講演情報
[U11-P22]Upwelling in the Timor Sea during the Last Glacial Maximum revealed by beryllium isotope
*根本 夏林1、横山 祐典1,2,3,4、オブラクタ スティーブン5、宮入 陽介1、阿瀬 貴博1 (1.東京大学大気海洋研究所、2.東京大学理学系研究科地球惑星科学専攻、3.東京大学総合文化研究科、4.オーストラリア国立大学、5.秋田大学大学院国際資源学研究科)
キーワード：
ティモール海、ベリリウム同位体、最終氷期最盛期、湧昇
Beryllium isotopes 9Be and 10Be are a unique pair of isotopes in terms of their different sources. Stable isotope 9Be is released from rocks in contrast to the source of radioisotope 10Be produced by nuclear spallation reaction in the atmosphere (meteoric production). The open ocean generally has 10Be/9Be values 100 times higher than the coastal margin reflecting different sources of these isotopes. The portion of beryllium isotopes that co-precipitate with Fe-and Al-oxides or hydroxides is called the authigenic or reactive phase and 10Be/9Be in authigenic and dissolved phases are interchangeable. Thus, it is possible to obtain the 10Be/9Be ratio of the past ocean or other bodies of water by extracting the authigenic phase of beryllium isotopes from marine or lake sediment cores.
The dynamic range of the 10Be/9Be ratio in the ocean has a potential to sensitively detect slight climate change such as the strength of a sea current. Another advantage of using both beryllium isotopes is that it is possible to cancel out secondary effects such as changes in sedimentation rate because each isotope is affected by such effects to the same degree. However, authigenic beryllium isotopes are not applied to the low-latitude continental margin despite its high potential for further application for paleoclimate studies. In this study, the first beryllium isotope record from the low-latitude continental margin was obtained to discuss beryllium isotope’s potential for paleoclimate reconstruction in the low-latitude region.
The analyzed sediment core MD05-2970 was recovered from the Timor Sea, one of the outlets of the Indonesian Throughflow, which is the only pathway to the Indian Ocean from the Pacific Ocean. Glacial topography around the Indonesian Archipelago is dramatically changed because of lower sea level and shallow shelves.
The 10Be/9Be ratio in the Timor Sea is determined by the variation of the 10Be/9Be ratio of the Pacific Ocean, the source of the Indonesian Throughflow, since 30 ka except for the interval around 20 ka. At around 20 ka, anomalously high 10Be/9Be ratios in the Timor Sea was achieved by upwelling of higher 10Be/9Be water because of the reduced and surface shifted Indonesian Throughflow. This interpretation is supported by smaller temperature differences between surface and thermocline water (ΔT), the increase of radiocarbon reservoir age and the increase of productivity in the Timor Sea.
The dynamic range of the 10Be/9Be ratio in the ocean has a potential to sensitively detect slight climate change such as the strength of a sea current. Another advantage of using both beryllium isotopes is that it is possible to cancel out secondary effects such as changes in sedimentation rate because each isotope is affected by such effects to the same degree. However, authigenic beryllium isotopes are not applied to the low-latitude continental margin despite its high potential for further application for paleoclimate studies. In this study, the first beryllium isotope record from the low-latitude continental margin was obtained to discuss beryllium isotope’s potential for paleoclimate reconstruction in the low-latitude region.
The analyzed sediment core MD05-2970 was recovered from the Timor Sea, one of the outlets of the Indonesian Throughflow, which is the only pathway to the Indian Ocean from the Pacific Ocean. Glacial topography around the Indonesian Archipelago is dramatically changed because of lower sea level and shallow shelves.
The 10Be/9Be ratio in the Timor Sea is determined by the variation of the 10Be/9Be ratio of the Pacific Ocean, the source of the Indonesian Throughflow, since 30 ka except for the interval around 20 ka. At around 20 ka, anomalously high 10Be/9Be ratios in the Timor Sea was achieved by upwelling of higher 10Be/9Be water because of the reduced and surface shifted Indonesian Throughflow. This interpretation is supported by smaller temperature differences between surface and thermocline water (ΔT), the increase of radiocarbon reservoir age and the increase of productivity in the Timor Sea.