日本地球惑星科学連合2022年大会

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[E] 口頭発表

セッション記号 U (ユニオン) » ユニオン

[U-05] Advanced understanding of Quaternary and Anthropocene hydroclimate changes in East Asia

2022年5月25日(水) 15:30 〜 17:00 302 (幕張メッセ国際会議場)

コンビーナ:窪田 薫(神戸大学大学院人間発達環境学研究科)、コンビーナ:横山 祐典(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)、Chuan-Chou Shen(National Taiwan University)、コンビーナ:Lo Li(Department of Geosciences, National Taiwan University)、座長:窪田 薫(海洋研究開発機構海域地震火山部門)、Li Lo(Department of Geosciences, National Taiwan University)、横山 祐典(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)、Chuan-Chou Shen(National Taiwan University)

16:42 〜 17:00

[U05-05] A multi-dimensional reconstruction of East Asian monsoon-related changes in the South China Sea

★Invited Papers

*Jeroen Groeneveld1、Ooi Ren Yi2、Kuo-Fang Huang3、Min-Te Chen4、Stephan Steinke5、Sze-Ling Ho2 (1.Center for Earth System Research and Sustainability, Institute for Geology, University of Hamburg, Hamburg, Germany、2.Institute of Oceanography, National Taiwan University, No. 1, Sec. 4, Roosevelt Road 10617 Taipei, Taiwan、3.Institute of Earth Sciences, Academia Sinica, Taipei, Taiwan、4.Institute of Applied Geosciences, National Taiwan Ocean University, Keelung, Taiwan、5.Department of Geological Oceanography and State Key Laboratory of Marine Environmental Science, College of Ocean and Earth Sciences, Xiamen University, China)

キーワード:South China Sea, sea water temperatures, east Asian monsoon, Mg/Ca, alkenones, TEX86

The complex oceanography in the South China Sea (SCS) is influenced by the East Asian Monsoon (EAM) and the Western Pacific Warm Pool (WPWP). The relative importance of these two factors vary in space and time, with the WPWP exerting stronger control in the southern SCS while the winter monsoon strongly affects the hydrography in the northern SCS. One of the major characteristics that can be used to reconstruct how water column conditions changed in the SCS through time related to the EAM and WPWP is sea water temperature. Multiple proxies can be used to reconstruct sea water temperatures, but they do not always agree due to differences in the type and ecology of their respective proxy carrier.
In this study we are using the relationships between the proxies to disentangle the spatial pattern of the temperature history of the SCS since the Last Glacial Maximum (LGM) using differences in seasonality and habitat depth of the proxy carriers. We compare two sediment records from the northern (MD97-2146) and southern (MD01-2390; Mg/Ca by Steinke et al., 2006, 2008) SCS. At both sites we have generated paleo-temperature reconstructions using alkenones-based UK’37, archaeal tetraether-based TEX86, and planktonic foraminiferal-based Mg/Ca using both mixed-layer and thermocline-dwelling species.
Reconstructed temperatures in the southern SCS show different trends between the surface and the thermocline. Thermocline temperatures are quite constant, not showing a glacial-interglacial (G-IG) transition suggesting stable subsurface conditions. Sea surface temperatures based on Mg/Ca show a “traditional” G-IG transition with ~3°C warming. Depending on the selected calibration TEX86 temperatures vary up to 6°C but the trend is very similar to mixed-layer Mg/Ca-based temperatures suggesting TEX86 may represent mixed-layer temperatures rather than thermocline temperatures as was suggested previously. Alkenones show as expected the highest SSTs, although there is no clear G-IG transition.
Temperature history in the northern part of the SCS is slightly different. Thermocline temperatures decrease into the Holocene rather than increase indicating that colder subsurface water from outside the SCS was increasingly able to enter the SCS, but it may not have reached the southern SCS. For the mixed layer proxies a similar pattern is present as in the southern SCS, although the magnitude of change varies between Mg/Ca and UK’37.
Our results show that the mixed-layer throughout the SCS is mainly controlled by variations in the summer monsoon related to insolation. The summer EAM was weak during the LGM but increased in strength into the Holocene. The subsurface temperatures are mainly controlled by the presence or absence of the inflow of watermasses from outside the SCS related to variability in the winter monsoon. This supports previous studies that the winter EAM decreased in strength into the Holocene. Further work will synchronize the different proxy records in order to calculate gradients with regard to stratification, seasonality, and north-south transects.