The field effort this season was basically focussed to objectives within the SCAR-ISMASS-ITASE-ANTIME initiatives. It is an extension of the programme which has been run by the Department of Physical Geography in Dronning Maud Land since 1987 (Jonsson et al. 1988, Holmlund et al. 1990, Holmlund, 1998, Holmlund et al. 1999). The programme concerns the mass balance of the Maudheimvidda basin, the balanced flow of the Veststraumen Ice Stream and glacial geological studies.

In 1993 the SCAR Group of Specialists on Global Change and the Antarctic (GLOCHANT) was formed by launching interdisciplinary research programmes. Ice Sheet Mass Balance and Sea Level (ISMASS) was aimed at addressing the requirements for a co-ordinated international approach to resolving the role of Antarctic Ice Sheet in sea-level change. The aim of this programme is to map the mass balance of the proper Antarctic Ice Sheet. The ice shelves are studied as well, but treated separately. The intention is to use available mass balance data from firn cores and snow radar records sampled within International Trans-Antarctic Scientific Expedition (ITASE), bedrock topography from the inland of the continent provided by BEDMAP and to balance accumulation rates against the ice flux over the grounding line. The paleo-record is provided by Late Quaternary Sedimentary Record of the Antarctic Ice Margin Evolution (ANTIME).

The objectives of ISMASS are:

1. To determine the present distribution of surface elevation change.
2. To determine the values of the mass balance components, calculate the net mass balance of the ice sheet, and determine how that net balance is distributed between the grounded and floating portions of the ice sheet, and hence determine the sea level contribution.
3. To identify and evaluate the physical controls on the motion and areal extent of ice streams and outlet glaciers.

ISMASS will also assist in the development of the ITASE-programme and to encourage the further theoretical development and application of passive microwave radiometry in determining surface mass balance. It will also promote theoretical and applied advances in calculating the snow accumulation rate in the Antarctic interior using moisture-flux -divergence techniques. The field surveys within the glaciological programme during the SWEDARP 1999/2000 were carried out by Rickard Pettersson and Mats Nilsson.

The stability and the balanced flow of the Veststraumen Ice Stream (ISMASS)

This year’s studies were Concentrated to the central and lower part of Veststraumen, covering approximately 1110 of the basin. The main outlet glacier draining Maudheimvidda is Veststraumen and drains a basin of 200 000 km²

Mass balance and mass flux calculations suggest a more or less steady state situation for the Maudheimvidda basin, though there are large uncertainties on the ice flux estimates. However, radio-echo soundings longitudinally along Veststraumen, as well as modeling experiments indicate an unbalanced state of the ice stream. This apparent paradox stresses the need of further investigations of outlet glaciers in Dronning Maud Land. Those would show whether the geometry of Veststraumen reflects a surge like behaviour or not. The ice stream becomes afloat about 100 km upstream where the shelf ice begins, indicating the appearance and importance of subglacial bedrock obstacles (so called pinning points). Small changes in the flux rates, due to minor sea level or ice thickness changes, may result in a significant surface elevation change within the Maudheimvidda basin.

The fact that the ice stream becomes afloat 100 km upstream the site where the proper ice shelf is formed is a large potential for error in mass balance calculations. Melt rates underneath floating parts of ice streams can be several times larger than the net accumulation at the surface indicating a substantial negative mass balance. Thus, though measurements at the boundary between the ice stream and the ice shelf indicate a balanced state between accumulation and ice mass transport at the boundary of the area, there might be a significant deficit of mass at present in the area. With this project we would like to analyse the dynamics of Veststraumen; to document ice velocity, mass balance parameters, ice thickness and ice surface elevations.

During the SWEDARP 1999/2000 expedition 11 new velocity stakes were surveyed with differential GPS. The stakes are supplements to the previous velocity measurements. The GPS survey was carried out in cooperation with the geodetic department at KTH Royal Institute of Technology.

The bed topography of Veststraumen was mapped from a helicopter using continuous wave step frequency radar with a center frequency of 157 MHz and a bandwidth of 5 MHz. The radar soundings were carried out in profiles evenly distributed in a net over the middle and lower part of Veststraumen.

The collected data makes a significant contribution to the mass balance study at Veststraumen aiming at highlighting the importance of the coastal areas for mass balance calculations of the entire ice sheet. In a smaller scale it will also increase our understanding of ice stream dynamics.

The variability in snow layer thicknesses with in the Maudheimvidda basin (ITASE)

In order to model ice sheets a reliable mass balance scheme is needed. Snow radar has been used successfully to map snow layering in Antarctica over large distances, showing a large variability in thicknesses, not simply described by elevation and distance to the coast. The soundings have so far been executed from bandwagons but we are developing the system to be useful from helicopter which certainly would be an improvement. The radar registrations are calibrated by shallow firn cores.

We do now have data from three long traverses, sampled during the 1993/94 and the 1996/97 field campaigns and now more detailed data is needed. The aim is to couple the surface layers to the shape and thickness of internal layers within the ice, and to bedrock topography.

This year included a survey of the spatial variability in the snow layer thickness along the same profiles as was used for the ice thickness soundings. We utilized same radar equipment as for the ice thickness hut used a center frequency of 1.5 GHz with a bandwidth of 1 GHz. A calibration of the radar recordings was carried out at a 5 km profile across Plogbreen, near the station Wasa. Five ten metre firn cores were collected along the calibration profile. Density was measured in the field and the cores were brought back to Sweden for further analysis on the electrical properties.

Changes in ice dynamics and ice thickness in Maudheimvidda over time (ANTIME)

This study includes both mapping of the subglacial relief and ice cores. Analysis of the subglacial relief provides us with data on the long-term development of the ice sheet such as how it was formed and whether there have been changes in the thermal conditions over time. In addition, bed topography data will be delivered to the BEDMAP initiative within SCAR aiming to compile all presently available thickness and bed topography data in one data base.

The glacial landscape beneath the Maudheimvidda Ice Sheet in East Antarctica was most probably formed during a more temperate phase of the Antarctic glaciation than the present. According to earlier work is the subglacial landscape found in the vicinity of the nunatak ranges Heimefrontfjella and Vestfjella has an alpine relief formed by glacial erosion. According to calculations of the temperature distribution within the ice sheet, the studied cirques and u-shaped valleys are at present covered by cold based ice, incapable of forming such features. This, together with the observation that individual mountain block topography has constrained the ice flow that eroded the cirques, indicates that these landforms predate the present ice sheet.

By using helicopter borne radar, bed topography mapping was carried out on two cirque glaciers and the topography of the subglacial landscape surrounding one of the cirques. The surrounding area was mapped in a 200×200 metre grid.