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Suzuki, Takashi; Otosaka, Shigeyoshi; Kuwabara, Jun; Kawamura, Hideyuki; Kobayashi, Takuya
Biogeosciences, 10(6), p.3839 - 3847, 2013/06
Times Cited Count：24 Percentile：57.25(Ecology)no abstracts in English
Co in the digestive glands of the common octopus, 
, in the East China SeaMorita, Takami*; Otosaka, Shigeyoshi; Fujimoto, Ken*; Nishiuchi, Ko*; Kimoto, Katsunori*; Yamada, Haruya*; Kasai, Hiromi*; Minakawa, Masayuki*; Yoshida, Katsuhiko*
Marine Pollution Bulletin, 60(8), p.1193 - 1199, 2010/08
Times Cited Count：3 Percentile：10.16(Environmental Sciences)Significant concentrations of Co, 
Cs and 
Ag were detected in common octopus specimens collected in the East China Sea during two periods, 1986-1989 and 1996-2005. The radionuclides detected in the former period were thought to originate from the global fallout. On the other hand, the source of Co in the latter period has remained unclear because the Co concentration decreased continuously with shorter half-lives than the physical half-lives. This tendency suggests that the source of Co in 1996-2005 was identical and was temporary supplied to the East China Sea. Investigations of common octopus in the other area indicated that the origin of the pollutant source of Co in 1996-2005 occurred locally in the restricted area in the East China Sea rather than in the coastal area of Japan.
Morita, Takami*; Niwa, Kentaro*; Fujimoto, Ken*; Kasai, Hiromi*; Yamada, Haruya*; Nishiuchi, Ko*; Sakamoto, Tatsuya*; Godo, Waichiro*; Taino, Seiya*; Hayashi, Yoshihiro*; et al.
Science of the Total Environment, 408(16), p.3443 - 3447, 2010/06
Times Cited Count：13 Percentile：32.79(Environmental Sciences)Iodine-131 (
I) was detected in brown algae collected off the Japanese coast. The maximum measured specific activity of I in brown algae was 0.37
0.010 Bq/kg-wet. Cesium-137 (Cs) was also detected in all brown algal samples used in this study. There was no correlation between specific activities of I and Cs in these seaweeds. Low specific activity and minimal variability of Cs in brown algae indicated that past nuclear weapon tests were the source of Cs. Although nuclear power facilities are known to be pollution sources of I, there was no relationship between the sites where I was detected and the locations of nuclear power facilities. Most of the sites where I was detected were near big cities with large populations. On the basis of the results, we suggest that the likely pollution source of I, detected in brown seaweeds, is not nuclear power facilities, but nuclear medicine procedures.
Suzuki, Takashi; Minakawa, Masayuki*; Kabuto, Shoji; Togawa, Orihiko
Dai-12-Kai AMS Shimpojiumu Hokokushu, p.69 - 72, 2010/05
no abstracts in English
Suzuki, Takashi; Minakawa, Masayuki*; Amano, Hikaru; Togawa, Orihiko
Nuclear Instruments and Methods in Physics Research B, 268, p.1229 - 1231, 2010/04
Times Cited Count：26 Percentile：84.94(Instruments & Instrumentation)no abstracts in English
C signaturesOtosaka, Shigeyoshi; Tanaka, Takayuki; Minakawa, Masayuki*
JAEA-Conf 2010-001, p.113 - 117, 2010/03
Transport processes of particulate materials were discussed from elemental and isotopic proxies of seabed sediment, suspended particles and sinking particles collected from northeastern region of the Japan Sea. Isotopic ratios of radiocarbon in suspended/sedimentary organic matter decreased with a horizontal distance from the shelf edge. Assuming that the decrease of the isotopic ratio is due to the radioactive decay of radiocarbon, the authors estimated that suspended particles were transported horizontally through the benthic layer at a speed of 200 m/year.
Otosaka, Shigeyoshi; Suzuki, Takashi; Tanaka, Takayuki
KURRI-KR-153, p.41 - 46, 2010/03
It is considered that recent distribution of anthropogenic radionuclides in the Japan Sea was controlled by supply of the radionuclides due to the global fallout and seawater circulation of the interior of the sea, rather than by a specific nuclear facility/incident. The detailed transport processes, however, have not been elucidated at the present. In this study, the authors surveyed distribution of radiocarbon at 81 stations in the Japan Sea and traced the fate of anthropogenic radiocarbon. As a result, principal transport process of radiocarbon, such as (1) supply from the East China Sea, (2) northward transport at the surface according to the Tsushima Warm Current, and (3) vertical transport in the northwestern region, were confirmed. In addition, the amount of anthropogenic radiocarbon in the sea was estimated by using a simple box-model.
I and C in the eastern Japan BasinSuzuki, Takashi; Minakawa, Masayuki*; Togawa, Orihiko
Dai-11-Kai AMS Shimpojiumu Hokokushu, p.31 - 34, 2009/01
no abstracts in English
Aramaki, Takafumi*; Togawa, Orihiko; Otosaka, Shigeyoshi; Suzuki, Takashi; Amano, Hikaru; Tanaka, Takayuki; Senju, Tomoharu*; Minakawa, Masayuki*
JAEA-Conf 2008-005, p.149 - 152, 2008/03
no abstracts in English
Takata, Hyoe*; Kuma, Kenshi*; Isoda, Yutaka*; Otosaka, Shigeyoshi; Senju, Tomoharu*; Minakawa, Masayuki*
Geophysical Research Letters, 35(2), p.L02606_1 - L02606_5, 2008/01
Times Cited Count：19 Percentile：44.02(Geosciences, Multidisciplinary)Concentrations of iron in seawater (dissolved and labile dissolved phases) in the two basins (Yamato Basin and Japan Basin) of the Japan Sea are measured and the origin and behavior of iron were discussed. Extremely high vertically integrated total dissolvable Fe inventories (300-350 
mol m
) were observed at the surface water in both basins (0-200 m depth), and was probably resulting from high atmospheric Fe input to the surface water. Labile dissolved Fe in both basins was characterized by mid-depth (1-2 km depth) maxima, which were regulated by the competition between dissolved Fe input from the microbial decomposition of sinking biogenic organic matter and Fe removal by particulate scavenging. The distributions of Fe in the Japan Sea would play an important role in understanding the biogeochemical cycle of iron in the ocean.
Suzuki, Takashi; Minakawa, Masayuki*; Amano, Hikaru; Togawa, Orihiko
Dai-10-Kai AMS Shimpojiumu Hokokushu, p.147 - 150, 2008/00
no abstracts in English
Otosaka, Shigeyoshi; Togawa, Orihiko; Tanaka, Takayuki; Amano, Hikaru; Minakawa, Masayuki*
no journal, ,
In order to understand biogeochemical cycles of particulate materials in the deep part of the Japan Sea, we assessed processes and a time scale of transport of particulate materials by measurements of particulate lead-210 (210Pb) and organic radiocarbon (14C) in settling particles collected in three regions of the Japan Sea; the western Japan Basin (WJB), the eastern Japan Basin (EJB) and the Yamato Basin (YB). Values of delta-14C in settling particles collected at 1 km depth ranged -1322 per mill, and there were little differences in delta-14C between sampling stations. In the YB, delta-14C values of settling particles collected in the bottom layer (about 200 m above the bottom) were similar to those in 1 km depth. On the other hand, the delta-14C values in bottom layer in the WJB and EJB were about 55 per mill smaller than those at shallower layers. These results in indicated that the deep part of the Japan Basin had a larger time scale of POC cycle than the Yamato Basin. By a comparison of mass balance of 210Pb between the WJB and EJB, it was estimated that about 60% of particulate 210Pb supplied to the WJB exported horizontally to the EJB.
Suzuki, Takashi; Minakawa, Masayuki*; Togawa, Orihiko
no journal, ,
no abstracts in English
Yoshida, Keisuke*; Inoue, Mutsuo*; Minakawa, Masayuki*; Nakano, Yusuke*; Kofuji, Hisaki*; Otosaka, Shigeyoshi; Kiyomoto, Yoko*; Shiomoto, Akihiro*; Hamajima, Yasunori*; Yamamoto, Masayoshi*
no journal, ,
The authors have developed an analytical method for Th-228, Ra-226 and Ra-228 measurements in seawater using an ultra-low background 
-ray detector. In this study, the authors measured the three radionuclides in surface seawater obtained from 16 stations in the Japan Sea, East China Sea and Okhotsk Sea. Concentrations of Ra-228 and Th-228 in surface waters in the southern Japan Sea were lower than those in the northern regions. Considering that the Th-228/Ra-228 activity ratios were not different between the northern and southern regions of the Japan Sea, we could conclude that (1) input of terrestrial materials from the East China Sea has not affected the distribution of the radionuclides in the Japan Sea, and (2) the efficiency of scavenging was not different between the regions.
Oku, Shunsuke*; Otosaka, Shigeyoshi; Minakawa, Masayuki*; Minami, Hideki*; Noriki, Shinichiro*
no journal, ,
Autochthonous Ba (Ba-xs) in seawater is enriched in particulate materials by marine biota and settles down to the seabed. Therefore, Ba-xs is known as a proxy of export production in the surface ocean. However, it is necessary to discuss the effect of lateral transport of Ba-xs for the accurate estimation of the export flux. In this study, the authors investigated the effect of lateral transport of Mn-xs from a sediment trap experiment in the Japan Sea. Particulate fluxes of Ba-xs showed a positive relationship between flux of autochthonous Mn (Mn-xs). The flux of Mn-xs was higher in winter and it might be caused by the lateral transport of particulate materials from the shelf regions. The results indicated that Ba-xs is transported laterally and the effect was on a par with the sinking of biogenic particles.
I in the Japan Basin and Yamato BasinSuzuki, Takashi; Minakawa, Masayuki*; Togawa, Orihiko
no journal, ,
no abstracts in English
Otosaka, Shigeyoshi; Tanaka, Takayuki; Amano, Hikaru; Togawa, Orihiko; Noriki, Shinichiro*; Minakawa, Masayuki*
no journal, ,
An apparent age of particulate organic matter (POM) in seawater that is estimated from isotopic ratio of radiocarbon is convenient indicator for verifying transport processes of POM in the ocean. However, it is suggested that isotopic ratio of radiocarbon also reflects mixing of old POM from the surrounding regions and seafloor as well as an age of the POM. In this study, we discuss the cause of the variation in apparent age of POM from radiocarbon measurements of various particulate materials obtained at the northeastern Japan Sea and the northwestern North Pacific.
Suzuki, Takashi; Amano, Hikaru; Togawa, Orihiko; Minakawa, Masayuki*
no journal, ,
no abstracts in English
Aramaki, Takafumi*; Togawa, Orihiko; Otosaka, Shigeyoshi; Suzuki, Takashi; Senju, Tomoharu*; Minakawa, Masayuki*
no journal, ,
no abstracts in English
Otosaka, Shigeyoshi; Amano, Hikaru; Tanaka, Takayuki; Togawa, Orihiko; Noriki, Shinichiro*; Kaba, Masato*; Minakawa, Masayuki*
no journal, ,
In order to understand biogeochemical cycles of particulate materials in the deep part of the Japan Sea, the authors assessed the processes and a time scale of transport of particulate materials by measurements of organic radiocarbon (C-14) in settling/suspended particles collected in three regions of the Japan Sea; the northwestern, northeastern and southeastern regions. Isotopic ratios of C-14 in settling particles collected at 1 km depth showed little differences between the sampling regions. In the southeastern region, isotopic ratios of C-14 of settling particles collected in the bottom layer (about 0.5 km above the bottom) were similar to those in 1 km depth. On the other hand, the ratios in bottom layer of the northern regions were smaller than those at the shallower layers significantly. These results in indicated that there are different origins of POC between the northern and southeastern regions of the Japan Sea.
