scholarly journals Investigation of a cold-based ice apron on a high-mountain permafrost rock wall using ice texture analysis and micro-14C dating: a case study of the Triangle du Tacul ice apron (Mont Blanc massif, France)

2021 ◽  
pp. 1-8
Author(s):  
Grégoire Guillet ◽  
Susanne Preunkert ◽  
Ludovic Ravanel ◽  
Maurine Montagnat ◽  
Ronny Friedrich
Keyword(s):  
Radiocarbon Dating ◽  
Boundary Migration ◽  
Ice Core ◽  
Ice Cores ◽  
Shear Plane ◽  
High Mountain ◽  
14C Dating ◽  
Rock Wall ◽  
Major Mechanism ◽  
Mont Blanc Massif

Abstract The current paper studies the dynamics and age of the Triangle du Tacul (TDT) ice apron, a massive ice volume lying on a steep high-mountain rock wall in the French side of the Mont-Blanc massif at an altitude close to 3640 m a.s.l. Three 60 cm long ice cores were drilled to bedrock (i.e. the rock wall) in 2018 and 2019 at the TDT ice apron. Texture (microstructure and lattice-preferred orientation, LPO) analyses were performed on one core. The two remaining cores were used for radiocarbon dating of the particulate organic carbon fraction (three samples in total). Microstructure and LPO do not substantially vary with along the axis of the ice core. Throughout the core, irregularly shaped grains, associated with strain-induced grain boundary migration and strong single maximum LPO, were observed. Measurements indicate that at the TDT ice deforms under a low strain-rate simple shear regime, with a shear plane parallel to the surface slope of the ice apron. Dynamic recrystallization stands out as the major mechanism for grain growth. Micro-radiocarbon dating indicates that the TDT ice becomes older with depth perpendicular to the ice surface. We observed ice ages older than 600 year BP and at the base of the lowest 30 cm older than 3000 years.

scholarly journals Radiocarbon dating of alpine ice cores with the dissolved organic carbon (DOC) fraction

2020 ◽  
Author(s):  
Ling Fang ◽  
Theo Jenk ◽  
Thomas Singer ◽  
Shugui Hou ◽  
Margit Schwikowski
Keyword(s):  
Organic Carbon ◽  
Dissolved Organic Carbon ◽  
Radiocarbon Dating ◽  
Ice Core ◽  
Extraction Procedure ◽  
Ice Cores ◽  
Complete Removal ◽  
Core Sample ◽  
Polar Regions ◽  
14C Dating

Abstract. High-alpine glaciers are valuable archives of past climatic and environmental conditions. The interpretation of the preserved signal requires a precise chronology. Radiocarbon (14C) dating of the water-insoluble organic carbon (WIOC) fraction has become an important dating tool to constrain the age of ice cores from mid-latitude and low-latitude glaciers. However, in some cases this method is restricted by the low WIOC concentration in the ice. In this work, we report first 14C dating results using the dissolved organic carbon (DOC) fraction, which is present at concentrations of at least a factor of two higher than the WIOC fraction. We evaluated this new approach by comparison to the established WIO14C dating based on parallel ice core sample sections from four different Eurasian glaciers covering an age range of several hundred to around 20’000 years. 14C dating of the two fractions yielded comparable ages with WIO14C revealing a slight, barely significant, systematic offset towards older ages. Our data suggests this to be caused by incompletely removed carbonate from mineral dust (14C depleted) contributing to the WIOC fraction. While in the DOC extraction procedure inorganic carbon is monitored to ensure complete removal, the average removal efficiency for WIOC samples was here estimated to be ~96%. We did not find any indication of in-situ production systematically contributing to DO14C as suggested in a previous study. By using the DOC instead of the WIOC fraction for 14C dating, the required ice mass can be reduced to typically ~250 g, yielding a precision of ±200 years or even better if sample sizes typically required for WIO14C dating are used. This study shows the potential of pushing radiocarbon dating of ice forward even to remote and Polar Regions, where the carbon content in the ice is particularly low, when applying the DOC fraction for 14C dating.

Constraining ice core chronologies with 39Ar and 81Kr

2021 ◽  
Author(s):  
Florian Ritterbusch ◽  
Jinho Ahn ◽  
Ji-Qiang Gu ◽  
Wei Jiang ◽  
Giyoon Lee ◽  
...  
Keyword(s):  
Sample Size ◽  
Half Life ◽  
Earth Science ◽  
Noble Gas ◽  
Ice Core ◽  
Ice Cores ◽  
High Mountain ◽  
National Academy Of Sciences ◽  
Geophysical Research ◽  
Mountain Glaciers

<p>Paleoclimate reconstructions from ice core records can be hampered due to the lack of a reliable chronology, especially when the stratigraphy is disturbed and conventional dating methods cannot be readily applied. The noble-gas radioisotopes <sup>81</sup>Kr and <sup>39</sup>Ar can in these cases provide robust constraints as they yield absolute, radiometric ages. <sup>81</sup>Kr (half-life 229 ka) covers the time span of 50-1300 ka, which is particularly relevant for polar ice cores, whereas <sup>39</sup>Ar (half-life 269 a) with a dating range of 50-1800 a is suitable for high mountain glaciers. For a long time the use of <sup>81</sup>Kr and <sup>39</sup>Ar for dating of ice samples was hampered by the lack of a detection technique that can meet its extremely small abundance at a reasonable sample size.</p><p>Here, we present <sup>81</sup>Kr and <sup>39</sup>Ar dating of Antarctic and Tibetan ice cores with the detection method Atom Trap Trace Analysis (ATTA), using 5-10 kg of ice for <sup>81</sup>Kr and 2-5 kg for <sup>39</sup>Ar. Recent advances in further decreasing the sample size and increasing the dating precision will be discussed. Current studies include <sup>81</sup>Kr dating in shallow ice cores from the Larsen Blue ice area, East Antarctica, in order to retrieve climate signals from the last glacial termination. Moreover, an <sup>39</sup>Ar profile from a central Tibetan ice core has been obtained in combination with layer counting based on isotopic and visual stratigraphic signals. The presented studies demonstrate how <sup>81</sup>Kr and <sup>39</sup>Ar can constrain the age range of ice cores and complement other methods in developing an ice core chronology.</p><p> </p><p>[1] Z.-T. Lu, Tracer applications of noble gas radionuclides in the geosciences, Earth-Science Reviews 138, 196-214, (2014)<br>[2] C. Buizert, Radiometric <sup>81</sup>Kr dating identifies 120,000-year-old ice at Taylor Glacier, Antarctica, Proceedings of the National Academy of Sciences, <strong>111</strong>, 6876, (2014)</p><p>[3] L. Tian, <sup>81</sup>Kr Dating at the Guliya Ice Cap, Tibetan Plateau, Geophysical Research Letters, (2019)</p><p>http://atta.ustc.edu.cn</p>

scholarly journals A model of crystal-size evolution in polar ice masses

2014 ◽  
Vol 60 (221) ◽  
pp. 463-477 ◽  
Author(s):  
Felix NG ◽  
T.H. Jacka
Keyword(s):  
Crystal Growth ◽  
Dislocation Density ◽  
Grain Boundary ◽  
Crystal Size ◽  
Boundary Migration ◽  
Ice Core ◽  
Ice Cores ◽  
Grain Boundary Migration ◽  
Shallow Subsurface ◽  
The Mean

AbstractIn the deep ice cores drilled at the GRIP, NGRIP and GISP2 sites in Greenland and at Byrd Station and the summit of Law Dome in Antarctica, the mean crystal size increases with depth in the shallow subsurface and reaches steady values at intermediate depth. This behaviour has been attributed to the competition between grain-boundary migration driven crystal growth and crystal polygonization, but the effects of changing crystal dislocation density and non-equiaxed crystal shape in this competition are uncertain. We study these effects with a simple model. It describes how the mean height and width of crystals evolve as they flatten under vertical compression, and as crystal growth and polygonization compete. The polygonization rate is assumed to be proportional to the mean dislocation density across crystals. Migration recrystallization, which can affect crystal growth via strain-induced grain boundary migration but whose impact on the mean crystal size is difficult to quantify for ice at present, is not accounted for. When applied to the five ice-core sites, the model simulates the observed crystal-size profiles well down to the bottom of their steady regions, although the match for Law Dome is less satisfactory. Polygonization rate factors retrieved for the sites range from 10–5 to 10–2 a–1. We conclude that since crystal size and dislocation density evolve in a strongly coupled manner, consistent modelling requires multiple differential equations to track both of these variables. Future ice-core analysis should also determine crystal size in all three principal directions.

Constraining ice core chronologies with 39Ar and 81Kr

2020 ◽  
Author(s):  
Florian Ritterbusch ◽  
Yan-Qing Chu ◽  
Ilaria Crotti ◽  
Xi-Ze Dong ◽  
Ji-Qiang Gu ◽  
...  
Keyword(s):  
Half Life ◽  
Earth Science ◽  
Noble Gas ◽  
Ice Core ◽  
Ice Cores ◽  
High Mountain ◽  
National Academy Of Sciences ◽  
Geophysical Research ◽  
Bottom Part ◽  
Mountain Glaciers

<p>Paleoclimate reconstructions from ice core records can be hampered due to the lack of a reliable chronology, especially when the stratigraphy is disturbed and conventional dating methods are not readily applied. The noble gas radioisotopes <sup>81</sup>Kr and <sup>39</sup>Ar can in these cases provide robust constraints as they yield absolute, radiometric ages. <sup>81</sup>Kr (half-life 229 ka) covers the time span from 50-1300 ka, which is particularly relevant for polar ice cores, whereas <sup>39</sup>Ar (half-life 269 a) with a dating range of 50-1400 a is suitable for high mountain glaciers. For a long time the use of <sup>81</sup>Kr and <sup>39</sup>Ar for dating of ice samples was hampered by the lack of a detection technique that can meet its extremely small abundance at a reasonable sample size. Here, we report on <sup>81</sup>Kr and <sup>39</sup>Ar dating of Antarctic and Tibetan ice cores with the detection method Atom Trap Trace Analysis (ATTA), using 5-10 kg of ice for <sup>81</sup>Kr and 2-5 kg for <sup>39</sup>Ar. Among others, we measured <sup>81</sup>Kr in the lower section of Taldice ice core, which is difficult to date by conventional methods, and in the meteoric bottom of the Vostok ice core in comparison with an age scale derived from hydrate growth. Moreover, we have obtained an <sup>39</sup>Ar profile for an ice core from central Tibet in combination with a timescale constructed by layer counting. The presented studies demonstrate how the obtained <sup>81</sup>Kr and <sup>39</sup>Ar ages can complement other methods in developing an ice core chronology, especially for the bottom part.</p><p>[1] Z.-T. Lu, Tracer applications of noble gas radionuclides in the geosciences, Earth-Science Reviews 138, 196-214, (2014)</p><p>[2] C. Buizert, Radiometric <sup>81</sup>Kr dating identifies 120,000-year-old ice at Taylor Glacier, Antarctica, Proceedings of the National Academy of Sciences, <strong>111</strong>, 6876, (2014)</p><p>[3] L. Tian, <sup>81</sup>Kr Dating at the Guliya Ice Cap, Tibetan Plateau, Geophysical Research Letters, (2019)</p><p>[4] http://atta.ustc.edu.cn</p>

scholarly journals Grain Growth in Polar Ice: II. Application

1986 ◽  
Vol 32 (112) ◽  
pp. 425-433 ◽  
Author(s):  
R.B. Alley ◽  
J.H. Perepezko ◽  
C.R. Bentley
Keyword(s):  
Grain Boundaries ◽  
Grain Growth ◽  
Growth Rates ◽  
Boundary Migration ◽  
Ice Core ◽  
Ice Cores ◽  
Geometric Constraints ◽  
Polar Ice ◽  
High Concentration ◽  
Micro Particles

AbstractGrain growth observed in polar ice that is not deforming rapidly can be accounted for if concentrations and distributions of extrinsic materials (microparticles, bubbles, and dissolved impurities) are characterized fully. Dissolved impurities segregate to grain boundaries and slow grain growth in all cold glacial ice. The high concentration of soluble impurities in Wisconsinan ice from the Dome C (Antarctica) ice core (and perhaps other ice cores) probably causes the small grain-sizes observed in that ice. Microparticles have little effect on grain growth in ordinary ice. In ice layers that appear dirty owing to concentrations of volcanic tephra (such as in the Byrd Station (Antarctica) ice core) or of morainal material, micro particles reduce grain-growth rates significantly. The relatively high vapor pressure of ice allows rapid growth and high mobility of intergranular necks, so grain growth in firn is limited by boundary migration rather than by neck growth. Bubbles formed by pore close-off at the firn-ice transition are less mobile than grain boundaries, causing bubble-boundary separation whenever geometric constraints are satisfied; however, such separation reduces grain-growth rates by only about 10%. The observed linear increase of grain area with time is thus predicted by theory, but the growth rate depends on soluble-impurity concentrations as well as on temperature.

scholarly journals Grain Growth in Polar Ice: II. Application

1986 ◽  
Vol 32 (112) ◽  
pp. 425-433 ◽  
Author(s):  
R.B. Alley ◽  
J.H. Perepezko ◽  
C.R. Bentley
Keyword(s):  
Grain Boundaries ◽  
Grain Growth ◽  
Growth Rates ◽  
Boundary Migration ◽  
Ice Core ◽  
Ice Cores ◽  
Geometric Constraints ◽  
Polar Ice ◽  
High Concentration ◽  
Micro Particles

AbstractGrain growth observed in polar ice that is not deforming rapidly can be accounted for if concentrations and distributions of extrinsic materials (microparticles, bubbles, and dissolved impurities) are characterized fully. Dissolved impurities segregate to grain boundaries and slow grain growth in all cold glacial ice. The high concentration of soluble impurities in Wisconsinan ice from the Dome C (Antarctica) ice core (and perhaps other ice cores) probably causes the small grain-sizes observed in that ice. Microparticles have little effect on grain growth in ordinary ice. In ice layers that appear dirty owing to concentrations of volcanic tephra (such as in the Byrd Station (Antarctica) ice core) or of morainal material, micro particles reduce grain-growth rates significantly. The relatively high vapor pressure of ice allows rapid growth and high mobility of intergranular necks, so grain growth in firn is limited by boundary migration rather than by neck growth. Bubbles formed by pore close-off at the firn-ice transition are less mobile than grain boundaries, causing bubble-boundary separation whenever geometric constraints are satisfied; however, such separation reduces grain-growth rates by only about 10%. The observed linear increase of grain area with time is thus predicted by theory, but the growth rate depends on soluble-impurity concentrations as well as on temperature.

Microstructure through an Ice Sheet

2013 ◽  
Vol 753 ◽  
pp. 481-484 ◽  
Author(s):  
Tobias Binder ◽  
Ilka Weikusat ◽  
Johannes Freitag ◽  
Christoph S. Garbe ◽  
Dietmar Wagenbach ◽  
...  
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Driving Forces ◽  
Boundary Migration ◽  
Ice Core ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Ice Cores ◽  
Grain Size Analysis ◽  
Size Analysis

Ice cores through an ice sheet can be regarded as a sample of a unique natural deformation experiment lasting up to a million years. Compared to other geological materials forming the earth‘s crust, the microstructure is directly accessible over the full depth. Controlled sublimation etching of polished ice sections reveals pores, air bubbles, grain boundaries and sub-grain boundaries at the surface. The microstructural features emanating at the surface are scanned. A dedicated method of digital image processing has been developed to extract and characterize the grain boundary networks. First preliminary results obtained from an ice core drilled through the Greenland ice sheet are presented. We discuss the role of small grains in grain size analysis and derive from the shape of grain boundaries the acting driving forces for grain boundary migration.

scholarly journals Radiocarbon dating of glacier ice

2016 ◽  
Author(s):  
Chiara Uglietti ◽  
Alexander Zapf ◽  
Theo M. Jenk ◽  
Sönke Szidat ◽  
Gary Salazar ◽  
...  
Keyword(s):  
Information Needs ◽  
Ice Core ◽  
Ice Cores ◽  
European Alps ◽  
Carbonaceous Aerosols ◽  
14C Dating ◽  
Tropical Regions ◽  
Annual Layer ◽  
Glacier Ice ◽  
Depth Relationship

Abstract. High altitude glaciers and ice caps from mid-latitudes and tropical regions contain valuable signals of past climatic and environmental conditions as well as human activities, but for a meaningful interpretation this information needs to be placed in a precise chronological context. For dating the upper part of ice cores from such sites several relatively precise methods exist, but they fail in the older and deeper part, where plastic deformation of the ice results in strong annual layer thinning and a non-linear age-depth relationship. If sufficient organic matter such as plant, wood or insect fragments were found, radiocarbon (14C) analysis had thus been the only option for a direct and absolute dating of deeper ice core sections. However such fragments are rarely found and even then very likely not at the depths and in the resolution desired. About 10 years ago, a new, complementary dating tool was therefore introduced by our group. It is based on extracting the μg-amounts of the water-insoluble organic carbon (WIOC) fraction of carbonaceous aerosols embedded in the ice matrix for subsequent 14C dating. Meanwhile this new approach was improved considerably, thereby reducing the measurement time and improving the overall precision. Samples with ~ 10 μg WIOC mass can now be dated with reasonable uncertainty of around 10–20 % (variable depending on sample age). This requires about 100 to 500 g of ice considering the WIOC concentrations typically found in mid- and low-latitude glacier ice. Dating polar ice with satisfactory age precision is still not possible since WIOC concentrations are around one order of magnitude lower. The accuracy of the 14C WIOC method was validated by applying it to independently dated ice. With this method the deepest parts of the ice cores from Colle Gnifetti and Mt. Ortles glacier in the European Alps, Illimani glacier in the Bolivian Andes, Tsambagarav ice cap in the Mongolian Altai, and Belukha glacier in the Siberian Altai have been dated. In all cases a strong annual layer thinning towards bedrock was observed and the oldest ages obtained were in the range of 10 000 yrs. 14C WIOC-dating was not only crucial for interpretation of the embedded environmental and climatic histories, but additionally gave a better insight into glacier flow dynamics close to bedrock and past glacier coverage. For this the availability of multiple dating points in the deepest parts was essential, which is the strength of the presented WIOC 14C-dating method, allowing determination of absolute ages from principally every piece of ice.

scholarly journals On the role of grain growth, recrystallization and polygonization in a continuum theory for anisotropic ice sheets

2004 ◽  
Vol 39 ◽  
pp. 49-52 ◽  
Author(s):  
Luca Placidi ◽  
Sérgio H. Faria ◽  
Kolumban Hutter
Keyword(s):  
Grain Boundary ◽  
Grain Growth ◽  
Boundary Migration ◽  
Ice Core ◽  
Continuum Theory ◽  
Ice Cores ◽  
Grain Boundary Migration ◽  
Bending Stresses ◽  
Continuum Description ◽  
Continuous Diversity

AbstractWe outline how to incorporate microscale effects of polycrystalline ice into a continuum description. Actually, analyses of ice cores in Antarctica show that different microstructures generally produce different responses, i.e. a non-uniform distribution of c axes gives rise to anisotropic behaviour. It has been recognized that, to describe certain microstructural processes, like recrystallization or polygonization, we need a parameter able to switch them on (e.g. dislocation density or its associated lattice distortion energy). With this in mind, balance equations for a continuum theory of an anisotropic ice sheet undergoing recrystallization have been recently proposed. In this work, we examine relations for some constitutive quantities, in order to take into account the effects of grain-boundary migration, nucleation and polygonization. We check our assumptions by explicit comparison with the first 1200 m of the Byrd (Antarctica) ice core. Current literature usually gives a relation between normal grain growth and grain boundary migration rate. Here, an equation for normal grain growth which also incorporates the influence of polygonization is suggested. It is based on experimental data from the same core in Antarctica. Polygonization is a microscopic process, but here we present a continuum description of the bending stresses which promote the fragmentation of crystallites in terms of the theory of mixtures with continuous diversity.

scholarly journals Application of AMS 14C Dating to Ice Core Research

Radiocarbon ◽  
1995 ◽  
Vol 37 (2) ◽  
pp. 637-641 ◽  
Author(s):  
A T. Wilson
Keyword(s):  
Ice Core ◽  
Ice Sheets ◽  
Ice Cores ◽  
Unexpected Result ◽  
Polar Ice ◽  
14C Dating ◽  
The Past ◽  
Accelerator Mass Spectrometer ◽  
Polar Ice Sheets ◽  
Ams 14C Dating

I describe here the use of the accelerator mass spectrometer (AMS) sublimation technique to 14C-date polar ice cores. An unexpected result of this work has been to extend the understanding of how polar ice sheets entrap and record the past composition of the Earth's atmosphere. This work has led to the discovery of a new phenomenon in which CO2 and other greenhouse gases can be entrapped in cold (never melted) polar ice sheets.

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