Geochemical, thermal and petrofabric analyses of Antarctic ice wedges: environmental influences

From 1998 to 2006, during four summer field seasons, ice wedges were found in 45 sites at depths ranging from 10 to 74 cm beneath the ground surface. The tops of the ice wedges ranged from 5 to 155 cm wide, and their heights varied from 20 to over 150 cm in length. A co-isotopic study was performed by measuring both the oxygen (Delta 18O) and hydrogen (Delta D) isotope compositions and the tritium activity. Petrofabric analyses were also performed on ice-wedge ice to investigate changes in fabric across wedges in relation to the growth mechanism. Data loggers were installed at three ice-wedge polygon sites to monitor the ice-wedge thermal regime. The measurements obtained for Delta 18O and Delta D had extremely negative d- excess values, showing a strong divergence from the snowfalls expected to occur at the elevation of the sites. Sublimation processes were taken into account to define the origin of the ice-wedge ice. The presence of hoarfrost crystals, observed in the ice-wedge cracks during summer field surveys, corroborate that sublimation processes may control the formation of ice in the growth processes of ice wedges. Petrofabric analyses indicated the increasing of crystal size from the ice-wedge centre outward, and in c-axis directions they showed a rotation of crystals from the centre towards the sides. The monitoring of the thermal regime of three ice wedges over a five-year period highlighted that, in winter, extreme gradients between the temperatures at the ground surface and those at the tops of the ice wedges may trigger cracking. Moreover, the presence of open cracks in the ice wedges, in summer, indicates that the growth processes are still active under the present climatic conditions.