Total gas content and surface elevation of polar ice sheets

Abstract

Interpretation of stable isotope profiles from polar ice cores in terms of past climate requires a knowledge of the elevation at which the ice found at any depth was formed. Measurement of the total gas content of polar ice, V, can give such information if the volume of the pores in ice is known for the time they close off from the atmosphere at the ice formation site¹. For the 1,387-m long core from Camp Century in north-west Greenland, estimates, based on the assumption of a constant pore volume at close-off, suggested that, on the average, ice from the Wisconsin/Weichsel period was formed at an elevation about 1,200–1,400 m higher than that from the Holocene². This would account for an important part of the large shift in the stable oxygen isotopic ratio in this core between late Wisconsin and Holocene ice that was observed by Dansgaard and others³. However, if the pore volume at close-off depends on the site of origin for the ice, estimates of elevation of origin by the gas content method can be seriously in error unless the effect can be allowed for quantitatively. We present here results that enable us to describe the variations in the total gas content of ice that has been formed in present-day conditions in Antarctica and Greenland for a wide range of temperature (−12 to −53 °C) and elevation (400 to 3,200 m). Using these results, the gas content method can now be applied with much greater confidence than before to indicate past elevation changes.