[M-IS20] 南大洋・南極氷床が駆動する全球気候変動

[MIS20-04] Synchronous Holocene ice sheet thinning across coastal Dronning Maud Land, East Antarctica

*菅沼 悠介^1,2、金田 平太郎³、Mas e Braga Martim ^7,9、石輪 健樹¹、小山 拓志⁴、Newall Jennifer ^7,9,10、奥野 淳一^1,2、小長谷 貴志⁸、齋藤 冬樹¹¹、Rogozhina Irina ¹²、Andersen Jane ^7,9,13、川又 基人^5,1、平林 幹啓¹、Lifton Nathaniel^10,14、Fredin Ola^12,6、Harbor Jonathan ^9,10,7、Stroeven Arjen ^7,9、阿部 彩子^8,1 (1.国立極地研究所、2.総合研究大学院大学、3.中央大学、4.大分大学、5.寒地土木研究所、6.Geological Survey of Norway、7.Geomorphology and Glaciology, Department of Physical Geography, Stockholm University、8.東大大気海洋研、9.Bolin Centre for Climate Research, Stockholm University、10.Department of Earth, Atmospheric, and Planetary Sciences, Purdue University、11.海洋研究開発機構、12.Department of Geography, Norwegian University of Science and Technology、13.Department of Geosciences, Aarhus University、14.Department of Physics and Astronomy, Purdue University)

キーワード：南大洋・南極氷床、新学術、固体班

Reconstructing past variability of the Antarctic ice sheets is essential to understand their response to future climate change and to anticipate their contribution to global sea-level change. Recent satellite observations show that ice-mass loss has accelerated not only from the West Antarctic Ice Sheet but also from some sectors of the East Antarctic Ice Sheet (EAIS). However, uncertainties in past ice-sheet reconstructions, especially for the EAIS, impede validation of ice sheet and glacial isostatic adjustment (GIA) models, and thus estimations of ice mass change based on satellite measurements. Here, we present a new deglacial chronology based on surface exposure dating of erratic rock samples from Gjelsvikfjella in the drainage basin of Jutulstraumen ice stream, central Dronning Maud Land (DML), East Antarctica. Thirty-nine cosmogenic ¹⁰Be exposure ages from two nunataks (Grotfjellet and Rabben) cluster around 5.7-8.4 ka. These exposure ages and a new high-resolution ice sheet model over the Jutulstraumen catchment suggest that the EAIS around these nunataks lowered by ~ 100 m during the early- to mid-Holocene. This timing of ice thinning around Gjelsvikfjella matches the recently reported deglacial chronology from the Soya Coast, Lutzow-Holm Bay (Kawamata et al. 2020), indicating that ice-sheet thinning was synchronous throughout Dronning Maud Land. The newly obtained deglacial chronology allows us to constrain and refine GIA-derived ice load histories and sea-level changes. These data further indicate that a warming of the Circumpolar Deep Water, simulated by a coupled ocean-atmosphere climate model, and following a regional sea-level high stand due to GIA, may be responsible for the early- to mid-Holocene rapid ice sheet thinning in DML.