Documentation for Firn Permeability and Density at WAIS Divide, Version 1

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Detailed Data Description


Data are provided in Microsoft Excel format (.xlsx).

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File and Directory Structure

Data are available on the FTP site in the directory. Within this directory, there is one file:WAISDivide_FirnProperties.xlsx.

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File Size

The data file is 30 KB.

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Spatial Coverage

The WDC05C firn core was retrieved from a previously undisturbed site at 79.46300° S, 112.12317° W near the WAIS Divide ice coring site for firn air measurements in December 2005 to January 2006 (Battle et al. 2011).

As described in Gregory et al. 2014 measurements of firn air and extraction of a firn core from a megadunes site in East Antarctica were accomplished at an undisturbed site during December 2004 to January 2005 at 80.77914° S, 124.48796° E.

Spatial Resolution

3" diameter cores drilled vertically from the firn.

Depth of center of sample from 55.87 m to 77.82 m.

Comparison of bulk properties taken from 5–10 cm-long samples to microstructural properties taken from 8 mm x 8 mm x 10 mm was done on visually homogenous 5–10 cm long samples (Gregory et al. 2014).

Measurements of density, permeability, and microstructure in very deep firn are investigated starting at 55 m, approximately ten meters above the start of the Lock-In Zone (LIZ) at both sites that had been determined through in situ firn air measurements, to a few meters below the close-off depth at each site. The deepest measurements at WAIS Divide were 78 m, while the deepest measurements done at Megadunes were 75 m (Gregory et al. 2014).

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Temporal Coverage

Collection period 2004 - 2005.

Temporal Resolution

One-time firn core retrieval.

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Parameter or Variable

Parameter Description

The principal parameters in this data are Firn Density and Firn Permeability. The rows of the file are sequential segments of firn.

Sample Data Record

Figure 1 shows a sample of records from the WAISDivide_FirnProperties.xlsx data file.

sample data
Figure 1. Sample Data Record

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Software and Tools

Software and Tools

The data file can be opened using any software capable of reading Microsoft Excel files.

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Data Acquisition and Processing

Theory of Measurements

Density, permeability, and microstructure measurements were made on firn cores from the West Antarctic Ice Sheet (WAIS) Divide, a site that has moderate accumulation rates with a seasonal climate archive, and Megadunes in East Antarctica, a site that is a natural laboratory for accumulation rate effects in the cold low-accumulation desert (Gregory et al. 2014).

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Data Acquisition Methods

The firn core was drilled by others at WAIS Divide, and also at Megadunes, stored at the National Ice Core Laboratory (NICL), and then shipped to Dartmouth, where the cores were stored at -20 C. Measurements of density and permeability were made in the -20 C cold room at Dartmouth.

Stratigraphy was noted, the core cut in segments ranging from 3-10 cm long, and then density and permeability were both measured on each piece. The permeameter was M. Albert's custom permeameter, which had been verified on glass beads.

Measurements of permeability and density profiles were correlated with microstructures quantified using advanced materials characterization techniques including scanning electron microscopy and x-ray computed tomography. The firn from several meters above the lock-in zone down to pore close-off was investigated.

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Derivation Techniques and Algorithms

As described in Gregory et al. 2014, stratigraphic layering of the firn was observed and recorded using a backlit light table in a cold room at the Cold Regions Research and Engineering Laboratory in Hanover, NH. Meter-long core sections were placed on the light table where grain size and wind crusts were recorded to the 1 mm scale. Relative grain size was qualitatively described from visual inspection using a five tier scale from coarse to fine for each meter length section. Coarse grains and fine grains were defined relative to other layers within the meter-long section.

Comparison between the WAIS Divide site and the Megadunes site was also done visually with a backlit light table in which the coarse-grain layers at WAIS Divide below 55 m were observed to be smaller relative to the fine-grain layers at Megadunes below 55 m. Samples of 5–10 cm of similar grain size were cut for further analysis.

Bulk density measurements were made on the same 5–10 cm resolution samples using volumetric measurements and the mass of the sample.

Error Sources

Error in density measurements was small, with less than 0.5 percent standard deviation for 10 repeat measurements on a single sample. The mass of the sample from scale measurement is accurate to 1 percent, and the volume of the sample calculated from caliper measurements is accurate to within approximately 2 percent. To increase the accuracy of bulk property measurements, broken and chipped samples, not of an ideal cylindrical shape, were not included in bulk density or permeability measurements (Gregory et al. 2014).

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Sensor or Instrument Description

Firn microstructure properties were obtained using X4-ray microtomography. A Skyscan 1172 model microCT was used in a cold room. Scans were run at 40 kV, a 250 μA current intensity, and a rotation step of 0.7 degrees completing 180 degrees rotation for each run. A total of 275 shadow images were obtained and reconstructed using Skyscan's NRecon software for two-dimensional slice reconstruction (Gregory et al. 2014).

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References and Related Publications

Contacts and Acknowledgments

Mary Albert
Thayer School at Dartmouth
14 Engineering Road
Hanover, NH 03755


Grant number: NSF-OPP 0944078.

Document Information

Document Creation Date

11 March 2015