Chemical and visual characterisation of EGRIP glacial ice and cloudy bands within

Impurities in polar ice play a critical role in ice flow, deformation, and the integrity of the ice core record. Especially cloudy bands, visible layers with high impurity concentrations are prominent features in ice from the last glacial. Their physical and chemical properties are poorly understood, highlighting the need to analyse them in more detail. We bridge the gap between decimetre and micrometre scales by combining the visual stratigraphy line scanner, fabric analyser, microstructure mapping, Raman spectroscopy, and laser ablation inductively coupled plasma mass spectrometry 2D impurity imaging. We classified almost 1300 cloudy bands from glacial ice from the East Greenland Ice-core Project (EGRIP) ice core into seven different types. We determine the localisation and mineralogy of more than 1000 micro-inclusions at 13 depths. The majority of the found minerals are related to terrestrial dust, such as quartz, feldspar, mica, and hematite. We further found carbonaceous particles, dolomite, and gypsum in high abundance. Rare minerals are e.g., rutile, anatase, epidote, titanite, and grossular. 2D impurity imaging with 20 &mu;m resolution revealed that Na, Mg and Sr are mainly at grain boundaries. Dust-related analytes, such as Al, Fe, and Ti, are also located in the grain interior forming clusters of insoluble impurities. Cloudy bands are thus clearly distinguishable in the chemical data. We present novel vast micron-resolution insights into cloudy bands and describe the differences within and outside these bands. Combining the visual and chemical data results in new insights into the formation of different cloudy band types and could be the starting point for future in-depth studies on impurity signal integrity and internal deformation.</p

Van der Waals forces in density functional theory: perturbational long-range electron interaction corrections

Long-range exchange and correlation effects, responsible for the failure of currently used approximate density functionals in describing van der Waals forces, are taken into account explicitly after a separation of the electron-electron interaction in the Hamiltonian into short- and long-range components. We propose a "range-separated hybrid" functional based on a local density approximation for the short-range exchange-correlation energy, combined with a long-range exact exchange energy. Long-range correlation effects are added by a second-order perturbational treatment. The resulting scheme is general and is particularly well-adapted to describe van der Waals complexes, like rare gas dimers.Comment: 8 pages, 1 figure, submitted to Phys. Rev.

Simple model of the static exchange-correlation kernel of a uniform electron gas with long-range electron-electron interaction

A simple approximate expression in real and reciprocal spaces is given for the static exchange-correlation kernel of a uniform electron gas interacting with the long-range part only of the Coulomb interaction. This expression interpolates between the exact asymptotic behaviors of this kernel at small and large wave vectors which in turn requires, among other thing, information from the momentum distribution of the uniform electron gas with the same interaction that have been calculated in the G0W0 approximation. This exchange-correlation kernel as well as its complement analogue associated to the short-range part of the Coulomb interaction are more local than the Coulombic exchange-correlation kernel and constitute potential ingredients in approximations for recent adiabatic connection fluctuation-dissipation and/or density functional theory approaches of the electronic correlation problem based on a separate treatment of long-range and short-range interaction effects.Comment: 14 pages, 14 figures, to be published in Phys. Rev.

Long-range/short-range separation of the electron-electron interaction in density functional theory

By splitting the Coulomb interaction into long-range and short-range components, we decompose the energy of a quantum electronic system into long-range and short-range contributions. We show that the long-range part of the energy can be efficiently calculated by traditional wave function methods, while the short-range part can be handled by a density functional. The analysis of this functional with respect to the range of the associated interaction reveals that, in the limit of a very short-range interaction, the short-range exchange-correlation energy can be expressed as a simple local functional of the on-top pair density and its first derivatives. This provides an explanation for the accuracy of the local density approximation (LDA) for the short-range functional. Moreover, this analysis leads also to new simple approximations for the short-range exchange and correlation energies improving the LDA.Comment: 18 pages, 14 figures, to be published in Phys. Rev.

Comment on “Exceptionally high heat flux needed to sustain the Northeast Greenland Ice Stream” by Smith-Johnsen et al. (2020)

Smith-Johnsen et al. (The Cryosphere, 14, 841–854, https://doi.org/10.5194/tc-14-841-2020, 2020) model the effect of a potential hotspot on the Northeast Greenland Ice Stream (NEGIS). They argue that a heat flux of at least 970 mW m−2 is required to have initiated or to control NEGIS. Such an exceptionally high heat flux would be unique in the world and is incompatible with known geological processes that can raise the heat flux. Fast flow at NEGIS must thus be possible without the extraordinary melt rates invoked in Smith-Johnsen et al. (2020)

Issues with fracturing ice during an ice drilling project in Greenland (EastGRIP)

Drilling an ice core through an ice sheet (typically 2000 to 3000 m thick) is a technical challenge that nonetheless generates valuable and unique information on palaeo-climate and ice dynamics. As technically the drilling cannot be done in one run, the core has to be fractured approximately every 3 m to retrieve core sections from the bore hole. This fracture process is initiated by breaking the core with core-catchers which also clamp the engaged core in the drill head while the whole drill is then pulled up with the winch motor. This standard procedure is known to become difficult and requires extremely high pulling forces (Wilhelms et al. 2007), in the very deep part of the drill procedure, close to the bedrock of the ice sheet, especially when the ice material becomes warm (approximately -2°C) due to the geothermal heat released from the bedrock. Recently, during the EastGRIP (East Greenland Ice coring Project) drilling we observed a similar issue with breaking off cored sections only with extremely high pulling forces, but started from approximately 1800 m of depth, where the temperature is still very cold (approximately -20°C). This has not been observed at other ice drilling sites. As dependencies of fracture behaviour on crystal orientation and grain size are known (Schulson & Duval 2009) for ice, we thus examined the microstructure in the ice samples close to and at the core breaks. First preliminary results suggest that these so far unexperienced difficulties are due to the profoundly different c-axes orientation distribution (CPO) in the EastGRIP ice core. In contrast to other deep ice cores which have been drilled on ice domes or ice divides, EastGRIP is located in an ice stream. This location means that the deformation geometry (kinematics) is completely different, resulting in a different CPO (girdle pattern instead of single maximum pattern). Evidence regarding additional grain-size dependence will hopefully help to refine the fracturing procedure, which is possible due to a rather strong grain size layering observed in natural ice formed by snow precipitation. --------------------- Wilhelms, F.; Sheldon, S. G.; Hamann, I. & Kipfstuhl, S. Implications for and findings from deep ice core drillings - An example: The ultimate tensile strength of ice at high strain rates. Physics and Chemistry of Ice (The proceedings of the International Conference on the Physics and Chemistry of Ice held at Bremerhaven, Germany on 23-28 July 2006), 2007, 635-639 Schulson, E. M. & Duval, P. Creep and Fracture of Ice. Cambridge University Press, 2009, 40

Impurities throughout the EGRIP ice core – a microstructural perspective

Impurities in polar ice cores are analyzed for various reasons, ranging from the reconstruction of the climate of the past to the absolute positioning of age markers. In particular, microstructural impurity research provides insights into the internal deformation of ice and post-depositional stratigraphy changes. However, most stud- ies offer limited snapshots of impurity characteristics at a few specific depth regimes, highlighting the need to determine the localization and chemistry of impurities throughout one ice core with complementary methods. We report a detailed investigation of solid and dissolved impurities throughout the 2120 m long East Green- land Ice Core Project (EGRIP) ice core. Using microstructure mapping and confocal Cryo-Raman spectroscopy, we analyzed solid micro-inclusions inside 25 solid ice samples covering the last 50 ka. Micro-inclusions are heterogeneously distributed inside the ice matrix and in Holocene ice, as an upper limit assumption, between 22.3 and 42.4% are located in the vicinity of grain boundaries. We identified the mineralogy of more than 1600 solid inclusions. Most are terrestrial dust minerals, such as quartz, feldspar, mica, carbonaceous particles, and sulfate minerals, such as gypsum. Less common minerals are e.g., dolomite, hematite, nitrates, rutile, and anatase. However, the upper 900 m are characterized by various sulfate minerals, while gypsum is the domi- nant sulfate species below. In the deepest 400 m of the core, we expose the mineralogy inside and surrounding distinct cloudy bands. Aiming at a holistic picture of soluble and insoluble impurities, we combined two meth- ods for the first time: We further analyzed most samples with laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Due to recent adaptions, LA-ICP-MS now enables us to image the 2D distribution of elements, such as Na, Mg, Al, and Fe, with a resolution of up to 10 microns showing element-depended dif- ferences in localization. For example, Na is primarily located at grain boundaries, and Al indicates dispersed particle clusters. Mg, and to some extent also Fe, are found in both regimes. Our results illustrate the merit of combining cryo-Raman spectroscopy and LA-ICP-MS to obtain new insights into small-scale deformation, chemical stratigraphy, and processes in deep ice and the future potential to enhance our understanding of impurities by exploiting such a multi-method approach

ESID: A Visual Analytics Tool to Epidemiological Emergencies

Visual analysis tools can help illustrate the spread of infectious diseases and enable informed decisions on epidemiology and public health issues. To create visualisation tools that are intuitive, easy to use, and effective in communicating information, continued research and development focusing on user-centric and methodological design models is extremely important. As a contribution to this topic, this paper presents the design and development of the visual analytics application ESID (Epidemiological Scenarios for Infectious Diseases). The goal of ESID is to provide a platform for rapid assessment of the most effective interventions for infectious disease control. ESID provides spatial-temporal analysis, forecasting, comparison of simulations, interactive filters, and accessibility options. In its current form, it shows the simulations of a hybrid graph-equation-based model as introduced in for infection control. The model can be stratified for different age groups and takes into account the properties of the infectious disease as well as human mobility and contact behaviour.Comment: 6 pages, 5 images and 1 table, Eurovis workshop on visual analytics (EuroVA) 202

News from the EastGRIP ice core - on microstructure, impurities and the bridging of different scales

A better understanding of ice flow and deformation is needed to improve the projections of future sea level rise. Especially ice streams, the main contributors to solid ice discharge, still require more observational data to be represented sufficiently in computer models. The East Greenland Ice-core Project (EastGRIP) thus successfully drilled the first continuous deep ice core from an ice stream, the Northeast Greenland Ice Stream (NEGIS) while serving as a hub for geophysical measurements. A major unknown is the ice microstructure, i.e. the size and orientation of ice crystals (CPO) and its interplay with chemical impurities. Impurities are a climate proxy but are also assumed to impact microstructural processes, such as deformation and grain growth, and it is thus crucial to investigate where impurities are located in the microstructure. By combining microstructural (fabric analyser, microstructure-mapping, large area scanning macroscope) and impurity (Raman spectroscopy, inductively coupled plasma mass spectrometry 2D imaging) methods, we here present a systematic overview of the evolution of the microstructure and of the location of impurities throughout the EastGRIP ice core. Solid impurities, such as dust, are preferably located in the grain interior, while soluble impurities are mainly in the grain boundaries. This shows that microstructure should be considered when using impurities as a climate proxy due to the large spatial variability on the (sub-) millimetre scale. The analysed microstructure in the EastGRIP ice core further assists in reconstructing the original orientation of the ice core via visual stratigraphy, delivering the ground-truthing for an improved method of interfering horizontal fabric with co-polarised phase-sensitive radar and gaining new insights into the spatial variability of anisotropy and ice viscosity within NEGIS. Combining microstructural data with numerical modelling enables new insights into the processes underlying CPO formation and the bridging of different spatial scales to derive a more holistic picture of NEGIS and the governing processes

Lévy defects in matrix-immobilized J aggregates : tracing intra-and intersegmental exciton relaxation

L.L. thanks the EC for financial support by the cofunded Amarout program and the Spanish Ministry for economy and competitiveness (plan nacional, Project MultiCrom (CTQ2014-58801)). G.C. acknowledges financial support by the European Research Council (ERC-2011-AdG No. 291198). D.G.L. and D.C. thank the UK EPSRC for funding via research grant EP/M025330/1 “Hybrid Polaritonics”One-dimensional J aggregates present narrow and intense absorption and emission spectra that are interesting for photonics applications. Matrix immobilization of the aggregates, as required for most device architectures, has recently been shown to induce a non-Gaussian (Lévy type) defect distribution with heavy tails, expected to influence exciton relaxation. Here we perform two-dimensional electronic spectroscopy (2DES) in one-dimensional J aggregates of the cyanine dye TDBC, immobilized in a gel matrix, and we quantitatively model 2DES maps by nonlinear optimization coupled to quantum mechanical calculations of the transient excitonic response. We find that immobilization causes strong non-Gaussian off-diagonal disorder, leading to a segmentation of the chains. Intersegmental exciton transfer is found to proceed on the picosecond time scale, causing a long-lasting excitation memory. These findings can be used to inform the design of optoelectronic devices based on J aggregates as they allow for control of exciton properties by disorder management.PostprintPostprintPeer reviewe