[A-CC37] [EJ] Ice cores and past environmental changes

[ACC37-13] On the possibility of radiometric dating on the “oldest ice” using cosmogenic ²⁶Al/¹⁰Be ratio: Insights from the Dome Fuji second deep (DF2) ice core

*Kazuho Horiuchi¹, Tomoko Uchida², Ai Sugawara¹, Shoko Seino¹, Saya Matsuda¹, Hiroyuki Matsuzaki³, Hideaki Motoyama⁴ (1.Graduate School of Science and Technology, Hirosaki University, 2.Institute of Geology and Paleontology, Tohoku University, 3.MALT, The University of Tokyo, 4.National Institute of Polar Research)

Deep ice core records have been playing a crucial role in paleooclimatology. However, there are no records that have reached over ca. 800 ka. To overcome this problem, several research groups are planning to recover the “oldest ice” (~1.5 Ma) from near the bases of ice-sheets overlying inland Antarctica (see e.g. Schiermeier, 2016). Nevertheless, it may be not an easy task to obtain an accurate chronology from such deepest parts of ice cores, because layer inclination and/or folding may prevent us to construct accurate stable-isotope chronologies, which usually rely on normal stratigraphy.

Cosmogenic ²⁶Al and ¹⁰Be are produced by interactions of comic rays with specific elements in the atmosphere. Because the atmospheric production is similar between ²⁶Al and ¹⁰Be, an exponential decrease of the ²⁶Al/¹⁰Be ratio with time, in ordinary cases, should represents the difference of the decay constants of the nuclides (T_1/2 of the ²⁶Al/¹⁰Be ratio is 1.45 Myr). In this presentation, we show the profiles of the ²⁶Al/¹⁰Be ratios of certain stratigraphic intervals of the Dome Fuji second deep (DF2) ice core, plotted against the latest age model for this core (Dome Fuji ice core project members, 2017). By investigating these data, we discuss about the possibility of the radiometric dating on the “oldest ice” of an age of up to 1.5 Ma.