[M-IS01] アジア・モンスーンの進化と変動，新生代寒冷化との関連

[MIS01-10] History of the Leeuwin Current during the last 5 million years: Evidence from seawater Neodymium isotope variation

★Invited Papers

*高柳 栄子¹、若木 重行²、Irwan Irwan¹、関根 直紀¹、De Vleeschouwer David³、Groeneveld Jeroen³、Bogus Kara⁴、石輪 健樹⁵、佐藤 時幸⁶、Mamo L. Briony⁷、He Yuxin⁸、McHugh M. Cecilia⁹、Reuning Lars¹⁰、Renema Willem¹¹、Christensen A. Beth¹²、Henderiks Jorijntje¹³、Gallagher J. Stephen¹⁴、Fulthorpe S. Craig¹⁵、石川 剛志²、横山 祐典¹⁶、井龍 康文¹ (1.東北大学、2.海洋研究開発機構、3.ブレーメン大学海洋環境科学センター、4.テキサスA&M大学、5.国立極地研究所、6.秋田大学、7.香港大学、8.浙江大学、9.ニューヨーク市立大学、10.アーヘン工科大学、11.ナチュラリス生物多様性センター、12.アデルファイ大学、13.ウプサラ大学、14.メルボルン大学、15.テキサス大学、16.東京大学)

キーワード：レーヴィン海流、ネオジム同位体、西オーストラリア沖、浅海性炭酸塩堆積物、過去500万年間、炭素・酸素同位体比

The Leeuwin Current (LC), a shallow (<300 m depth) and narrow (<100 km width) eastern boundary warm current, transports relatively warm, less saline, and oligotrophic tropical seawater poleward along the Western Australian coastline. The water mass of the LC mainly originates from the Indonesian Throughflow (ITF), which connects the upper ocean circulation of the Pacific and Indian oceans and transports heat and freshwater through the Indonesian Gateway: consequently, a secular variation in strength and volume of the ITF relate closely to that of the LC. Since the ITF associated with the subsequent LC is regarded as one of the significant thermohaline circulations in the Southern Hemisphere, it is crucial to reconstruct a detailed history of these surface currents and to reveal their relationships to regional and global climates.
Orbital- to million-scale variations in the ITF with the subsequent LC during the last 5 Myr are assumed to be related to the tectonic history of the Indonesian seaway restriction/unrestriction and paleoceanographic conditions (e.g., glacial/deglacial sea-level change, El Niño/La Niño-like state of the Pacific Ocean, and variability of the Western Pacific Warm Pool). However, the detailed timing of major restriction/unristriction of the ITF and the initiation and development of the Leeuwin Current are still unclear. The International Ocean Discovery Program (IODP) Expedition 356 recovered continuous Cenozoic (mainly the Miocene or younger) shallow-water carbonates, off northwestern Australia. Since some of the drilled sites are considered to be strongly influenced by the LC, Neodymium isotopes of foraminifers in the shallow-water carbonates are expected to record direct evidence of changes in the water mass along the Western Australian coastline. The objective of our research is to elucidate the long-term history of the Leeuwin Current during the last 5 Myr based on carbon, oxygen, and neodymium isotope records of foraminifers from IODP sites U1460 and U1463.