Densité de la glace et étude des gaz en profondeur dam un glacier antarctique

Different measurements have been performed on ice samples taken from a drilling about 100 meters deep in the coastal region of Terre Adelie (Antarctica); the mean temperature in the hole was approximately – 10°C. The results show that the pressure of gaz inclusions and the density of the ice increase with the depth. The values of the density increase from 0.880 g/cm³ to 0.918 g/cm³ while the total volume of air decreases from 10 cm³/100 g of ice for the samples taken from the surface to 6 cm³/100 g at a depth of about 80 meters. At a greater depth, in the section of the drilling containing morainic debris, values of approximately 4 cm³/100 g have been found. Lastly, in the blue ice which exists in contact with rock sediments, the volume of air becomes practically nil; this observation confirms that the blue ice has been formed through freezing. The gaz inclusions that are generally spherical show a definite lengthening in the samples taken from a depth of approximately 30 to 50 meters. This is in accordance with the appearance in the drilling of ice from a far-off origin characterized by its deuterium content. The total volume of gaz depends on the place where the ice was formed and the shape of the inclusions is linked to deformations due to ice flow phenomena.

The concentrations of carbonic anhydride and argon found in the gaz contained within the ice approach the concentrations found in atmospheric air. The steady variations of about 1% observed for oxygen proportions (decreasing with the depth) and nitrogen proportions (increasing with the depth) suggest that the composition of the gaz contained within the ice could depend on the conditions prevalent during the formation of this ice, even in the absence of fusion, through adsorption phenomena. Knowledge of the fundamental processes which take part in the formation of gaz inclusions is thus necessary in order to undertake the study of the ancient atmosphere through the gaz contained within the ice.