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Journal Articles

Grain size dependence of meteoric $$^{10}$$Be concentrations in bed-sediments of Ado and Yasu rivers flowing into Lake Biwa

Fujisawa, Jumpei*; Minami, Masayo*; Kokubu, Yoko; Matsuzaki, Hiroyuki*

JAEA-Conf 2018-002, p.91 - 94, 2019/02

https://doi.org/10.11484/jaea-conf-2018-002

Beryllium-10 ($$^{10}$$Be) of a cosmogenic nuclide precipitates in forms of BeO and Be(OH)$$_{2}$$ attaching with aerosol on the Earth surface. It is accumulated on the sea- and lake-bottoms. Recently, the meteoric $$^{10}$$Be is attracting attention as a powerful tool for investigating the past climate change, because it is affected by the earth- and lorcal- cyclical changes of materials such as atmosphere and water circulation. The $$^{10}$$Be exists mostly as hydroxide at pH $$>$$5, and is easy to adhere to soil and mineral surface. Therefore, $$^{10}$$Be concentration in sediment could be influenced by its grain size composition because fine-grained sediment has a big surface area per unit mass. The purpose of this study is to reveal the relationship between $$^{10}$$Be concentrations and the grain-size of river sediments. The samples used were bottom-sediments of 18 rivers flowing into Lake Biwa, Japan. The sediments were sieved to 5 fractions and analyzed each for $$^{10}$$Be concentration by JAEA-AMS-TONO.

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Meteoric $$^{10}$$Be in bed-sediments of Ado and Yasu rivers flowing into Lake Biwa

Fujisawa, Jumpei*; Minami, Masayo*; Kokubu, Yoko

no journal, , 

To investigate grain size dependency on concentration of meteoric $$^{10}$$Be extracted from river bed-sediment, we analyzed the $$^{10}$$Be in bed-sediments of Yasu and Ado rivers flowing into Lake Biwa, Shiga Prefecture. Each of 5 grain size fractions was sequentially leached to extract Ex (Exchangeable), Am-Ox (amorphous oxy-hydroxide) and X-Ox (crystalline oxy-hydroxide) phases, respectively, and the $$^{10}$$Be concentrations of the leachates were measured. Most meteoric $$^{10}$$Be was located in the Am-Ox and X-Ox phases. The concentrations of bulk and extracted fractions decreased with increasing grain size. Furthermore, the bed-sediments from upper stream showed higher concentration than those from downstream, and this tendency was stronger in Yasu river than in Ado river. The difference between Yasu and Ado river sediments could be due to lower pH of water in Yasu river than in Ado river, that is, due to more partitioning of Be into water relative to sediment particles in Yasu river.

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