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Victoria University Antarctic Research Expedition Science and Logistics Reports 2007-08: VUWAE 52
d. Methodology
d. Methodology
Ground Penetrating Radar
For mapping glacier flow structures and the glacier-bedrock interface a 'GSSI SIR 3000 and GSSI SIR 10 A were used with a maximum time window of 8,000 and 10,000 ns, respectively. A 35MHz antennae-pair (Bistatic Radarteam SE-40), a 200MHz antennae-pair, and a single 500MHz antenna are pulled by a Nansen Sledge, which carries the control units. A Trimble 5700 differential, kinematic GPS, provides absolute positioning of the GPR data and allows survey of the glacier surface topography. GPR and GPS measurements are taken in kinematic mode.
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Fig. 7: Photo showing Nansen sledge carrying GPR and crevasse rescue equipment
Submergence Velocity Measurements at Victoria Lower and Evans Piedmont Glaciers
During the 1999/2000 season three submergence velocity devices (Hamilton & Whillans, 2000) for mass balance measurements in the McMurdo Dry Valleys were installed. During the 2004/2005 season two submergence velocity devices have also been installed at EPG. This method is used to determine mass balance by comparing vertical velocity of a marker in firn or ice with long-term, average snow accumulation rates. The movement of the marker is the result of three motions: firn compaction, gravitational glacial flow, and changes in mass balance. High precision GPS measurements are used to determine absolute position of the tracking point during subsequent years. Trimble 5700 base station and rover unit were used to measure the absolute position of the tracking point of the mass balance devices.
The rate of thickness change H, can then be calculated using (Hamilton et al., 1998):
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H=rate of thickness change (myr−1)
bm=accumulation rate (Mgm−2yr−1)
ρ=density at marker depth (Mgm−3)
z=vertical component of ice velocity(myr−1)
α=surface slope (radians)
u=horizontal velocity (myr−1 with azimuth)
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Fig. 8 Cartoon of the 'coffee can' submergence mass balance device (modified after Hamilton and Whillans 2000)and picture of coffee can device deployed at Victoria Lower Glacier.
Shallow Firn Core Analysis
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Oxygen and Hydrogen Isotope Ratio
Oxygen isotope ratios are measured using a CO2 dual-inlet system coupled to a Micromass Isoprime mass spectrometer at GNS Science. The sample is measured in the presence of a standard CO2 gas. Sample duplicates and standard measurements showed a precision of ±0.08‰. Samples are analysed for stable hydrogen isotope radios δD via Cr reduction with a continuous Helium flow Eurovector elemental analyser coupled to a Micromass Isoprime mass spectrometer. Sample duplicates and standard measurements showed a precision of ±0.6‰.
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Major Cations, Anions, and Methylsulfonate
Major ion concentrations are measured for cations (Na, K, Mg, Ca, NH3) using a Dionex™ Ion Chromatograph with Dionex CS12 column and 20 mM methanesulfonic acid eluent. Anion concentrations (Cl, NO3, SO4) are measured with a Dionex AS11 column, 6.0 mM NaOH eluent. For both measurements a 0.25 mL sample loop is used. Methylsulfonate (MS) content is measured using a Dionex AS11 column with 0.1 mM NaOH eluent and a 1.60 mL sample loop
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Trace Elements and Cations
Samples are analysed for trace elements and cations (Al, Ca, Cu, Fe, K, Mg, Mn, Na, P, S, Si, Sr, and Zn) using a Perkin-Elmer Optima 3000 XL axial inductively coupled plasma optical emission spectroscopy with a CETAC ultrasonic nebuliser (ICP-OES-USN at UMaine) and a Finnigan Thermo inductively coupled plasma mass spectrometer (ICP-MS at VUW) for all other trace elements and selected isotopic ratios.
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Dust concentration and mineralogy
500cm3 volume of snow/ice is filtered through Whatman quantative 2.5μm ashless filter paper. The filter is burnt in a Vulcan A-550 furnace at 500°C for 24 hours. The residue is weight with a AG204 Mettler Toledo analytical balance, and reweighed after 24hours to check for moisture absorbance during cooling. Mineralogy is determined by mounting the dust samples in glycerol gelatine for examination under an optical particles found in the dust are analysed in a JEOL 733 Electron Microprobe at VUW.