[M-IS08] 南大洋・南極氷床が駆動する全球気候変動

[MIS08-05] 東南極リュツォ・ホルム湾における周極深層水流入に起因した完新世の氷床融解

*菅沼 悠介^1,2、川又 基人³、草原 和弥⁵、Lifton Nathaniel⁶、石輪 健樹^1,2、香月 興太⁴、藤井 昌和^1,2、平林 幹啓¹、奥野 淳一^1,2 (1.国立極地研究所、2.総合研究大学院大学、3.寒地土木研究所、4.島根大学、5.海洋研究開発機構、6.Department of Earth, Atmospheric, and Planetary Sciences, Purdue University)

キーワード：南大洋・南極氷床、大規模氷床融解、表面露出年代測定

Recent observations and model simulations show that the inflow of warm Circumpolar Deep Water (CDW) causes rapid melting and thinning of the ice shelves of the West Antarctic Ice Sheet, contributing to the ongoing increase in discharge of grounded ice and to sea-level rise. This process is also thought to contribute to the deglaciation of the West Antarctic Ice Sheet after the Last Glacial Maximum (LGM) ca. 21 ka. However, unlike West Antarctica, the role of the CDW in a potential large-scale ice-mass loss in the East Antarctic is unclear. Here, we present a new, well-constrained ice retreat history since the LGM for Lützow-Holm Bay, East Antarctica, based on a detailed geomorphological survey and ¹⁰Be and ¹⁴C surface exposure dating of erratics and bedrock. These show that ice sheet melting in Lutzow-Holm Bay began in the southeastern part of the bay along the Shirase submarine valley from ca. 9 to 5 ka and eventually spread to the northeast ca. 8–4 ka. Regional high-resolution oceanographic modeling shows that the current warmer ocean temperature in the southeastern part of the bay results from the inflow of warm CDW via the submarine valley. Thus, these oceanographic and bathymetric characteristics likely caused the asymmetric early to mid-Holocene deglaciation in Lützow-Holm Bay, East Antarctica.