Seawater circulation in the Japan Sea based on iodine-129

Suzuki, Takashi; Minakawa, Masayuki*; Kabuto, Shoji; Togawa, Orihiko

Dai-12-Kai AMS Shimpojiumu Hokokushu, p.69 - 72, 2010/05

no abstracts in English

The Estimation of turnover time in the Japan Sea bottom water by I

Suzuki, Takashi; Minakawa, Masayuki*; Togawa, Orihiko

JAEA-Conf 2010-001, p.15 - 18, 2010/03

https://jopss.jaea.go.jp/pdfdata/JAEA-Conf-2010-001.pdf

no abstracts in English

Establishment of database for Japan Sea parameters on marine environment and radioactivity (JASPER), 2; Radiocarbon and oceanographic properties

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.

Deep sea circulation of particulate organic carbon in the Japan Sea

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

https://doi.org/10.1007/s10872-008-0075-4

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.

Iron in the Japan Sea and its implications for the physical processes in deep water

Takata, Hyoe*; Kuma, Kenshi*; Isoda, Yutaka*; Otosaka, Shigeyoshi; Senju, Tomoharu*; Minakawa, Masayuki*

Geophysical Research Letters, 35(2), p.L02606_1 - L02606_5, 2008/01

https://doi.org/10.1029/2007GL031794

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.

Lateral distributions of Th-228 activity and Ra-228/Ra-226 activity ratio of surface water within the Sea of Japan, the East China Sea, and the Sea of Okhotsk

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.

Transport processes of particulate materials and biogeochemical cycle of trace elements in the western North Pacific and the Japan Sea

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.

Factors controlling an apparent age of particulate organic matter in seawater

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.

Temporal change in elemental composition of sinking particles in the eastern Japan Sea

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.

The Evaluation for the turnover time of the Japan Sea bottom water by iodine-129

Suzuki, Takashi; Minakawa, Masayuki*; Togawa, Orihiko

no journal, , 

no abstracts in English