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29 December, 2002

Firn Permeability

Date: 12/29/02  

Latitude: 88° 00’ 07.70” S

Longitude: 107° 58’ 58.47” W

Time of Observations: 6:00 PM local time

Temperature: -23 C / -9.5 F

Wind speed: 10 knot

Wind Chill: -34 C/ -29 F

Wind direction: Southerly

Meters of ice collected: 575 m  

By Jim Laatsch

Site 5! This is our last stop before the pole and its proximity has motivated everyone’s energy levels despite the many hours of exhausting driving.  This log is actually going to backtrack a bit and talk about a project that we worked on at the last site (Site 4) and at Site 2. ITASE is a broad scientific endeavor and there are actually many more people who work with ITASE data than just those of us down here on the traverse. One prime example of this is the work done for Dr. Mary Albert, a research scientist at the US Cold Regions Research and Engineering Laboratory (CRREL). Mary is one of the world’s experts on the physical properties of snow and firn and part of her work with ITASE focuses on snow microstructure and permeability to investigate how chemicals are redistributed in firn. (Firn is the term used for any snow that has survived the first melt season before it becomes solid ice.)

One of the characteristics of firn that is very important to Mary’s work is the pore space within the snow column. Porosity refers to the amount of interstitial space between snow grains, the amount of space that is filled up with air.  Imagine if you took a glass and filled it with Styrofoam packing peanuts, there would be a lot of empty space between the peanuts.  This empty space is essentially porosity.  If you were to blow down into the glass, the air would easily circulate through the big empty spaces around the peanuts.  If instead of peanuts, you were to fill up the glass with fine sand there wouldn’t be much free space available between the tiny sand grains and if you blew into the glass this time the air wouldn’t easily circulate through it.  The glass full of sand would have comparatively less porosity than the glass full of Styrofoam peanuts.  By understanding how much pore space is available in the snow Mary can investigate how easily air can circulate around in the firn column and redistribute chemical species which might effect the concentrations and layering of ions within the snow.  Mary has been working in a different part of Antarctica this season so she left us some wonderfully detailed instructions and we were able to collect data for her independently.

To start off, we drilled three ice cores, one 15 meters deep and two 2 meters deep.  The 15 meter core will be shipped back to CRREL intact and the 2 meter cores were processed in the field.  The first 2 meter core was cut up into sections about 10 cm each, then it was coated with a chemical called Dimethyl Phthalate that seeps into the pore space, freezes, and thus preserves the original shape of the interstitial pathways within the core. By far the most difficult part of this job is keeping from spilling the Dimethyl because it isn’t a terribly nice chemical. Luckily Dan, who is much neater and more experienced than I am, was able to provide some ultra valuable assistance with this.  The other 2 meter core was sliced up into similar sized chunks and run through a machine called a Permeameter that was built by Mary Albert and Frank Perron back at CRREL. The Permeameter forces air through the core at varying flow rates and measures the amount of pressure buildup.  From this Mary can begin to quantify how much pore space these is in the firn and how easily air can flow through it.  Is it like the glass full of sand or Styrofoam pieces?  The vast majority of the work on this project will be done by Mary and her students, Ursula, Zoe, and Margie back at CRREL but it was nice to be involved for a bit down here in the field and get to learn more about an entirely different project than my own.

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