Our 2005/60 field season comprises 4 objectives.

Automatic weather station maintenance and data retrieval

In 2004/05 we deployed an automatic weather station on Evans Piedmont Glacier. We anticipate to collect data from the site for at least two years. The data permit the calculation of transfer functions between ice core proxies and meteorological parameters, such as temperature, precipitation, meso-scale atmospheric circulation pattern, katabatic winds, and seasonality of snow accumulation. In addition a new snow accumulation sensor and high precision snow temperature probes allow us to monitor snow accumulation rates, the potential influence of snow loss through sublimation, wind erosion or melt, and the quality of preservation of the meteorological signal in the snow. Furthermore, the data allow us to estimate the uncertainty of re-analysis data (NCEP/NCAR and ERA-40 data) in the region.

Submergence Velocity Measurements at Victoria Lower and Evans Piedmont Glacier

The response time of a glacier to changes in accumulation or ablation is dependent on the size and thickness of the ice mass. In general, the response time of cold-based glaciers is positively correlated with the size of its ice mass, leading to long response times in Antarctica. For glaciers in the McMurdo Dry Valleys, with lengths on average of 5-10km and flow rates of 1 to 3 m/a, the response times are thought to range from 1,500a to 15,000a [Chinn 1987; Chinn 1998]. Consequently, annual variations in surface elevation may only reflect changes in loss rates. As a result surface measurements of mass balance are difficult to interpret in terms of long-term mass balance [Hamilton and Whillans 2000]. This is especially the case in places like the McMurdo Dry Valleys where mass loss is thought to be predominately due to sublimation at ice cliffs and glacier surface caused by wind and solar radiation [Chinn 1987; Chinn 1998]. For Victoria Lower Glacier, two mass balance measurements are available in the literature for 1983 and 1991 based on ice cliff characteristics and the motion of the glacier snout [Chinn 1998]. The measurements indicate that VLG was advancing 1.24m/a into Victoria Valley during this time period. However, the small number of observations (2) and the cliff's sensitivity to sublimation (contemporary surface ablation) result in a high uncertainty of longer term mass balance. To determine the longer-term mass balance of the glaciers, unaffected by annual surface variations, three 'coffee-can' or 'submergence velocity' devices [Hamilton and Whillans 2000; Hamilton et al. 1998] were deployed at Victoria Lower Glacier in 1999/2000 and two at Evans Piedmont Glacier in 2004/05.

High resolution snow pit sampling at Victoria Lower and Evans Piedmont Glacier

Intermediate length cores were recovered from Victoria Lower Glacier and Evans Piedmont Glacier in 2001/02 and 2004/05, respectively. High resolution samples from shallow snow pits are used to update the records and to investigate post-depositional changes in the snow signal, such as isotopic diffusion or nitrate loss. Furthermore, meteorological data recorded at Evans Piedmont Glacier and re-analysis data are used to calculate transfer functions and establish seasonality in the ice core record. In order to estimate the influence of small-scale local page 3 influences such as sastrugi features, we investigate spatial variability by studying physical properties of multiple snow pits at each location.

Snow Accumulation at Mt Erebus Saddle

We have recovered a 200m deep ice core from the slopes of Mt Erebus Saddle during the 2004/05 Antarctic field season. The site topography promotes strong winds leading to significant compaction of the surface snow (~0.45 gcm⁻³). Furthermore, average snow accumulation lies in the range of 72 – 150 cm yr⁻¹ water equivalent. This is more than one order of magnitude higher than the regional average [Bertler et al. 2004a; Bertler et al. 2004b; Bromwich 1988; Bromwich et al. 1998] and provides ideal characteristics for a high resolution ice core gas record. To measure the accumulation rate at the drill site we deployed three snow stakes, which we hope will endure the high wind velocities and snow accumulation.