[M-IS19] 古気候・古海洋変動

[MIS19-22] 最終氷期最盛期とそれに続く急激な氷床成長および崩壊と海水準変動

*横山 祐典¹、エサット テザー⁹、トンプソン ウィリアム¹⁰、トーマス アレクサンダー¹¹、ウェブスター ジョディ²、宮入 陽介¹、沢田 近子¹、阿瀬 貴博¹、松崎 浩之¹、奥野 淳一³、ファロン スチュワート⁹、ブラガ フアンカルロス¹²、マーク ハンブレ⁴、井龍 康文⁵、ポッツ ドナルド¹³、藤田 和彦⁶、鈴木 淳⁷、菅 浩伸⁸ (1.東京大学　大気海洋研究所 高解像度環境解析研究センター、2.シドニー大学　、3.国立極地研究所、4.名古屋大学、5.東北大学、6.琉球大学、7.産業技術総合研究所、8.九州大学、9.オーストラリア国立大学　地球科学研究所、10.ウッズホール海洋研究所、11.エジンバラ大学、12.グラナダ大学、13.カリフォルニア大学　サンタクルーズ校)

キーワード：海水準、氷床、最終氷期最盛期

Studying changes in rates and magnitudes of glaciations/deglaciations during the past is a key to understand global climate system. The Last Glacial Maximum (LGM), centered around 20,000 years ago, as well as period after the LGM, therefore, represents key period to investigate. Sea level observations from sites far from the former ice sheets (far-field) are well suited due to the relatively small influence of surface deformation caused by glacio-hydro-isostatic adjustments (GIA). Australian coastlines are located in such regions and were targeted in this study of sea level changes over the past 30,000 years. The sites are situated off the North Eastern and North Western coasts of Australia respectively the Great Barrier Reef (GBR) and Bonaparte Gulf. Over thirty fossil reef cores were obtained from GBR shelf edge and two transects in northern and southern sites and >1,000 radiometric dating were conducted, in combination with detailed sedimentogic and biologic studies (Yokoyama et al., 2018). GIA modeling was also conducted to deduce global mean sea level (GMSL) from relative sea level records obtained from these regions. The results show that the LGM started when GMSL abruptly dropped by about 40 metres at around 31,000 years ago. The sea level at the shelf edge of the Great Barrier Reef then dropped by around 20 metres between 22,000 and 21,500 years ago, to -118 metres below the present and similar changes are observed in Bonaparte Gulf samples. Sea level began to rise just after the full extent of the LGM, consistent with previous studies. The LGM GMSL obtained from our study is about -125 to -130 metres. Sea level records from the North Australian coasts suggest that glaciers may have behaved more dynamically during the LGM than previously thought. The GBR had been existed despite from severe environmental changes during the last 30,000 years (Webster et al., 2018).

References:
Yokoyama et al. (2018) Nature, v559, p603-607
Webster, Yokoyama et al (2018) Nature Geoscience, v11, p426-432