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Journal Articles

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

 Times Cited Count:20 Percentile:45.51(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 $$^{14}$$C/$$^{12}$$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.

Journal Articles

Anthropogenic radionuclides in sediment in the Japan Sea; Distribution and transport processes of particulate radionuclides

Otosaka, Shigeyoshi; Amano, Hikaru; Ito, Toshimichi; Kawamura, Hideyuki; Kobayashi, Takuya; Suzuki, Takashi; Togawa, Orihiko; Chaykovskaya, E. L.*; Lishavskaya, T. S.*; Novichkov, V. P.*; et al.

Journal of Environmental Radioactivity, 91(3), p.128 - 145, 2006/00

 Times Cited Count:16 Percentile:35.71(Environmental Sciences)

Distributions of radionuclides ($$^{90}$$Sr, $$^{137}$$Cs and $$^{239+240}$$Pu) in seabed sediment in the Japan Sea were observed during 1998-2002. Observed inventories of anthropogenic radionuclides in sediment ranged 0.1-86 Bq m$$^{-2}$$ for $$^{90}$$Sr, 23-379 Bq m$$^{-2}$$ for $$^{137}$$Cs and 0.1-86 Bq m$$^{-2}$$ for $$^{239+240}$$Pu. In the deep part ($$>$$ 2 km depth) of the western Japan Basin, $$^{239+240}$$Pu/$$^{137}$$Cs inventory ratios were larger than those in the central Yamato Basin although inventories of radionuclides were not different between basins. The higher $$^{239+240}$$Pu/$$^{137}$$Cs ratios in the western Japan Basin were derived by the production of Pu-enriched particle in the surface layer and effective sinking of particulate materials in this region. In the marginal Yamato Basin and the Ulleung Basin, both inventories and $$^{239+240}$$Pu/$$^{137}$$Cs ratios in sediment were larger than those in the central Yamato Basin. In the eastern/southern Japan Sea, it was suggested that the supply of particulate radionuclides by the TWC enhanced accumulation of radionuclides in this region.

Journal Articles

Anthropogenic radionuclides in seawater of the Japan Sea; The Results of recent observations and the temporal change of concentrations

Ito, Toshimichi; Aramaki, Takafumi*; Otosaka, Shigeyoshi; Suzuki, Takashi; Togawa, Orihiko; Kobayashi, Takuya; Kawamura, Hideyuki; Amano, Hikaru; Senju, Tomoharu*; Chaykovskaya, E. L.*; et al.

Journal of Nuclear Science and Technology, 42(1), p.90 - 100, 2005/01

 Times Cited Count:14 Percentile:69.53(Nuclear Science & Technology)

During 1996-2002, a wide-area research project on anthropogenic radionuclides was done in the Japanese and Russian EEZ of the Japan Sea to investigate their migration. As the results of expeditions in 2001 and 2002, (1) the concentrations and distributions of radionuclides are similar to the results of previous, (2) inventories of these radionuclides indicate accumulation in the Japan Sea seawater compared to the amounts supplied by global fallout, (3) $$^{90}$$Sr and $$^{137}$$Cs concentrations in intermediate layer show temporal variations, and 4) the variations may reflect the water mass movement in upper part of the Japan Sea.

Journal Articles

Lithogenic flux in the Japan Sea measured with sediment traps

Otosaka, Shigeyoshi; Togawa, Orihiko; Baba, Masami*; Karasev, E.*; Volkov, Y. N.*; Omata, Nobutaka*; Noriki, Shinichiro*

Marine Chemistry, 91(1-4), p.143 - 163, 2004/11

 Times Cited Count:38 Percentile:70.33(Chemistry, Multidisciplinary)

Spatial and temporal variations of particulate flux were observed by sediment trap experiments at three areas of the Japan Sea (western Japan Basin, eastern Japan Basin and Yamato Basin) during 1999-2002. Mass flux in the Japan Sea showed remarkable regional distribution. Annual mean mass flux at 1 km depth was 455 mg/m$$_{2}$$/day in the eastern Japan Basin, 252 mg/m$$_{2}$$/day in the eastern Japan Basin and 147 mg/m$$_{2}$$/day in the Yamato Basin. Mass fluxes were especially large in spring (March-May). From the distribution of elemental abundance in sediments, La/Yb and Mn/Al ratios as indicators of the origin of aluminosilicates and the "freshness" of particles, respectively. These proxies suggested three sources of lithogenic material for the Japan Sea, (1) atmospheric input of Kosa particles, (2) lateral transport from the East China Sea, and (3) lateral transport from Island-Arc such as the Japan Islands.

Journal Articles

Fluxes and balance of $$^{210}$$Pb in the northwestern Japan Sea

Otosaka, Shigeyoshi; Baba, Masami*; Togawa, Orihiko; Karasev, E. V.*

Pacific Oceanography, 1(2), p.149 - 157, 2003/12

A sediment trap experiment and sediment coring were carried out in the northwestern Japan Sea (Sta MS), and lead-210 ($$^{210}$$Pb) and major components in settling particles were measured. By drawing up a balance of $$^{210}$$Pb in the water column, it was estimated that the cycle of $$^{210}$$Pb in the Sta MS was controlled by 3 processes, (1) removal and vertical transport of $$^{210}$$Pb from the surface layer by settling particles, (2) decomposition of particles in the deep layer, and (3) export by the deep current. Flux of $$^{210}$$Pb at 3 km depth was large in winter and spring. The large $$^{210}$$Pb flux in this season would be caused by the horizontal import of $$^{210}$$Pb -rich seawater from the coastal region to the bottom layer of Sta MS. It was suggested that seasonal variation of particulate $$^{210}$$Pb flux at the deep layer in the northwestern Japan Basin indicated the renewal of the deep water in this area.

Journal Articles

Anthropogenic radionuclides in seawater of the Japan Sea; The Results of recent expeditions carried out in the Japanese and Russian EEZ

Ito, Toshimichi; Aramaki, Takafumi*; Otosaka, Shigeyoshi; Suzuki, Takashi; Togawa, Orihiko; Kobayashi, Takuya; Senju, Tomoharu*; Chaykovskaya, E. L.*; Lishavskaya, T. S.*; Karasev, E. V.*; et al.

Proceedings of International Symposium on Radioecology and Environmental Dosimetry, p.396 - 401, 2003/10

no abstracts in English

Journal Articles

Anthropogenic radionuclides in sediment in the Japan Sea

Otosaka, Shigeyoshi; Aramaki, Takafumi*; Suzuki, Takashi; Kobayashi, Takuya; Ito, Toshimichi; Togawa, Orihiko; Chaykovskaya, E. L.*; Dunaev, A. L.*; Karasev, E. V.*; Novichkov, V. P.*; et al.

Proceedings of International Symposium on Radioecology and Environmental Dosimetry, p.390 - 395, 2003/10

Seabed sediments were collected at 22 stations in the Japan Sea, and anthropogenic radionuclides were measured in order to understand distributions and accumulation processes of these materials. Averaged concentrations of $$^{137}$$Cs in sediment in the Japan Basin and the Yamato Basin were 1.0 Bq/kg and 1.0 Bq/kg, respectively. Although there was no significant difference in mean $$^{137}$$Cs concentration between the Japan Basin and the Yamato Basin, distributions of radionuclides in these 2 basins showed different features. In the Japan Basin, the spatial variation of concentration of radionuclides was smaller than that at the Yamato Basin. At most stations in the Yamato Basin, significant concentrations of radionuclides were not detected, but remarkable large activities were observed at several stations in the Yamato Basin. For all radionuclides, the highest concentration was observed in the southeastern margin of the Yamato Basin. These results would suggest that there were different accumulation processes of radionuclides between the Japan Basin and the Yamato Basin.

Journal Articles

Monitoring of potential environmental effects of oil exploration in the Sea of Okhotsk and distribution of artificial radionuclides in the Sea of Japan

Tkalin, A. V.*; Lishavskaya, T. S.*; Belan, T. A.*; Karasev, E. V.*; Togawa, Orihiko

Pacific Oceanography, 1(1), p.42 - 52, 2003/08

no abstracts in English

Journal Articles

Anthropogenic radionuclides in the Japan Sea; Their distributions and transport processes

Ito, Toshimichi; Aramaki, Takafumi; Kitamura, Toshikatsu; Otosaka, Shigeyoshi; Suzuki, Takashi; Togawa, Orihiko; Kobayashi, Takuya; Senju, Tomoharu*; Chaykovskaya, E. L.*; Karasev, E. V.*; et al.

Journal of Environmental Radioactivity, 68(3), p.249 - 267, 2003/07

 Times Cited Count:35 Percentile:60.32(Environmental Sciences)

The anthropogenic radionuclides, $$^{90}$$Sr, $$^{137}$$Cs and $$^{239+240}$$Pu, in the seawater column of the Japan Sea were measured during 1997-2000. The vertical profiles of radionuclide concentrations showed their typical features; exponential decrease with depth for the $$^{90}$$Sr and $$^{137}$$Cs and surface minimum - subsurface maximum for the $$^{239+240}$$Pu, and there are no substantial differences between the present study and the previous ones. The area-averaged concentrations and the inventories of radionuclides in the Japan Sea are higher than those in the Northwest Pacific Ocean. In the spatial distributions, high inventory area extends and intrudes from the Japan Basin into the Yamato Basin. It is suggested that radionuclides sink by the vertical transport occurring mainly in the Japan Basin then advect into the Yamato Basin after detouring around the Yamato Rise, and finally, they are accumulated in the deep seawater of the Japan Sea.

Journal Articles

Renewal of the bottom water after the winter 2000-2001 may spin-up the thermohaline circulation in the Japan Sea

Senju, Tomoharu*; Aramaki, Takafumi; Otosaka, Shigeyoshi; Togawa, Orihiko; Danchenkov, M. A.*; Karasev, E.*; Volkov, Y. N.*

Geophysical Research Letters, 29(7), p.53_1 - 53_4, 2002/04

The newly formed bottom water in the Japan Sea was observed in the summer of 2001 after the severe winter 2000-2001. The new bottom water, which was observed in the northwestern Japan Sea, showed low temperature, high salinity, high dissolved oxygen and low nutrients concentration compared to the old bottom water. The distribution of the bottom water indicates that the deep convection occurred in the area of south off Vladivostok, not the northern Japan Sea, and then the bottom water was advected to the observation area from the convection region. The record of current meters suggests that the deep convection occurred in the early-February, because strong flows faster than 10 cms-1 appeared abruptly from mid-February 2001. This formation event may contribute not only the relaxation of the anoxic trend in the bottom layer but also the spin-up of the thermohaline circulation in the Japan Sea.

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