[A-CC26] アイスコアと古環境モデリング

[ACC26-03] ドームふじ氷床コアの年代構築（DF2021）

*大藪 幾美¹、川村 賢二^1,2,3、Buizert Christo⁴、Parrenin Frédéric⁵、Orsi Anais⁶、北村 享太郎¹、青木 周司⁷、中澤 高清⁷ (1.情報・システム研究機構　国立極地研究所、2.総合研究大学院大学、3.海洋研究開発機構、4.オレゴン州立大学、5.フランス環境地球科学研究所、6.フランス気候環境科学研究所、7.東北大学)

キーワード：アイスコア 、南極、年代、ドームふじ

Precise ice-core chronologies are essential for identifying the timing and duration of polar climatic changes as well as their phasing with the changes in other parts of the globe. However, existing ice-core chronologies beyond the last 60 kyr show relatively large disagreements with each other and with U-Th chronologies of speleothems. Here, we constructed new ice and gas age scales for the Dome Fuji (DF) core (DF2021) over the last 207 kyr by combining a Bayesian dating model and firn densification model, constrained by various types of chronological and glaciological information including new δO₂/N₂ age markers, precise synchronization to other high-quality chronologies (volcanic, cosmogenic, and CH₄ signals), and high-resolution δ¹⁵N of N₂ (reflecting past firn thickness). The new chronology is tightly constrained by synchronization to other well-dated records for the last 60 kyr, whereas it is independent from other chronologies for the older period. For the last 60 kyr, the DF2021 chronology agrees with the layer-counted ice core chronologies (GICC05 and a part of WD2014) and U-Th chronologies of speleothems within ~200 years. For the period 60 – 130 kyr BP, the timing of all Dansgaard-Oeschger warming events on DF2021 agree with those of corresponding events in the U-Th dated Chinese or European speleothems mostly within 1 kyr (well within 2σ uncertainty of DF2021). The excellent agreement suggests high accuracy of our chronology, and supports the assumption of negligible phasing between the past local summer solstice insolation and δO₂/N₂ fractionation at bubble close-off (the basis for constructing the δO₂/N₂ age markers). Between 130 and 207 kyr BP (penultimate glacial period), there is a lower degree of similarity between the variations in atmospheric CH₄ and speleothem calcite δ¹⁸O than in the last glacial period, making the age comparison challenging. The comparison of DF2021 with 9 U-Th dates at 7 abrupt events shows the mean difference of -0.2 ± 0.8 kyr, which is within the DF2021 uncertainty (on the order of 1.5 kyr). The DF2021 chronology agrees with the AICC2012 chronology within 2 kyr except between ~103 and 128 kyr BP where AICC2012 is likely too young by up to ~4 kyr. We also estimated accumulation rate and surface temperature using the firn densification model. Our result shows that surface temperature at Dome Fuji during the last interglacial period was ~2 K higher than preindustrial, which is lower than the estimates from water isotopes.