[U-13] Advanced understanding of Quaternary and Anthropocene hydroclimate changes in East Asia:

[U13-05] Sub-surface water mass exchanges around the eastern equatorial Indian Ocean during the last 50,000 years

★Invited Papers

*高柳 栄子¹、若公 良太¹、木本 ゆうな¹、若木 重行²、黒柳 あずみ¹、石輪 健樹³、横山 祐典⁴、若木 仁美⁵、石川 剛志²、井龍 康文¹ (1.東北大学、2.JAMSTEC、3.極地研、4.東京大学、5.高知大学)

キーワード：インド洋東部、水温躍層、水塊、インドネシア通過流

The eastern equatorial Indian Ocean (EEIO) is part of the Indo-Pacific Warm Pool and its oceanographic conditions change responding to that of the Indonesian Through Flow (ITF). The EEIO plays an important role in the global ocean overturning circulation. Therefore, it is crucial to unravel temporal variations in the interaction between the Pacific and Indian oceans and their relationships with local (around EEIO) and global paleoclimate and paleoceanography at various time scales. In this study, we studied neodymium (Nd) isotope composition (εNd) of bulk benthic foraminifers from a shallow-water to hemipelagic carbonate sediment core drilled at northwestern Australia (IODP Exp. 356, Hole U1464B) to understand changes in surface to sub-surface water mass structures induced probably by the strength of the ITF in the EEIO for the last 50,000 years.
Nd isotope results showed that εNd values of bulk benthic foraminifers fluctuated between –9.1 and –5.2, and its variations accord well with the phase and periodicity of the Earth’s axial obliquity. The εNd values indicated that such variations were caused by exchanges of the source of sub-surface water masses between the Pacific and Indian oceans. Since an increased/decreased axial obliquity is known to result in a reduced/enhanced meridional gradient of solar insolation, respectively, our results indicate that such water mass exchanges in the sub-surface layer around the EEIO are caused by changes in atmospheric and oceanic circulation (including the ITF) as well as those in thermocline depths in the northwestern Pacific Ocean during the last 50,000 years.