Snow stratigraphy and oxygen isotope variations in the glaciological pit of King Baudouin Station, Queen Maud Land, Antarctica

Abstract

O18/O16 ratios have been measured along a firn profile extending from the surface to a depth of 16 meters in the shelf ice of King Baudouin station (East Antarctica, 70°26′S, 24°19′E). Periodical variations are found which are believed to reflect the seasonal variations in the O18/O10 ratio of precipitations. They allow the identification of annual layers following the method suggested by Epstein and Sharp. The oxygen isotope variations are compared with the stratigraphic features of the same profile. The notion ‘winter’ or ‘summer’ layers is shown to be meaningless when the layers are derived from stratigraphie criteria only. Very often the fine-grained unmetamorphosed layers (generally called ‘winter’ layers) are made up of snow with high O18 content which must represent summer precipitation. On the other hand, the coarse-grained recrystallized layers (‘summer’ layers) often display a minimum O18 content and are composed of snow that fell in the winter. Identification of annual layers involves a similar degree of uncertainty from personal interpretation in the stratigraphic method as well as in the isotope ratio method, but the two methods are complementary, being affected differently by natural circumstances. A good agreement is found between the average accumulation rates deduced from both methods.