Grain Growth in Polar Ice: II. Application

Alley, Richard B.; Perepezko, J. H.; Bentley, C. R.

doi:10.3189/s0022143000012132

Cited by 50 publications

(63 citation statements)

References 35 publications

(86 reference statements)

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“…Although the detailed estimates of ice grain size in clean and dirty ice vary from core to core (clean, interglacial ice has d $ 0.8 to 4 mm, whereas dusty, cloudy, glacial ice has d $ 0.6 to 3.5 mm); within each core, grains in impurity-laden ice are invariably smaller than those in clean ice. These values lend support to the ''rule of thumb'' within the glacial community that ice that looks dirty, cloudy, or bubbly has smaller grains than ice that looks clear and clean [Alley et al, 1986a[Alley et al, , 1986b.…”

Section: Effect Of Impuritiessupporting

confidence: 59%

Convection in ice I shells and mantles with self‐consistent grain size

Barr

McKinnon²

2007

J. Geophys. Res.

106

111

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[1] The viscosity of ice I is grain size dependent for temperature and stress conditions appropriate for ice I shells and mantles of large and midsized icy satellites. Satellite thermal evolution, heat flux, critical shell thickness for convection, brittle/ductile transition temperature, and potential for surface deformation are therefore grain size dependent. Using measured grain sizes from terrestrial ice sheets experiencing temperature and strain rate conditions similar to convecting ice shells in icy satellites, we develop two end-member models of grain size and its evolution. In the absence of non-water ice impurities, grain size in a convecting ice shell of a large icy satellite will evolve over time to an equilibrium value, which we determine to be between 30 and 80 mm, because of dynamic recrystallization. Such large grains imply viscous ice, so convection in an ice shell thinner than 35 km in a large icy satellite such as Ganymede and Callisto would be sluggish at best and may cease after a few convective overturns (if it starts). Soluble ions and silicate microparticles may keep grains small, however, of order 1-5 mm, and permit convection in shells as thin as 30 km in large icy satellites. The dynamic recrystallization model provides a plausible upper limit on grain size in a geodynamically evolved ice shell, whereas grain sizes from dust-contaminated terrestrial ice cores provide a plausible lower limit on grain size in an icy satellite. On the basis of these constraints, grain sizes in evolved ice shells of large water ice satellites, in the absence of tidal forcing, should be of order 1 mm to 10 cm.

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Section: Effect Of Impuritiessupporting

confidence: 59%

Convection in ice I shells and mantles with self‐consistent grain size

Barr

McKinnon²

2007

J. Geophys. Res.

106

111

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“…The drag effects of impurities, discussed below, thus appear to be a and concluded that the dust concentration in polar ice cores was too low to have a significant effect on grain growth rates. On the other hand,Alley et al [1986b] concluded that higher concentrations of soluble impurities, mainly chloride and sulphate, in Wisconsin ice from the Dome C ice core slowed the migration of grain boundaries and thereby reduced grain growth rates. variations in the core can be assumed to mirror those in dust quite closely.…”

mentioning

confidence: 99%

Textures and fabrics in the GRIP ice core

Þorsteinsson¹,

Kipfstuhl²,

Miller³

1997

J. Geophys. Res.

249

297

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Abstract. A comprehensive study of textures and fabrics has been carried out on the Greenland Ice Core Project (GRIP) ice core. Crystal sizes and c axis orientations have been measured on thin sections with conventional techniques, yielding new information on the growth, rotation and recrystallization of ice crystals in the Greenland Ice Sheet. Normal grain growth is found to persist to a depth of 700 m in the core, where the onset of polygonization due to increasing strain prevents a further increase in grain size in the Holocene ice. Smaller crystals are observed in the Wisconsin ice, larger crystals are found in the Eemian ice, and the crystal size is found to vary with climatic parameters in these periods. This dependence, which probably results from variable impurity content in the ice, persists to a depth of 2930 m. Coarse-grained ice, probably resulting from rapid growth of crystals at comparatively high temperatures, is found in the lowest 100 m of the core. The data on c axis orientations reveal a steady evolution of the fabric from random near the surface to a strong single maximum in the lower part of the ice sheet. A significant strengthening is not observed at the Holocene-Wisconsin transition. The fabric development indicates that vertical compression at the ice divide is the main mode of deformation down to a depth of 2850 m. The evolution toward a single maximum fabric hardens the ice against vertical compression but softens it against simple shear. Evidence of simple shear deformation is clearly observed between 2850 m and 2950 m depth. Stretched fabrics in coarse-grained ice in the lowest 100 m could be due to tensional stresses; this ice is unlikely to be undergoing any significant horizontal deformation at the present time.

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“…During this open system refreezing, most of the gases remain dissolved into the water reservoir, although the TGC of DRL is slightly higher (2-6 mL gas kg −1 ice , Fig. 2c of small crystals reflects the inhibition of their normal grain growth from the presence of debris (Alley et al, 1986). While the melting-refreezing DRL have to be formed at the ice-sediment interface, several processes have been proposed to explain their occurrence higher up in the basal ice sequence.…”

Section: A Scenario For the Build-up Of The Neem Basal Ice Sequencementioning

confidence: 99%

A comprehensive interpretation of the NEEM basal ice build-up using a multi parametric approach

Goossens¹,

Sapart²,

Dahl‐Jensen³

et al. 2015

Preprint

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Basal ice is a common expression to describe bottom ice layers of glaciers, ice caps and ice sheets in which the ice is primarily conditioned by processes operating at the bed. It is chemically and/or physically distinct from the ice above and can be characterized by a component of basally derived sediments. The study of basal ice properties provides a rare opportunity to improve our understanding of subglacial environments and processes and to refine ice sheet behaviour modelling. Here, we present and discuss the results of water stable isotopes (δ 18 O and δD), ice fabrics, debris weight/size distribution and gas content of the basal part of the NEEM (North Greenland Eemian Ice Drilling Project) ice core. Below a depth of 2533.85 m, almost 10 m of basal debris-rich material was retrieved from the borehole, and regular occurrence of frozen sediments with only interstitial ice lenses in the bottom 5 m suggest that the ice-bedrock interface was reached. The sequence is composed of an alternation of three visually contrasting types of ice: clear ice with specks (very small amounts) of particulate inclusions, stratified debrisrich layers and ice containing dispersed debris. The use of water stable isotope signatures (δ 18 O and δD), together with other parameters, allows discrimination between the different types of ice and to unravel the processes involved in their formation and transformation. The basal debris-rich material presents δ 18 O values [−39.9 ‰; −34.4 ‰] within the range of the above last 300 m of unaltered meteoric ice [−44.9 ‰; −30.6 ‰] spanning a glacial-interglacial range of values. This rules out the hypothesis of a basal ice layer originating from pre-ice sheet ice overridden by the growing ice sheet, as previously suggested e.g. in the case of GRIP (Greenland Ice Core Project). We show that clear basal ice with specks corresponds to altered meteoric glacial ice where some of the climatic signal could have been preserved. However, the stratified debris-rich layers and the ice containing dispersed debris layers respectively express an "open" or "closed" system melting/refreezing signature, somewhat blurred by mixing processes in the upper part of the sequence. Climatic reconstruction is therefore prohibited from these ice types. We propose a first interpretative framework for the build-up of the NEEM basal ice sequence, based on the origin of the various ice types.

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Grain Growth in Polar Ice: II. Application

Cited by 50 publications

References 35 publications

Convection in ice I shells and mantles with self‐consistent grain size

Convection in ice I shells and mantles with self‐consistent grain size

Textures and fabrics in the GRIP ice core

A comprehensive interpretation of the NEEM basal ice build-up using a multi parametric approach

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