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Journal Articles

$$delta^{13}$$C and $$delta^{15}$$N values of sediment-trap particles in the Japan and Yamato Basins and comparison with the core-top values in the East/Japan Sea

Khim, B.-K.*; Otosaka, Shigeyoshi; Park, K.-A.*; Noriki, Shinichiro*

Ocean Science Journal, 53(1), p.17 - 29, 2018/03

 Times Cited Count:1 Percentile:84.38(Marine & Freshwater Biology)

Distribution of carbon and nitrogen stable isotope ratios ($$delta$$$$^{13}$$C, $$delta$$$$^{15}$$N) in sinking particles collected in four stations in the Japan Sea was summarized. The $$delta$$$$^{13}$$C and $$delta$$$$^{15}$$N values in the sinking particles showed a clear seasonal variation, which agreed well with the variation in the chlorophyll a concentration in the surface seawater and in the sinking flux of biogenic particles. In particular, during the highly productive season of phytoplankton, a remarkable isotopic fractionation of $$delta$$$$^{13}$$N was found in the sinking particles, and it was inferred that the fractionation indicates the degree of nitrogen uptake by diatoms in the surface layer. These results are helpful information for linking the phenomenon in the ocean surface and the isotopic information recorded in the seafloor.

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:13 Percentile:65.62(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

Benthic front and the Yamato Basin Bottom Water in the Japan Sea

Senju, Tomoharu*; Isoda, Yutaka*; Aramaki, Takafumi*; Otosaka, Shigeyoshi; Fujio, Shinzo*; Yanagimoto, Daigo*; Suzuki, Takashi; Kuma, Kenshi*; Mori, Kosuke*

Journal of Oceanography, 61(6), p.1047 - 1058, 2005/12

 Times Cited Count:6 Percentile:84.94(Oceanography)

The detail structure of the Bottom Water in the Japan Sea was revealed by the hydrographic observations. The Yamato Basin Bottom Water (YBBW) exhibits higher temperature, lower dissolved oxygen, and higher nutrients concentrations than those in the Japan Basin Bottom Water (JBBW). Both Bottom Waters meet around the boundary region between the Yamato and the Japan Basins, and form a clear benthic front. It is inferred from the property distributions that the JBBW flowing into the Yamato Basin is trapped by the cyclonic circulation in the basin, and modified to the YBBW in the course of the circulation through the vertical diffusion, geothermal heating and oxygen consumption. The thermal balance of in the YYBW was examined using a box-model. The results show that the effect of geothermal heating has about 70 per-cent of magnitude to the vertical thermal diffusion and both terms cancel the advection term of the cold JBBW from the Japan Basin. The box-model also estimated the averaged residence time for the YBBW was 9.1 years.

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:34 Percentile:30.78(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

Simulation of the formation process of the Japan/East Sea intermediate water with the nested model

Kawamura, Hideyuki; Yoon, J.-H.*; Ito, Toshimichi

Umi To Sora, 80(1), p.37 - 45, 2004/07

The Japan/East Sea Intermediate Water (JESIW) characterized by Salinity Minimum Layer (SML) with dissolved oxygen (DO) maximum was frequently observed in the Japan Sea. It is suggested that the origin of the JESIW is the coastal fresh water along the Primorye and North Korean coasts. The fresh water near the subpolar front along 40$$^{circ}$$N advected from the coastal region has the possibility to sink into intermediate depth. This study aims to understand the formation mechanism of the JESIW by using the three-dimensional nested model. The results show that 1/18$$^{circ}$$-resolution model can reproduce the strong downward velocity with the maximum of about 0.05 cm/s along the subpolar front in the Japan Sea. It results in the patch of low salinity water in the intermediate depth, which is consistent with the observational result. It is indicated that the high-resolution model is useful to reproduce the JESIW, since it can reproduce the meso-scale phenomenon such as baroclinicity near the frontal area, which is an important factor for surface water transport into the intermediate depth.

Journal Articles

Distribution of radiocarbon in the Sea of Japan (prompt report)

Aramaki, Takafumi*; Togawa, Orihiko; Kitamura, Toshikatsu

Dai-16-Kai Tandemu Kasokuki Oyobi Sono Shuhen Gijutsu No Kenkyukai Hokokushu, p.170 - 172, 2004/02

no abstracts in English

Journal Articles

A Study on migration behavior of anthropogenic radionuclides in the Japan/East Sea, 2

Otosaka, Shigeyoshi; Ito, Toshimichi; Kawamura, Hideyuki; Kobayashi, Takuya; Suzuki, Takashi; Togawa, Orihiko

Dai-45-Kai Kankyo Hoshano Chosa Kenkyu Seika Rombun Shorokushu (Heisei-14-Nendo), p.77 - 78, 2003/12

no abstracts in English

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

Benthic front between the Japan Basin and the Yamato Basin in the Japan Sea

Senju, Tomoharu*; Isoda, Yutaka*; Aramaki, Takafumi; Otosaka, Shigeyoshi; Suzuki, Takashi; Kuma, Kenshi*; Mori, Kosuke*

Proceedings of 12th PAMS/JECSS Workshop, p.3_4_1 - 3_4_4, 2003/11

Abyssal water mass distribution from the Yamato Basin to the Japan Basin in the Japan Sea was observed on the R/V Hakuho-Maru cruise, KH02-3 (October 14-19, 2002). The bottom layer in the Yamato Basin was occupied by the water of higher temperature and lower oxygen compared to that in the Japan Basin. As a result, a benthic front of potential temperature and dissolved oxygen was formed between the Yamato and Japan Basins. Dissolved oxygen and nutrients concentrations show that the bottom water in the Yamato Basin is older than that in the Japan Basin. This indicates the existence of the Yamato Basin Water, which is modified bottom water by the closed circulation in the Yamato Basin. The structure of the benthic front suggests an estuary-like circulation around the mouth of the Yamato Basin; outflow from the Yamato Basin lying on the inflow from the Japan Basin. The highest oxygen water was found on the slope of southern periphery of the Japan Basin. This is considered to be the bottom water from the west transported by the cyclonic circulation in the Japan Basin.

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

JAEA Reports

JAEA Reports



PNC-TJ1604 96-003, 26 Pages, 1996/03


no abstracts in English

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