[M-IS05] 南大洋・南極氷床が駆動する全球気候変動

[MIS05-07] Abrupt Holocene ice-sheet retreat in Lutzow-Holm Bay, East Antarctica

*菅沼 悠介^1,2、羽田 裕貴³、板木 拓也³、関 宰⁴、石輪 健樹¹、川又 基人²、藤井 昌和^1,2、草原 和弥⁸、平野 大輔⁴、岩井 雅夫⁹、加藤 悠爾⁹、松井 浩紀⁶、天野 敦子³、香月 興太⁵、大森 貴之⁷、平林 幹啓¹、松崎 浩之⁷、山形 武靖⁷、伊藤 優人⁸、杉山 慎⁴、西田 尚央¹⁰、奥野 淳一^1,2、池原 実⁹、三浦 英樹^1,2 (1.国立極地研究所、2.総合研究大学院大学、3.産業技術総合研究所、4.北海道大学、5.島根大学、6.秋田大学、7.東京大学、8.海洋研究開発機構、9.高知大学海洋コア総合研究センター、10.東京学芸大学)

キーワード：南大洋・南極氷床、新学術、固体班

The Antarctic Ice Sheet (AIS) is one of the most significant potential contributors to future sea-level changes. Recently, the acceleration of AIS’s mass loss has been reported based on satellite observations, such as radar altimetry, interferometer, and gravity measurements, and shipboard observations coupled with modeling studies. In these studies, the main cause of the modern ice mass loss is thought to be iceberg calving and basal melting due to an inflow of modified Circumpolar Deep Water (mCDW). However, the role of the mCDW for the large-scale deglaciation of the AIS, such as the deglaciation since the Last Glacial Maximum (LGM), remains unclear due to the lack of the geological data-based constraint. Therefore, marine and land-based reconstruction of the deglaciation process of the AIS since the LGM is essential to understand the role of the mCDW for a large-scale ice mass loss, which will be a useful analog to calibrate the climate and ice sheet models and to refine the future ice sheet retreat projection. In this presentation, we show an overview of our recent activities in the Lützow-Holm Bay (LHB), Dronning Maud Land, East Antarctica. Newly obtained sedimentary cores and legacy samples from the LHB are used for detailed lithofacies analysis, authigenic Be-10 measurement, hydrogen isotopic compositions analysis, and benthic foraminiferal assemblage of the sedimentary cores. And also, a hybrid age model is constructed by foraminiferal and calibrated bulk organic carbon AMS C-14 dates. These indicate that the East AIS rapidly retreated since the Early Holocene due to an intensified incision of the mCDW. This retreat propagated from the submarine trough to shallower vicinity and then ceased by the Mid-Holocene coincide with the weakening of the mCDW incision. This phenomenon is consistent with the abrupt ice sheet thinning observed along the eastern coast of the bay (Soya Coast) revealed by surface exposure ages and clear lithofacies change of lake sediments and its AMS C-14 dates. This is the first clear terrestrial and marine-based geological constraint for the large-scale deglaciation of the East AIS, driven by a modulation of the mCDW incision, since the LGM.