Preliminary results for stratigraphy and chronology of blue ice in Larsen Glacier, East Antarctica

Among the paleoclimate archives, we may take advantage of ice cores to directly measure greenhouse compositions of ancient air. Nevertheless, ice cores from deep drilling projects recover limited amount of ice for a given time period and hence limiting the studies that need an extensive amount of ice such as trace gas isotopes. In contrast, blue ice areas (BIAs) may provide a large amount of ancient ice outcropped at the surface. However, ice flow makes the blue ice stratigraphy complicated in many areas, and accordingly makes it difficult to reconstruct a continuous stratigraphy. Recently, the oldest ice was discovered at Allan Hills BIA (about 2.7 Ma). However, the stratigraphy is not continuous for the older part. Here we show preliminary results from Larsen Glacier, East Antarctica. The Ground Penetrating Radar (GPR) results show parallel ice layers near the surface with dips of 1-5° and indicate that the ice thickness ranges of 200–400 m. δD_ice of a vertical core sample matches well with that in the horizontally spaced surface ice samples. Greenhouse gas concentrations are significantly altered at shallow depths of < ~4.5 m. The δ¹⁸O_atm, CH₄ concentration and stable isotopes of ice (δ¹⁸O_ice, δD_ice) indicate that the Larsen BIA cover the Last Glacial Termination at the studied sites. ⁸¹Kr ages, corrected by ⁸⁵Kr for the modern air contamination, are less than 54 ka, supporting the ages constrained by the other chemistry data.