Rapid Microstructure Analysis of Polar Ice Cores

Krischke, Anja; Oechsner, Ulrich; Kipfstuhl, Sepp

doi:10.1002/opph.201500016

Cited by 14 publications

(9 citation statements)

References 2 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Since the effect of premelting is expected to start close to the Glacial-Eemian interface at about T > 262 K this paper (Part 1) focuses on the relatively cold Holocene and Glacial ice in the upper 2207 m of NEEM. The deeper, possibly pre-melted ice will be the subject of a companion paper (Part 2, Kuiper et al, 2020), which will analyze the combined effects of grain size and pre-melting on deformation in the NEEM ice core. The method of Heilbronner and Bruhn (1998) was used to convert 2D sectional areas to 3D volume fractions.…”

Section: Creep Regimementioning

confidence: 99%

“…7a). A transition temperature of 262 K was taken for both dislocation creep and GBS-limited creep, as this is the expected temperature threshold at which pre-melting starts to dominate ice rheology (see Kuiper et al, 2020). The modified flow law parameters for dislocation creep that are proposed here are shown in Table 2; the flow law parameters for GBS-limited creep are the same as given in Table 1 except for the temperature threshold.…”

Section: Creep Regimementioning

confidence: 99%

See 1 more Smart Citation

Using a composite flow law to model deformation in the NEEM deep ice core, Greenland – Part 1: The role of grain size and grain size distribution on deformation of the upper 2207 m

et al. 2020

View full text Add to dashboard Cite

Abstract. The effect of grain size on strain rate of ice in the upper 2207 m in the North Greenland Eemian Ice Drilling (NEEM) deep ice core was investigated using a rheological model based on the composite flow law of Goldsby and Kohlstedt (1997, 2001). The grain size was described by both a mean grain size and a grain size distribution, which allowed the strain rate to be calculated using two different model end-members: (i) the microscale constant stress model where each grain deforms by the same stress and (ii) the microscale constant strain rate model where each grain deforms by the same strain rate. The model results predict that grain-size-sensitive flow produces almost all of the deformation in the upper 2207 m of the NEEM ice core, while dislocation creep hardly contributes to deformation. The difference in calculated strain rate between the two model end-members is relatively small. The predicted strain rate in the fine-grained Glacial ice (that is, ice deposited during the last Glacial maximum at depths of 1419 to 2207 m) varies strongly within this depth range and, furthermore, is about 4–5 times higher than in the coarser-grained Holocene ice (0–1419 m). Two peaks in strain rate are predicted at about 1980 and 2100 m depth. The prediction that grain-size-sensitive creep is the fastest process is inconsistent with the microstructures in the Holocene age ice, indicating that the rate of dislocation creep is underestimated in the model. The occurrence of recrystallization processes in the polar ice that did not occur in the experiments may account for this discrepancy. The prediction of the composite flow law model is consistent with microstructures in the Glacial ice, suggesting that fine-grained layers in the Glacial ice may act as internal preferential sliding zones in the Greenland ice sheet.

show abstract

Section: Creep Regimementioning

confidence: 99%

Section: Creep Regimementioning

confidence: 99%

Using a composite flow law to model deformation in the NEEM deep ice core, Greenland – Part 1: The role of grain size and grain size distribution on deformation of the upper 2207 m

et al. 2020

View full text Add to dashboard Cite

show abstract

“…Calculations using the GSS composite flow law of Goldsby and Kohlstedt require grain size as an input variable. The grain size data in the lowest 540 m of the NEEM ice core were obtained using 224 large area scanning macroscope (LASM) images (Kipfstuhl, 2010) taken using reflective light macroscopy (Krischke et al, 2015). This method uses thermal etching by sublimation to reveal (sub)grain boundaries as grooves on the surface of the ice core sample (e.g.…”

Section: The Neem Ice Core and Ice Microstructure Datamentioning

confidence: 99%

Using a composite flow law to model deformation in the NEEM deep ice core, Greenland: Part 2 the role of grain size and premelting on ice deformation at high homologous temperature

Kuiper¹,

Bresser²,

Drury³

et al. 2019

Preprint

View full text Add to dashboard Cite

Abstract. The ice microstructure in the lower part of the North Greenland Eemian Ice Drilling (NEEM) ice core consists of relatively fine grained glacial ice with a single maximum crystallographic preferred orientation (CPO) alternated by much coarser grained Eemian ice with a partial girdle type of CPO. In this study, the grain size sensitive (GSS) composite flow law of Goldsby and Kohlstedt (2001) was used to study the effects of grain size and premelting on strain rate in the lower part of the NEEM ice core. The results show that the strain rates predicted in the fine grained glacial layers are about an order of magnitude higher than in the much coarser grained Eemian layers. The dominant deformation mechanisms between the layers is also different with basal slip accommodated by grain boundary sliding (GBS-limited creep) being the dominant deformation mechanism in the glacial layers, while GBS-limited creep and dislocation creep (basal slip accommodated by non-basal slip) contribute both roughly equally to bulk strain in the coarse grained layers. Due to the large difference in microstructure between the impurity-rich glacial ice and the impurity-depleted Eemian ice at premelting temperatures (T>262 K), it is expected that the fine grained layers deform mainly by simple shear at high strain rates, while the coarse grained layers are relatively stagnant. The difference in microstructure, and consequently in viscosity, between glacial and interglacial ice at temperatures just below the melting point can have important consequences for ice dynamics close to the bedrock.

show abstract

“…The NEEM deep ice core was chosen because a comprehensive light microscope data set was available (Kipfstuhl, 2010) enabled by a fast line scan technique with microscopic resolution (LASM -Large Area Scanning Macroscope; Krischke et al, 2015). From these LM images the grain size distribution is available (Binder et al, 2013).…”

Section: Study Site and Ice Microstructurementioning

confidence: 99%

Using a composite flow law to model deformation in the NEEM deep ice core, Greenland: Part 1 the role of grain size and grain size distribution on the deformation of Holocene and glacial ice

Kuiper

Weikusat

Bresser

et al. 2019

Preprint

View full text Add to dashboard Cite

Abstract. The effect of grain size on strain rate of ice in the upper 2207 m in the North Greenland Eemian Ice Drilling (NEEM) deep ice core was investigated using a rheological model based on the composite flow law of Goldsby and Kohlstedt (1997, 2001). The grain size was described by both a mean grain size and a grain size distribution, which allowed the strain rate to be calculated using two different model end members: (i) the micro-scale constant stress model where each grain deforms by the same stress and (ii) the micro-scale constant strain rate model where each grain deforms by the same strain rate. The model results show that basal slip accommodated by grain boundary sliding produces almost all of the deformation in the upper 2207 m of the NEEM ice core, while dislocation creep (basal slip accommodated by non-basal slip) hardly contributes to deformation. The difference in calculated strain rate between the two model end members is relatively small. The calculated strain rate in the fine grained glacial ice (1419–2207 m) varies strongly with depth and is about 4–5 times higher than in the coarser grained Holocene ice (0–1419 m). Two peaks in strain rate are predicted at about 1980 and 2100 m of depth. The results from the rheological model and microstructures in the glacial ice indicate that fine grained layers in the glacial ice will act as internal preferential sliding zones in the Greenland ice sheet.

show abstract

Rapid Microstructure Analysis of Polar Ice Cores

Cited by 14 publications

References 2 publications

Using a composite flow law to model deformation in the NEEM deep ice core, Greenland – Part 1: The role of grain size and grain size distribution on deformation of the upper 2207 m

Using a composite flow law to model deformation in the NEEM deep ice core, Greenland – Part 1: The role of grain size and grain size distribution on deformation of the upper 2207 m

Using a composite flow law to model deformation in the NEEM deep ice core, Greenland: Part 2 the role of grain size and premelting on ice deformation at high homologous temperature

Using a composite flow law to model deformation in the NEEM deep ice core, Greenland: Part 1 the role of grain size and grain size distribution on the deformation of Holocene and glacial ice

Contact Info

Product

Resources

About