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Victoria University Antarctic Research Expedition Science and Logistics Reports 2002-03: VUWAE 47

Pearse Valley

Pearse Valley

Our camp in Pearse Valley was on an alluvial terrace located at the eastern edge of Lake House (325m; S77°42.101′ E161°26.924′) and was selected for its proximity to a source of water (Schlatter Glacier). Wind direction and strength seems highly variable throughout the valley and diurnal variations were common. During the field visit, winds did not exceed 20 knots and seemed strongest from 2 – 5 am. Pearse Valley contains mostly glacial deposits representing the retreat of the main Taylor Glacier and subsequent retreat of the lateral valley glaciers. Polygonal ground covers 40 – 50% of the valley floor and slopes at different altitudes.

About 10% of the valley floor is covered by sand from eolian deposition and this does not include numerous pockets of sand lodged in troughs of polygons and in other sheltered areas. Much of this sand is protected by a lag of 5 – 8 mm granules and therefore is not mobile under winds of about 50 knots. Much of the sand probably came from stream systems draining meltwater from the retreating glaciers. The main sand dune, climbing the northeast slope of the valley apparently has brine flowing on top of ice cemented sand which accumulates in salt pond (dry on the surface) at the base of the dunes.

Sixteen pits were dug out of which three were also cored and sampled for OSL and soil chemistry. Depth to ice cement and massive ground ice under moraines varied from 0.25 m to >1m and was encountered in 8 out of 16 pits. In the eastern part of the valley clear ice was found extruding from a slope side of what looked like a gelifluction lobe. It is not clear what factors control the depth to ice cement and the massive ground ice but aspect and moisture regime do not seem to have a direct relationship.

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In addition to the ice core and soil samples a comprehensive set of hand specimens and surface material was collected. These samples represent the petrologic modal distribution in the till within the valley and reflect the different source areas from which they were transported (ie. direction of glacial transport).

The massive ground ice possibly represents an ice cored moraine which may have derived from the Schlatter Glacier. The surface of this ice is smooth and undulating and it is not clear how the contact between it and loose sand above can be so sharp. Why there is not ice cemented sand above, suggests the clear ice is ablating under the sand. Although the clear ice seems to have a limited extent, it may have a greater extent if it lies below ice cemented soil in other parts of the valley. It is also possible that the ice is somehow related to development of patterned ground which in Pearse Valley is still of relatively limited extent. Initial visual analysis of the ice core at Scott Base confirms the appearance of remnant basal glacier ice. If the ice originates exclusively from ancient glaciers it should be geochemically distinguishable from modern glacier ice.

If the massive ground ice in Pearse Valley is remnant ancient glacier ice it is the oldest preserved ice on earth and has the potential to significantly expand the current palaeoclimatic record obtained from ice cores. Furthermore, preservation of ancient basal glacier ice underneath the valley floors would provide evidence for the stability of the climate in the area for extended periods of time despite of the Holocene climatic fluctuations.