Ice Texture Research Articles

Cometary ice texture and the thermal evolution of comets

KOSI comet simulation experiments have shown strong evidence for significant modifications of the texture of porous ice within typical experiment durations of a few ten hours. Initially, the textures of the fluffy ice samples were obviously not in their equilibrium states. During the cause of the experiments the textures modified through growth of the bond sizes between individual grains which caused significant increases in compressive strength and intrinsic thermal conductivity. The near-surface layers of cometary nuclei may evolve similarly as they are heated during perihelion passage. As a consequence, the heat wave may penetrate into increasingly deeper layers to depths greater than generally expected.

The nutrient status in sea ice of the Weddell Sea during winter: effects of sea ice texture and algae

Cores and brine samples from sea ice of the Weddell Sea were analyzed for nutrients (phosphate, nitrate and silicate), salinity and chlorophyll a during winter. Stratigraphic analyses of the cores were also carried out. Bulk nutrient concentrations in the sea ice fluctuated widely and did not correlate with salinity. Nutrient concentrations in cores were normalized to sea-water salinity to facilitate comparison. They varied between zero and two or three times those measured in the water column. Differentiation into young and old sea ice, however, revealed that nutrient concentrations in the young ice in many cases corresponded to those in surface seawater. In older ice, nutrients showed signs of increase as well as depletion or exhaustion relative to the water column. Differentiation of core sections according to ice textural classes and analyses of brine samples clarified some relationships between nutrients, salinity and algal biomass. Most of the changes in the nutrient concentrations are attributed to an increase in biological activity as the seasons progress. Silicate is expected to become the first nutrient likely to limit growth of diatoms in the ice which is ascribed to slower regeneration or dissolution of this nutrient relative to phosphate and nitrate. A consequence of silicate exhaustion may be the succession of different algal assemblages, from a diatom dominated community to one in which autotrophic flagellates form the largest component.

The sea ice thickness distribution in the northwestern Weddell Sea

We present new data on distribution of snow and sea ice thicknesses in the northwestern Weddell Sea. The data were obtained through direct measurements along 19 profiles, each approximately 100 m long on 17 different floes located between 54°–46°W and 59°–64°S. The overall probability density functions (PDFs) for ice thicknesses reflect the complex mixture of first‐, second‐, and multi‐year ice to be expected in the outflowing branch of the Weddell Gyre. Further differentiation of the data reveals four distinct thickness classes which reflect differences in the formation and subsequent histories of the ice encountered. These classes (I–IV) represent strongly deformed first year ice, less deformed first‐ and second‐year ice, and deformed second‐ or multi‐year ice, respectively. Each of the classes is characterized by a specific set of quantities related to ice texture and surface snow characteristics and by distinct PDFs for snow and ice thicknesses. In addition, geometric surface and bottom roughness characteristics differ significantly for each of the floe classes.

18O Concentrations In Sea Ice Of The Weddell Sea, Antarctica

AbstractWe present data on ice texture, salinity, and δ18O obtained from identical sections of ice cores during the Winter Weddell Sea Project 1986 on RV Polarstern from July through August 1986, in the longitude range between 5°W. and 7°E. We find no uniquely definable relationship between δ18O values and ice texture in a particular section. However, most of the snow ice as well as some sections of frazil ice are found to have negative δ18O concentrations. This is due to varying degrees of admixtures of meteoric ice (snow) and sea-water during formation of snow ice. In contrast to common assumptions, our results seem to indicate that a snow cover contributes positively to sea-ice growth rather than slowing down the overall growth rate. Based on a simple model, we have estimated the contributions of meteoric ice (mean of 3 ± 3%) and the combined meteoric ice/sea-water fraction (a minimum of 7 ± 6%) to the total ice thickness for the majority of the sampled floes. Although this is only a moderate contribution to the overall mass balance, in the absence of congelation growth it nevertheless enhances ice growth in general. This hypothesis is independently supported by our snow- and ice-thickness data (Wadhams and others, 1987), which demonstrate that the depression of the snow/ice interface below the water line (i.e. a negative freeboard) and the formation of snow ice is a common occurrence in the Weddell Sea. Therefore, we hypothesize that the major part of the observed apparent increase in ice thickness between our inbound and outbound tracks of WWSP’86 may not be derived from “regular”, thermodynamically driven congelation growth, but rather from the snow-ice component in floes of the Weddell Sea.

Ice Core Evidence for Extensive Melting of the Greenland Ice Sheet in the Last Interglacial

Evidence from ice at the bottom of ice cores from the Canadian Arctic Islands and Camp Century and Dye-3 in Greenland suggests that the Greenland ice sheet melted extensively or completely during the last interglacial period more than 100 ka (thousand years ago), in contrast to earlier interpretations. The presence of dirt particles in the basal ice has previously been thought to indicate that the base of the ice sheets had melted and that the evidence for the time of original growth of these ice masses had been destroyed. However, the particles most likely blew onto the ice when the dimensions of the ice caps and ice sheets were much smaller. Ice texture, gas content, and other evidence also suggest that the basal ice at each drill site is superimposed ice, a type of ice typical of the early growth stages of an ice cap or ice sheet. If the present-day ice masses began their growth during the last interglacial, the ice sheet from the earlier (Illinoian) glacial period must have competely or largely melted during the early part of the same interglacial period. If such melting did occur, the 6-meter higher-than-present sea level during the Sangamon cannot be attributed to disintegration of the West Antarctic ice sheet, as has been suggested.

Basic Properties of Antarctic Sea Ice as Revealed by Textural Analysis of Ice Cores

Sea ice constitutes a major element in the atmospheric, oceanographic and biological regime of the polar regions. Assessment of its fundamental properties requires interdisciplinary investigations on local, regional and global scales. Sea-ice structure and textural parameters of individual ice cores play a key role in such investigations. A proper characterization of sea-ice micro-structure is essential for an adequate classification of ice cores, an understanding of the growth processes of the sampled floe, and the identification of possible relationships between ice texture, and the physical, chemical and biological properties of sea ice. Investigations on ice cores which were obtained during three recent Antarctic expeditions (1983–85) in coastal waters of the eastern and southern Weddell Sea are reported. The basis for a number of physical, chemical and biological investigations is an assessment of the textural characteristics of each sea-ice core. These are derived by inspection of continuous thick sections, supplemented by an analysis of selected vertical and horizontal thin sections. Major results of this study can be summarized as follows: (i) in addition to the common ice classes, another sea-ice type, platelet ice, is identified; it is apparently unique to the coastal waters of Antarctica, near the ice-shelf edge, and (ii) different physical, chemical and biological sea-ice properties vary systematically with and are probably related to / controlled by the ice texture of the cores.

Basic Properties of Antarctic Sea Ice as Revealed by Textural Analysis of Ice Cores

Sea ice constitutes a major element in the atmospheric, oceanographic and biological regime of the polar regions. Assessment of its fundamental properties requires interdisciplinary investigations on local, regional and global scales. Sea-ice structure and textural parameters of individual ice cores play a key role in such investigations. A proper characterization of sea-ice micro-structure is essential for an adequate classification of ice cores, an understanding of the growth processes of the sampled floe, and the identification of possible relationships between ice texture, and the physical, chemical and biological properties of sea ice. Investigations on ice cores which were obtained during three recent Antarctic expeditions (1983–85) in coastal waters of the eastern and southern Weddell Sea are reported. The basis for a number of physical, chemical and biological investigations is an assessment of the textural characteristics of each sea-ice core. These are derived by inspection of continuous thick sections, supplemented by an analysis of selected vertical and horizontal thin sections. Major results of this study can be summarized as follows: (i) in addition to the common ice classes, another sea-ice type, platelet ice, is identified; it is apparently unique to the coastal waters of Antarctica, near the ice-shelf edge, and (ii) different physical, chemical and biological sea-ice properties vary systematically with and are probably related to / controlled by the ice texture of the cores.

Discontinuous Flow, Ice Texture, and Dirt Content in the Basal Layers of the Devon Island Ice Cap

AbstractSurface-to-bedrock cores obtained with a CRREL thermal drill were taken in 1972 and 1973 from the top of the Devon Island ice cap. There are very pronounced variations in oxygen isotope, micro-particle concentration, and ice texture in the lowermost 5 m of the core. There is a section of isotopically cold, very fine bubbly ice with high micro-particle concentrations between 2.6 and 4.4 m above the bed, considered to represent the Last Ice Age. There is coarse, isotopically warm, clean ice above and below this. For 1.2 m above the bed, the ice is finer again with high micro-particle concentrations but it shows very low bubble concentration and is isotopically the warmest in the core. While the broad variations are common to both cores, in detail there are significant variations despite the fact that the cores were taken only 27 m apart. The variations, when analysed statistically, show that at least 25–30% of the originally continuous profile is missing from each core. Faulting within the near-bedrock ice may be responsible for some of the effect but bubble fabric also gives evidence for irregular non-laminar flow. Because of the strong relationship between crystal size and micro-particle concentrations in the Devon Island cores, it is suggested that the fine-grained nature of dirty layers in the Antarctic and Greenland ice sheets is due to the effect of the dirt inclusions and not of shearing. Steep isotopic gradients in the Devon Island cores are shown to be evidence for possible shearing, which does not effect any change in the crystal texture. Clear ice near the bed is considered a tectonic feature, but the lack of effect on its bed by the ice cap confirms the non-erosional nature of an ice cap frozen to its bed.In terms of paleoclimatic history, it means that, because of bedrock effects, ice caps of intermediate depth (i.e. <400 m) can give continuous information only over the last approximate 5 000 years. Between 5 000 and 10 000 B.P. the time series becomes slightly discontinuous and beyond 10 000 B.P. so discontinuous as to allow only broad climatic inferences to be drawn.

Discontinuous Flow, Ice Texture, and Dirt Content in the Basal Layers of the Devon Island Ice Cap

AbstractSurface-to-bedrock cores obtained with a CRREL thermal drill were taken in 1972 and 1973 from the top of the Devon Island ice cap. There are very pronounced variations in oxygen isotope, micro-particle concentration, and ice texture in the lowermost 5 m of the core. There is a section of isotopically cold, very fine bubbly ice with high micro-particle concentrations between 2.6 and 4.4 m above the bed, considered to represent the Last Ice Age. There is coarse, isotopically warm, clean ice above and below this. For 1.2 m above the bed, the ice is finer again with high micro-particle concentrations but it shows very low bubble concentration and is isotopically the warmest in the core. While the broad variations are common to both cores, in detail there are significant variations despite the fact that the cores were taken only 27 m apart. The variations, when analysed statistically, show that at least 25–30% of the originally continuous profile is missing from each core. Faulting within the near-bedrock ice may be responsible for some of the effect but bubble fabric also gives evidence for irregular non-laminar flow. Because of the strong relationship between crystal size and micro-particle concentrations in the Devon Island cores, it is suggested that the fine-grained nature of dirty layers in the Antarctic and Greenland ice sheets is due to the effect of the dirt inclusions and not of shearing. Steep isotopic gradients in the Devon Island cores are shown to be evidence for possible shearing, which does not effect any change in the crystal texture. Clear ice near the bed is considered a tectonic feature, but the lack of effect on its bed by the ice cap confirms the non-erosional nature of an ice cap frozen to its bed.In terms of paleoclimatic history, it means that, because of bedrock effects, ice caps of intermediate depth (i.e. <400 m) can give continuous information only over the last approximate 5 000 years. Between 5 000 and 10 000 B.P. the time series becomes slightly discontinuous and beyond 10 000 B.P. so discontinuous as to allow only broad climatic inferences to be drawn.

The Debris-Laden Ice at the Bottom of the Greenland Ice Sheet

Abstract The Camp Century, Greenland, ice core was recovered from a bore hole which extended 1 375 m from the surface of the Greenland ice sheet to the ice/sub-ice interface. The bottom 15.7 m of the core contain over 300 alternating bands of clear and debris-laden ice. The size of the included debris ranges from particles less than 2 μm in diameter to particle aggregates which are a maximum of 3 cm in diameter: the average debris concentration is 0.24º º by weight. The debris size, concentration, and composition indicate that the debris originates from the till-like material directly below the debris-laden ice. The total gas concentration averages 51 ml/kg ice compared to the average of 101 ml/kg ice for the top 1 340 m. The gas composition of debris-bearing ice has apparently been modified by the oxidation of methane as reflected by traces of methane, high CO2 levels, and low O2 levels with respect to atmospheric air. Argon, which is not affected by the oxidation, shows an enrichment in samples with lower gas concentrations. Both the low gas concentrations in the debris-laden zone and the argon enrichment may be explained by the downward diffusion of gases from bubbly glacier ice into an originally bubble-free zone of refrozen debris-laden ice. Ice texture and ice-fabric analyses reveal extremely fine-grained ice and highly preferred crystal orientation in the lowermost 10 m of the core, indicating a zone of high deformation.

The Debris-Laden Ice at the Bottom of the Greenland Ice Sheet

AbstractThe Camp Century, Greenland, ice core was recovered from a bore hole which extended 1 375 m from the surface of the Greenland ice sheet to the ice/sub-ice interface. The bottom 15.7 m of the core contain over 300 alternating bands of clear and debris-laden ice. The size of the included debris ranges from particles less than 2 μm in diameter to particle aggregates which are a maximum of 3 cm in diameter: the average debris concentration is 0.24ººby weight. The debris size, concentration, and composition indicate that the debris originates from the till-like material directly below the debris-laden ice. The total gas concentration averages 51 ml/kg ice compared to the average of 101 ml/kg ice for the top 1 340 m. The gas composition of debris-bearing ice has apparently been modified by the oxidation of methane as reflected by traces of methane, high CO2levels, and low O2levels with respect to atmospheric air. Argon, which is not affected by the oxidation, shows an enrichment in samples with lower gas concentrations. Both the low gas concentrations in the debris-laden zone and the argon enrichment may be explained by the downward diffusion of gases from bubbly glacier ice into an originally bubble-free zone of refrozen debris-laden ice. Ice texture and ice-fabric analyses reveal extremely fine-grained ice and highly preferred crystal orientation in the lowermost 10 m of the core, indicating a zone of high deformation.

Fabric Analysis of a Core from the Meighen Ice cap, Northwest Territories, Canada

AbstractIce samples from a 121 m core, representing the total thickness of the Meighen Ice Cap near its highest point, were studied for ice fabric, firn- and dirt-layer distribution. The absence of a strongly preferred fabric between the surface and the base of the ice cap at the core site suggests an absence of past or present ice movement at this point. From the variations of ice texture, am- and dirt-layer distribution with depth it is concluded that the ice cap post-dates the climatic optimum and has never been much thicker than it is at present. There is a possible relic ablation surface at a depth of 50 m which is estimated to be at least 500–600 years old.

Fabric Analysis of a Core from the Meighen Ice cap, Northwest Territories, Canada

AbstractIce samples from a 121 m core, representing the total thickness of the Meighen Ice Cap near its highest point, were studied for ice fabric, firn- and dirt-layer distribution. The absence of a strongly preferred fabric between the surface and the base of the ice cap at the core site suggests an absence of past or present ice movement at this point. From the variations of ice texture, am- and dirt-layer distribution with depth it is concluded that the ice cap post-dates the climatic optimum and has never been much thicker than it is at present. There is a possible relic ablation surface at a depth of 50 m which is estimated to be at least 500–600 years old.

Relation of Temperature of Ice Cream to the Distribution of Certain of its Components Between the Liquid and Solid Phases

The of ice results in physical changes, most important of which, from the point of view of the texture of ice cream, is the manner in which the ice is formed. Many discussions on freezing ice cream deal largely with factors affecting the whipping properties of mixes, but give little consideration to the actual itself. Literally speaking, does not start until ice begins to form and is not completed, providing the temperature is lowered sufficiently, until all of the free water has been changed to ice. This report is confined largely to a consideration of the relation of temperature to the distribution of various components of the mix between the liquid and solid phases. The amount of ice formed at certain temperatures and the rate at which crystallization takes place are considered in relation to their influence upon the quality of ice manufactured under commercial conditions. I t is recognized, however, that ice texture is influenced by factors other than methods of freezing.