Summary

Various people from the event spent 24 days in the field from 16 Nov to 9 Dec. Daniel Pringle (VUW) from K131 joined K047 at Table Mountain to reprogram the data loggers on two temperature probes for 2003. Samples and soil pits were dug as outlined in Table 1. Soil pits were generally dug either in the centers of polygons or between them, and in locations picked in relation to the previous pits containing massive ground ice. Polygon centres are thought to be the least active area and hence should contain the oldest most chemically developed soil.

Method

The following method was used in digging most all of the soil pits: In the area to be excavated (1m × 1m × .5m), the surface material was scrapped off and placed on a 2m square polythene tarpaulin. The underlying soil was then dug out and placed on another 2m square polythene tarpaulin. Loose soil material was dug to a depth of one metre or the top of the ice-cemented soil which ever was the shallowest. After the final pit depth, soil profile and possible permafrost or massive ground ice were described and sampled, all material from the respective polythene tarpaulins was replaced. The ground surface was raked and swept to restore as much as possible of the original appearance. Analyses of the samples will include; OSL (Optically Stimulated Luminescence) of selected dune and pit soil samples, stable oxygen and hydrogen isotopes and ¹⁰Be dating for the ice core, and major cation and anion chemistry of soluble salts for the soil samples.

The term "ground ice" refers to all types of ice formed in freezing and frozen ground (Permafrost Subcommittee, 1988 p 46). Permafrost refers to the permanently frozen (<0° C) condition and includes both dry and wet (ice) materials. "Massive ground ice" in this report refers to clear ice with a variable content of sediment >10% of the ice by weight.. Subsurface conditions in the Dry Valleys are generally different from those in arctic and alpine environments in that there is usually 30 to 60 cm of dry frozen sediments above ice cemented sediments. However, because most workers think of permafrost as ice cemented, the term permafrost in this report will include only the ice cemented materials.

Table Mountain

The Table Mountain camp site was chosen close to the temperature probes on a patch of snow at S77°57.631′ E161°57.324′, altitude 1850m. We experienced winds of up to 40 knots with the temperatures remaining relatively constant around –18 °C.

On the floor of Columnar Valley (adjacent to Table Mtn) polygons have a diameter of 4-10 m and <1 m height differential between trough and polygon centres. Polygons extend from the valley floor up the valley walls up to slopes dipping up to 25° right to the debris flow boundary. The distribution and appearance of the surface material of the polygons in Columnar Valley varies with some polygons having a "brick wall-like page 4 appearance with whilst others were covered by randomly distributed boulders and cobbles of varying sizes.

Six pits were dug in total and in all pits permafrost was encountered at depths between 7 and 16 cm. Three pits dug in the cracks between the polygons contained clear ice at depths between 14 and 23 cm. The permafrost boundary appears to follow the surface topography of the polygon.

In general, the activity of any single polygon or part of it may be reflected by the distribution of the material in the troughs. Parts of troughs are flat having been filled with sand while other parts are steep and rocky with angular cobbles and boulders. This angular material may be sorted or unsorted. On the active part of a polygon, clasts may roll off the steep sides and into the trough. Sorting of clasts in the trough may occur by what the center crack is able to accommodate. On the inactive part of a polygon, wind blown sand may accumulate in the trough. This observation suggests that polygon activity may be dynamic so parts of it are active while at the same time other parts are inactive.

A major problem apparent from the fieldwork is to understand what controls the age of the surface and the relationship to polygon development in Columnar Valley. Alternatively, it may be the ice content below the surface that controls polygon development. Soil development and age may be more of a function of the material, aspect and moisture regime, rather than the depositional age of the material in which the soil is forming.

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.

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.