Metamorphism of stratified firn at Dome Fuji, Antarctica: A mechanism for local insolation modulation of gas transport conditions during bubble close off

Fujita, Shuji; Okuyama, Junichi; Hori, Akihiro; Hondoh, Takeo

doi:10.1029/2008jf001143

Cited by 79 publications

(160 citation statements)

References 73 publications

(170 reference statements)

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“…Freitag et al (2004) explained this feature as "cross-over" behavior, where initially low-density layers reach similar density values as initially high-density layers, the former compacting faster than the latter. This view is supported by findings of Gerland et al (1999) and Fujita et al (2009). However, a well-tested explanation, supported by detailed data comparison of density of layers from the near surface to layers from greater depths, is still lacking.…”

Section: Introductionsupporting

confidence: 60%

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On the impact of impurities on the densification of polar firn

Hörhold

Laepple

Freitag

et al. 2012

Earth and Planetary Science Letters

153

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Editor: P. DeMenocalKeywords: polar firn density densification impurity density variability Understanding polar firn densification is crucial for reconstructing the age of greenhouse gas concentrations extracted from ice cores, and for the interpretation of air in ice as a dating tool or as a climate proxy. Firn densification is generally modeled as a steady burial and sintering process of defined layers, where the structure of the layering is maintained along the whole firn and ice column. However, available high-resolution density data, as well as firn air samples, question this picture and point to a lack of understanding of firn densification. Based on analysis of high-resolution density and calcium concentration records from Antarctic and Greenland ice cores, we show for the first time that also impurities may have a significant impact on the densification. Analysis of firn cores shows a correlation between density and the calcium ion (Ca++) concentration, and this correlation increases with depth. The existence of this relationship is independent of the local climatic conditions at the core sites analyzed. The strong positive correlation between the density and the logarithm of Ca++ concentration indicates that impurities induce softening and lead to faster densification over a wide range of concentrations. In one core, the impurity effect manifests itself so strongly that the density develops a seasonal cycle closely following the seasonal cycle of Ca++. Our results clearly show that the structure of the firn layering changes with depth and suggest that the increased variability in density observed in deep firn, recently described as a universal feature of polar firn, may arise from the influence of Ca++ and/or other impurities. The impurity effect is likely to have direct implications on our understanding of glacial firn densification and on glacial gas age estimates.

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Section: Introductionsupporting

confidence: 60%

“…These variations are caused by size-dependent fractionation during the bubble close-off . Fujita et al (2009) link the initial layering at the surface (i.e. summer and winter layers) and the strength of insolation with the gas transport processes at close-off and the measured O2/N2 ratios.…”

Section: Discussionmentioning

confidence: 99%

On the impact of impurities on the densification of polar firn

Hörhold

Laepple

Freitag

et al. 2012

Earth and Planetary Science Letters

153

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“…Using open microwave resonators of the design of Jones (1976), Matsuoka et al (1996Matsuoka et al ( , 1997 measured the dielectric anisotropy of ice, which is caused by the c-axis orientation of the crystal fabric. With the same method, the dielectric anisotropy in snow, caused by a structural anisotropy of the ice matrix, has been measured and higher permittivities have been found in the vertical than the horizontal direction in multiyear firn on both the Greenland ice sheet (Fujita et al, 2014) and on the Antarctic ice sheet (Fujita et al, 2009(Fujita et al, , 2016; Fujita et al (2009) did the analysis in conjunction with a CT analysis. Using a method of microwave propagation, Lytle and Jezek (1994) also detected a higher vertical than horizontal permittivity in multiyear firn on the Greenland ice sheet combined with a photographic analysis.…”

Section: Field Observations Of the Dielectric Anisotropymentioning

confidence: 99%

“…Vertical as well as horizontal structures have been found in artificial snow from the cold laboratory as well as in natural seasonal snow (Calonne et al, 2012). In polar firn, vertical structures are commonly found in firn cores at different depths (e.g., Hörhold et al, 2009;Fujita et al, 2009;Lomonaco et al, 2011).…”

Section: Observations Of the Structural Anisotropymentioning

confidence: 99%

Anisotropy of seasonal snow measured by polarimetric phase differences in radar time series

Leinß

Löwe²,

Proksch³

et al. 2016

The Cryosphere

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Abstract. The snow microstructure, i.e., the spatial distribution of ice and pores, generally shows an anisotropy which is driven by gravity and temperature gradients and commonly determined from stereology or computer tomography. This structural anisotropy induces anisotropic mechanical, thermal, and dielectric properties. We present a method based on radio-wave birefringence to determine the depth-averaged, dielectric anisotropy of seasonal snow with radar instruments from space, air, or ground. For known snow depth and density, the birefringence allows determination of the dielectric anisotropy by measuring the copolar phase difference (CPD) between linearly polarized microwaves propagating obliquely through the snowpack. The dielectric and structural anisotropy are linked by MaxwellGarnett-type mixing formulas. The anisotropy evolution of a natural snowpack in Northern Finland was observed over four winters (2009)(2010)(2011)(2012)(2013) with the ground-based radar instrument "SnowScat". The radar measurements indicate horizontal structures for fresh snow and vertical structures in old snow which is confirmed by computer tomographic in situ measurements. The temporal evolution of the CPD agreed in ground-based data compared to space-borne measurements from the satellite TerraSAR-X. The presented dataset provides a valuable basis for the development of new snow metamorphism models which include the anisotropy of the snow microstructure.

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“…On the contrary, at the end of spring, the increase of snow temperature causes significant metamorphism, which leads to an overall decrease of snow SSA (e.g. Picard et al, 2012), densification (Fujita et al, 2009) and other morphological changes of the surface snow (Gow, 1965). As a result, albedo decreases by several percents (Jin et al, 2008;Wang and Zender, 2011), which significantly alters the surface energy budget of the snowpack .…”

Section: Introductionmentioning

confidence: 99%

Summertime evolution of snow specific surface area close to the surface on the Antarctic Plateau

et al. 2015

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Abstract. On the Antarctic Plateau, snow specific surface area (SSA) close to the surface shows complex variations at daily to seasonal scales which affect the surface albedo and in turn the surface energy budget of the ice sheet. While snow metamorphism, precipitation and strong wind events are known to drive SSA variations, usually in opposite ways, their relative contributions remain unclear. Here, a comprehensive set of SSA observations at Dome C is analysed with respect to meteorological conditions to assess the respective roles of these factors. The results show an average 2-to-3-fold SSA decrease from October to February in the topmost 10 cm in response to the increase of air temperature and absorption of solar radiation in the snowpack during spring and summer. Surface SSA is also characterized by significant daily to weekly variations due to the deposition of small crystals with SSA up to 100 m 2 kg −1 onto the surface during snowfall and blowing snow events. To complement these field observations, the detailed snowpack model Crocus is used to simulate SSA, with the intent to further investigate the previously found correlation between interannual variability of summer SSA decrease and summer precipitation amount. To this end, some Crocus parameterizations have been adapted to Dome C conditions, and the model was forced by ERAInterim reanalysis. It successfully matches the observations at daily to seasonal timescales, except for the few cases when snowfalls are not captured by the reanalysis. On the contrary, the interannual variability of summer SSA decrease is poorly simulated when compared to 14 years of microwave satellite data sensitive to the near-surface SSA. A simulation with disabled summer precipitation confirms the weak influence in the model of the precipitation on metamorphism, with only 6 % enhancement. However, we found that disabling strong wind events in the model is sufficient to reconciliate the simulations with the observations. This suggests that Crocus reproduces well the contributions of metamorphism and precipitation on surface SSA, but snow compaction by the wind might be overestimated in the model.

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Metamorphism of stratified firn at Dome Fuji, Antarctica: A mechanism for local insolation modulation of gas transport conditions during bubble close off

Cited by 79 publications

References 73 publications

On the impact of impurities on the densification of polar firn

On the impact of impurities on the densification of polar firn

Anisotropy of seasonal snow measured by polarimetric phase differences in radar time series

Summertime evolution of snow specific surface area close to the surface on the Antarctic Plateau

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