scholarly journals Seasonal variability in ice crystal properties at NorthGRIP: a case study around 301 m depth

2003 ◽  
Vol 37 ◽  
pp. 119-122 ◽  
Author(s):  
Anders Svensson ◽  
Pauli Baadsager ◽  
Asbjørn Persson ◽  
Christine Schøtt Hvidberg ◽  
Marie-Louise Siggaard-Andersen
Keyword(s):  
Seasonal Variability ◽  
Ice Core ◽  
Ice Crystal ◽  
Axis Orientation ◽  
Annual Cycles ◽  
Average Value ◽  
The North ◽  
Chemical Impurities ◽  
Crystal Properties

AbstractThe aim of this case study is to quantify the seasonal variability in crystal properties and to discuss the reason for the variability. A continuous 1.10 m long vertical thin-section profile covering approximately five annual cycles has been obtained from the North Greenland Icecore Project (NorthGRIP) ice core at around 301 m depth. The crystal outline and the c-axis orientation of more than 13000 crystals in the profile have been measured on a new Australian automated ice-crystal analyzer. In 2.5 cm resolution we observe a strong seasonal variability in crystal areas of >30%deviation from the average value of 6.7 mm2. Each year, a band of smaller crystals is observed in ice deposited during spring. The area distribution function is found to be close to a lognormal distribution. The crystal areas are compared to the concentration of chemical impurities in the ice; at a 5 cm resolution, the best correlation is found with the concentration of Ca2+. Our results show no seasonal variability of the average c-axis orientation of ice crystals.

scholarly journals Study of an ice core to the bedrock in the accumulation zone of an Alpine glacier

1976 ◽  
Vol 17 (75) ◽  
pp. 13-28 ◽  
Author(s):  
M. Vallon ◽  
J.-R. Petit ◽  
B. Fabre
Keyword(s):  
Water Content ◽  
Ice Core ◽  
Ice Crystal ◽  
Vertical Orientation ◽  
Axis Orientation ◽  
Alpine Glacier ◽  
Small Crystals ◽  
Average Water ◽  
Intermediate Size ◽  
Average Size

AbstractA water table appearing every summer where the ice begins, at a gerpth of approximately 30 m, accelerates the transformation of firn into ice during the summer (80% of the ice formed every year appears in less than 2 months). The ice formed in this way contains from 0 to 0.6% water. The average water content increases gradually with the gerpth because of the heat of gerformation. But, near bedrock, between 180 and 187 m, the permeability of the blue ice is such that the water content drops (0.3% as compared to 1.3% between 160 and 180 m).From a gerpth of 33 m, a foliation of sedimentary origin gradually gervelops in the ice. Its dip increases regularly to a gerpth of 145 m. At 145 m it jumps sudgernly freom 20° to 40°, then at 170 m freom 40° to 65°, which can be explained by old modifications in the bergschrund. This foliation disappears near bedrock (180-187 m), where there are no bubbles in the ice.The average size of an ice crystal increases slowly in the firn, shows seasonal fluctuations between 30 and 50 m, then jumps freom a diameter of 1 or 2 mm to 10 or 20 mm between 50 and 80 m. Between 180 and 187 m, the ice is mager of large crystals (3-10 cm diameter; the figure, however, is probably inexact due to a recrystallization of the samples).The very strong sub-vertical orientation of the optic axes of the firn crystals disappears quickly, and freom 66 m on, in ice with large crystals, a fabric of multiple maxima appears (generally, 3 or 4 directions, forming a triangle or a rhombus). On the other hand, in the small crystals that form bands parallel to the plane of foliation, only one direction of preferential orientation can be seen, or two close to one another. Crystals of intermediate size (10 to 50 mm) generally have two directions of preferred orientation at an angle of approximately 50° to one another. No matter how big the crystals are, the angle between the most commonc-axis orientation and the vertical does not change freom 60 to 170 m gerpth.

scholarly journals Crystal Size and Orientation Patterns in the Wisconsin-Age Ice from Dye 3, Greenland

1988 ◽  
Vol 10 ◽  
pp. 109-115 ◽  
Author(s):  
C.C. Langway ◽  
H. Shoji ◽  
N. Azuma
Keyword(s):  
Crystal Size ◽  
Ice Core ◽  
Ice Crystal ◽  
Axis Orientation ◽  
Measuring Device ◽  
Thin Sections ◽  
Core Samples ◽  
Physical Measurements ◽  
Ice Crystal Size ◽  
Velocity Measuring

Crystal size and c-axis orientation patterns were measured on the Dye 3, Greenland, deep ice core in order to investigate time-dependent changes or alterations in the physical character of the core as a function of time after recovery. The physical measurements were expanded to include depth intervals not previously studied in the field. The recent study focused on core samples located between 1786 m and the bottom of the ice sheet at 2037 m.Manual c-axis measurements were made on 23 new thin sections using a Rigsby-type universal stage. A new semi-automatic ultrasonic wave-velocity measuring device was developed in order to compare the results with the earlier manual measurements and to study an additional 114 ice-core samples in the Wisconsin-age ice. Crystal-size measurements were made on specimen surfaces by inducing evaporation grooves at crystal boundaries and measuring linear intercepts. The ultrasonically measured test samples were subsequently cleaned and analyzed by ion chromatography in order to measure impurity concentration levels of Cl−, NO3− and SO42− and study their effects on crystal growth and c-axis orientation.

scholarly journals Complete determination of ice crystal orientation using Laue X-ray diffraction method

2011 ◽  
Vol 57 (201) ◽  
pp. 103-110 ◽  
Author(s):  
Atsushi Miyamoto ◽  
Ilka Weikusat ◽  
Takeo Hondoh
Keyword(s):  
Crystal Orientation ◽  
Ice Core ◽  
Ice Sheets ◽  
Diffraction Method ◽  
Ice Cores ◽  
Ice Crystals ◽  
Ice Crystal ◽  
X Ray Diffraction ◽  
Axis Orientation ◽  
X Ray

AbstractIce crystal orientation fabric data from ice cores contain important information concerning the internal structure and the flow behaviour of ice sheets. When ice cores are recovered from the Antarctic and Greenland ice sheets, crystal orientation measurements are performed immediately to obtain fundamental physical property information. In the past, we have measured the c-axis orientation of ice crystals by a manual optical method using a universal stage. This method is very time-consuming, involving tedious work in a cold laboratory. Recently, automated systems have been developed that enable measurement of c-axis orientation, grain size and other microstructures. However, in order to detect the full crystal orientation of an ice crystal, we also need information on its a-axis orientation. A variety of other crystal orientation measurement methods have previously been discussed, but some shortcomings for ice-core studies cannot be neglected. We have developed a crystal-orientation analysing device using the Laue X-ray diffraction method. As this device can measure the orientations of all crystal axes with high accuracy, it is possible to obtain new microstructure information on natural ice crystals. For the first time, we are able to quantify very low subgrain misorientation angles in polar ice-core samples, allowing us to investigate micro-deformation features of individual crystals. Here we discuss the analysis process, which is customized to measure standard ice thin sections, and show preliminary results.

scholarly journals Textures and fabrics in the Dome F (Antarctica) ice core

1999 ◽  
Vol 29 ◽  
pp. 163-168 ◽  
Author(s):  
N. Azuma ◽  
Y. Wang ◽  
K. Mori ◽  
H. Narita ◽  
T. Hondoh ◽  
...  
Keyword(s):  
Crystal Size ◽  
Ice Core ◽  
Clear Correlation ◽  
Crystal Shape ◽  
Ice Crystal ◽  
Axis Orientation ◽  
Thin Sections ◽  
Crystal Axis ◽  
Orientation Pattern ◽  
Comprehensive Study

AbstractA comprehensive study of ice-crystal fabrics and textures was conducted on the Dome F (Antarctica) ice core. Crystal ,-axis orientations, crystal sizes and crystal shape were measured on thin sections with an automatic ice-fabric analyzer. The general feature of textural and fabric development through a 2500 m long core was obtained by a 20 m interval study. Crystal size steadily increases with depth except for depths of about 500,1800, 2000, 2200 and 2300 m, at which depths crystal size decreases suddenly. There is a clear correlation between crystal-size and ´18O values. Crystals tend to elongate horizontally with depth, and the aspect ratio (long axis vs short axis of a grain) increases twofold at 1600 m depth and fluctuates below that depth. The .-axis orientation fabrics gradually change with depth from a random orientation pattern near the surface to a strong vertical single maximum at 2500 m. These are very similar to those from the GRIP (Greenland) core The observations of crystal shape and the fabric measurements indicate that nucleation-recrystallization does not take place at Dome F.

scholarly journals Ice crystal properties of amber ice and strain enhancement at the base of cold Antarctic glaciers

2005 ◽  
Vol 40 ◽  
pp. 185-190 ◽  
Author(s):  
Denis Samyn ◽  
Anders Svensson ◽  
Sean J. Fitzsimons ◽  
Reginald D. Lorrain
Keyword(s):  
Impurity Content ◽  
Ice Crystal ◽  
Fine Grained ◽  
Automated Method ◽  
Lattice Preferred Orientation ◽  
High Impurity ◽  
Deformation Properties ◽  
Crystal Properties ◽  
Analytical Accuracy

AbstractTo improve our understanding of the deformation properties of cold-based polar glaciers, we examine here some of the factors leading to the localization of strain within the amber ice facies. We present a crystallographic case study of amber ice (a fine-grained bubbly ice containing a relatively high impurity content) sampled at the base of two Antarctic glaciers. The crystal fabrics and textures of amber ice were computed by application of a recently developed automated method. To date, it was tedious and awkward to determine amber ice facies accurately because of the sub-millimetric crystal size and relatively high debris content of this facies. The authomatic analytical method applied in this study allows not only for improving analytical accuracy in this task but also for considerably reducing the time of analysis. Our investigations reveal highly homogeneous crystallographic properties for the studied amber ice. The ice crystals are mainly polygonal, equant and sub-millimetric, and show a strong lattice-preferred orientation. These properties, beside the relatively high impurity content, are likely to exert a major control on strain enhancement in amber ice when this facies is present at the base of cold glaciers.

scholarly journals Deadwood volume and quality in recreational forests: the case study of the Belgrade forest (Turkey)

2020 ◽  
Vol 29 (2) ◽  
pp. e008
Author(s):  
Selim Bayraktar ◽  
Alessandro Paletto ◽  
Antonio Floris
Keyword(s):  
Forest Management ◽  
Stand Age ◽  
Forest Types ◽  
Wood Decomposition ◽  
Average Value ◽  
The North ◽  
Management Objectives ◽  
Water Resource Conservation ◽  
Qualitative Characteristics

Aim of the study: The aim of this study is to understand quantitative and qualitative characteristics of deadwood in recreational forests.Area of study: Belgrade forest in the North of Istanbul city (Turkey).Material and methods: The data has been collected through a stratified sampling scheme that has randomly located 50 clusters formed by 3 sample plots each (150 sample plots).Main results: The results show an average deadwood volume of 16.49 m3 ha-1 (81.5% in logs, 16.4% in snags, 2.1% in stumps). The highest volume of deadwood is in oldest forests (age over 180 years) with an average value of 20.39 m3 ha-1, followed by forests with 61-120 years with 15.77 m3 ha-1. Concerning forest management objectives, the results show that average deadwood volume is 13.66 m3 ha-1 in the forest section managed for water resource conservation and 21.14 m3 ha-1 in the forest section managed for recreational purposes.Research highlights: Deadwood management in the recreational forests must consider both biodiversity conservation and recreational attractiveness of an area.Keywords: forest management; forest types; forest accessibility; stand age; wood decomposition rate.

scholarly journals A Lagrangian analysis of the present-day sources of moisture for major ice-core sites

2016 ◽  
Vol 7 (3) ◽  
pp. 549-558 ◽  
Author(s):  
Anita Drumond ◽  
Erica Taboada ◽  
Raquel Nieto ◽  
Luis Gimeno ◽  
Sergio M. Vicente-Serrano ◽  
...  
Keyword(s):  
North Atlantic ◽  
Ice Core ◽  
Specific Humidity ◽  
The Arctic ◽  
Lagrangian Analysis ◽  
Annual Cycles ◽  
The North ◽  
The Indian Ocean ◽  
The Antarctic ◽  
Evaporation Minus Precipitation

Abstract. A Lagrangian approach was used to identify the moisture sources for 14 ice-core sites located worldwide for the period of 1980–2012. The sites were classified into three domains: Arctic, Central (Andes, Alps, and Kilimanjaro), and Antarctic. The approach was used to compute budgets of evaporation minus precipitation by calculating changes in the specific humidity along 10-day backward trajectories. The results indicate that the oceanic regions around the subtropical high-pressure centres provide most of moisture, and their contribution varies throughout the year following the annual cycles of the centres. For the Arctic Domain, the sources lie in the subtropical North Atlantic and Pacific. The subtropical South Atlantic, Indian, and Pacific oceans provide moisture for the Antarctic Domain. The sources for South America are the Atlantic and South Pacific, for Europe the sources are in the Mediterranean and the North Atlantic, and for Asia the sources are the Indian Ocean and the Arabian Sea.

scholarly journals Crystal Size and Orientation Patterns in the Wisconsin-Age Ice from Dye 3, Greenland

1988 ◽  
Vol 10 ◽  
pp. 109-115 ◽  
Author(s):  
C.C. Langway ◽  
H. Shoji ◽  
N. Azuma
Keyword(s):  
Crystal Size ◽  
Ice Core ◽  
Ice Crystal ◽  
Axis Orientation ◽  
Measuring Device ◽  
Thin Sections ◽  
Core Samples ◽  
Physical Measurements ◽  
Ice Crystal Size ◽  
Velocity Measuring

Crystal size and c-axis orientation patterns were measured on the Dye 3, Greenland, deep ice core in order to investigate time-dependent changes or alterations in the physical character of the core as a function of time after recovery. The physical measurements were expanded to include depth intervals not previously studied in the field. The recent study focused on core samples located between 1786 m and the bottom of the ice sheet at 2037 m. Manual c-axis measurements were made on 23 new thin sections using a Rigsby-type universal stage. A new semi-automatic ultrasonic wave-velocity measuring device was developed in order to compare the results with the earlier manual measurements and to study an additional 114 ice-core samples in the Wisconsin-age ice. Crystal-size measurements were made on specimen surfaces by inducing evaporation grooves at crystal boundaries and measuring linear intercepts. The ultrasonically measured test samples were subsequently cleaned and analyzed by ion chromatography in order to measure impurity concentration levels of Cl−, NO3− and SO4 2− and study their effects on crystal growth and c-axis orientation.

scholarly journals Reconnaissance of chemical and isotopic firn properties on top of Berkner Island, Antarctica

1994 ◽  
Vol 20 ◽  
pp. 307-312 ◽  
Author(s):  
D. Wagenhach ◽  
W. Graf ◽  
A. Minikin ◽  
U. Trefzer ◽  
J. Kipfstuhl ◽  
...  
Keyword(s):  
Ice Core ◽  
Depth Resolution ◽  
Snow Accumulation ◽  
Weddell Sea ◽  
Sea Salt ◽  
The South ◽  
Ice Shelf ◽  
Annual Cycles ◽  
Ice Cap ◽  
The North

The ice cap on Berkner Island is grounded on bedrock within the Filchner-Ronne Ice Shelf and is, therefore, expected to be a well-suited place to retrieve long-term ice-core records reflecting the environmental situation of the Weddell Sea region. Shallow firn cores were drilled to 11 m at the two main summits of Berkner Island and analysed in high depth resolution for electrical d.c. conductivity(ECM), stable isotopes, chloride, sulphate, nitrate and methane-sulphonate (MSA).From the annual layering of δD and non-sea-salt (nss) sulphate, a mean annual snow accumulation of 26.6 cm water at the north dome and 17.4cm water at the south domeare obtained. As a result of ineffective wind scouring indicated by a relatively lownear-surface snow density, regular annual cycles are found for all species at least in the upper 4-5 m. Post-depositional changes are responsible for a substantial decrease o[the seasonal δD and nitrate amplitude as well as for considerable migration of the MSA signal operating below a depth of 3-4 m. The mean chemical and isotopic firn properties at the south dome correspond to the situation on the Filchner-Ronne Ice Shelf at a comparable distance to the coast, whereas the north dome is found to be much more influenced by maritime air masses. Persistent high sea-salt levels in winter snow at Berkner Island heavily obscure the determination of nss sulphate probably due to sulphate fractionation in the Antarctic sea-salt aerosol. Estimated time-scale spredict ages at 400 m depth to be ~2000 years for the north and ~3000 years for the south dome. Pleistocene ice is expected in the bottom 200 and 300 m, respectively.

scholarly journals A Lagrangian analysis of the present-day sources of moisture for major ice-core sites

2016 ◽  
Author(s):  
A. Drumond ◽  
E. Taboada ◽  
R. Nieto ◽  
L. Gimeno ◽  
S. M. Vicente-Serrano ◽  
...  
Keyword(s):  
North Atlantic ◽  
Ice Core ◽  
Specific Humidity ◽  
The Arctic ◽  
Lagrangian Analysis ◽  
Annual Cycles ◽  
The North ◽  
The Indian Ocean ◽  
The Antarctic ◽  
Evaporation Minus Precipitation

Abstract. A Lagrangian approach was used to identify the moisture sources for fourteen ice-core sites located worldwide for the period 1980–2012. The sites were classified into three domains: Arctic, Central (Andes, Alps and Kilimanjaro), and Antarctic. The approach was used to compute budgets of evaporation minus precipitation by calculating changes in the specific humidity along 10-day backward trajectories. The results indicate that the oceanic regions around the subtropical high-pressure centers provide most of moisture, and their contribution varies throughout the year following the annual cycles of the centers. For the Arctic domain, the sources lie in the subtropical North Atlantic and Pacific. The subtropical south Atlantic, Indian and Pacific provide moisture for the Antarctic domain. The sources for South America are the Atlantic and southern Pacific, for Europe the sources are in the Mediterranean and the north Atlantic, and for Asia the sources are the Indian Ocean and the Arabian Sea.

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