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Victoria University Antarctic Research Expedition Science and Logistics Reports 1996-97: VUWAE 41

3.3 Ice and Temperature Signals from Sirius Group, Table Mountain Warren Dickinson

3.3 Ice and Temperature Signals from Sirius Group, Table Mountain Warren Dickinson

Core hole drilling of the Sirius Group at Table Mountain provided the opportunity to measure closely spaced (10-30cm) ground temperatures from the surface to four metres deep. These temperatures will provide background data for two areas of study. 1) Determination of the potential for periglacial or active ground movement that could produce patterned ground on Sirius Group sediments. 2) Calibration of oxygen isotope temperatures obtained from ice in fractures and in pores of the sediment. Although the Sirius was thought to have ice-filled pores below 50 cm, the amount and number of ice filled fractures found in the core was a surprise. Although this ice cannot be directly dated, stable isotopic measurements are critical to understanding its origin.

The equipment and methods used for measuring the temperatures were designed to be simple and economic. They also had to page break accommodate a range of unknown conditions. At the outset of the project, the depth and number of core holes was uncertain as well as the ability to actually measure the core hole temperatures.

The measuring system consisted of a digital thermometer calibrated for K-type thermocouples and 15 thermocouple wires from 0.5m to 4.5m in length. The core holes varied in diameter between 70 and 90mm and for this particular range a 50mm OD plastic pipe worked best for holding the wires down the hole. The relatively loose fit ensured that the plastic pipe would not get stuck in the hole. Thermocouple wires were brought down the centre of the pipe and out through holes at 0.25m intervals. The wires were taped to the outside of the pipe and bent to form whiskers protruding about 10mm outwards from the pipe. In this way, the wire whisker with the thermocouple junction on the end contacted the side of the core hole. Temperature measurements were taken over a period of five days at one hole but only for one day periods at four other holes.

Temperatures decreased with depth by 3.5_C per metre up to four metres depth (Figure 2). At four metres depth the average temperature, which varied by 2_C between the five holes, was −21.5_C. Temperatures measured 3-5cm below the surface in loose soil showed large variations. This was probably due to the degree of sunlight exposure at the surface. These variations appeared to affect temperatures down the hole to 0.5 m and possibly 1.0 metre deep. To confirm these temperature variations, measurements must be made over a period of weeks and probably through the winter.