Slip-band distributions and microstructural fading memory beneath the firn ice transition of polar ice sheets

The Antarctic Ice Sheet is a continental ice mass with circa 23 million gigatons of ice, which represent roughly 67 % of world's freshwater supply. This colossal mass of ice is by no means static, as the old ice slowly creeps under its own weight towards the ocean, while new ice is continually formed through the sintering of snow deposited on the ice sheet surface. A crucial role in this metamorphism is played by firn, which is the porous material in an intermediate state between the granular snow and the solid polycrystalline ice. Understanding the snow firn ice metamorphism is essential not only for a precise determination of the mechanical (creep) properties of polar ice, but also for comprehending the formation and decay of climate proxies widely used in ice-core studies. This work investigates the transition from firn to ice through the spatial and directional distributions of slip bands in bubbly ice. The analysis of high-resolution micrographs of ice sections extracted from the EPICA-DML Deep Ice Core allows us to identify a clear influence of strain-induced anisotropy (viz. c-axis preferred orientations) on the evolution of slip-band inclinations in deep bubbly ice. In contrast, we discover an unanticipated behaviour of slip bands in shallow bubbly ice, which prompts the introduction of the hypothesis of microstructural fading memory and the definition of a stabilization zone that may penetrate hundreds of metres into the bubbly ice. Within this stabilization zone, highly localized concentrations of strain energy and internal stresses once generated by force chains in the ancient firn are gradually redistributed by the newly formed bubbly-ice microstructure. We show that this hypothesis is compatible with the localized dynamic recrystallization episodes observed in polar firn (even at temperatures close to -45°C), and it may also explain the sluggish rotation of c-axes observed in the upper hundreds of metres of polar ice sheets. © 2018 Elsevier LtdFinancial support from the Ramón y Cajal grant RYC-2012-12167 of the Spanish Ministry of Economy, Industry and Competitiveness is kindly acknowledged. This work is a contribution to the European Project for Ice Coring in Antarctica (EPICA), a joint European Science Foundation/European Commission scientific programme, funded by the EU and by national contributions from Belgium, Denmark, France, Germany, Italy, the Netherlands, Norway, Sweden, Switzerland and the United Kingdom. The main logistic support was provided by IPEV and PNRA (at Dome C) and AWI (at Dronning Maud Land). This is EPICA publication no. 310

Unravelling Antarctica’s past through the stratigraphy of a deep ice core: an image-analysis study of the EPICA-DML line-scan images

Polar ice research has undergone great progress in the last six decades. One of its recent technological achievements has been the development of new techniques for digital image recording and analysis of ice-core stratigraphy and microstructure. In this work we investigate one such image records, namely the line-scan image records of the EPICA-DML (European Project for Ice Coring in Antarctica, Dronning Maud Land) deep ice core. These images provide a multiscale depiction of the stratigraphy and structure of the Antarctic Ice Sheet. While previous studies have focused on the ice-core optical stratigraphy on the micro- and mesoscale (<1 mm and 10−3–1 m, respectively), in this work we present several methods to obtain fast and reliable information on the ice-core stratigraphy on the macroscale (1–103 m), including the full ice-sheet thickness. The paleoclimatic relevance of the ice-core optical stratigraphy on the macroscale is demonstrated through the comparison of the line-scan grey-value record of the EPICA-DML deep ice core with its mineral dust record, which is used as a proxy for microinclusions and for several other types of climate proxies. Additionally, we introduce a novel method to estimate the macroscopic air-bubble concentration (including number and size of bubbles) in ice cores, which is simpler, faster, and almost as reliable as painstaking microscopic studies. After a brief excursion on the relation between macroscopic and mesoscopic measures of optical stratigraphy, we close this work by making the case for a multi-measure analysis of ice-core line-scan images, which enables us to obtain a broad perspective of the optical stratigraphy of the whole ice core, with relevance for paleoclimate and ice-sheet-flow studies.This research is supported by the Spanish Government through the María de Maeztu excellence accreditation 2018–2022 (Ref. MDM-2017-0714), and by the Basque Government through the BERC 2018–2021 programme. SHF acknowledges support from the Spanish Ministry of Science, Innovation, and Universities (MCIU) through the project iMechPro (RTI2018–100696–B–I00), and from the Ramón y Cajal grant RYC–2012–12167 of the Spanish Ministry of Economy, Industry and Competitiveness (MINECO

A pre-crisis vs. crisis analysis of peripheral EU stock markets by means of wavelet transform and a nonlinear causality test

This paper presents an analysis of EU peripheral (so-called PIIGS) stock market indices and the SandP Europe 350 index (SPEURO), as a European benchmark market, over the pre-crisis (2004 2007) and crisis (2008 2011) periods. We computed a rolling-window wavelet correlation for the market returns and applied a non-linear Granger causality test to the wavelet decomposition coefficients of these stock market returns. Our results show that the correlation is stronger for the crisis than for the pre-crisis period. The stock market indices from Portugal, Italy and Spain were more interconnected among themselves during the crisis than with the SPEURO. The stock market from Portugal is the most sensitive and vulnerable PIIGS member, whereas the stock market from Greece tends to move away from the European benchmark market since the 2008 financial crisis till 2011. The non-linear causality test indicates that in the first three wavelet scales (intraweek, weekly and fortnightly) the number of uni-directional and bi-directional causalities is greater during the crisis than in the pre-crisis period, because of financial contagion. Furthermore, the causality analysis shows that the direction of the Granger cause effect for the pre-crisis and crisis periods is not invariant in the considered time-scales, and that the causality directions among the studied stock markets do not seem to have a preferential direction. These results are relevant to better understand the behaviour of vulnerable stock markets, especially for investors and policymakers. © 2017 Elsevier B.V

Effects of impurities on the ice microstructure of Monte Perdido Glacier, Central Pyrenees, NE Spain

Monte Perdido Glacier, located in the central Pyrenees, is one of the southernmost glaciers in Europe. Due to climate change, this glacier is suffering an accelerated mass loss, especially in the last decades. If the current trends persist, this glacier is expected to disappear in the next 50 years. As part of the efforts of the scientific community to increase the knowledge about this glacier, this research presents the first microstructural characterization of the Monte Perdido Glacier, focused on a high-impurity concentration segment that belongs to an ice core drilled in 2017. The results reveal the ice has a layering defined by air bubbles and non-soluble impurities. The bubble-defined layering exhibits features of both a primary (sedimentary) and a secondary (strain-induced) origin. We found a clear inverse correspondence between the particle concentration and the grains' size and roundness index. A preliminary micro-Raman characterization of the particles shows the occurrence of atacamite, anatase (likely related to ancient mining activities in the vicinity of the glacier) and quartz. The latter could be an indicator of mineral dust, probably suggesting the arrival of dust-laden air masses from the north of the African continent.This research was supported by the Spanish Government through the María de Maeztu excellence accreditation 2018–2022 (MDM-2017-0714) and by the Spanish Agencia Estatal de Investigación (AEI Spain) through the projects PaleoICE EXPLORA (CGL2015-72167-EXP) and iMechPro (RTI2018-100696-B-I00). NGS acknowledges a PhD grant from the Basque Government (PRE-2018-1-0116). We thank the directorate of the Parque Nacional de Ordesa y Monte Perdido (Spain) for permission to investigate the Monte Perdido glacier. We also thank Ibai Rico ( https://basquemountainguides.com/ , UPV/EHU), Maria Leunda (UPV/EHU), and Juan Ignacio López-Moreno (IPE-CSIC) for their help during the sampling of the MP1 ice core, and Pedro Sanchez Navarrete (IPE-CSIC) for transporting the ice samples. Finally, we would like to extend our appreciation to the anonymous reviewers, the Scientific Editor, Christine Hvidberg, and the Chief Editor, Hester Jiskoot, for their valuable comments on this manuscript

Continuum-mechanical, Anisotropic Flow model for polar ice masses, based on an anisotropic Flow Enhancement factor

A complete theoretical presentation of the Continuum-mechanical, Anisotropic Flow model, based on an anisotropic Flow Enhancement factor (CAFFE model) is given. The CAFFE model is an application of the theory of mixtures with continuous diversity for the case of large polar ice masses in which induced anisotropy occurs. The anisotropic response of the polycrystalline ice is described by a generalization of Glen's flow law, based on a scalar anisotropic enhancement factor. The enhancement factor depends on the orientation mass density, which is closely related to the orientation distribution function and describes the distribution of grain orientations (fabric). Fabric evolution is governed by the orientation mass balance, which depends on four distinct effects, interpreted as local rigid body rotation, grain rotation, rotation recrystallization (polygonization) and grain boundary migration (migration recrystallization), respectively. It is proven that the flow law of the CAFFE model is truly anisotropic despite the collinearity between the stress deviator and stretching tensors.Comment: 22 pages, 5 figure

Noise Sources in Photometry and Radial Velocities

The quest for Earth-like, extrasolar planets (exoplanets), especially those located inside the habitable zone of their host stars, requires techniques sensitive enough to detect the faint signals produced by those planets. The radial velocity (RV) and photometric transit methods are the most widely used and also the most efficient methods for detecting and characterizing exoplanets. However, presence of astrophysical "noise" makes it difficult to detect and accurately characterize exoplanets. It is important to note that the amplitude of such astrophysical noise is larger than both the signal of Earth-like exoplanets and state-of-the-art instrumentation limit precision, making this a pressing topic that needs to be addressed. In this chapter, I present a general review of the main sources of noise in photometric and RV observations, namely, stellar oscillations, granulation, and magnetic activity. Moreover, for each noise source I discuss the techniques and observational strategies which allow us to mitigate their impact.Comment: 11 pages, 2 tables, Lecture presented at the IVth Azores International Advanced School in Space Sciences on "Asteroseismology and Exoplanets: Listening to the Stars and Searching for New Worlds" (arXiv:1709.00645), which took place in Horta, Azores Islands, Portugal in July 201

Framing, Context, and Methods (Chapter 1)

Working Group I (WGI) of the Intergovernmental Panel on Climate Change (IPCC) assesses the current evidence on the physical science of climate change, evaluating knowledge gained from observations, reanalyses, paleoclimate archives and climate model simulations, as well as physical, chemical and biological climate processes. This chapter sets the scene for the WGI Assessment, placing it in the context of ongoing global and regional changes, international policy responses, the history of climate science and the evolution from previous IPCC assessments, including the Special Reports prepared as part of this Assessment Cycle. This chapter presents key concepts and methods, relevant recent developments, and the modelling and scenario framework used in this Assessment

Measurement of the polarisation of W bosons produced with large transverse momentum in pp collisions at sqrt(s) = 7 TeV with the ATLAS experiment

This paper describes an analysis of the angular distribution of W->enu and W->munu decays, using data from pp collisions at sqrt(s) = 7 TeV recorded with the ATLAS detector at the LHC in 2010, corresponding to an integrated luminosity of about 35 pb^-1. Using the decay lepton transverse momentum and the missing transverse energy, the W decay angular distribution projected onto the transverse plane is obtained and analysed in terms of helicity fractions f0, fL and fR over two ranges of W transverse momentum (ptw): 35 < ptw < 50 GeV and ptw > 50 GeV. Good agreement is found with theoretical predictions. For ptw > 50 GeV, the values of f0 and fL-fR, averaged over charge and lepton flavour, are measured to be : f0 = 0.127 +/- 0.030 +/- 0.108 and fL-fR = 0.252 +/- 0.017 +/- 0.030, where the first uncertainties are statistical, and the second include all systematic effects.Comment: 19 pages plus author list (34 pages total), 9 figures, 11 tables, revised author list, matches European Journal of Physics C versio

Observation of a new chi_b state in radiative transitions to Upsilon(1S) and Upsilon(2S) at ATLAS

The chi_b(nP) quarkonium states are produced in proton-proton collisions at the Large Hadron Collider (LHC) at sqrt(s) = 7 TeV and recorded by the ATLAS detector. Using a data sample corresponding to an integrated luminosity of 4.4 fb^-1, these states are reconstructed through their radiative decays to Upsilon(1S,2S) with Upsilon->mu+mu-. In addition to the mass peaks corresponding to the decay modes chi_b(1P,2P)->Upsilon(1S)gamma, a new structure centered at a mass of 10.530+/-0.005 (stat.)+/-0.009 (syst.) GeV is also observed, in both the Upsilon(1S)gamma and Upsilon(2S)gamma decay modes. This is interpreted as the chi_b(3P) system.Comment: 5 pages plus author list (18 pages total), 2 figures, 1 table, corrected author list, matches final version in Physical Review Letter

Search for displaced vertices arising from decays of new heavy particles in 7 TeV pp collisions at ATLAS

We present the results of a search for new, heavy particles that decay at a significant distance from their production point into a final state containing charged hadrons in association with a high-momentum muon. The search is conducted in a pp-collision data sample with a center-of-mass energy of 7 TeV and an integrated luminosity of 33 pb^-1 collected in 2010 by the ATLAS detector operating at the Large Hadron Collider. Production of such particles is expected in various scenarios of physics beyond the standard model. We observe no signal and place limits on the production cross-section of supersymmetric particles in an R-parity-violating scenario as a function of the neutralino lifetime. Limits are presented for different squark and neutralino masses, enabling extension of the limits to a variety of other models.Comment: 8 pages plus author list (20 pages total), 8 figures, 1 table, final version to appear in Physics Letters