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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：2 Percentile：8.41(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.
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：24 Percentile：86.24(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.
ISuzuki, Takashi; Minakawa, Masayuki*; Togawa, Orihiko
JAEA-Conf 2010-001, p.15 - 18, 2010/03
no abstracts in English
Otosaka, Shigeyoshi; Suzuki, Takashi; Tanaka, Takayuki; Ito, Toshimichi; Kobayashi, Takuya; Kawamura, Hideyuki; Minakawa, Masayuki*; Aramaki, Takafumi*; Senju, Tomoharu*; Togawa, Orihiko
JAEA-Data/Code 2009-020, 27 Pages, 2010/02
JAEA-Data-Code-2009-020.pdf:2.45MB
The database for the Japan Sea parameters on marine environment and radionuclides (JASPER) has been established by the Japan Atomic Energy Agency as a product of the Japan Sea Expeditions. By the previous version of the database, data for representative anthropogenic radionuclides were opened to public. And now, data for radiocarbon and fundamental oceanographic properties (salinity, temperature, dissolved oxygen) including nutrients (silicate, phosphate, nitrate and nitrite) are released as the second volume of the database. In the second volume, 20,398 data records are stored including 2,695 data for temperature, 2,883 data for salinity, 2,109 data for dissolved oxygen, 11,051 data for the nutrients, and 1,660 data for radiocarbon. The database will be a strong tool for the continuous monitoring for contamination by anthropogenic radionuclides, studies on biogeochemical cycle, and development and validation of models for numerical simulations in the sea.
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
Otosaka, Shigeyoshi; Tanaka, Takayuki; Togawa, Orihiko; Amano, Hikaru; Karasev, E. V.*; Minakawa, Masayuki*; Noriki, Shinichiro*
Journal of Oceanography, 64(6), p.911 - 923, 2008/12
Times Cited Count：19 Percentile：45.18(Oceanography)Transport processes of particulate organic carbon (POC) were inferred from sediment trap experiments in the three regions of the Japan Sea (western and eastern Japan Basin and Yamato Basin) and radiocarbon measurement. Annual mean C/
C isotopic ratio decreased with depth and the vertical changes in the isotopic signature were considered to indicate mixing of two fractions; labile POC produced in the surface and refractory POC. From seasonal variations of POC flux of the two fractions, transport processes of POC in the Japan Sea were summarized as follows: (1) In the Japan Basin, both labile and refractory POC were supplied in spring and a reservoir of refractory POC was formed, and (2) in the Yamato Basin, larger amount of refractory POC were carried the interior and accumulated rapidly.
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
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 -13
22 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.
Otosaka, Shigeyoshi; Minakawa, Masayuki*; Noriki, Shinichiro*
no journal, ,
Sediment trap experiments in the Japan Sea are useful in order to know trends of transport processes of particulate materials in the world's ocean, because the Japan Sea is known as a "miniature" of the ocean. In this study, results of sediment trap experiments in the Japan Sea that were carried out by JAEA, Hokkaido University and Fishery Research Association of Japan from 1999 to 2002 were summarized. Particulate fluxes in the Japan Sea were larger in the western Japan Basin where nutrients were effectively supplied to surface layers. Using elemental composition of rare earth elements in settling particles as a indicator of the origin of lithogenic particles, three source materials of lithogenic particles to the Japan Sea were defined. It was also suggested that about 60% of particulate materials supplied to the deep part of the western Japan Basin were transported horizontally to the eastern Japan Basin through the deep layers. The biogeochemical cycle of particulate materials in the "model-ocean" such as Japan Sea would strongly help the study on global cycles of major/trace materials in the ocean by combining long-term observations of particulate flux in the North Pacific.
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.
Aramaki, Takafumi*; Togawa, Orihiko; Otosaka, Shigeyoshi; Suzuki, Takashi; Senju, Tomoharu*; Minakawa, Masayuki*
no journal, ,
no abstracts in English
Suzuki, Takashi; Amano, Hikaru; Togawa, Orihiko; Minakawa, Masayuki*
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.
Otosaka, Shigeyoshi; Tanaka, Takayuki; Togawa, Orihiko; Amano, Hikaru; Minakawa, Masayuki*; Khim, B.-K.*; Noriki, Shinichiro*
no journal, ,
A time-scale of particulate organic carbon (POC) in the Japan Sea, a marginal sea of the North Pacific, was quantified from radiocarbon (C-14) and stable carbon (C-13) measurements. Delta C-14 in POC decreased with depth, and the value was higher in the order of sinking POC, suspended POC and seabed sediment. delta C-13 values in suspended POC were higher than those in sinking POC obtained from the similar depth. From the radiocarbon signatures and elemental compositions of sinking POC, it was considered that Delta C-14 in sinking POC was determined by a mixing ratio of terrestrial and surface-produced POC. In addition, the difference of Delta C-14 and delta C-13 between the terrestrial and suspended POC was considered to indicate migration process of POC in the water column. From the difference of the C-14 age between terrestrial and suspended POC, it was estimated that an actual age of suspended POC at 3 km depth in the Japan Sea was about 300 years.
Otosaka, Shigeyoshi; Oku, Shunsuke*; Minami, Hideki*; Minakawa, Masayuki*; Noriki, Shinichiro*
no journal, ,
The Japan Sea is regarded as a miniature of the ocean because of its bowl-like topography and unique seawater circulation. Recent studies have suggested that biogeochemical processes in the Japan Sea correspond with the global climate change. In this study, we assessed decadal changes in particulate flux and elemental composition of sinking particle in the Japan Sea by comparing results of a sediment trap experiment in September 1984 with those in 1999-2001. Total mass flux did not show remarkable temporal change, however, biogenic opal/carbonate ratios observed recently were lower than those from the previous observation. In addition, relative content of scavenging elements such as manganese and cobalt also showed a decrease between the 15 years. These results may indicate decadal changes in ecological characteristics at the surface and transport processes of particulate materials in the deep water.
Otosaka, Shigeyoshi; Oku, Shunsuke*; Minami, Hideki*; Minakawa, Masayuki*; Noriki, Shinichiro*
no journal, ,
Many researchers pointed out that decadal change in deep-sea circulation in the Japan Sea are strongly related with the global climate change. However, little is known about changes in fluxes and elemental composition of sinking particles in the sea. In this study, we assessed temporal changes in elemental composition of sinking particle in the Japan Sea by comparing results of a sediment trap experiment in middle 1980s with those in end of 1990s. The result indicated that (1) the contribution of Asian dust in sinking particles decreased significantly, (2) horizontal transport of re-suspended particles from the slope regions was weakened, and (3) there was no significant increase in vertical transport of anthropogenic heavy metals to the interior of the Japan Sea.
