Modelling of the densification of polar firn: characterization of the snow–firn transition

Arnaud, Laurent; Lipenkov, V. Ya.; Barnola, Jean-Marc; Gay, Michel; Duval, Paul

doi:10.1017/s026030550001452x

Cited by 38 publications

(60 citation statements)

References 15 publications

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“…We have used the Herron and Langway density-depth model in the diffusion model after comparing 5 density depth models. We found that the model of Arnaud et al (1998), Pimienta (Barnola et al, 1992 and Herron and Langway, (1980) pro-Fig. 12.…”

Section: Discussionmentioning

confidence: 68%

“…7 represent the ten firn sites used in this study. Here, the accumulation ranges from 0 to 1.2 m.w.eq.a −1 and temperature from 210 to 260 K. The figure indicates that the rather uncommon combination of low temperature and high accumulation will generally result in a deeper PCOD, which is consisted with other density depth models (Arnaud et al, 1998;Barnola et al, 1991;Kameda et al, 1994;Craven and Allison, 1998;and Spencer et al, 2001). This uncommon combination can explain the relatively deep PCOD at the South Pole (119 m) compared to Site M and Dome C (98.6 m).…”

Section: Results For Densitymentioning

confidence: 84%

“…In literature a number of density models are described in the past. Most of these density models are based on semi-empirical relations, like Herron and Langway (1980), Barnola et al (1991)(density model of Pimienta), Kameda et al (1994), Craven and Allison (1998) and Spencer et al (2001), whereas the density model of Arnaud et al (1998) relays on the physical processes of grain-boundary sliding and power-law creep. Because all these density-models use meteorological parameters (temperature, accumulation, surface pressure and wind speed) as input parameters, they can all be used in this study.…”

Section: Comparison Study Of Several Density-depth Modelsmentioning

confidence: 99%

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Model calculations of the age of firn air across the Antarctic continent

Kaspers¹,

Wal²,

Broeke³

et al. 2004

Preprint

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Abstract. The age of firn air in Antarctica at pore close-off depth is only known for a few specific sites where firn air has been sampled for analyses. We present a model that calculates the age of firn air at pore close-off depth for the entire Antarctic continent. The model basically uses four meteorological parameters as input (surface temperature, pressure, accumulation rate and wind speed). Using parameterisations for surface snow density, pore close-off density and tortuosity, in combination with a density-depth model and data of a regional atmospheric climate model, distribution of pore close-off depth for the entire Antarctic continent is determined. The deepest pore close-off depth was found for the East Antarctic Plateau near 72° E, 82° S, at 150±15 m (2σ). A firn air diffusion model was applied to calculate the age of CO2 at pore close-off depth. The results predict that the oldest firn gas (CO2 age) is located between Dome Fuji, Dome Argos and Vostok at 43° E, 78° S being 148±23 (1σ or 38 for 2σ) years old. At this location an atmospheric trace gas record should be obtained. In this study we show that methyl chloride could be recorded with a predicted length of 125 years as an example for trace gas records at this location. The longest record currently available from firn air is derived at South Pole, being 80 years. Sensitivity tests reveal that the locations with old firn air (East Antarctic Plateau) have an estimated uncertainty (2σ) for the modelled CO2 age at pore close-off depth of 30% and of about 40% for locations with younger firn air (CO2 age typically 40 years). Comparing the modelled age of CO2 at pore close-off depth with directly determined ages at seven sites yielded a correlation coefficient of 0.90 and a slope close to 1, suggesting a high level of confidence for the modelled results in spite of considerable remaining uncertainties.

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Section: Discussionmentioning

confidence: 68%

Section: Results For Densitymentioning

confidence: 84%

Section: Comparison Study Of Several Density-depth Modelsmentioning

confidence: 99%

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Model calculations of the age of firn air across the Antarctic continent

Kaspers¹,

Wal²,

Broeke³

et al. 2004

Preprint

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“…[20] Figure 6 shows vertical and horizontal cross sections of five firn samples selected from a total of 23 samples, obtained using X-ray absorption microtomography. White and black areas indicate ice and pore space, respectively, and while grain boundaries are not observable with this method, they should exist at the site of bonding [e.g., Alley, 1987a;Arnaud et al, 1998]. The data provide the 3-D structure of firn and the progress of pore spaces toward bubble formation.…”

Section: Geometrical Structure Of Firnmentioning

confidence: 94%

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

et al. 2009

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[1] The evolution of the structure of a 112.59 m long firn core recovered at Dome Fuji, East Antarctica, was investigated in order to improve understanding of firn densification and bubble formation processes, which are important for interpreting local insolation proxies used for astronomical dating of deep ice cores. Using selected samples, we measured physical properties including (1) the relative dielectric permittivities in both the vertical and horizontal planes, (2) the bulk density at a resolution of millimeters, (3) the three-dimensional geometric structure of pore space, and (4) crystal orientation fabrics. We found that the firn at Dome Fuji contains horizontal strata with thicknesses of several centimeters. Near the surface of the ice sheet, these strata are characterized by contrasting bulk density. Earlier field studies suggest that summer insolation causes densification of surface firn. Down to $30 m, density maxima exhibited a clear positive correlation with the strength of structural anisotropy and c axis clustering around the vertical. In contrast, the correlation is negative in deeper firn, confirming previous findings that initially less dense firn became denser than initially dense firn. In addition, numerous examples of textures indicating that deformation preferentially occurred in weaker layers were found. Moreover, the initially dense firn layers were more permeable for air near the bottom of firn. We propose a model linking firn properties with conditions for the gas transport processes near the bottom of firn. The model explains how stronger insolation can lead to bulk ice with a lower O 2 /N 2 ratio and smaller total gas content.Citation: Fujita, S., J. Okuyama, A. Hori, and T. Hondoh (2009), Metamorphism of stratified firn at Dome Fuji, Antarctica: A mechanism for local insolation modulation of gas transport conditions during bubble close off,

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“…In this case, diffusional water vapor transport in the pore space is solely driven by Kelvin effects. Conditions for long-term isothermal metamorphism occur in nature only in the center of the polar ice shields [Arnaud et al, 1998].…”

Section: Introductionmentioning

confidence: 99%

Observation of isothermal metamorphism of new snow and interpretation as a sintering process

2007

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[1] Isothermal snow metamorphism is based on the fundamental process of sintering. However, the relative weights of the physical processes responsible for sintering between ice grains are still debated. The most active are expected to be grain boundary diffusion or sublimation-condensation. We performed four isothermal experiments, starting with fresh snow, at temperatures of À1.6, À8.3, À19.1, and À54°C during nearly 1 year. Monthly, we imaged the snow samples by X-ray microtomography. We monitored the changes in density, specific surface area, structure model index, and several structural parameters based on the distance transform of the ice matrix and pore space in the snow, as the trabecular number and thickness. At À54°C, the metamorphism process was very slow, and during 1 year the specific surface area decreased by only 19%. For the other samples, the results can be interpreted as a two-stage process with a first phase of rapid change in trabecular number and structure model index and a second phase where the trabecular number and structure model index were constant. An increase in density and trabecular thickness together with a decrease of the specific surface area following a power law were observed throughout the experiments. The increase in ice thickness (coarsening) related linearly to the densification. The continuous densification implies that volume processes like grain boundary diffusion have to occur. The linear relation between densification and coarsening suggests that the same mechanism governs both processes. The logarithmic decrease of the specific surface area is an indication that the coarsening is rate limiting.Citation: Kaempfer, T. U., and M. Schneebeli (2007), Observation of isothermal metamorphism of new snow and interpretation as a sintering process,

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Modelling of the densification of polar firn: characterization of the snow–firn transition

Cited by 38 publications

References 15 publications

Model calculations of the age of firn air across the Antarctic continent

Model calculations of the age of firn air across the Antarctic continent

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

Observation of isothermal metamorphism of new snow and interpretation as a sintering process

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