Sources, distributions and transport processes of Pu isotopes in NW Pacific margin

• Main Authors: Zheng Jian, Yamada Masatoshi
• Format: Conference Object
• Language: English
• Published: 2019
• Subjects: Okhotsk; Pacific; okhotsk sea
• Online Access: https://repo.qst.go.jp/?action=repository_uri&item_id=63125; http://id.nii.ac.jp/1657/00063113/

Plutonium was introduced into the environment mainly from the fallout of atmospheric nuclear weapons tests. Over the past years, we have made a systematic investigation on the distribution of Pu isotopes in the NW Pacific Ocean and its adjacent seas: the East China Sea, Okinawa Trough, the Japan Sea and the Okhotsk Sea. Based on the obtained 240Pu/239Pu ratio signature, we identified the wide presence of Bikini close-in fallout Pu in the studied regions, which contributed to the excess Pu inventories. We proposed that the oceanic process is responsible for the wide presence of Bikini close-in fallout Pu. Using a two fallout end-member model, we resolved the relative contribution of Pu between global fallout and close-in fallout in sediments. We concluded that the contribution of Bikini close-in fallout Pu ranged from 10 % to 60 % in the studied regions [1-5]. To verify our hypothesis on the oceanic process for the transport of Pu in the Pacific Ocean, we further investigated the Pu isotopic signature in seawater and settling particles in the western Northwest Pacific [6-7]. Three transport processes were identified to be responsible for the distribution and fate of Pu isotopes in the NW Pacific margin: (1) advective lateral transport of dissolved Pu from open ocean to ocean margin; (2) vertical transport of Pu isotopes via particle scavenging; and (3) the bottom layer lateral transport and redistribution of Pu isotopes. \n[1] Zheng & Yamada (2004) ES&T 38, 3498-3504. [2] Zheng &Yamada, (2005) Stoten 340, 199-211. [3] Wang & Yamada (2005) EPSL 233, 441-453. [4] Zheng & Yamada (2006) JRNC 267, 73-83. [5] Zheng & Yamada (2005) JEM 7, 792-797. [6] Yamada et al. (2007) JER 98, 274-284. [7] Zheng & Yamada (2006) ES&T 40, 4103-4108. Goldschmidt 2009