[A-CC37] [EJ] アイスコアと古環境変動

[ACC37-13] 「最古の氷」に対する²⁶Al/¹⁰Be放射年代決定の可能性：ドームふじ第二期深層コアからの洞察

*堀内 一穂¹、内田 智子²、菅原 愛¹、清野 祥子¹、松田 紗耶¹、松崎 浩之³、本山 秀明⁴ (1.弘前大学、2.東北大学、3.東京大学、4.極地研)

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.