Evans Piedmont Glacier is one of the three drilling targets planned for season 2004/05. The site reconnaissance included a GPS and GRP survey and closer investigation of the snow properties from a snow profile.

Ground Penetrating Radar (GPR)

Ground penetrating radar (GPR) measurements provide an image of the internal layering of a glacier and the topography of the ice-rock interface beneath. We applied low and high frequency radar pulses (35 MHz, 200MHz, and 400MHz) to map the bedrock interface and internal flow structures in the glacier. Those features are identified through reflectors that result from changes in physical and chemical properties, such as dust layers or aerosol and density variations and are thought to represent isochrones [Morse et al., 1998; Vaughan et al., 1999]. The choice of antenna frequency involves a trade-off between penetration depth and mapping resolution. The control units were mounted on a Nansen Slege, pulling transmitter and transceiver antennae. page 4 The sledge also carried high precision GPS antenna, which is tied to the temporary GPS base station deployed at the Evans Piedmont Glacier camp.

Fig.3: GPR/GPS set-up. A 400MHz antenna travels in front of the first skidoo. A second skidoo tails the set-up for crevasse safety.

Traverses totaling approximately 30km have been surveyed with GPR. The measurements show that the glacier thickness exceeds on average 150m (Fig.4) and is well over 200m deep at the identified drilling location. Excellent isochrone reflections are visible throughout the profile (Fig. 4), which will also be used to investigate geographical and chronological accumulation changes. Further post-processing will enhance the reflectors and will correct for surface topography.

Fig.4: Radar profile from Evans Piedmont Glacier showing bedrock topography, ice thickness and internal flow structures

Analyses of Snow Properties

A 4m deep snow pit was excavated to allow high resolution snow analysis. The snow profile was sampled with 1cm resolution for analysis on snow chemistry (Na, Ca, K, Mg, Cl, NO₃, SO₄, MS, Al, Fe, Si, Sr, Tr, Zn) and isotopic composition (δ¹⁸O and δD), dust content and mineralogy (Fig.5). The data are used to establish transfer functions between meteorological records and the snow/ice core record, for temperature, precipitation, airmass origin, wind strength and direction, storm frequency, etc. The high sampling resolution provides sub-annual resolution of the climate record. Furthermore density and temperature of the snow pack was measured with 5cm resolution (Fig.5), and snow crystal structure was investigated. This information is important to calculate annual accumulation rates and to evaluate the potential of re-crystallisation in the snow pack. Our initial results suggest excellent characteristics for ice core analysis.

Fig.5: Analysis of snow properties including high resolution snow sampling (left), and density and temperature measurements with 5cm resolution (right).

During our stay at Evans Piedmont Glacier two snow precipitation events occurred which provided the opportunity to sample hourly throughout the snowfall (Fig.6). This will allow us to fingerprint snow chemistry and isotopic composition with the meteorological situation as seen in the satellite image, enabling airmass trajectory reconstruction in ice core material from this site. While the first event was caused by mesoscale cyclonic activity and consisted of blowing and precipitating snow, the second event was caused by intrusion of local moist, marine airmass, leading to crystal growth at the snow surface.

Fig.6: Two snowfall events at Evans Piedmont Glacier.

Mt Erebus Saddle is one of the three drilling targets planned for season 2004/05. Due to bad weather that shortened the field time available, we were not able to set up camp at this site. A one-day site reconnaissance included a GPS and GRP survey and initial investigation of the snow properties from a shallow snow pit and core. The results from this initial investigation suggest that the proposed drilling site has the necessary characteristics for a suitable drilling site.

Ground Penetrating Radar (GPR)

As bad weather prohibited a full camp set-up at Mt Erebus Saddle the GPR measurement was done by manhauling a lightweight version of our Evans Piedmont Glacier GPR setup (Fig.7). For this reason only one 35MHz antenna was used. An example of the raw data is shown in Fig.7. A strong bedrock reflection indicates that ice depth exceeds 200m. The prominent isochrones seen at about 50m are potentially tephra layers. The sparse coverage does not permit investigating spatial accumulation pattern. However, the persistence of isochrones throughout the profile, their horizontal direction and the total depth of the glacier at the proposed drilling site indicate promising characteristics for a potential ice core record from Mt Erebus Saddle.

Fig.7: Manhaul of a lightweight GPR and high resolution GPS equipment (right). Radar profile from Mt Erebus Saddle showing bedrock topography, ice thickness and internal flow structures (left).

Analyses of Snow Properties

While high resolution snow sampling was not possible in the time available, investigation of a 2.50m firn core and a 1m deep snow pit indicates that Mt Erebus Saddle is a high accumulation site, likely in excess of 40cm water equivalent per year. For this reason Mt Erebus Saddle potentially contains a climate record of sub-seasonal resolution.