scholarly journals Microstructure, micro-inclusions, and mineralogy along the EGRIP ice core – Part 1: Localisation of inclusions and deformation patterns

2021 ◽  
Vol 15 (12) ◽  
pp. 5717-5737
Author(s):  
Nicolas Stoll ◽  
Jan Eichler ◽  
Maria Hörhold ◽  
Tobias Erhardt ◽  
Camilla Jensen ◽  
...  
Keyword(s):  
Spatial Variability ◽  
Grain Boundaries ◽  
Deformation Behaviour ◽  
Ice Core ◽  
Late Glacial ◽  
Holistic Approaches ◽  
Crystal Preferred Orientation ◽  
Dynamic Recrystallisation ◽  
Core Project ◽  
Deformation Patterns

Abstract. Impurities deposited in polar ice enable the reconstruction of the atmospheric aerosol concentration of the past. At the same time they impact the physical properties of the ice itself such as its deformation behaviour. Impurities are thought to enhance ice deformation, but observations are ambiguous due to a shortage of comprehensive microstructural analyses. For the first time, we systematically analyse micro-inclusions in polar fast flowing ice, i.e. from the East Greenland Ice Core Project ice core drilled through the Northeast Greenland Ice Stream. In direct relation to the inclusions we derive the crystal preferred orientation, fabric, grain size, and microstructural features at 10 depths, covering the Holocene and Late Glacial. We use optical microscopy to create microstructure maps to analyse the in situ locations of inclusions in the polycrystalline, solid ice samples. Micro-inclusions are more variable in spatial distribution than previously observed and show various distributional patterns ranging from centimetre-thick layers to clusters and solitary particles, independent of depth. In half of all samples, micro-inclusions are more often located at or close to the grain boundaries by a slight margin (in the areas occupied by grain boundaries). Throughout all samples we find strong indications of dynamic recrystallisation, such as grain islands, bulging grains, and different types of sub-grain boundaries. We discuss the spatial variability in micro-inclusions, the link between spatial variability and mineralogy, and possible effects on the microstructure and deformation behaviour of the ice. Our results emphasise the need for holistic approaches in future studies, combining microstructure and impurity analysis.

scholarly journals Microstructure, Micro-inclusions and Mineralogy along the EGRIP ice core – Part 1: Localisation of inclusions and deformation patterns

2021 ◽  
Author(s):  
Nicolas Stoll ◽  
Jan Eichler ◽  
Maria Hörhold ◽  
Tobias Erhardt ◽  
Camilla Jensen ◽  
...  
Keyword(s):  
Spatial Variability ◽  
Grain Boundaries ◽  
Deformation Behaviour ◽  
Ice Core ◽  
Late Glacial ◽  
Holistic Approaches ◽  
Crystal Preferred Orientation ◽  
Dynamic Recrystallisation ◽  
Core Project ◽  
Deformation Patterns

Abstract. Impurities deposited in polar ice allow the reconstruction of the atmospheric aerosol concentration of the past. At the same time they impact the physical properties of the ice itself such as its deformation behaviour. Impurities are thought to enhance ice deformation, but observations are ambiguous due to a shortage of comprehensive microstructural analyses. For the first time, we systematically analyse micro-inclusions in polar fast flowing ice, i.e. from the East Greenland Ice Core Project ice core drilled trough the Northeast Greenland Ice Stream. In direct relation to the inclusions we derive the crystal-preferred orientation, fabric, grain size, and microstructural features at ten depths, covering the Holocene and Late Glacial. We use optical microscopy to create microstructure maps to analyse the in situ locations of inclusions in the polycrystalline, solid ice samples. Micro-inclusions are more variable in spatial distribution than previously observed, and show various distributional patterns ranging from centimetre-thick layers to clusters and solitary particles, independent of depth. Analysing the area occupied by grain boundaries in the respective samples shows that micro-inclusions are slightly more often located at or close to grain boundaries in half of all samples. Throughout all samples we find strong indications of dynamic recrystallisation, such as grain islands, bulging grains and different types of subgrain boundaries. We discuss the spatial variability of micro-inclusions, the link between spatial variability and mineralogy, and possible effects on the microstructure and deformation behaviour of the ice. Our results emphasise the need for holistic approaches in future studies, combining microstructure and impurity analysis.

scholarly journals Characterization of late glacial continental dust in the Greenland Ice Core Project ice core

2000 ◽  
Vol 105 (D4) ◽  
pp. 4637-4656 ◽  
Author(s):  
Anders Svensson ◽  
Pierre E. Biscaye ◽  
Francis E. Grousset
Keyword(s):  
Ice Core ◽  
Late Glacial ◽  
Core Project

scholarly journals Restoration Mechanisms at Moderate Temperatures for As-Cast ZK40 Magnesium Alloys Modified with Individual Ca and Gd Additions

Crystals ◽  
2020 ◽  
Vol 10 (12) ◽  
pp. 1140
Author(s):  
Ricardo Henrique Buzolin ◽  
Leandro Henrique Moreno Guimaraes ◽  
Julián Arnaldo Ávila Díaz ◽  
Erenilton Pereira da Silva ◽  
Domonkos Tolnai ◽  
...  
Keyword(s):  
Grain Boundaries ◽  
Dynamic Recovery ◽  
Deformation Behaviour ◽  
Compression Tests ◽  
Electron Backscattered Diffraction ◽  
Ca Addition ◽  
Synchrotron Radiation Diffraction ◽  
Dynamic Recrystallisation ◽  
Restoration Mechanism ◽  
Continuous Dynamic

The deformation behaviour of as-cast ZK40 alloys modified with individual additions of Ca and Gd is investigated at 250 °C and 300 °C. Compression tests were carried out at 0.0001 s−1 and 0.001 s−1 using a modified Gleeble system during in-situ synchrotron radiation diffraction experiments. The deformation mechanisms are corroborated by post-mortem investigations using scanning electron microscopy combined with electron backscattered diffraction measurements. The restoration mechanisms in α-Mg are listed as follows: the formation of misorientation spread within α-Mg, the formation of low angle grain boundaries via dynamic recovery, twinning, as well as dynamic recrystallisation. The Gd and Ca additions increase the flow stress of the ZK40, which is more evident at 0.001 s−1 and 300 °C. Dynamic recovery is the predominant restoration mechanism in all alloys. Continuous dynamic recrystallisation only occurs in the ZK40 at 250 °C, competing with discontinuous dynamic recrystallisation. Discontinuous dynamic recrystallisation occurs for the ZK40 and ZK40-Gd. The Ca addition hinders discontinuous dynamic recrystallisation for the investigated temperatures and up to the local achieved strain. Gd addition forms a semi-continuous network of intermetallic compounds along the grain boundaries that withstand the load until their fragmentation, retarding discontinuous dynamic recrystallisation.

scholarly journals Spatial variations of local climate at Taylor Dome, Antarctica: implications for paleoclimate from ice cores

1994 ◽  
Vol 20 ◽  
pp. 219-225 ◽  
Author(s):  
E.D. Waddington ◽  
D.L. Morse
Keyword(s):  
Spatial Variability ◽  
Source Region ◽  
Ice Core ◽  
Ice Cores ◽  
Temperature Inversion ◽  
Related Factors ◽  
Local Climate ◽  
Air Masses ◽  
Air Temperatures ◽  
Inversion Strength

10m firn temperatures are commonly used on the Antarctic plateau to estimate mean annual air temperatures. 10m firn temperatures measured at Taylor Dome (also referred to as McMurdo Dome in the literature), Antarctica, are influenced by a factor other than altitude and latitude that varies systematically across Taylor Dome. Some inter-related factors possibly contributing to the modern temperature variability are differences in sensible heat from warm or cold air masses, differences in wind strength and source region, differences in temperature inversion strength and differences in cloudiness. Our preliminary data are compatible with spatially variable katabatic winds that could control the winter temperature inversion strength to provide a large part of the signal. This has implications for paleoclimate studies.(1) Variations of the stable isotopes δ18O and δD from ice cores are a proxy for paleotemperature. The isotope thermometer is calibrated by comparing local isotope ratios with corresponding measured temperatures. In order to derive a useful isotope-temperature calibration, we must understand the processes that control the modern spatial variability of temperature. (2) In order to quantify past changes in local climate, we must understand processes that influence local spatial variability. If those processes differed in the past, ice-core climate reconstruction would be affected in two ways: through alteration of the geochemical record and through alteration of deep ice and firn temperatures.

Multifractal analysis of the Greenland Ice‐Core Project climate data

1995 ◽  
Vol 22 (13) ◽  
pp. 1689-1692 ◽  
Author(s):  
François Schmitt ◽  
Shaun Lovejoy ◽  
Daniel Schertzer
Keyword(s):  
Multifractal Analysis ◽  
Ice Core ◽  
Climate Data ◽  
Core Project

Late-Glacial Cooling in Amazonia Inferred from Pollen at Lagoa do Caçó, Northern Brazil

2001 ◽  
Vol 55 (1) ◽  
pp. 47-56 ◽  
Author(s):  
Marie-Pierre Ledru ◽  
Renato Campello Cordeiro ◽  
José Maria Landim Dominguez ◽  
Louis Martin ◽  
Philippe Mourguiart ◽  
...  
Keyword(s):  
Amazon Basin ◽  
Ice Core ◽  
Late Glacial ◽  
Climatic Conditions ◽  
Convective Precipitation ◽  
Pollen Data ◽  
Moisture Source ◽  
Northern Latitudes ◽  
Low Latitudes ◽  
Northern Brazil

AbstractNew pollen data from a core at Lagoa do Caçó, Maranhão state, Brazil (2°58′S 43°25′W; 120 m elevation), show higher frequencies of Podocarpus at the end of the Pleistocene than today. The increase in Podocarpus, which follows the successive increase of various pioneer species such as Didymopanax, Melastomataceae/Combretaceae, and Cecropia, implies a progressive late-glacial increase of moist and cool climatic conditions. A comparable increase in Podocarpus is found in other lowland records in Amazonia. A review of published pollen data from Amazonia suggests that the moisture source was from the southeast. By contrast, present-day moisture comes from the tropical Atlantic and from the Amazon basin, with its convective precipitation. The likely cause for the southeastern moisture source between ca. 15,000 and 14,500 cal yr B.P. was enhanced polar (Antarctic) advection that reached low latitudes and maintained year-round the meteorological equator in its austral-winter position at northern latitudes or reduced drastically its southward summer displacement. This hypothesis is consistent with marine and ice core records.

scholarly journals Air clathrate crystals from the GRIP deep ice core, Greenland: a number-, size- and shape-distribution study

1999 ◽  
Vol 45 (149) ◽  
pp. 22-30 ◽  
Author(s):  
F. Pauer ◽  
S. Kipfstuhl ◽  
W. F. Kuhs ◽  
H. Shoji
Keyword(s):  
Diffusion Processes ◽  
Climatic Factors ◽  
Ice Core ◽  
Number Concentration ◽  
Depth Range ◽  
Shape Distribution ◽  
Climatic Oscillations ◽  
Size And Shape ◽  
Distribution Study ◽  
Core Project

AbstractWe performed microscopic observations and a statistical study of the number, size and shape distribution of clathrates in the GRIP (Greenland Ice Core Project) deep ice core, using 185 samples from a depth range of 1016–3014 m, spanning a period of 6 to >110 ka BP and encompassing the Holocene, Wisconsin and Eemian periods. The number concentration of the clathrates varied considerably with climatic changes. It was possible to detect the rapid climatic oscillations in the last glacial between 13 and 110 ka BP, the Dansgaard–Oeschger cycles, in the number-concentration profile of clathrates. The mean volume of clathrates is less clearly influenced by climatic factors, with a tendency towards greater volumes in warmer periods, but also a growth of clathrates with depth could be detected. This growth rate was calculated to be 3.1 × 10-12 cm3 a-1. The amount of gases captured in the clathrates is estimated to be significantly smaller than the total amount of air determined by gas-concentration measurements. This points to diffusion processes of atmospheric gases within the ice matrix.

scholarly journals Texture Evolution in AA6082-T6 BFSW Welds: Optical Microscopy and EBSD Characterisation

Materials ◽  
2019 ◽  
Vol 12 (19) ◽  
pp. 3215 ◽  
Author(s):  
Abbas Tamadon ◽  
Dirk J. Pons ◽  
Don Clucas ◽  
Kamil Sued
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Optical Microscopy ◽  
Electron Backscatter Diffraction ◽  
Texture Evolution ◽  
Grain Structure ◽  
Friction Stir ◽  
Fine Grain ◽  
Grain Structures ◽  
Dynamic Recrystallisation

One of the difficulties with bobbin friction stir welding (BFSW) has been the visualisation of microstructure, particularly grain boundaries, and this is especially problematic for materials with fine grain structure, such as AA6082-T6 aluminium as here. Welds of this material were examined using optical microscopy (OM) and electron backscatter diffraction (EBSD). Results show that the grain structures that form depend on a complex set of factors. The motion of the pin and shoulder features transports material around the weld, which induces shear. The shear deformation around the pin is non-uniform with a thermal and strain gradient across the weld, and hence the dynamic recrystallisation (DRX) processes are also variable, giving a range of observed polycrystalline and grain boundary structures. Partial DRX was observed at both hourglass boundaries, and full DRX at mid-stirring zone. The grain boundary mapping showed the formation of low-angle grain boundaries (LAGBs) at regions of high shear as a consequence of thermomechanical nature of the process.

scholarly journals Surface accumulation in Northern Central Greenland during the last 300 years

2020 ◽  
Vol 61 (81) ◽  
pp. 214-224 ◽  
Author(s):  
Nanna B. Karlsson ◽  
Sebastian Razik ◽  
Maria Hörhold ◽  
Anna Winter ◽  
Daniel Steinhage ◽  
...  
Keyword(s):  
Large Scale ◽  
Climate Models ◽  
Regional Climate ◽  
Ice Core ◽  
Regional Climate Models ◽  
Radar Data ◽  
Accumulation Rates ◽  
Ground Penetrating ◽  
Core Project ◽  
North Greenland

AbstractThe internal stratigraphy of snow and ice as imaged by ground-penetrating radar may serve as a source of information on past accumulation. This study presents results from two ground-based radar surveys conducted in Greenland in 2007 and 2015, respectively. The first survey was conducted during the traverse from the ice-core station NGRIP (North Greenland Ice Core Project) to the ice-core station NEEM (North Greenland Eemian Ice Drilling). The second survey was carried out during the traverse from NEEM to the ice-core station EGRIP (East Greenland Ice Core Project) and then onwards to Summit Station. The total length of the radar profiles is 1427 km. From the radar data, we retrieve the large-scale spatial variation of the accumulation rates in the interior of the ice sheet. The accumulation rates range from 0.11 to 0.26 m a−1 ice equivalent with the lowest values found in the northeastern sector towards EGRIP. We find no evidence of temporal or spatial changes in accumulation rates when comparing the 150-year average accumulation rates with the 321-year average accumulation rates. Comparisons with regional climate models reveal that the models underestimate accumulation rates by up to 35% in northeastern Greenland. Our results serve as a robust baseline to detect present changes in either surface accumulation rates or patterns.

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