ICECAP (Investigating the Cryospheric Evolution of the Central Antarctic Plate) is the first airborne geophysical survey to cover large areas of central East Antarctica (Fig. 1). The technique of airborne radio-echo sounding enables us to measure the ice thickness, detect englacial structure, image the subglacial topography, discover subglacial lakes and asses the basal thermal conditions of the region for the first time. Simultaneous airborne magnetic and gravity measurements are giving us a first look at the gross lithology of the central Antarctic Plate and aiding in the interpretation of its large scale structural geology. The collection of this data will fill one of the largest gaps in our knowledge of Antarctica and represents a significant step forward in our understanding of the past, present and future behaviour of the largest ice sheet on Earth.

An improved knowledge of the bed of the ice sheet is fundamental to the progress of Antarctic glaciology. Maps of the bedrock topography, such as that produced by the BEDMAP project (Fig. 2), are used by ice sheet modellers who aim to predict the behaviour of the ice sheet under scenarios of future climate change. To construct these maps two data sets are necessary, the surface height of the ice sheet and the thickness of the ice. Geophysical surveys gathering this information have been undertaken in Antarctica since the 1960's, however, there are still large areas for which no ice thickness data currently exists (Fig. 3). In these areas the bed topography must be estimated using a variety of interpolation techniques in order to create a continuous data set for ice sheet modelling. The use of interpolation introduces errors into the model results and presently represents one of the greatest sources of uncertainty in predictions of future sea-level rise due to global warming.

In addition to bed topography, the airborne ice penetrating radar flown by ICECAP will collect information about internal ice sheet structure which can provide a record of changes in ice flow velocity, rates of ice accumulation and conditions at the base of the ice sheet. Basal conditions are of particular interest to glaciologists as to a large degree they determine the speed at which ice can flow. The horizontal layers detected by radio-echo sounding between the ice surface and the bed are known to represent deposition horizons of constant age. By tracing these layers from the site of an ice core (where their age has been directly measured) we can determine the age of the ice at different depths throughout our survey. The Aurora Basin, one of the main targets for the ICECAP project, is one of the few sites in Antarctica where ice may still exist which pre-dates the mid-Pleistocene climate transition, the 'holy grail' of ice core paleoclimatology. The results of this project will be used to identify sites for future ice coring that will attempt to retrieve some of the oldest ice on the planet.

Figure 2: The gridded product of the BEDMAP project shows the topography of Antarctica with the ice removed (not isostatically rebounded). The Dashed square shows the location of Figure 3.

Figure 1: Topographic map of Antarctica with names of major regions. Contours are at 500m intervals.

Looking into the Deep

Beneath the inland ice which forms the catchment of Totten Glacier lies the vast and deep Aurora Subglacial Basin. This is one of the least known parts of the continent and represents one of the last frontiers of exploration. One of the key aims of the ICECAP project is to use the subglacial topography, gravity and magnetic field measurements to characterise the underlying geology of this area. In particular we will be looking for gravitational and magnetic signatures that indicate crustal boundaries/tectonic activity as well as volcanism.

South of the Aurora Basin one of the major ice divides in East Antarctica is found at Dome Concordia (Dome C). Akin to a continental watershed, such as that associated with the spine of the Rocky Mountains in North America, the ice divide in East Antarctica marks the site of the lowest ice flow velocities and the lowest rates of ice accumulation on the continent. The summit of Dome C is the site from which the longest ice core record drilled so far was retrieved (see the EPICA website). As part of the ICECAP project we will fly radar lines which join up the sites of the Dome C and Vostok ice cores. The identification of internal layering within the radar returns should then allow these cores to be stratigraphically linked.

The Dome C ice core contains a record of the last 8 glacial-interglacial cycles, each of which had a duration of around 100,000 years. Climate records from marine sediments stretch back much further and tell us that prior to some, presently uncertain, change in the climate system which occurred around 1 million years ago it was usual for glacial-interglacial cycles to last for only around 40,000 years. One reason to carry out a detailed survey of the Aurora Basin is that it represents one of the few sites in Antarctica where ice may still exist which pre-dates the mid-Pleistocene climate transition. A detailed study of the internal layers detected by radar will be used to identify potential sites for future ice cores that will attempt to retrieve a sample of the oldest ice on the planet (See the 'Oldest Ice Core' white paper on the IPICS website)

Figure 3: The Aurora Basin according to the BEDMAP dataset. The red lines show the locations of ice thickness measurements that were included in the BEDMAP compilation, green lines show the geophysical surveys that have been undertaken in the period since the publication of BEDMAP. Large areas of the basin, particularly to the east of the overland traverse route between Casey and Vostok, are very poorly known. The effects of the interpolation algorithms used to grid the data in these sparsely sampled regions can be clearly seen.