pCO2. This offset in pH between ocean basins is not supported by models. To calculate pCO2 in surface waters out of the δ11B-based pH some assumptions on either total alkalinity or dissolved inorganic carbon are necessary. However, the assumed values of these under-constrained variables were according to my results partly inconsistent with chemically possible combinations within the marine carbonate system. The model results show glacial/interglacial variability in total alkalinity of the order of 100 μmol/kg, which is rarely applied to proxy reconstructions. Simulated atmospheric pCO2 is tightly (r2 〉 0.9) related to equatorial surface-ocean pH, which can be used for consistency checks. Long-term trends in volcanic CO2 outgassing and the strength of the continental weathering fluxes are still unconstrained, allowing for a wide range of possible atmospheric pCO2 across the Plio-Pleistocene. Nevertheless, this carbon cycle analysis suggests that reported atmospheric pCO2 above 500 ppm in the Pliocene might, for various reasons, need to be revised to smaller numbers.
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    Stable Carbon Isotope Signature of Methane Released From Phytoplankton (2023)
    American Geophysical Union (AGU)
    In:  EPIC3Geophysical Research Letters, American Geophysical Union (AGU), 50(12), ISSN: 0094-8276
    Details
    Publication Date: 2023-09-01
    Description: Aquatic ecosystems play an important role in global methane cycling and many field studies have reported methane supersaturation in the oxic surface mixed layer (SML) of the ocean and in the epilimnion of lakes. The origin of methane formed under oxic condition is hotly debated and several pathways have recently been offered to explain the “methane paradox.” In this context, stable isotope measurements have been applied to constrain methane sources in supersaturated oxygenated waters. Here we present stable carbon isotope signatures for six widespread marine phytoplankton species, three haptophyte algae and three cyanobacteria, incubated under laboratory conditions. The observed isotopic patterns implicate that methane formed by phytoplankton might be clearly distinguished from methane produced by methanogenic archaea. Comparing results from phytoplankton experiments with isotopic data from field measurements, suggests that algal and cyanobacterial populations may contribute substantially to methane formation observed in the SML of oceans and lakes.
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  • 35
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    Teardrop and Parabolic Lens Yield Curves for Viscous‐Plastic Sea Ice Models: New Constitutive Equations and Failure Angles (2023)
    American Geophysical Union (AGU)
    In:  EPIC3Journal of Advances in Modeling Earth Systems, American Geophysical Union (AGU), 15(9), ISSN: 1942-2466
    Details
    Publication Date: 2023-09-04
    Description: 〈jats:title〉Abstract〈/jats:title〉〈jats:p〉Most viscous‐plastic sea ice models use the elliptical yield curve. This yield curve has a fundamental flaw: it excludes acute angles between deformation features at high resolution. Conceptually, the teardrop (TD) and parabolic lens (PL) yield curves offer an attractive alternative. These yield curves feature a non‐symmetrical shape, a Coulombic behavior for the low‐medium compressive stress, and a continuous transition to the ridging‐dominant mode, but their published formulation leads to negative or zero bulk and shear viscosities and, consequently, poor numerical convergence with stress states at times outside the yield curve. These issues are a consequence of the original assumption that the constitutive equations of the commonly used elliptical yield curve are also applicable to non‐symmetrical yield curves and yield curves with tensile strength. We derive a corrected formulation for the constitutive relations of the TD and PL yield curves. Results from simple uni‐axial loading experiments show that with the new formulation the numerical convergence of the solver improves and much smaller nonlinear residuals after a smaller number of total solver iterations can be reached, resulting in significant improvements in numerical efficiency and representation of the stress and deformation fields. The TD and PL yield curves lead to smaller angles of failure that better agree with observations. They are promising candidates to replace the elliptical yield curve in high‐resolution pan‐Arctic sea ice simulations.〈/jats:p〉
    Repository Name: EPIC Alfred Wegener Institut
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  • 36
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    Energy‐dispersive X‐ray stress analysis under geometric constraints: exploiting the material's inherent anisotropy (2023)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2023-09-12
    Description: Two data evaluation concepts for X‐ray stress analysis based on energy‐dispersive diffraction on polycrystalline materials with cubic crystal structure, almost random crystallographic texture and strong single‐crystal elastic anisotropy are subjected to comparative assessment. The aim is the study of the residual stress state in hard‐to‐reach measurement points, for which the sin2ψ method is not applicable due to beam shadowing at larger sample tilting. This makes the approaches attractive for stress analysis in engineering parts with complex shapes, for example. Both approaches are based on the assumption of a biaxial stress state within the irradiated sample volume. They exploit in different ways the elastic anisotropy of individual crystallites acting at the microscopic scale and the anisotropy imposed on the material by the near‐surface stress state at the macroscopic scale. They therefore complement each other, in terms of both their preconditions and their results. The first approach is based on the evaluation of strain differences, which makes it less sensitive to variations in the strain‐free lattice parameter a0. Since it assumes a homogeneous stress state within the irradiated sample volume, it provides an average value of the in‐plane stresses. The second approach exploits the sensitivity of the lattice strain to changes in a0. Consequently, it assumes a homogeneous chemical composition but provides a stress profile within the information depth. Experimental examples from different fields in materials science, namely shot peening of austenitic steel and in situ stress analysis during welding, are presented to demonstrate the suitability of the proposed methods.
    Description: The single‐crystal elastic anisotropy and the anisotropy of the near‐surface (residual) stress state of polycrystalline materials with random texture are exploited in energy‐dispersive X‐ray stress analysis to study samples under constrained measurement conditions.
    Keywords: ddc:548 ; X‐ray stress analysis ; energy‐dispersive diffraction ; polycrystalline materials ; single‐crystal elastic anisotropy
    Language: English
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    Antarctic Sedimentary Basins and Their Influence on Ice‐Sheet Dynamics (2023)
    American Geophysical Union (AGU)
    In:  EPIC3Reviews of Geophysics, American Geophysical Union (AGU), 61(3), ISSN: 8755-1209
    Details
    Publication Date: 2023-10-09
    Description: Knowledge of Antarctica's sedimentary basins builds our understanding of the coupled evolution of tectonics, ice, ocean, and climate. Sedimentary basins have properties distinct from basement-dominated regions that impact ice-sheet dynamics, potentially influencing future ice-sheet change. Despite their importance, our knowledge of Antarctic sedimentary basins is restricted. Remoteness, the harsh environment, the overlying ice sheet, ice shelves, and sea ice all make fieldwork challenging. Nonetheless, in the past decade the geophysics community has made great progress in internationally coordinated data collection and compilation with parallel advances in data processing and analysis supporting a new insight into Antarctica's subglacial environment. Here, we summarize recent progress in understanding Antarctica's sedimentary basins. We review advances in the technical capability of radar, potential fields, seismic, and electromagnetic techniques to detect and characterize basins beneath ice and advances in integrated multi-data interpretation including machine-learning approaches. These new capabilities permit a continent-wide mapping of Antarctica's sedimentary basins and their characteristics, aiding definition of the tectonic development of the continent. Crucially, Antarctica's sedimentary basins interact with the overlying ice sheet through dynamic feedbacks that have the potential to contribute to rapid ice-sheet change. Looking ahead, future research directions include techniques to increase data coverage within logistical constraints, and resolving major knowledge gaps, including insufficient sampling of the ice-sheet bed and poor definition of subglacial basin structure and stratigraphy. Translating the knowledge of sedimentary basin processes into ice-sheet modeling studies is critical to underpin better capacity to predict future change.
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  • 38
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    Use of electron backscatter diffraction patterns to determine the crystal lattice. Part 3. Pseudosymmetry (2023)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2023-07-20
    Description: A pseudosymmetric description of the crystal lattice derived from a single wide‐angle Kikuchi pattern can have several causes. The small size (〈15%) of the sector covered by an electron backscatter diffraction pattern, the limited precision of the projection centre position and the Kikuchi band definition are crucial. Inherent pseudosymmetries of the crystal lattice and/or structure also pose a challenge in the analysis of Kikuchi patterns. To eliminate experimental errors as much as possible, simulated Kikuchi patterns of 350 phases have been analysed using the software CALM [Nolze et al. (2021). J. Appl. Cryst.54, 1012–1022] in order to estimate the frequency of and reasons for pseudosymmetric crystal lattice descriptions. Misinterpretations occur in particular when the atomic scattering factors of non‐equivalent positions are too similar and reciprocal‐lattice points are systematically missing. As an example, a pseudosymmetry prediction depending on the elements involved is discussed for binary AB compounds with B1 and B2 structure types. However, since this is impossible for more complicated phases, this approach cannot be directly applied to compounds of arbitrary composition and structure.
    Description: Distinguishing between actual and apparent pseudosymmetry in electron backscatter diffraction patterns is nearly impossible, even for simulated patterns. However, the resulting lattice is always a superlattice as long as the signal is not a superposition of multiple patterns.
    Keywords: ddc:548 ; Bravais lattices ; pseudosymmetry ; lattice point density ; ordered/disordered structures ; lattice distortion ; electron backscatter diffraction ; backscattered Kikuchi diffraction patterns ; lattice parameters ; Funk transform
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  • 39
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    Combining reverse Monte Carlo analysis of X‐ray scattering and extended X‐ray absorption fine structure spectra of very small nanoparticles (2022)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
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    Publication Date: 2023-07-21
    Description: Finite size effects in partial pair distribution functions generate artefacts in the scattering structure factor and scattering intensity. It is shown how they can be overcome using a binned version of the Debye scattering equation. Accordingly, reverse Monte Carlo simulations are used for very small nanoparticles of LaFeO3 with diameters below 10 nm to simultaneously analyse X‐ray scattering data and extended X‐ray absorption fine structure spectra at the La K and Fe K edges. The structural information obtained is consistent regarding local structure and long‐range order.
    Description: Computing scattering intensity using the Debye scattering equation after binning interatomic distances avoids finite size artefacts and is efficient enough for simultaneous refinement of scattering data and extended X‐ray absorption spectra by reverse Monte Carlo simulations.
    Keywords: ddc:548 ; extended X‐ray absorption fine structure ; EXAFS ; wide‐angle X‐ray scattering ; WAXS ; reverse Monte Carlo ; RMC ; nanocrystals ; LaFeO3
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  • 40
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    Use of electron backscatter diffraction patterns to determine the crystal lattice. Part 2. Offset corrections (2023)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2023-07-21
    Description: A band width determination using the first derivative of the band profile systematically underestimates the true Bragg angle. Corrections are proposed to compensate for the resulting offset Δa/a of the mean lattice parameters derived from as many Kikuchi band widths as possible. For dynamically simulated Kikuchi patterns, Δa/a can reach up to 8% for phases with a high mean atomic number Z, whereas for much more common low‐Z materials the offset decreases linearly. A predicted offset Δa/a = f(Z) is therefore proposed, which also includes the unit‐cell volume and thus takes into account the packing density of the scatterers in the material. Since Z is not always available for unknown phases, its substitution by Zmax, i.e. the atomic number of the heaviest element in the compound, is still acceptable for an approximate correction. For simulated Kikuchi patterns the offset‐corrected lattice parameter deviation is Δa/a 〈 1.5%. The lattice parameter ratios, and the angles α, β and γ between the basis vectors, are not affected at all.
    Description: Automatically determined band widths in simulated backscatter Kikuchi patterns exhibit differences from the double Bragg angles that correlate with the scatterer density. Corrections are proposed to compensate for this.
    Keywords: ddc:548 ; mean atomic number ; Kikuchi patterns ; lattice parameters ; automated Bragg angle determination ; lattice parameter determination ; dynamical theory of electron diffraction ; electron backscatter diffraction ; Funk transform
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    POWTEX visits POWGEN (2023)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2023-07-21
    Description: 〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉The high‐intensity time‐of‐flight (TOF) neutron diffractometer POWTEX for powder and texture analysis is currently being built prior to operation in the eastern guide hall of the research reactor FRM II at Garching close to Munich, Germany. Because of the world‐wide 〈sup〉3〈/sup〉He crisis in 2009, the authors promptly initiated the development of 〈sup〉3〈/sup〉He‐free detector alternatives that are tailor‐made for the requirements of large‐area diffractometers. Herein is reported the 2017 enterprise to operate one mounting unit of the final POWTEX detector on the neutron powder diffractometer POWGEN at the Spallation Neutron Source located at Oak Ridge National Laboratory, USA. As a result, presented here are the first angular‐ and wavelength‐dependent data from the POWTEX detector, unfortunately damaged by a 50〈italic〉g〈/italic〉 shock but still operating, as well as the efforts made both to characterize the transport damage and to successfully recalibrate the voxel positions in order to yield nonetheless reliable measurements. Also described is the current data reduction process using the 〈italic〉PowderReduceP2D〈/italic〉 algorithm implemented in 〈italic〉Mantid〈/italic〉 [Arnold 〈italic〉et al.〈/italic〉 (2014). 〈italic〉Nucl. Instrum. Methods Phys. Res. A〈/italic〉, 〈bold〉764〈/bold〉, 156–166]. The final part of the data treatment chain, namely a novel multi‐dimensional refinement using a modified version of the 〈italic〉GSAS‐II〈/italic〉 software suite [〈ext-link ext-link-type="uri" xlink:href="http://scripts.iucr.org/cgi-bin/paper?aj5212"〉Toby & Von Dreele (2013). 〈italic〉J. Appl. Cryst.〈/italic〉〈bold〉46〈/bold〉, 544–549〈/ext-link〉], is compared with a standard data treatment of the same event data conventionally reduced as TOF diffraction patterns and refined with the unmodified version of 〈italic〉GSAS‐II〈/italic〉. This involves both determining the instrumental resolution parameters using POWGEN's powdered diamond standard sample and the refinement of a friendly‐user sample, BaZn(NCN)〈sub〉2〈/sub〉. Although each structural parameter on its own looks similar upon comparing the conventional (1D) and multi‐dimensional (2D) treatments, also in terms of precision, a closer view shows small but possibly significant differences. For example, the somewhat suspicious proximity of the 〈italic〉a〈/italic〉 and 〈italic〉b〈/italic〉 lattice parameters of BaZn(NCN)〈sub〉2〈/sub〉 crystallizing in 〈italic〉Pbca〈/italic〉 as resulting from the 1D refinement (0.008 Å) is five times less pronounced in the 2D refinement (0.038 Å). Similar features are found when comparing bond lengths and bond angles, 〈italic〉e.g.〈/italic〉 the two N—C—N units are less differently bent in the 1D results (173 and 175°) than in the 2D results (167 and 173°). The results are of importance not only for POWTEX but also for other neutron TOF diffractometers with large‐area detectors, like POWGEN at the SNS or the future DREAM beamline at the European Spallation Source.〈/p〉
    Description: 〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉The first real‐world neutron diffraction data have been collected with one of the POWTEX detectors (FRM II, Garching, Germany) mounted for testing at the Spallation Neutron Source (Oak Ridge National Laboratory, USA). They allow for angular‐ and wavelength‐dispersive Rietveld refinement using a modified version of 〈italic〉GSAS‐II〈/italic〉.〈boxed-text position="anchor" content-type="graphic" xml:lang="en"〉〈graphic position="anchor" id="jats-graphic-1" xlink:href="urn:x-wiley:16005767:jcr2tu5033:jcr2tu5033-fig-0001"〉 〈/graphic〉〈/boxed-text〉〈/p〉
    Keywords: ddc:548 ; neutron detectors ; POWGEN beamline ; POWTEX detector ; DREAM beamline ; time‐of‐flight diffraction ; angular‐dispersive refinement ; wavelength‐dispersive refinement ; powder diffraction ; Rietveld refinement ; multi‐dimensional refinement
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  • 42
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    A note on the wedge reversion antisymmetry operation and 51 types of physical quantities in arbitrary dimensions (2023)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2023-07-21
    Description: 〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉The paper by Gopalan [〈ext-link ext-link-type="uri" xlink:href="http://scripts.iucr.org/cgi-bin/paper?ib5086"〉(2020). 〈italic〉Acta Cryst.〈/italic〉 A〈bold〉76〈/bold〉, 318–327〈/ext-link〉] presented an enumeration of the 41 physical quantity types in non‐relativistic physics, in arbitrary dimensions, based on the formalism of Clifford algebra. Gopalan considered three antisymmetries: spatial inversion, 〈overline〉1〈/overline〉, time reversal, 1′, and wedge reversion, 1〈sup〉†〈/sup〉. A consideration of the set of all seven antisymmetries (〈overline〉1〈/overline〉, 1′, 1〈sup〉†〈/sup〉, 1′〈sup〉†〈/sup〉, 〈overline〉1〈/overline〉〈sup〉†〈/sup〉, 〈overline〉1〈/overline〉′, 〈overline〉1〈/overline〉′〈sup〉†〈/sup〉) leads to an extension of the results obtained by Gopalan. It is shown that there are 51 types of physical quantities with distinct symmetry properties in total.〈/p〉
    Description: 〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉It is shown that there are 51 types of physical quantities in arbitrary dimensions with distinct transformations by wedge reversion symmetry. In the paper by 〈ext-link ext-link-type="uri" xlink:href="http://scripts.iucr.org/cgi-bin/paper?ib5086"〉Gopalan [(2020). 〈italic〉Acta Cryst.〈/italic〉 A〈bold〉76〈/bold〉, 318–327]〈/ext-link〉 only 41 types were enumerated.〈boxed-text position="anchor" content-type="graphic" xml:lang="en"〉〈graphic position="anchor" id="jats-graphic-1" xlink:href="urn:x-wiley:20532733:aya2ib5117:aya2ib5117-fig-0001"〉 〈alt-text〉image〈/alt-text〉 〈/graphic〉〈/boxed-text〉〈/p〉
    Keywords: ddc:548 ; multivectors ; wedge reversion ; antisymmetry ; Clifford algebra
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  • 43
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    Use of electron backscatter diffraction patterns to determine the crystal lattice. Part 1. Where is the Bragg angle? (2023)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2023-07-19
    Description: The derivation of a crystal structure and its phase‐specific parameters from a single wide‐angle backscattered Kikuchi diffraction pattern requires reliable extraction of the Bragg angles. By means of the first derivative of the lattice profile, an attempt is made to determine fully automatically and reproducibly the band widths in simulated Kikuchi patterns. Even under such ideal conditions (projection centre, wavelength and lattice plane traces are perfectly known), this leads to a lattice parameter distribution whose mean shows a linear offset that correlates with the mean atomic number Z of the pattern‐forming phase. The consideration of as many Kikuchi bands as possible reduces the errors that typically occur if only a single band is analysed. On the other hand, the width of the resulting distribution is such that higher image resolution of diffraction patterns, employing longer wavelengths to produce wider bands or the use of higher interference orders is less advantageous than commonly assumed.
    Description: The lattice parameters of more than 350 phases have been determined from simulated backscatter Kikuchi patterns. The deviations correlating with the mean atomic number correspond to those observed previously for experimental electron backscatter diffraction patterns.
    Keywords: ddc:548 ; Bragg angles ; Kikuchi bands ; Kikuchi patterns ; first derivative ; lattice parameters ; lattice parameter determination ; Bravais lattice type ; electron backscatter diffraction ; Radon transform
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  • 44
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    Data reduction for X‐ray serial crystallography using machine learning (2023)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
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    Publication Date: 2023-07-19
    Description: Serial crystallography experiments produce massive amounts of experimental data. Yet in spite of these large‐scale data sets, only a small percentage of the data are useful for downstream analysis. Thus, it is essential to differentiate reliably between acceptable data (hits) and unacceptable data (misses). To this end, a novel pipeline is proposed to categorize the data, which extracts features from the images, summarizes these features with the `bag of visual words' method and then classifies the images using machine learning. In addition, a novel study of various feature extractors and machine learning classifiers is presented, with the aim of finding the best feature extractor and machine learning classifier for serial crystallography data. The study reveals that the oriented FAST and rotated BRIEF (ORB) feature extractor with a multilayer perceptron classifier gives the best results. Finally, the ORB feature extractor with multilayer perceptron is evaluated on various data sets including both synthetic and experimental data, demonstrating superior performance compared with other feature extractors and classifiers.
    Description: A machine learning method for distinguishing good and bad images in serial crystallography is presented. To reduce the computational cost, this uses the oriented FAST and rotated BRIEF feature extraction method from computer vision to detect image features, followed by a multilayer perceptron (neural network) to classify the images.
    Keywords: ddc:548 ; serial crystallography ; data reduction ; machine learning ; feature extraction
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  • 45
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    Towards joint in situ determination of pressure and temperature in the large volume press exclusively from X‐ray diffraction (2023)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
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    Publication Date: 2023-07-19
    Description: Since high‐pressure devices have been used at synchrotron facilities, accurate determination of pressure and temperature in the sample has been a crucial objective, particularly for experiments that simulate the Earth's interior. However, in some cases using a thermocouple may have a high likelihood of failure or is incompatible with a high‐pressure assembly. To address these challenges and similar issues, we aim to expand a previously proposed solution: to jointly estimate pressure and temperature (〈italic〉PT〈/italic〉) through 〈italic〉in situ〈/italic〉 X‐ray diffraction, to cover a wider range of internal 〈italic〉PT〈/italic〉 calibrants tested over larger 〈italic〉PT〈/italic〉 ranges. A modifiable Python‐based software is offered to quickly obtain results. To achieve these aims, 〈italic〉in situ〈/italic〉 large volume press experiments are performed on pellets of intimately mixed powders of a halide (NaCl, KCl, KBr, CsCl) or MgO and a metal (Pt, Re, Mo, W, Ni) in the pressure range 3–11 GPa and temperature range 300–1800 K. Although the pressure range was chosen for practical reasons, it also covers an equally important depth range in the Earth (down to 350 km) for geoscience studies. A thermocouple was used to validate the 〈italic〉PT〈/italic〉 conditions in the cell assemblies. The key results show that choosing the appropriate calibrant materials and using a joint 〈italic〉PT〈/italic〉 estimation can yield surprisingly small uncertainties (〈italic〉i.e.〈/italic〉 〈±0.1 GPa and 〈±50 K). This development is expected to benefit current and future research at extreme conditions, as other materials with high compressibility or high thermal pressure, stable over large 〈italic〉PT〈/italic〉 ranges, may be discovered and used as 〈italic〉PT〈/italic〉 calibrants.〈/p〉
    Description: Research in high‐pressure devices, such as the diamond anvil cell and the large volume press, requires knowledge of the pressure and temperature in the sample. Here, a large volume press and an internal resistive heater were used to generate high load and heat to various combinations of intimately mixed powders of materials. X‐ray diffraction and custom software were used to jointly estimate the pressures and temperatures in the samples and establish calibrants for 〈italic〉in situ〈/italic〉 experiments at extreme conditions.〈boxed-text position="anchor" content-type="graphic" xml:lang="en"〉〈graphic position="anchor" id="jats-graphic-1" xlink:href="urn:x-wiley:16005775:jsy2vl5008:jsy2vl5008-fig-0001"〉
    Description: https://gitlab.desy.de/robert.farla/eoscross
    Keywords: ddc:548 ; equations of state ; X‐ray diffraction ; large volume press ; high pressure ; resistive heating
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  • 46
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    Farm-waste-derived recyclable photothermal evaporator (2022)
    Cell Press
    Details
    Publication Date: 2022-11-18
    Description: © The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Tian, Y., Liu, X., Li, J., Deng, Y., DeGiorgis, J. A., Zhou, S., Caratenuto, A., Minus, M. L., Wan, Y., Xiao, G., & Zheng, Y. Farm-waste-derived recyclable photothermal evaporator. Cell Reports Physical Science, 2(9), (2021): 100549, https://doi.org/10.1016./j.xcrp.2021.100549
    Description: Interfacial solar steam generation is emerging as a promising technique for efficient desalination. Although increasing efforts have been made, challenges exist for achieving a balance among a plethora of performance indicators—for example, rapid evaporation, durability, low-cost deployment, and salt rejection. Here, we demonstrate that carbonized manure can convert 98% of sunlight into heat, and the strong capillarity of porous carbon fibers networks pumps sufficient water to evaporation interfaces. Salt diffusion within microchannels enables quick salt drainage to the bulk seawater to prevent salt accumulation. With these advantages, this biomass-derived evaporator is demonstrated to feature a high evaporation rate of 2.81 kg m−2 h−1 under 1 sun with broad robustness to acidity and alkalinity. These advantages, together with facial deployment, offer an approach for converting farm waste to energy with high efficiency and easy implementation, which is particularly well suited for developing regions.
    Description: This project is supported by the National Science Foundation through grant no. CBET-1941743. This project is based upon work supported in part by the National Science Foundation under EPSCoR Cooperative Agreement no. OIA-1655221.
    Keywords: Biomass ; Recyclable ; Manure ; Farm waste ; Photothermal evaporation ; Desalination
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    Stable Barium Isotope Fractionation in Pore Waters of Estuarine Sediments (2023)
    American Geophysical Union (AGU)
    In:  EPIC3Geochemistry, Geophysics, Geosystems, American Geophysical Union (AGU), 24(6), ISSN: 1525-2027
    Details
    Publication Date: 2023-06-01
    Repository Name: EPIC Alfred Wegener Institut
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    HTD2: a single‐crystal X‐ray diffractometer for combined high‐pressure/low‐temperature experiments at laboratory scale (2022)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2022-12-15
    Description: High‐pressure (HP) X‐ray diffraction experiments at low temperature (LT) require dedicated instruments as well as non‐standard sample environments and measuring strategies. This is especially true when helium cryogenic temperatures below 80 K are targeted. Furthermore, only experiments on single‐crystalline samples provide the prerequisites to study subtle structural changes in the p–T phase diagram under extreme LT and HP conditions in greater detail. Due to special hardware requirements, such measurements are usually in the realm of synchrotron beamlines. This contribution describes the design of an LT/HP diffractometer (HTD2) to perform single‐crystal X‐ray diffraction experiments using a laboratory source in the temperature range 400 〉 T 〉 2 K while applying pressures of up to 20 GPa.
    Description: The design and operation of a newly commissioned single‐crystal X‐ray diffractometer (HTD2) are presented. The device enables experiments under simultaneous low‐temperature and high‐pressure conditions using a laboratory X‐ray source.
    Keywords: ddc:548 ; HTD2 ; low temperature ; high pressure ; single crystals ; instrumentation
    Language: English
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    New Insights Into Cyclone Impacts on Sea Ice in the Atlantic Sector of the Arctic Ocean in Winter (2022)
    American Geophysical Union (AGU)
    In:  EPIC3Geophysical Research Letters, American Geophysical Union (AGU), 49(22), ISSN: 0094-8276
    Details
    Publication Date: 2023-06-21
    Description: Based on the ERA5 reanalysis, we report on statistically significant impacts of transient cyclones on sea ice concentration (SIC) in the Atlantic sector of the Arctic Ocean in winter under “New Arctic” conditions (2000–2020). This includes a pattern of reduced SIC prior to and during cyclones for the whole study domain, while a regional difference between increased SIC in the Barents Sea and reduced SIC in the Greenland Sea is found as the net effect from 3 days prior to 5 days after the cyclone passage. Generally, locally low to medium SIC conditions combined with intense cyclones drive highest SIC changes. There are indications that both thermodynamic and dynamic effects contribute to the SIC changes, but a detailed quantification is required in future research. We provide evidence that cyclone impacts on SIC have amplified compared to the “Old Arctic” (1979–1999), particularly in the Barents Sea.
    Repository Name: EPIC Alfred Wegener Institut
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    X‐ray diffraction with micrometre spatial resolution for highly absorbing samples (2022)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2023-01-21
    Description: X‐ray diffraction with high spatial resolution is commonly used to characterize (poly)crystalline samples with, for example, respect to local strain, residual stress, grain boundaries and texture. However, the investigation of highly absorbing samples or the simultaneous assessment of high‐Z materials by X‐ray fluorescence have been limited due to the utilization of low photon energies. Here, a goniometer‐based setup implemented at the P06 beamline of PETRA III that allows for micrometre spatial resolution with a photon energy of 35 keV and above is reported. A highly focused beam was achieved by using compound refractive lenses, and high‐precision sample manipulation was enabled by a goniometer that allows up to 5D scans (three rotations and two translations). As experimental examples, the determination of local strain variations in martensitic steel samples with micrometre spatial resolution, as well as the simultaneous elemental distribution for high‐Z materials in a thin‐film solar cell, are demonstrated. The proposed approach allows users from the materials‐science community to determine micro‐structural properties even in highly absorbing samples.
    Description: A demonstration of high‐resolution micro X‐ray diffraction at high photon energies for highly absorbing samples.
    Keywords: ddc:548 ; X‐ray diffraction ; high spatial resolution ; high photon energy ; X‐ray fluorescence ; goniometers
    Language: English
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    Domain Auto Finder (DAFi) program: the analysis of single‐crystal X‐ray diffraction data from polycrystalline samples (2022)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2023-01-21
    Description: This paper presents the Domain Auto Finder (DAFi) program and its application to the analysis of single‐crystal X‐ray diffraction (SC‐XRD) data from multiphase mixtures of microcrystalline solids and powders. Superposition of numerous reflections originating from a large number of single‐crystal domains of the same and/or different (especially unknown) phases usually precludes the sorting of reflections coming from individual domains, making their automatic indexing impossible. The DAFi algorithm is designed to quickly find subsets of reflections from individual domains in a whole set of SC‐XRD data. Further indexing of all found subsets can be easily performed using widely accessible crystallographic packages. As the algorithm neither requires a priori crystallographic information nor is limited by the number of phases or individual domains, DAFi is powerful software to be used for studies of multiphase polycrystalline and microcrystalline (powder) materials. The algorithm is validated by testing on X‐ray diffraction data sets obtained from real samples: a multi‐mineral basalt rock at ambient conditions and products of the chemical reaction of yttrium and nitrogen in a laser‐heated diamond anvil cell at 50 GPa. The high performance of the DAFi algorithm means it can be used for processing SC‐XRD data online during experiments at synchrotron facilities.
    Description: This paper presents the Domain Auto Finder (DAFi) program and its application to the analysis of single‐crystal X‐ray diffraction (SC‐XRD) data from multiphase mixtures of microcrystalline solids and powders. The DAFi algorithm is designed to quickly find subsets of reflections from individual domains in a whole set of SC‐XRD data and neither requires a priori crystallographic information nor is limited by the number of phases or individual domains.
    Keywords: ddc:548 ; single‐crystal domain auto finder ; DAFi ; single‐crystal X‐ray diffraction ; polycrystalline samples ; multiphase mixtures
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    High‐resolution XEOL spectroscopy setup at the X‐ray absorption spectroscopy beamline P65 of PETRA III (2022)
    Levcenko, S. ; Biller, R. ; Pfeiffelmann, T. ; [et al.]
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2023-01-25
    Description: A newly designed setup to perform steady‐state X‐ray excited optical luminescence (XEOL) spectroscopy and simultaneous XEOL and X‐ray absorption spectroscopy characterization at beamline P65 of PETRA III is described. The XEOL setup is equipped with a He‐flow cryostat and state‐of‐the‐art optical detection system, which covers a wide wavelength range of 300–1700 nm with a high spectral resolution of 0.4 nm. To demonstrate the setup functioning, low‐temperature XEOL studies on polycrystalline CuInSe2 thin film, single‐crystalline GaN thin film and single‐crystalline ZnO bulk semiconductor samples are performed.
    Description: X‐ray excited optical luminescence (XEOL) spectroscopy is increasingly important to understand the interplay between the optical properties, structure and chemical composition, providing insights into the mechanism of radiative recombination for a wide range of materials. This study demonstrates a newly implemented setup to perform steady‐state XEOL and simultaneous XEOL and XAFS characterizations at beamline P65 of PETRA III.
    Keywords: ddc:550.2 ; XEOL ; XAS ; CuInSe2 ; ZnO ; GaN
    Language: English
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    The Arctic Ocean’s Beaufort Gyre (2023)
    Annual Reviews
    Details
    Publication Date: 2023-02-28
    Description: © The Author(s), 2023. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Timmermans, M.-L., & Toole, J. The Arctic Ocean’s Beaufort Gyre. Annual Review of Marine Science, 15(1), (2023): 223-248, https://doi.org/10.1146/annurev-marine-032122-012034.
    Description: The Arctic Ocean's Beaufort Gyre is a dominant feature of the Arctic system, a prominent indicator of climate change, and possibly a control factor for high-latitude climate. The state of knowledge of the wind-driven Beaufort Gyre is reviewed here, including its forcing, relationship to sea-ice cover, source waters, circulation, and energetics. Recent decades have seen pronounced change in all elements of the Beaufort Gyre system. Sea-ice losses have accompanied an intensification of the gyre circulation and increasing heat and freshwater content. Present understanding of these changes is evaluated, and time series of heat and freshwater content are updated to include the most recent observations.
    Description: Support was provided by the National Science Foundation Office of Polar Programs and the Office of Naval Research.
    Keywords: Arctic Ocean ; Beaufort Gyre ; Circulation ; Sea ice ; Freshwater ; Ocean heat content
    Repository Name: Woods Hole Open Access Server
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    The Impact of Different Atmospheric CO2 Concentrations on Large Scale Miocene Temperature Signatures (2023)
    American Geophysical Union (AGU)
    In:  EPIC3Paleoceanography and Paleoclimatology, American Geophysical Union (AGU), ISSN: 2572-4517
    Details
    Publication Date: 2023-02-03
    Repository Name: EPIC Alfred Wegener Institut
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    Hydroxyapatite catalyzed hydrothermal liquefaction transforms food waste from an environmental liability to renewable fuel (2023)
    Cell Press
    Details
    Publication Date: 2023-03-08
    Description: © The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in LeClerc, H., Tompsett, G., Paulsen, A., McKenna, A., Niles, S., Reddy, C., Nelson, R., Cheng, F., Teixeira, A., & Timko, M. Hydroxyapatite catalyzed hydrothermal liquefaction transforms food waste from an environmental liability to renewable fuel. IScience, 25(9), (2022): 104916, https://doi.org/10.1016/j.isci.2022.104916.
    Description: Food waste is an abundant and inexpensive resource for the production of renewable fuels. Biocrude yields obtained from hydrothermal liquefaction (HTL) of food waste can be boosted using hydroxyapatite (HAP) as an inexpensive and abundant catalyst. Combining HAP with an inexpensive homogeneous base increased biocrude yield from 14 ± 1 to 37 ± 3%, resulting in the recovery of 49 ± 2% of the energy contained in the food waste feed. Detailed product analysis revealed the importance of fatty-acid oligomerization during biocrude formation, highlighting the role of acid-base catalysts in promoting condensation reactions. Economic and environmental analysis found that the new technology has the potential to reduce US greenhouse gas emissions by 2.6% while producing renewable diesel with a minimum fuel selling price of $1.06/GGE. HAP can play a role in transforming food waste from a liability to a renewable fuel.
    Description: This work was funded by the DOE Bioenergy Technology Office (DE-EE0008513), a DOE DBIR (DE-SC0015784) and the MassCEC. The authors thank WenWen Yao, Department of Environmental Science at WPI, for TOC analysis, Mainstream Engineering for heating value characterization of the oil and solid samples, Wei Fan for assistance in obtaining SEM images and, Julia Martin and Ronald Grimm for their assistance in collecting XPS data, and Jeffrey R. Page for his assistance with oil upgrading and analysis. HOL was partially funded for this work by NSF Graduate Research Fellowship award number 2038257. A portion of this work was performed at the National High Magnetic Field Laboratory Ion Cyclotron Resonance user facility, which is supported by the NSF Division of Materials Research and Division of Chemistry through DMR 16-44779 and the State of Florida.
    Keywords: Chemistry ; Chemical engineering ; Catalysis
    Repository Name: Woods Hole Open Access Server
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    Permafrost Carbon: Progress on Understanding Stocks and Fluxes Across Northern Terrestrial Ecosystems (2024)
    American Geophysical Union (AGU)
    In:  EPIC3Journal of Geophysical Research: Biogeosciences, American Geophysical Union (AGU), 129(3), ISSN: 2169-8953
    Details
    Publication Date: 2024-02-27
    Description: Significant progress in permafrost carbon science made over the past decades include the identification of vast permafrost carbon stocks, the development of new pan‐Arctic permafrost maps, an increase in terrestrial measurement sites for CO〈jats:sub〉2〈/jats:sub〉 and methane fluxes, and important factors affecting carbon cycling, including vegetation changes, periods of soil freezing and thawing, wildfire, and other disturbance events. Process‐based modeling studies now include key elements of permafrost carbon cycling and advances in statistical modeling and inverse modeling enhance understanding of permafrost region C budgets. By combining existing data syntheses and model outputs, the permafrost region is likely a wetland methane source and small terrestrial ecosystem CO〈jats:sub〉2〈/jats:sub〉 sink with lower net CO〈jats:sub〉2〈/jats:sub〉 uptake toward higher latitudes, excluding wildfire emissions. For 2002–2014, the strongest CO〈jats:sub〉2〈/jats:sub〉 sink was located in western Canada (median: −52 g C m〈jats:sup〉−2〈/jats:sup〉 y〈jats:sup〉−1〈/jats:sup〉) and smallest sinks in Alaska, Canadian tundra, and Siberian tundra (medians: −5 to −9 g C m〈jats:sup〉−2〈/jats:sup〉 y〈jats:sup〉−1〈/jats:sup〉). Eurasian regions had the largest median wetland methane fluxes (16–18 g CH〈jats:sub〉4〈/jats:sub〉 m〈jats:sup〉−2〈/jats:sup〉 y〈jats:sup〉−1〈/jats:sup〉). Quantifying the regional scale carbon balance remains challenging because of high spatial and temporal variability and relatively low density of observations. More accurate permafrost region carbon fluxes require: (a) the development of better maps characterizing wetlands and dynamics of vegetation and disturbances, including abrupt permafrost thaw; (b) the establishment of new year‐round CO〈jats:sub〉2〈/jats:sub〉 and methane flux sites in underrepresented areas; and (c) improved models that better represent important permafrost carbon cycle dynamics, including non‐growing season emissions and disturbance effects.〈/jats:p〉
    Repository Name: EPIC Alfred Wegener Institut
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    Late Holocene Dust Deposition Fluxes Over the Entire South Atlantic Ocean (2024)
    American Geophysical Union (AGU)
    In:  EPIC3Geochemistry Geophysics Geosystems, American Geophysical Union (AGU), 25(1), ISSN: 1525-2027
    Details
    Publication Date: 2024-03-04
    Description: Mineral dust accumulated on the ocean floor is an important archive for reconstructing past atmospheric circulation changes and climatological conditions in the source areas. Dust emitted from Southern Hemisphere dust sources is widely deposited over the oceans. However, there are few records of dust deposition over the open ocean, and a large need for extended geographical coverage exists. We present a large data set (134 surface sediment samples) of Late Holocene dust deposition from seafloor surface sediments covering the entire South Atlantic Ocean. Polymodal grain-size distributions of the lithogenic fraction indicate that the sediments are composed of multiple sediment components. By using end-member modeling, we attempt to disentangle the dust signal from non-aeolian sediments. Combined with 230Th-normalized lithogenic fluxes, we quantified the specific deposition fluxes for mineral dust, crrent-sorted sediments and ice-rafted debris (IRD). Although the method could not completely separate the different components in every region, it shows that dust deposition off the most prominent dust source for the South Atlantic Ocean—southern South America—amounts up to approximately 0.7 g cm−2 Kyr−1 and decreases downwind. Bottom-current-sorted sediments and IRD are mostly concentrated around the continental margins. The ratio of the coarse to fine dust end members reveals input from north African dust sources to the South Atlantic. The majority of the observations are in good agreement with new model simulations. This extensive and relevant data set of dust grain size and deposition fluxes to the South Atlantic could be used to calibrate and validate further model simulations.
    Repository Name: EPIC Alfred Wegener Institut
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    Phaeocystis: A Global Enigma (2024)
    Annual Reviews
    In:  EPIC3Annual Review of Marine Science, Annual Reviews, 16(1), pp. 417-441, ISSN: 1941-1405
    Details
    Publication Date: 2024-03-01
    Description: The genus Phaeocystis is globally distributed, with blooms commonly occurring on continental shelves. This unusual phytoplankter has two major morphologies: solitary cells and cells embedded in a gelatinous matrix. Only colonies form blooms. Their large size (commonly 2 mm but up to 3 cm) and mucilaginous envelope allow the colonies to escape predation, but data are inconsistent as to whether colonies are grazed. Cultured Phaeocystis can also inhibit the growth of co-occurring phytoplankton or the feeding of potential grazers. Colonies and solitary cells use nitrate as a nitrogen source, although solitary cells can also grow on ammonium. Phaeocystis colonies might be a major contributor to carbon flux to depth, but in most cases, colonies are rapidly remineralized in the upper 300 m. The occurrence of large Phaeocystis blooms is often associated with environments with low and highly variable light and high nitrate levels, with Phaeocystis antarctica blooms being linked additionally to high iron availability. Emerging results indicate that different clones of Phaeocystis have substantial genetic plasticity, which may explain its appearance in a variety of environments. Given the evidence of Phaeocystis appearing in new systems, this trend will likely continue in the near future.
    Repository Name: EPIC Alfred Wegener Institut
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    Hard X‐ray full‐field nanoimaging using a direct photon‐counting detector (2023)
    Flenner, Silja ; Hagemann, Johannes ; Wittwer, Felix ; [et al.]
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2024-03-05
    Description: Full‐field X‐ray nanoimaging is a widely used tool in a broad range of scientific areas. In particular, for low‐absorbing biological or medical samples, phase contrast methods have to be considered. Three well established phase contrast methods at the nanoscale are transmission X‐ray microscopy with Zernike phase contrast, near‐field holography and near‐field ptychography. The high spatial resolution, however, often comes with the drawback of a lower signal‐to‐noise ratio and significantly longer scan times, compared with microimaging. In order to tackle these challenges a single‐photon‐counting detector has been implemented at the nanoimaging endstation of the beamline P05 at PETRA III (DESY, Hamburg) operated by Helmholtz‐Zentrum Hereon. Thanks to the long sample‐to‐detector distance available, spatial resolutions of below 100 nm were reached in all three presented nanoimaging techniques. This work shows that a single‐photon‐counting detector in combination with a long sample‐to‐detector distance allows one to increase the time resolution for in situ nanoimaging, while keeping a high signal‐to‐noise level.
    Description: A direct photon‐counting detector was used for different nanoimaging phase contrast techniques, increasing the temporal resolution.
    Keywords: ddc:548 ; nanotomography ; full‐field X‐ray microscopy ; near‐field holography ; near‐field ptychography ; Zernike phase contrast ; single‐photon‐counting detector ; phase contrast
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    Automatic bad‐pixel mask maker for X‐ray pixel detectors with application to serial crystallography (2022)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2024-02-14
    Description: X‐ray crystallography has witnessed a massive development over the past decade, driven by large increases in the intensity and brightness of X‐ray sources and enabled by employing high‐frame‐rate X‐ray detectors. The analysis of large data sets is done via automatic algorithms that are vulnerable to imperfections in the detector and noise inherent with the detection process. By improving the model of the behaviour of the detector, data can be analysed more reliably and data storage costs can be significantly reduced. One major requirement is a software mask that identifies defective pixels in diffraction frames. This paper introduces a methodology and program based upon concepts of machine learning, called robust mask maker (RMM), for the generation of bad‐pixel masks for large‐area X‐ray pixel detectors based on modern robust statistics. It is proposed to discriminate normally behaving pixels from abnormal pixels by analysing routine measurements made with and without X‐ray illumination. Analysis software typically uses a Bragg peak finder to detect Bragg peaks and an indexing method to detect crystal lattices among those peaks. Without proper masking of the bad pixels, peak finding methods often confuse the abnormal values of bad pixels in a pattern with true Bragg peaks and flag such patterns as useful regardless, leading to storage of enormous uninformative data sets. Also, it is computationally very expensive for indexing methods to search for crystal lattices among false peaks and the solution may be biased. This paper shows how RMM vastly improves peak finders and prevents them from labelling bad pixels as Bragg peaks, by demonstrating its effectiveness on several serial crystallography data sets.
    Description: Attention is focused on perhaps the biggest bottleneck in data analysis for serial crystallography at X‐ray free‐electron lasers, which has not received serious enough examination to date. An effective and reliable way is presented to identify anomalies in detectors, using machine learning and recently developed mathematical methods in the field referred to as `robust statistics'. image
    Keywords: ddc:548 ; bad‐pixel masks ; robust mask maker ; machine learning ; robust statistics ; serial crystallography
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    Machine learning for scattering data: strategies, perspectives and applications to surface scattering (2023)
    Hinderhofer, Alexander ; Greco, Alessandro ; Starostin, Vladimir ; [et al.]
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2024-02-14
    Description: Machine learning (ML) has received enormous attention in science and beyond. Discussed here are the status, opportunities, challenges and limitations of ML as applied to X‐ray and neutron scattering techniques, with an emphasis on surface scattering. Typical strategies are outlined, as well as possible pitfalls. Applications to reflectometry and grazing‐incidence scattering are critically discussed. Comment is also given on the availability of training and test data for ML applications, such as neural networks, and a large reflectivity data set is provided as reference data for the community.
    Description: The status, opportunities, challenges and limitations of machine learning are discussed as applied to X‐ray and neutron scattering techniques, with an emphasis on surface scattering.
    Keywords: ddc:548 ; surface scattering ; X‐ray diffraction ; neutron scattering ; machine learning ; data analysis
    Language: English
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    Beam‐induced redox chemistry in iron oxide nanoparticle dispersions at ESRF–EBS (2023)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2024-02-21
    Description: The storage ring upgrade of the European Synchrotron Radiation Facility makes ESRF–EBS the most brilliant high‐energy fourth‐generation light source, enabling in situ studies with unprecedented time resolution. While radiation damage is commonly associated with degradation of organic matter such as ionic liquids or polymers in the synchrotron beam, this study clearly shows that highly brilliant X‐ray beams readily induce structural changes and beam damage in inorganic matter, too. Here, the reduction of Fe3+ to Fe2+ in iron oxide nanoparticles by radicals in the brilliant ESRF–EBS beam, not observed before the upgrade, is reported. Radicals are created due to radiolysis of an EtOH–H2O mixture with low EtOH concentration (∼6 vol%). In light of extended irradiation times during insitu experiments in, for example, battery and catalysis research, beam‐induced redox chemistry needs to be understood for proper interpretation of insitu data.
    Description: With the increased brilliance at the European Research Facility–Extremely Brilliant Source (ESRF–EBS), a beam‐induced reduction of non‐stochiometric iron oxide nanoparticles (almost maghemite composition) to magnetite was observed in a mixture of ethanol and water with low ethanol concentration.
    Keywords: ddc:548 ; beam‐induced radiolysis ; radiation damage on inorganic materials ; ESRF–EBS
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    Updates in SASfit for fitting analytical expressions and numerical models to small‐angle scattering patterns (2022)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2024-02-22
    Description: Small‐angle scattering is an increasingly common method for characterizing particle ensembles in a wide variety of sample types and for diverse areas of application. SASfit has been one of the most comprehensive and flexible curve‐fitting programs for decades, with many specialized tools for various fields. Here, a selection of enhancements and additions to the SASfit program are presented that may be of great benefit to interested and advanced users alike: (a) further development of the technical basis of the program, such as new numerical algorithms currently in use, a continuous integration practice for automated building and packaging of the software, and upgrades on the plug‐in system for easier adoption by third‐party developers; (b) a selection of new form factors for anisotropic scattering patterns and updates to existing form factors to account for multiple scattering effects; (c) a new type of a very flexible distribution called metalog [Keelin (2016). Decis. Anal.13, 243–277], and regularization techniques such as the expectation‐maximization method [Dempster et al. (1977). J. R. Stat. Soc. Ser. B (Methodological), 39, 1–22; Richardson (1972) J. Opt. Soc. Am.62, 55; Lucy (1974). Astron. J.79, 745; Lucy (1994). Astron. Astrophys.289, 983–994], which is compared with fits of analytical size distributions via the non‐linear least‐squares method; and (d) new structure factors, especially for ordered nano‐ and meso‐scaled material systems, as well as the Ornstein–Zernike solver for numerical determination of particle interactions and the resulting structure factor when no analytical solution is available, with the aim of incorporating its effects into the small‐angle scattering intensity model used for fitting with SASfit.
    Description: Recent enhancements and additions to the SASfit program are discussed, including anisotropic scattering models, flexible distributions, regularization techniques such as the expectation‐maximization method, and new structure factors, especially for ordered nano‐ and meso‐scaled material. The Ornstein–Zernike solver for numerical structure factors is also introduced. image
    Keywords: ddc:548 ; small‐angle scattering ; SASfit ; numerical models ; structure factors ; form factors ; regularization techniques
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    The Role of Coastal Yedoma Deposits and Continental Shelf Sediments in the Arctic Ocean Silicon Cycle (2024)
    American Geophysical Union (AGU)
    In:  EPIC3Global Biogeochemical Cycles, American Geophysical Union (AGU), 38(1), ISSN: 0886-6236
    Details
    Publication Date: 2024-02-13
    Description: The availability of silicon (Si) in the ocean plays an important role in regulating biogeochemical and ecological processes. The Si budget of the Arctic Ocean appears balanced, with inputs equivalent to outputs, though it is unclear how a changing climate might aggravate this balance. In this study, we focus on Si cycling in Arctic coastal areas and continental shelf sediments to better constrain the Arctic Ocean Si budget. We provide the first estimate of amorphous Si (ASi) loading from erosion of coastal Yedoma deposits (30–90 Gmol yr−1), demonstrating comparable rates to particulate Si loading from rivers (10–90 Gmol yr−1). We found a positive relationship between surface sediment ASi and organic matter content on continental shelves. Combining these values with published Arctic shelf sediment properties and burial rates we estimate 70 Gmol Si yr−1 is buried on Arctic continental shelves, equivalent to 4.5% of all Si inputs to the Arctic Ocean. Sediment dissolved Si fluxes increased with distance from river mouths along cruise transects of shelf regions influenced by major rivers in the Laptev and East Siberian seas. On an annual basis, we estimate that Arctic shelf sediments recycle approximately up to twice as much DSi (680 Gmol Si) as is loaded from rivers (340–500 Gmol Si).
    Repository Name: EPIC Alfred Wegener Institut
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    A Synthesis of Global Coastal Ocean Greenhouse Gas Fluxes (2024)
    American Geophysical Union (AGU)
    In:  EPIC3Global Biogeochemical Cycles, American Geophysical Union (AGU), 38(1), ISSN: 0886-6236
    Details
    Publication Date: 2024-02-13
    Description: The coastal ocean contributes to regulating atmospheric greenhouse gas concentrations by taking up carbon dioxide (CO2) and releasing nitrous oxide (N2O) and methane (CH4). In this second phase of the Regional Carbon Cycle Assessment and Processes (RECCAP2), we quantify global coastal ocean fluxes of CO2, N2O and CH4 using an ensemble of global gap-filled observation-based products and ocean biogeochemical models. The global coastal ocean is a net sink of CO2 in both observational products and models, but the magnitude of the median net global coastal uptake is ∼60% larger in models (−0.72 vs. −0.44 PgC year−1, 1998–2018, coastal ocean extending to 300 km offshore or 1,000 m isobath with area of 77 million km2). We attribute most of this model-product difference to the seasonality in sea surface CO2 partial pressure at mid- and high-latitudes, where models simulate stronger winter CO2 uptake. The coastal ocean CO2 sink has increased in the past decades but the available time-resolving observation-based products and models show large discrepancies in the magnitude of this increase. The global coastal ocean is a major source of N2O (+0.70 PgCO2-e year−1 in observational product and +0.54 PgCO2-e year−1 in model median) and CH4 (+0.21 PgCO2-e year−1 in observational product), which offsets a substantial proportion of the coastal CO2 uptake in the net radiative balance (30%–60% in CO2-equivalents), highlighting the importance of considering the three greenhouse gases when examining the influence of the coastal ocean on climate.
    Repository Name: EPIC Alfred Wegener Institut
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    Quantifying Sub\xe2\x80\x90Seasonal Growth Rate Changes in Fossil Giant Clams Using Wavelet Transformation of Daily Mg/Ca Cycles (2023)
    American Geophysical Union (AGU)
    In:  Geochemistry, Geophysics, Geosystems vol. 24 no. 10
    Details
    Publication Date: 2024-02-08
    Description: Shells of the giant clam Tridacna can provide decade-long records of past environmental conditions via their geochemical composition and structurally through growth banding. Counting the daily bands can give an accurate internal age model with high temporal resolution, but daily banding is not always visually retrievable, especially in fossil specimens. We show that daily geochemical cycles (e.g., Mg/Ca) are resolvable via highly spatially resolved laser-ablation inductively coupled plasma mass spectrometry (LA-ICPMS; 3 \xc3\x97 33 \xce\xbcm laser slit) in our Miocene (\xe2\x88\xbc10 Ma) specimen, even in areas where daily banding is not visually discernible. By applying wavelet transformation on the measured daily geochemical cycles, we quantify varying daily growth rates throughout the shell. These growth rates are thus used to build an internal age model independent of optical daily band countability. Such an age model can be used to convert the measured elemental ratios from a function of distance to a function of time, which helps evaluate paleoenvironmental proxy data, for example, regarding the timing of sub-seasonal events. Furthermore, the quantification of daily growth rates across the shell facilitates the evaluation of (co)dependencies between growth rates and corresponding elemental compositions.
    Keywords: Tridacna
    Repository Name: National Museum of Natural History, Netherlands
    Type: info:eu-repo/semantics/article
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    Selective Sorting and Degradation of Permafrost Organic Matter in the Nearshore Zone of Herschel Island (Yukon, Canada) (2024)
    American Geophysical Union (AGU)
    In:  EPIC3Journal of Geophysical Research Biogeosciences, American Geophysical Union (AGU), 129(1), ISSN: 2169-8953
    Details
    Publication Date: 2024-01-26
    Description: 〈jats:title〉Abstract〈/jats:title〉〈jats:p〉Erosion of permafrost coasts due to climate warming releases large quantities of organic carbon (OC) into the Arctic Ocean. While burial of permafrost OC in marine sediments potentially limits degradation, resuspension of sediments in the nearshore zone potentially enhances degradation and greenhouse gas production, adding to the “permafrost carbon feedback.” Recent studies, focusing on bulk sediments, suggest that permafrost OC derived from coastal erosion is predominantly deposited close to shore. However, bulk approaches disregard sorting processes in the coastal zone, which strongly influence the OC distribution and fate. We studied soils and sediments along a transect from the fast‐eroding shoreline of Herschel Island—〈jats:italic〉Qikiqtaruk〈/jats:italic〉 (Yukon, Canada) to a depositional basin offshore. Sample material was fractionated by density (1.8 g cm〈jats:sup〉−3〈/jats:sup〉) and size (63 μm), separating loose OC from mineral‐associated OC. Each fraction was analyzed for element content (TOC, TN), carbon isotopes (δ〈jats:sup〉13〈/jats:sup〉C, Δ〈jats:sup〉14〈/jats:sup〉C), molecular biomarkers (〈jats:italic〉n〈/jats:italic〉‐alkanes, 〈jats:italic〉n〈/jats:italic〉‐alkanoic acids, lignin phenols, cutin acids), and mineral surface area. The OC partitioning between fractions changes considerably along the transect, highlighting the importance of hydrodynamic sorting in the nearshore zone. Additionally, OC and biomarker loadings decrease along the land‐ocean transect, indicating significant loss of OC during transport. However, molecular proxies for degradation show contrasting trends, suggesting that OC losses are not always well reflected in its degradation state. This study, using fraction partitioning that crosses land‐ocean boundaries in a way not done before, aids to disentangle sorting processes from degradation patterns, and provides quantitative insight into losses of thawed and eroded permafrost OC.〈/jats:p〉
    Repository Name: EPIC Alfred Wegener Institut
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    Extending MIEZE spectroscopy towards thermal wavelengths (2022)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2024-02-05
    Description: A modulation of intensity with zero effort (MIEZE) setup is proposed for high‐resolution neutron spectroscopy at momentum transfers up to 3 Å〈sup〉−1〈/sup〉, energy transfers up to 20 meV and an energy resolution in the microelectronvolt range using both thermal and cold neutrons. MIEZE has two prominent advantages compared with classical neutron spin echo. The first is the possibility to investigate spin‐depolarizing samples or samples in strong magnetic fields without loss of signal amplitude and intensity. This allows for the study of spin fluctuations in ferromagnets, and facilitates the study of samples with strong spin‐incoherent scattering. The second advantage is that multi‐analyzer setups can be implemented with comparatively little effort. The use of thermal neutrons increases the range of validity of the spin‐echo approximation towards shorter spin‐echo times. In turn, the thermal MIEZE option for greater ranges (TIGER) closes the gap between classical neutron spin‐echo spectroscopy and conventional high‐resolution neutron spectroscopy techniques such as triple‐axis, time‐of‐flight and back‐scattering. To illustrate the feasibility of TIGER, this paper presents the details of its implementation at the RESEDA beamline at FRM II by means of an additional velocity selector, polarizer and analyzer.
    Description: A modulation of intensity with zero effort (MIEZE) setup is proposed for high‐resolution neutron spectroscopy at momentum transfers up to 3 Å〈sup〉−1〈/sup〉, energy transfers up to 20 meV and an energy resolution in the microelectronvolt range using both thermal and cold neutrons.
    Keywords: ddc:548 ; neutron resonant spin echo ; MIEZE ; quasielastic scattering ; thermal neutrons
    Language: English
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    Extreme conditions research using the large‐volume press at the P61B endstation, PETRA III (2022)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2024-02-05
    Description: 〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉Penetrating, high‐energy synchrotron X‐rays are in strong demand, particularly for high‐pressure research in physics, chemistry and geosciences, and for materials engineering research under less extreme conditions. A new high‐energy wiggler beamline P61 has been constructed to meet this need at PETRA III in Hamburg, Germany. The first part of the paper offers an overview of the beamline front‐end components and beam characteristics. The second part describes the performance of the instrumentation and the latest developments at the P61B endstation. Particular attention is given to the unprecedented high‐energy photon flux delivered by the ten wigglers of the PETRA III storage ring and the challenges faced in harnessing this amount of flux and heat load in the beam. Furthermore, the distinctiveness of the world's first six‐ram Hall‐type large‐volume press, Aster‐15, at a synchrotron facility is described for research with synchrotron X‐rays. Additionally, detection schemes, experimental strategies and preliminary data acquired using energy‐dispersive X‐ray diffraction and radiography techniques are presented.〈/p〉
    Description: 〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉The operation of the P61B endstation large‐volume press and optics of P61 are reviewed. The instrumentation at P61B, including the large‐volume press, detection systems and data acquisition for 〈italic〉in situ〈/italic〉 high‐pressure experiments are described.〈boxed-text position="anchor" content-type="graphic" xml:lang="en"〉〈graphic position="anchor" id="jats-graphic-1" xlink:href="urn:x-wiley:16005775:jsy2ju5040:jsy2ju5040-fig-0001"〉 〈/graphic〉〈/boxed-text〉〈/p〉
    Keywords: ddc:550.724 ; extreme conditions ; high‐pressure ; large‐volume press ; energy‐dispersive X‐ray diffraction ; radiography ; resistive heating ; ultrasonic interferometry ; acoustic emissions detection
    Language: English
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    Postdepositional Behavior of Molybdenum in Deep Sediments and Implications for Paleoredox Reconstruction (2023)
    American Geophysical Union (AGU)
    In:  EPIC3Geophysical Research Letters, American Geophysical Union (AGU), 50(21), ISSN: 0094-8276
    Details
    Publication Date: 2023-11-01
    Description: Molybdenum (Mo) is a trace element sensitive to oceanic redox conditions. The fidelity of sedimentary Mo as a paleoredox proxy of coeval seawater depends on the extent of Mo remobilization during postdepositional processes. Here we present the Mo content and isotope profiles for deep sediments from the Nankai Trough, Japan. The Mo signature suggests that these sediments have experienced extensive early diagenesis and hydrothermal alteration at depth. Iron (Fe)‐manganese (Mn) (oxyhydr)oxide alteration combined with Mo thiolation leads to a more than twenty‐fold enrichment of Mo within the sulfate reduction zone. Hydrothermal fluids and Mo adsorption onto Fe‐Mn (oxyhydr)oxides cause extremely negative Mo‐isotope values at the underthrust zone. These postdepositional Mo signals might be misinterpreted as expanded anoxia in the water column. Our findings highlight the importance of constraining postdepositional effects on Mo‐based proxies during paleoredox reconstruction.
    Repository Name: EPIC Alfred Wegener Institut
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    Quantifying electron cascade size in various irradiated materials for free‐electron laser applications (2022)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2023-12-12
    Description: 〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉Studying electron‐ and X‐ray‐induced electron cascades in solids is essential for various research areas at free‐electron laser facilities, such as X‐ray imaging, crystallography, pulse diagnostics or X‐ray‐induced damage. To better understand the fundamental factors that define the duration and spatial size of such cascades, this work investigates the electron propagation in ten solids relevant for the applications of X‐ray lasers: Au, B〈sub〉4〈/sub〉C, diamond, Ni, polystyrene, Ru, Si, SiC, Si〈sub〉3〈/sub〉N〈sub〉4〈/sub〉 and W. Using classical Monte Carlo simulation in the atomic approximation, we study the dependence of the cascade size on the incident electron or photon energy and on the target parameters. The results show that an electron‐induced cascade is systematically larger than a photon‐induced cascade. Moreover, in contrast with the common assumption, the maximal cascade size does not necessarily coincide with the electron range. It was found that the cascade size can be controlled by careful selection of the photon energy for a particular material. Photon energy, just above an ionization potential, can essentially split the absorbed energy between two electrons (photo‐ and Auger), reducing their initial energy and thus shrinking the cascade size. This analysis suggests a way of tailoring the electron cascades for applications requiring either small cascades with a high density of excited electrons or large‐spread cascades with lower electron densities.〈/p〉
    Description: 〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉Studying electron‐ and X‐ray‐induced electron cascades in solids is essential for various research areas at free‐electron laser facilities, such as X‐ray imaging, crystallography, pulse diagnostics or X‐ray‐induced damage. To better understand the fundamental factors that define the duration and spatial size of such cascades, this work investigates the electron propagation in ten solids relevant for the applications of X‐ray lasers. Using classical Monte Carlo simulation in the atomic approximation, the dependence of the cascade size on the incident electron or photon energy and on the target parameters is studied.〈boxed-text position="anchor" content-type="graphic" xml:lang="en"〉〈graphic position="anchor" id="jats-graphic-1" xlink:href="urn:x-wiley:16005775:jsy2gb5123:jsy2gb5123-fig-0001"〉 〈/graphic〉〈/boxed-text〉〈/p〉
    Keywords: ddc:548 ; electron cascades ; X‐ray free‐electron lasers ; Monte Carlo ; photon‐induced cascade ; electron transport
    Language: English
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    A Modeling Perspective on the Lingering Glacial Sea Surface Temperature Conundrum (2022)
    American Geophysical Union (AGU)
    In:  EPIC3Geophysical Research Letters, American Geophysical Union (AGU), 49(23), ISSN: 0094-8276
    Details
    Publication Date: 2023-09-19
    Description: The strong cooling during the Last Glacial Maximum (LGM, 21 ka BP) provides a rigorous test of climate models' ability to simulate past and future climate changes. We force an atmospheric general circulation model with two recent global LGM sea surface temperature (SST) reconstructions, one suggesting a weak and the other a more pronounced cooling, and compare the simulated land surface temperatures (LSTs) to reconstructed data. Our results do not confirm either SST reconstruction. The cold SST data set leads to good agreement between simulated and observed LSTs at low latitudes, but is systematically too cold at mid-latitudes. The opposite is true for the warm SST data set. Differences between the simulated LSTs are caused by varying land surface albedos, which is lower for the warmer SST reconstruction. The inconsistency between reconstructed and simulated climate points to a potentially significant bias in the proxy reconstructions and/or the climate sensitivity of current climate models.
    Repository Name: EPIC Alfred Wegener Institut
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    Cyclone Impacts on Sea Ice Concentration in the Atlantic Arctic Ocean: Annual Cycle and Recent Changes (2023)
    American Geophysical Union (AGU)
    In:  EPIC3Geophysical Research Letters, American Geophysical Union (AGU), 50(17), ISSN: 0094-8276
    Details
    Publication Date: 2023-09-08
    Description: We quantify sea ice concentration (SIC) changes related to synoptic cyclones separately for each month of the year in the Greenland, Barents and Kara Seas for 1979–2018. We find that these SIC changes can be statistically significant throughout the year. However, their strength varies from region to region and month to month, and their sign strongly depends on the considered time scale (before/during vs. after cyclone passages). Our results show that the annual cycle of cyclone impacts on SIC is related to varying cyclone intensity and traversed sea ice conditions. We further show that significant changes in these cyclone impacts have manifested in the last 40 years, with the strongest changes occurring in October and November. For these months, SIC decreases before/during cyclones have more than doubled in magnitude in the Barents and Kara Seas, while SIC increases following cyclones have weakened (intensified) in the Barents Sea (Kara Sea).
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    An Assessment of CO2 Uptake in the Arctic Ocean From 1985 to 2018 (2023)
    American Geophysical Union (AGU)
    In:  EPIC3Global Biogeochemical Cycles, American Geophysical Union (AGU), 37(11), ISSN: 0886-6236
    Details
    Publication Date: 2023-12-19
    Description: As a contribution to the Regional Carbon Cycle Assessment and Processes phase 2 (RECCAP2) project, we present synthesized estimates of Arctic Ocean sea-air CO2 fluxes and their uncertainties from surface ocean pCO2-observation products, ocean biogeochemical hindcast and data assimilation models, and atmospheric inversions. For the period of 1985–2018, the Arctic Ocean was a net sink of CO2 of 116 ± 4 TgC yr−1 in the pCO2 products, 92 ± 30 TgC yr−1 in the models, and 91 ± 21 TgC yr−1 in the atmospheric inversions. The CO2 uptake peaks in late summer and early autumn, and is low in winter when sea ice inhibits sea-air fluxes. The long-term mean CO2 uptake in the Arctic Ocean is primarily caused by steady-state fluxes of natural carbon (70% ± 15%), and enhanced by the atmospheric CO2 increase (19% ± 5%) and climate change (11% ± 18%). The annual mean CO2 uptake increased from 1985 to 2018 at a rate of 31 ± 13 TgC yr−1 dec−1 in the pCO2 products, 10 ± 4 TgC yr−1 dec−1 in the models, and 32 ± 16 TgC yr−1 dec−1 in the atmospheric inversions. Moreover, 77% ± 38% of the trend in the net CO2 uptake over time is caused by climate change, primarily due to rapid sea ice loss in recent years. Furthermore, true uncertainties may be larger than the given ensemble standard deviations due to common structural biases across all individual estimates.
    Repository Name: EPIC Alfred Wegener Institut
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    Mapping the 3D position of battery cathode particles in Bragg coherent diffractive imaging (2023)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2023-12-14
    Description: In Bragg coherent diffractive imaging, the precise location of the measured crystals in the interior of the sample is usually missing. Obtaining this information would help the study of the spatially dependent behavior of particles in the bulk of inhomogeneous samples, such as extra‐thick battery cathodes. This work presents an approach to determine the 3D position of particles by precisely aligning them at the instrument axis of rotation. In the test experiment reported here, with a 60 µm‐thick LiNi0.5Mn1.5O4 battery cathode, the particles were located with a precision of 20 µm in the out‐of‐plane direction, and the in‐plane coordinates were determined with a precision of 1 µm.
    Description: A method to determine the 3D position of particles in Bragg coherent diffractive imaging experiments is proposed. Test measurements demonstrate depth‐resolution with a precision of 20 µm along the beam. image
    Keywords: ddc:548 ; extra‐thick battery cathodes ; Bragg coherent X‐ray diffractive imaging ; battery cathodes ; Bragg diffraction ; sphere of confusion ; 3D mapping
    Language: English
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    Seasonal Variability of the Surface Ocean Carbon Cycle: A Synthesis (2023)
    American Geophysical Union (AGU)
    In:  EPIC3Global Biogeochemical Cycles, American Geophysical Union (AGU), 37(9), ISSN: 0886-6236
    Details
    Publication Date: 2024-01-06
    Description: The seasonal cycle is the dominant mode of variability in the air-sea CO2 flux in most regions of the global ocean, yet discrepancies between different seasonality estimates are rather large. As part of the Regional Carbon Cycle Assessment and Processes Phase 2 project (RECCAP2), we synthesize surface ocean pCO2 and air-sea CO2 flux seasonality from models and observation-based estimates, focusing on both a present-day climatology and decadal changes between the 1980s and 2010s. Four main findings emerge: First, global ocean biogeochemistry models (GOBMs) and observation-based estimates (pCO2 products) of surface pCO2 seasonality disagree in amplitude and phase, primarily due to discrepancies in the seasonal variability in surface DIC. Second, the seasonal cycle in pCO2 has increased in amplitude over the last three decades in both pCO2 products and GOBMs. Third, decadal increases in pCO2 seasonal cycle amplitudes in subtropical biomes for both pCO2 products and GOBMs are driven by increasing DIC concentrations stemming from the uptake of anthropogenic CO2 (Cant). In subpolar and Southern Ocean biomes, however, the seasonality change for GOBMs is dominated by Cant invasion, whereas for pCO2 products an indeterminate combination of Cant invasion and climate change modulates the changes. Fourth, biome-aggregated decadal changes in the amplitude of pCO2 seasonal variability are largely detectable against both mapping uncertainty (reducible) and natural variability uncertainty (irreducible), but not at the gridpoint scale over much of the northern subpolar oceans and over the Southern Ocean, underscoring the importance of sustained high-quality seasonally resolved measurements over these regions.
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    Magnitude, Trends, and Variability of the Global Ocean Carbon Sink From 1985 to 2018 (2023)
    American Geophysical Union (AGU)
    In:  EPIC3Global Biogeochemical Cycles, American Geophysical Union (AGU), 37(10), ISSN: 0886-6236
    Details
    Publication Date: 2024-01-06
    Description: This contribution to the RECCAP2 (REgional Carbon Cycle Assessment and Processes) assessment analyzes the processes that determine the global ocean carbon sink, and its trends and variability over the period 1985–2018, using a combination of models and observation-based products. The mean sea-air CO2 flux from 1985 to 2018 is −1.6 ± 0.2 PgC yr−1 based on an ensemble of reconstructions of the history of sea surface pCO2 (pCO2 products). Models indicate that the dominant component of this flux is the net oceanic uptake of anthropogenic CO2, which is estimated at −2.1 ± 0.3 PgC yr−1 by an ensemble of ocean biogeochemical models, and −2.4 ± 0.1 PgC yr−1 by two ocean circulation inverse models. The ocean also degasses about 0.65 ± 0.3 PgC yr−1 of terrestrially derived CO2, but this process is not fully resolved by any of the models used here. From 2001 to 2018, the pCO2 products reconstruct a trend in the ocean carbon sink of −0.61 ± 0.12 PgC yr−1 decade−1, while biogeochemical models and inverse models diagnose an anthropogenic CO2-driven trend of −0.34 ± 0.06 and −0.41 ± 0.03 PgC yr−1 decade−1, respectively. This implies a climate-forced acceleration of the ocean carbon sink in recent decades, but there are still large uncertainties on the magnitude and cause of this trend. The interannual to decadal variability of the global carbon sink is mainly driven by climate variability, with the climate-driven variability exceeding the CO2-forced variability by 2–3 times. These results suggest that anthropogenic CO2 dominates the ocean CO2 sink, while climate-driven variability is potentially large but highly uncertain and not consistently captured across different methods.
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    The soft X‐ray and XUV split‐and‐delay unit at beamlines FL23/24 at FLASH2 (2023)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2024-01-12
    Description: A split‐and‐delay unit for the extreme ultraviolet and soft X‐ray spectral regions has been built which enables time‐resolved experiments at beamlines FL23 and FL24 at the Free‐electron LASer in Hamburg (FLASH). Geometric wavefront splitting at a sharp edge of a beam splitting mirror is applied to split the incoming soft X‐ray pulse into two beams. Ni and Pt coatings at grazing incidence angles have been chosen in order to cover the whole spectral range of FLASH2 and beyond, up to hν = 1800 eV. In the variable beam path with a grazing incidence angle of ϑd = 1.8°, the total transmission (T) ranges are of the order of 0.48 〈 T 〈 0.84 for hν 〈 100 eV and T 〉 0.50 for 100 eV 〈 hν 〈 650 eV with the Ni coating, and T 〉 0.06 for hν 〈 1800 eV for the Pt coating. For a fixed beam path with a grazing incidence angle of ϑf = 1.3°, a transmission of T 〉 0.61 with the Ni coating and T 〉 0.23 with a Pt coating is achieved. Soft X‐ray pump/soft X‐ray probe experiments are possible within a delay range of −5 ps 〈 Δt 〈 +18 ps with a nominal time resolution of tr = 66 as and a measured timing jitter of tj = 121 ± 2 as. First experiments with the split‐and‐delay unit determined the averaged coherence time of FLASH2 to be τc = 1.75 fs at λ = 8 nm, measured at a purposely reduced coherence of the free‐electron laser.
    Description: The properties of the recently installed split‐and‐delay unit at beamlines FL23 and FL24 at FLASH2 are presented. Its operational range, performance parameters and results of a first experiment are described. image
    Keywords: ddc:550.724 ; time‐resolved pump–probe ; XUV ; soft X‐rays ; free‐electron laser
    Language: English
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    XDSGUI: a graphical user interface for XDS, SHELX and ARCIMBOLDO (2023)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2024-01-12
    Description: 〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉〈italic〉XDSGUI〈/italic〉 is a lightweight graphical user interface (GUI) for the 〈italic〉XDS〈/italic〉, 〈italic〉SHELX〈/italic〉 and 〈italic〉ARCIMBOLDO〈/italic〉 program packages that serves both novice and experienced users in obtaining optimal processing and phasing results for X‐ray, neutron and electron diffraction data. The design of the program enables data processing and phasing without command line usage, and supports advanced command flows in a simple user‐modifiable and user‐extensible way. The GUI supplies graphical information based on the tabular log output of the programs, which is more intuitive, comprehensible and efficient than text output can be.〈/p〉
    Description: 〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉A customizable stateless graphical user interface simplifies the processing, analysis and phasing of diffraction data.〈boxed-text position="anchor" content-type="graphic" xml:lang="en"〉〈graphic position="anchor" id="jats-graphic-1" xlink:href="urn:x-wiley:16005767:jcr2yr5110:jcr2yr5110-fig-0001"〉 〈alt-text〉image〈/alt-text〉 〈/graphic〉〈/boxed-text〉〈/p〉
    Keywords: ddc:548 ; X‐ray diffraction ; neutron diffraction ; electron diffraction ; data processing ; graphical user interfaces ; phasing ; XDS ; ARCIMBOLDO ; SHELX
    Language: English
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    Reversals in Temperature‐Precipitation Correlations in the Northern Hemisphere Extratropics During the Holocene (2022)
    American Geophysical Union (AGU)
    In:  EPIC3Geophysical Research Letters, American Geophysical Union (AGU), 49(22), ISSN: 0094-8276
    Details
    Publication Date: 2024-04-23
    Description: Future precipitation levels remain uncertain because climate models have struggled to reproduce observed variations in temperature-precipitation correlations. Our analyses of Holocene proxy-based temperature-precipitation correlations and hydrological sensitivities from 2,237 Northern Hemisphere extratropical pollen records reveal a significant latitudinal dependence and temporal variations among the early, middle, and late Holocene. These proxy-based variations are largely consistent with patterns obtained from transient climate simulations (TraCE21k). While high latitudes and subtropical monsoon areas show mainly stable positive correlations throughout the Holocene, the mid-latitude pattern is temporally and spatially more variable. In particular, we identified a reversal from positive to negative temperature-precipitation correlations in the eastern North American and European mid-latitudes from the early to mid-Holocene that mainly related to slowed down westerlies and a switch to moisture-limited convection under a warm climate. Our palaeoevidence of past temperature-precipitation correlation shifts identifies those regions where simulating past and future precipitation levels might be particularly challenging.
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  • 81
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    Interdecadal Pacific Oscillation in Northern Greenland Dust Concentration Variability During the Last 400 Years (2022)
    American Geophysical Union (AGU)
    In:  EPIC3Geophysical Research Letters, American Geophysical Union (AGU), 49(24), ISSN: 0094-8276
    Details
    Publication Date: 2024-04-22
    Description: Statistical analysis of reanalysis and observed data reveals that high dust surface mass concentration in northern Greenland is associated with a Pacific Decadal Oscillation like pattern in its negative phase in the North Pacific as well as with La Niña conditions in the tropical Pacific region. The sea surface temperature anomalies in the Pacific realm resemble the Interdecadal Pacific Oscillation (IPO). The associated atmospheric circulation pattern, in the form of a wave-train from the North Pacific to the Eurasian continent, favors enhanced dust uptake and transport toward the northern Greenland. Similar patterns are associated with a low-resolution stacked record of five Ca2+ ice cores, that is, ngt03C93.2 (B16), ngt14C93.2 (B18), ngt27C94.2 (B21), GISP2−B, and NEEM-2011-S1, from northern Greenland, a proxy for regional dust concentration, during the last 400 years. We argue that northern Greenland ice core dust records could be used as proxies for the IPO and related teleconnections.
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  • 82
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    Tectono‐Stratigraphic Evolution of the Kerguelen Large Igneous Province: The Conjugate William’s Ridge‐Broken Ridge Rifted Margins (2024)
    American Geophysical Union (AGU)
    In:  EPIC3Journal of Geophysical Research: Solid Earth, American Geophysical Union (AGU), 129(3), ISSN: 2169-9313
    Details
    Publication Date: 2024-04-24
    Description: 〈jats:title〉Abstract〈/jats:title〉〈jats:p〉Extensive investigation of continental rift systems has been fundamental for advancing the understanding of extensional tectonics and modes of formation of new ocean basins. However, current rift classification schemes do not account for conjugate end members formed by Large Igneous Province crust, referring to thick mafic crust, sometimes including continental fragments. Here, we investigate the rifting of William's Ridge (Kerguelen Plateau) and Broken Ridge, components of the Kerguelen Large Igneous Province now situated in the Southeast Indian Ocean, and incorporate these end members into the deformation migration concept for rifted margins. We use multichannel seismic reflection profiles and data from scientific drill cores acquired on both conjugate margins to propose, for the first time, a combined tectono‐stratigraphic framework. We interpret seismic patterns, tectonic features, and magnetic anomaly picks to determine an across‐strike structural domain classification. This interpretation considers the rift system overall to be “magma‐poor” despite being located proximal to the Kerguelen plume but suggests that syn‐rift interaction between the Kerguelen mantle plume and the lithospheric structure of William's Ridge and Broken Ridge has controlled the along‐strike segmentation of both conjugates. We integrate seismic reflection and bathymetric data to test the hypothesis of predominantly transform motion, between the Australian and Antarctic plates, in Late Cretaceous and Paleogene time.〈/jats:p〉
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    INSIGHT: in situ heuristic tool for the efficient reduction of grazing‐incidence X‐ray scattering data (2024)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2024-04-25
    Description: 〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉〈italic〉INSIGHT〈/italic〉 is a Python‐based software tool for processing and reducing 2D grazing‐incidence wide‐ and small‐angle X‐ray scattering (GIWAXS/GISAXS) data. It offers the geometric transformation of the 2D GIWAXS/GISAXS detector image to reciprocal space, including vectorized and parallelized pixel‐wise intensity correction calculations. An explicit focus on efficient data management and batch processing enables full control of large time‐resolved synchrotron and laboratory data sets for a detailed analysis of kinetic GIWAXS/GISAXS studies of thin films. It processes data acquired with arbitrarily rotated detectors and performs vertical, horizontal, azimuthal and radial cuts in reciprocal space. It further allows crystallographic indexing and GIWAXS pattern simulation, and provides various plotting and export functionalities. Customized scripting offers a one‐step solution to reduce, process, analyze and export findings of large 〈italic〉in situ〈/italic〉 and 〈italic〉operando〈/italic〉 data sets.〈/p〉
    Keywords: ddc:548 ; grazing‐incidence X‐ray scattering ; time‐resolved studies ; in situ studies ; operando studies ; computer programs
    Language: English
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  • 84
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    Structure and Seasonal Variability of the Arctic Boundary Current North of Severnaya Zemlya (2023)
    American Geophysical Union (AGU)
    In:  EPIC3Journal of Geophysical Research - Oceans, American Geophysical Union (AGU), 128(1), ISSN: 2169-9275
    Details
    Publication Date: 2024-05-08
    Description: We assessed the spatial and temporal variability of the Arctic Boundary Current (ABC) using seven oceanographic moorings, deployed across the continental slope north of Severnaya Zemlya in 2015–2018. Transports and individual water masses were quantified based on temperature and salinity recorders and current profilers. Our results were compared with observations from the northeast Svalbard and the central Laptev Sea continental slopes to evaluate the hydrographic transformation along the ABC pathway. The highest velocities (〉0.30 m s−1) of the ABC occurred at the upper continental slope and decreased offshore to below 0.03 m s−1 in the deep basin. The ABC showed seasonal variability with velocities two times higher in winter than in summer. Compared to upstream conditions in Svalbard, water mass distribution changed significantly within 20 km of the shelf edge due to mixing with- and intrusion of shelf waters. The ABC transported 4.15 ± 0.3 Sv in the depth range 50–1,000 m, where 0.88 ± 0.1, 1.5 ± 0.2, 0.61 ± 0.1 and 1.0 ± 0.15 Sv corresponded to Atlantic Water (AW), Dense Atlantic Water (DAW), Barents Sea Branch Water (BSBW) and Transformed Atlantic Water (TAW). 62–70% of transport was constrained to within 30–40 km of the shelf edge, and beyond 84 km, transport increases were estimated to be 0.54 Sv. Seasonality of TAW derived from local shelf-processes and advection of seasonal-variable Fram Strait waters, while BSBW transport variability was dominated by temperature changes with maximum transport coinciding with minimum temperatures. Further Barents Sea warming will likely reduce TAW and BSBW transport leading to warmer conditions along the ABC pathway.
    Repository Name: EPIC Alfred Wegener Institut
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    Moisture Sources and Pathways Determine Stable Isotope Signature of Himalayan Waters in Nepal (2023)
    American Geophysical Union (AGU)
    In:  EPIC3AGU Advances, American Geophysical Union (AGU), 4(1), ISSN: 2576-604X
    Details
    Publication Date: 2024-05-08
    Description: The Himalayan mountain range produces one of the steepest and largest rainfall gradients on Earth, with 〉3 m/yr rainfall difference over a ∼100 km distance. The Indian Summer Monsoon (ISM) contributes more than 80% to the annual precipitation budget of the central Himalayas. The remaining 20% falls mainly during pre-ISM season. Understanding the seasonal cycle and the transfer pathways of moisture from precipitation to the rivers is crucial for constraining water availability in a warming climate. However, the partitioning of moisture into the different storage systems such as snow, glacier, and groundwater and their relative contribution to river discharge throughout the year remains under-constrained. Here, we present novel field data from the Kali Gandaki, a trans-Himalayan river, and use 4-year time series of river and rain water stable isotope composition (δ18O and δ2H values) as well as river discharge, satellite Global Precipitation Measurement amounts, and moisture source trajectories to constrain hydrological variability. We find that rainfall before the onset of the ISM is isotopically distinct and that ISM rain and groundwater have similar isotopic values. Our study lays the groundwork for using isotopic measurements to track changes in precipitation sources during the pre-ISM to ISM transition in this key region of orographic precipitation. Specifically, we highlight the role of pre-ISM precipitation, derived from the Gangetic plain, to define the seasonal river isotopic variability across the central Himalayas. Lastly, isotopic values across the catchment document the importance of a large well-mixed groundwater reservoir supplying river discharge, especially during the non-ISM season.
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  • 86
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    The Southern Ocean Carbon Cycle 1985–2018: Mean, Seasonal Cycle, Trends, and Storage (2023)
    American Geophysical Union (AGU)
    In:  EPIC3Global Biogeochemical Cycles, American Geophysical Union (AGU), 37(11), ISSN: 0886-6236
    Details
    Publication Date: 2023-12-20
    Description: We assess the Southern Ocean CO2 uptake (1985–2018) using data sets gathered in the REgional Carbon Cycle Assessment and Processes Project Phase 2. The Southern Ocean acted as a sink for CO2 with close agreement between simulation results from global ocean biogeochemistry models (GOBMs, 0.75 ± 0.28 PgC yr−1) and pCO2-observation-based products (0.73 ± 0.07 PgC yr−1). This sink is only half that reported by RECCAP1 for the same region and timeframe. The present-day net uptake is to first order a response to rising atmospheric CO2, driving large amounts of anthropogenic CO2 (Cant) into the ocean, thereby overcompensating the loss of natural CO2 to the atmosphere. An apparent knowledge gap is the increase of the sink since 2000, with pCO2-products suggesting a growth that is more than twice as strong and uncertain as that of GOBMs (0.26 ± 0.06 and 0.11 ± 0.03 Pg C yr−1 decade−1, respectively). This is despite nearly identical pCO2 trends in GOBMs and pCO2-products when both products are compared only at the locations where pCO2 was measured. Seasonal analyses revealed agreement in driving processes in winter with uncertainty in the magnitude of outgassing, whereas discrepancies are more fundamental in summer, when GOBMs exhibit difficulties in simulating the effects of the non-thermal processes of biology and mixing/circulation. Ocean interior accumulation of Cant points to an underestimate of Cant uptake and storage in GOBMs. Future work needs to link surface fluxes and interior ocean transport, build long overdue systematic observation networks and push toward better process understanding of drivers of the carbon cycle.
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    The Subglacial Lake That Wasn't There: Improved Interpretation From Seismic Data Reveals a Sediment Bedform at Isunnguata Sermia (2023)
    American Geophysical Union (AGU)
    In:  EPIC3Journal of Geophysical Research Earth Surface, American Geophysical Union (AGU), 128(10), ISSN: 2169-9003
    Details
    Publication Date: 2024-03-14
    Description: Radio Echo Sounding (RES) surveys conducted in May 2010 and April 2011 revealed a 2 km2 flat area with increased bed reflectivity at the base of Isunnguata Sermia at the western margin of the Greenland Ice Sheet. This flat reflector was located within a localized subglacial hydraulic potential (hydropotential) minimum, as part of a complex and elongated trough system. By analogy with comparable features in Antarctica, the initial interpretation of such a feature was a potential subglacial lake. In September 2013 a co-located seismic survey revealed a 1,750 m by 540 and 37 m thick stratified lens-shaped bedform at the base of a subglacial trough system. Amplitude Versus Angle (AVA) analysis yields a derived reflection coefficient R = 0.09 ± 0.14 indicative of consolidated sediments possibly overlain by dilatant till. The bed and flank on the northern side of the trough consist of unconsolidated, possibly water-bearing sediments with R = −0.10 ± 0.08, whereas on the southern side it consists of more consolidated material. We interpret the trough as a key component of the wider subglacial drainage network, for which the sediments on its northern side act as a localized water-storage reservoir. Given the observation of seasonally forming and rapidly draining supraglacial meltwater lakes in this area, we interpret the lens-shaped bedform as deposited by episodically ponding meltwater within the subglacial trough system. Our results highlight the importance of transient subglacial hydrological and sedimentological processes such as drainage events for the interaction of ice sheets and their substrates, to understand ice dynamics in a warming climate.
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  • 88
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    Clouds and Radiation Processes in Regional Climate Models Evaluated Using Observations Over the Ice‐free Arctic Ocean (2021)
    American Geophysical Union (AGU)
    In:  EPIC3Journal of Geophysical Research: Atmospheres, American Geophysical Union (AGU), 126(1), ISSN: 2169-897X
    Details
    Publication Date: 2024-03-14
    Description: The presence of clouds in the Arctic regulates the surface energy budget (SEB) over the sea-ice surface and the ice-free ocean. Following several previous field campaigns, the cloud-radiation relationship, including cloud vertical structure and phase, has been elucidated; however, modeling of this relationship has matured slowly. In recognition of the recent decline in the Arctic sea-ice extent, representation of the cloud system in numerical models should consider the effects of areas covered by sea ice and ice-free areas. Using an in situ stationary meteorological observation data set obtained over the ice-free Arctic Ocean by the Japanese Research Vessel Mirai (September 2014), coordinated evaluation of six regional climate models (RCMs) with nine model runs was performed by focusing on clouds and the SEB. The most remarkable findings were as follows: (1) reduced occurrence of unstable stratification with low-level cloud water in all models in comparison to the observations, (2) significant differences in cloud water representations between single- and double-moment cloud schemes, (3) extensive differences in partitioning of hydrometeors including solid/liquid precipitation, and (4) pronounced lower-tropospheric air temperature biases. These issues are considered as the main sources of SEB uncertainty over ice-free areas of the Arctic Ocean. The results from a coupled RCM imply that the SEB is constrained by both the atmosphere and the ocean (and sea ice) with considerable feedback. Coordinated improvement of both stand-alone atmospheric and coupled RCMs would promote a more comprehensive and improved understanding of the Arctic air-ice-sea coupled system.
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  • 89
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    Bedforms of Thwaites Glacier, West Antarctica: Character and Origin (2021)
    American Geophysical Union (AGU)
    In:  EPIC3Journal of Geophysical Research Earth Surface, American Geophysical Union (AGU), 126(12), ISSN: 2169-9003
    Details
    Publication Date: 2024-03-14
    Description: Bedforms of Thwaites Glacier, West Antarctica both record and affect ice flow, as shown by geophysical data and simple models. Thwaites Glacier flows across the tectonic fabric of the West Antarctic rift system with its bedrock highs and sedimentary basins. Swath radar and seismic surveys of the glacier bed have revealed soft-sediment flutes 100 m or more high extending 15 km or more across basins downglacier from bedrock highs. Flutes end at prominent hard-bedded moats on stoss sides of the next topographic highs. We use simple models to show that ice flow against topography increases pressure between ice and till upglacier along the bed over a distance that scales with the topography. In this basal zone of high pressure, ice-contact water would be excluded, thus increasing basal drag by increasing ice-till coupling and till flux, removing till to allow bedrock erosion that creates moats. Till carried across highlands would then be deposited in lee-side positions forming bedforms that prograde downglacier over time, and that remain soft on top through feedbacks that match till-deformational fluxes from well upglacier of the topography. The bedforms of the part of Thwaites surveyed here are prominent because ice flow has persisted over a long time on this geological setting, not because ice flow is anomalous. Bedform development likely has caused evolution of ice flow over time as till and lubricating water were redistributed, moats were eroded and bedforms grew.
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  • 90
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    Atmosphere‐Snow Exchange Explains Surface Snow Isotope Variability (2022)
    American Geophysical Union (AGU)
    In:  EPIC3Geophysical Research Letters, American Geophysical Union (AGU), 49(20), pp. e2022gl099529-e2022gl099529, ISSN: 0094-8276
    Details
    Publication Date: 2024-03-14
    Description: The climate signal imprinted in the snow isotopic composition allows to infer past climate variability from ice core stable water isotope records. The concurrent evolution of vapor and surface snow isotopic composition between precipitation events indicates that post-depositional atmosphere-snow humidity exchange influences the snow and hence the ice core isotope signal. To date, however, this is not accounted for in paeleoclimate reconstructions from isotope records. Here we show that vapor-snow exchange explains 36% of the summertime day-to-day δ18O variability of the surface snow between precipitation events, and 53% of the δD variability. Through observations from the Greenland Ice Sheet and accompanying modeling we demonstrate that vapor-snow exchange introduces a warm bias on the summertime snow isotope value relevant for ice core records. In case of long-term variability in atmosphere-snow exchange the relevance for the ice core signal is also variable and thus paleoclimate reconstructions from isotope records should be revisited.
    Repository Name: EPIC Alfred Wegener Institut
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  • 91
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    A Snapshot on the Buildup of the Stable Water Isotopic Signal in the Upper Snowpack at EastGRIP on the Greenland Ice Sheet (2023)
    American Geophysical Union (AGU)
    In:  EPIC3Journal of Geophysical Research Earth Surface, American Geophysical Union (AGU), 128(2), ISSN: 2169-9003
    Details
    Publication Date: 2024-04-29
    Description: The stable water isotopic composition in firn and ice cores provides valuable information on past climatic conditions. Because of uneven accumulation and post-depositional modifications on local spatial scales up to hundreds of meters, time series derived from adjacent cores differ significantly and do not directly reflect the temporal evolution of the precipitated snow isotopic signal. Hence, a characterization of how the isotopic profile in the snow develops is needed to reliably interpret the isotopic variability in firn and ice cores. By combining digital elevation models of the snow surface and repeated high-resolution snow sampling for stable water isotope measurements of a transect at the East Greenland Ice-core Project campsite on the Greenland Ice Sheet, we are able to visualize the buildup and post-depositional changes of the upper snowpack across one summer season. To this end, 30 cm deep snow profiles were sampled on six dates at 20 adjacent locations along a 40 m transect. Near-daily photogrammetry provided snow height information for the same transect. Our data shows that erosion and redeposition of the original snowfall lead to a complex stratification in the δ18O signature. Post-depositional processes through vapor-snow exchange affect the near surface snow with d-excess showing a decrease in surface and near-surface layers. Our data suggests that the interplay of stratigraphic noise, accumulation intermittency, and local post-depositional processes form the proxy signal in the upper snowpack.
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  • 92
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    Fast Ice Thickness Distribution in the Western Ross Sea in Late Spring (2023)
    American Geophysical Union (AGU)
    In:  EPIC3Journal of Geophysical Research - Oceans, American Geophysical Union (AGU), 128(2), ISSN: 2169-9275
    Details
    Publication Date: 2024-05-01
    Description: We present a 700 km airborne electromagnetic survey of late-spring fast ice and sub-ice platelet layer (SIPL) thickness distributions from McMurdo Sound to Cape Adare, providing a first-time inventory of fast ice thickness close to its annual maximum. The overall mode of the consolidated ice (including snow) thickness was 1.9 m, less than its mean of 2.6 ± 1.0 m. Our survey was partitioned into level and rough ice, and SIPL thickness was estimated under level ice. Although level ice, with a mode of 2.0 m and mean of 2.0 ± 0.6 m, was prevalent, rough ice occupied 41% of the transect by length, 50% by volume, and had a mode of 3.3 m and mean of 3.2 ± 1.2 m. The thickest 10% of rough ice was almost 6 m on average, inclusive of a 2 km segment thicker than 8 m in Moubray Bay. The thickest ice occurred predominantly along the northwestern Ross Sea, due to compaction against the coast. The adjacent pack ice was thinner (by ∼1 m) than the first-year fast ice. In Silverfish Bay, offshore Hells Gate Ice Shelf, New Harbor, and Granite Harbor, the SIPL transect volume was a significant fraction (0.30) of the consolidated ice volume. The thickest 10% of SIPLs averaged nearly 3 m thick, and near Hells Gate Ice Shelf the SIPL was almost 10 m thick, implying vigorous heat loss to the ocean (∼90 W m −2). We conclude that polynya-induced ice deformation and interaction with continental ice influence fast ice thickness in the western Ross Sea.
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  • 93
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    Spatial Variability of Dissolved Organic Carbon, Solutes, and Suspended Sediment in Disturbed Low Arctic Coastal Watersheds (2020)
    American Geophysical Union (AGU)
    In:  EPIC3Journal of Geophysical Research Biogeosciences, American Geophysical Union (AGU), 125(2), ISSN: 2169-8953
    Details
    Publication Date: 2024-01-30
    Description: Climate change in the Arctic leads to permafrost degradation and to associated changes infreshwater geochemistry. There is a limited understanding of how disturbances such as active layerdetachments or retrogressive thaw slumps impact water quality on a catchment scale. This study investigateshow permafrost degradation affects concentrations of dissolved organic carbon (DOC), total dissolvedsolids (TDS), suspended sediment, and stable water isotopes in adjacent Low Arctic watersheds. Weincorporated data on disturbance between 1952 and 2015, as well as sporadic runoff and geochemistry dataof streams nearby. Our results show that the total disturbed area decreased by 41% between 1952 and 2015,whereas the total number of disturbances increased by 66% in all six catchments. The spatial variabilityof hydrochemical parameters is linked to catchment properties and not necessarily reflected at the outflow.Degrading ice‐wedge polygons were found to increase DOC concentrations upstream in Ice Creek West,whereas hydrologically connected disturbances were linked to increases in TDS and suspended sediment.Although we found a great spatial variability of hydrochemical concentrations along the paired watershed,there was a linear relationship between catchment size and daily DOC, total dissolved nitrogen, and TDSfluxes for all six streams. Suspended sedimentflux on the contrary did not show a clear relationship as onehydrologically connected retrogressive thaw slump impacted the overallflux in one of the streams.Understanding the spatial variability of water quality will help to model the lateral geochemicalfluxes fromArctic catchments
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  • 94
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    Isotopic Characterization of Water Masses in the Southeast Pacific Region: Paleoceanographic Implications (2022)
    American Geophysical Union (AGU)
    In:  EPIC3Journal of Geophysical Research - Oceans, American Geophysical Union (AGU), 127(1), ISSN: 2169-9275
    Details
    Publication Date: 2024-01-31
    Description: In this study, we used stable isotopes of oxygen (δ18O), deuterium (δD), and dissolved inorganic carbon (δ13CDIC) in combination with temperature, salinity, oxygen, and nutrient concentrations to characterize the coastal (71°–78°W) and an oceanic (82°–98°W) water masses (SAAW—Subantarctic Surface Water; STW—Subtropical Water; ESSW—Equatorial Subsurface water; AAIW—Antarctic Intermediate Water; PDW—Pacific Deep Water) of the Southeast Pacific (SEP). The results show that δ18O and δD can be used to differentiate between SAAW-STW, SAAW-ESSW, and ESSW-AAIW. δ13CDIC signatures can be used to differentiate between STW-ESSW (oceanic section), SAAW-ESSW, ESSW-AAIW, and AAIW-PDW. Compared with the oceanic section, our new coastal section highlights differences in both the chemistry and geometry of water masses above 1,000 m. Previous paleoceanographic studies using marine sediments from the SEP continental margin used the present-day hydrological oceanic transect to compare against, as the coastal section was not sufficiently characterized. We suggest that our new results of the coastal section should be used for past characterizations of the SEP water masses that are usually based on continental margin sediment samples.
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  • 95
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    Designing More Informative Multiple-Driver Experiments (2024)
    Annual Reviews
    In:  EPIC3Annual Review of Marine Science, Annual Reviews, 16(1), pp. 513-536, ISSN: 1941-1405
    Details
    Publication Date: 2024-01-31
    Description: 〈jats:p〉 For decades, multiple-driver/stressor research has examined interactions among drivers that will undergo large changes in the future: temperature, pH, nutrients, oxygen, pathogens, and more. However, the most commonly used experimental designs—present-versus-future and ANOVA—fail to contribute to general understanding or predictive power. Linking experimental design to process-based mathematical models would help us predict how ecosystems will behave in novel environmental conditions. We review a range of experimental designs and assess the best experimental path toward a predictive ecology. Full factorial response surface, fractional factorial, quadratic response surface, custom, space-filling, and especially optimal and sequential/adaptive designs can help us achieve more valuable scientific goals. Experiments using these designs are challenging to perform with long-lived organisms or at the community and ecosystem levels. But they remain our most promising path toward linking experiments and theory in multiple-driver research and making accurate, useful predictions. 〈/jats:p〉
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , peerRev
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  • 96
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    Counteracting Contributions of the Upper and Lower Meridional Overturning Limbs to the North Atlantic Nutrient Budgets: Enhanced Imbalance in 2010 (2021)
    American Geophysical Union (AGU)
    In:  EPIC3Global Biogeochemical Cycles, American Geophysical Union (AGU), 35(6), ISSN: 0886-6236
    Details
    Publication Date: 2024-01-18
    Description: The North Atlantic Basin is a major sink for atmospheric carbon dioxide (CO2) due in part to the extensive plankton blooms which form there supported by nutrients supplied by the three-dimensional ocean circulation. Hence, changes in ocean circulation and/or stratification may influence primary production and biological carbon export. In this study, we assess this possibility by evaluating inorganic nutrient budgets for 2004 and 2010 in the North Atlantic based on observations from the transatlantic A05-24.5°N and the Greenland-Portugal OVIDE hydrographic sections, to which we applied a box inverse model to solve the circulation and estimate the across-section nutrient transports. Full water column nutrient budgets were split into upper and lower meridional overturning circulation (MOC) limbs. According to our results, anomalous circulation in early 2010, linked to extreme negative NAO conditions, led to an enhanced northward advection of more nutrient-rich waters by the upper overturning limb, which resulted in a significant nitrate and phosphate convergence north of 24.5°N. Combined with heaving of the isopycnals, this anomalous circulation event in 2010 favored an enhancement of the nutrient consumption (5.7 ± 4.1 kmol-P s−1) and associated biological CO2 uptake (0.25 ± 0.18 Pg-C yr−1, upper-bound estimate), which represents a 50% of the mean annual sea–air CO2 flux in the region. Our results also suggest a transient state of deep silicate divergence in both years. Both results are indicative of a MOC-driven modulation of the biological carbon uptake (by the upper MOC limb) and nutrient inventories (by the lower MOC limb) in the North Atlantic.
    Repository Name: EPIC Alfred Wegener Institut
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  • 97
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    On the polar bias in ice core 10Be data (2023)
    American Geophysical Union (AGU)
    In:  EPIC3Journal of Geophysical Research: Atmospheres, American Geophysical Union (AGU), ISSN: 2169-897X
    Details
    Publication Date: 2024-01-22
    Repository Name: EPIC Alfred Wegener Institut
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  • 98
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    Local Seismicity and Sediment Deformation in the West Svalbard Margin: Implications of Neotectonics for Seafloor Seepage (2023)
    American Geophysical Union (AGU)
    In:  EPIC3Geochemistry Geophysics Geosystems, American Geophysical Union (AGU), 24(12), ISSN: 1525-2027
    Details
    Publication Date: 2024-01-22
    Description: In the Fram Strait, mid-ocean ridge spreading is represented by the ultra-slow system of the Molloy Ridge, the Molloy Transform Fault and the Knipovich Ridge. Sediments on oceanic and continental crust are gas charged and there are several locations with documented seafloor seepage. Sedimentary faulting shows recent stress release in the sub-surface, but the drivers of stress change and its influence on fluid flow are not entirely understood. We present here the results of an 11-month-long ocean bottom seismometer survey conducted over the highly faulted sediment drift northwards from the Knipovich Ridge to monitor seismicity and infer the regional state of stress. We obtain a detailed earthquake catalog that improves the spatial resolution of mid-ocean ridge seismicity compared with published data. Seismicity at the Molloy Transform Fault is occurring southwards from the bathymetric imprint of the fault, as supported by a seismic profile. Earthquakes in the northern termination of the Knipovich Ridge extend eastwards from the ridge valley, which together with syn-rift faulting identified in seismic reflection data, suggests that a portion of the currently active spreading center is buried under sediments away from the bathymetric expression of the rift valley. This hints at the direct link between crustal rifting processes and faulting in shallow sediments. Two earthquakes occur close to the seepage system of the Vestnesa Ridge further north from the network. We suggest that deeper rift structures, reactivated by gravity and/or post-glacial subsidence, may lead to accommodation of stress through shallow extensional faults, therefore impacting seepage dynamics.
    Repository Name: EPIC Alfred Wegener Institut
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  • 99
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    Assessing Seasonal and Inter‐Annual Marine Sediment Climate Proxy Data (2023)
    American Geophysical Union (AGU)
    In:  EPIC3Paleoceanography and Paleoclimatology, American Geophysical Union (AGU), 38(10), ISSN: 2572-4517
    Details
    Publication Date: 2024-03-13
    Description: Three recently published papers including Napier et al. (2022, https://doi.org/10.1029/2021PA004355) utilize novel microanalytical approaches with varved marine sediments to demonstrate the potential to reconstruct seasonal and inter-annual climate variability. Obtaining paleoclimate data at a resolution akin to the observational record is vitally important for improving our understanding of climate phenomena such as monsoons and modes of variability such as the El Niño Southern Oscillation, for which appraisals of past inter-annual variability is critical. The ability to generate seasonal and inter annual resolution sea surface temperature proxy time series spanning a thousand years or more is revolutionary and has the potential to fill gaps in our knowledge of climate variability. Although generally limited to sediments from regions with oxygen depleted bottom waters, there is great potential to integrate shorter seasonal resolution climate “snap shots” from other archives such as annually banded corals into composite time series. But as paleoceanographic data are used more by the observational and modeling fields, we make the case for conducting a thorough case-by-case assessment of the processes that influence the climate signal recovered from proxies, using careful replication to validate new approaches. Understanding or exploring the potential influence of processes which effectively filter the climate signal will lead to more quantitative paleoceanographic data that will better serve the broader climate science community.
    Repository Name: EPIC Alfred Wegener Institut
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  • 100
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    Intensification of the East Australian Current After ∼1400 CE (2022)
    American Geophysical Union (AGU)
    In:  EPIC3Geophysical Research Letters, American Geophysical Union (AGU), 49(24), ISSN: 0094-8276
    Details
    Publication Date: 2024-03-13
    Description: The East Australian Current (EAC) is the western boundary current of the South Pacific Subtropical Gyre that transports warm tropical waters to higher southern latitudes and significantly impacts the climate of Australia and New Zealand. Modern observations show that the EAC has strengthened with rising global temperatures. However, little is known about the pre-industrial variability of the EAC and the forcing mechanisms. Planktic foraminifera Globigerinoides ruber (white) Mg/Ca-based sea surface temperature reconstructions offshore northeastern Australia between 15° and 26°S reveal an increase by ∼1.2°C after ∼1400 CE. We infer that the increase in temperature is related to a stronger EAC heat transport that is likely driven by a strengthening of the Southern Hemisphere subtropical gyre circulation due to a progressive shift of the Southern annular mode toward its positive phase and of El Niño-Southern Oscillation toward more El Niño-like conditions.
    Repository Name: EPIC Alfred Wegener Institut
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