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C and 
N values of sediment-trap particles in the Japan and Yamato Basins and comparison with the core-top values in the East/Japan SeaKhim, B.-K.*; Otosaka, Shigeyoshi; Park, K.-A.*; Noriki, Shinichiro*
Ocean Science Journal, 53(1), p.17 - 29, 2018/03
Times Cited Count：5 Percentile：27.02(Marine & Freshwater Biology)Distribution of carbon and nitrogen stable isotope ratios (
C, 
N) in sinking particles collected in four stations in the Japan Sea was summarized. The C and 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 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.
Cs activity concentrations in sediment collected off the coast of Fukushima Prefecture in 2013-2015Fukuda, Miho*; Aono, Tatsuo*; Yamazaki, Shinnosuke*; Ishimaru, Takashi*; Kanda, Jota*; Nishikawa, Jun*; Otosaka, Shigeyoshi
Geochemical Journal, 52(2), p.201 - 209, 2018/00
Times Cited Count：3 Percentile：16.65(Geochemistry & Geophysics)To elucidate recent activity levels and the behavior of radiocesium in the coast off Fukushima Prefecture, lateral and vertical distributions of Cs in sediment were observed in 2013-2015 at 12 monitoring stations. At stations around the water depth of 100 m, relatively higher Cs activities were observed from surface sedimentary layer (0-3 cm). In these stations, sediments had high content of silt to clay particles and organic matter. The high Cs activities in the surface sediments were attributed to accumulation of highly mobile sediment particles. In October 2014, at some coastal stations, sharp peaks of Cs activities were observed in the subsurface (5-16 cm) sediments, whereas such broad peaks were not found in October 2015. These results suggest that the Cs activities in sediment had largely changed by lateral transport and re-sedimentation on the surface, as well as sediment mixing in the middle-layers.
Fukuda, Miho*; Aono, Tatsuo*; Yamazaki, Shinnosuke*; Nishikawa, Jun*; Otosaka, Shigeyoshi; Ishimaru, Takashi*; Kanda, Jota*
Journal of Radioanalytical and Nuclear Chemistry, 311(2), p.1479 - 1484, 2017/02
Times Cited Count：6 Percentile：51.46(Chemistry, Analytical)In order to investigate processes affecting distribution of radiocaesium in seawater in the adjacent region of Fukushima Daiichi Nuclear Power Plant (FDNPP), relationships between 
Cs activity in seawater and physical properties of seawater (salinity, temperature, and potential density) were observed in seven stations within 10 km radius from the FDNPP. As a whole, Cs concentrations in seawater were higher in the vicinity of the FDNPP, and were negatively correlated with potential density. From these results, it can be considered that river water discharge or export of seawater from the FDNPP's harbor has affected the higher activity levels of Cs in seawater. It was also observed that the Cs-elevated seawater can be advected to the 20
50 m depths.
Buesseler, K. O.*; German, C. R.*; Honda, Makio*; Otosaka, Shigeyoshi; Black, E. E.*; Kawakami, Hajime*; Manganini, S. M.*; Pike, S.*
Environmental Science & Technology, 49(16), p.9807 - 9816, 2015/08
Times Cited Count：22 Percentile：55.84(Engineering, Environmental)A three year time-series of particle fluxes is presented from sediment traps deployed at 500 and 1000 m at a site 115 km southeast of Fukushima Daiichi Nuclear Power Plant (FDNPP). Results show a high fraction of lithogenic material, suggesting a lateral source of sediments. The accident-derived radiocesium were enhanced in flux peaks that, given variations in trap Cs/
Pb ratios, are characteristic of material derived from shelf and slope sediments found from 
120 to 
500 m. The fluxes of radiocesium are an order of magnitude higher than a previously reported for the trap located 100 km due east of FDNPP. We attribute the large difference due to the position of our trap under the southeasterly currents that carry contaminated waters and resuspended sediments in to the Pacific. These higher sedimentary fluxes of radiocesium to the offshore are still small relative to the inventory of radiocesium currently buried nearshore.
Otosaka, Shigeyoshi; Nakanishi, Takahiro; Suzuki, Takashi; Sato, Yuhi; Narita, Hisashi*
Environmental Science & Technology, 48(21), p.12595 - 12602, 2014/11
Times Cited Count：25 Percentile：58.66(Engineering, Environmental)From August 2011 to July 2013, a sediment trap was deployed at 100 km east of the Fukushima Daiichi Nuclear Power Plant and sinking particles were collected. Sinking flux of Cs decreased over time with seasonal fluctuation. The Cs fluxes were mainly affected by two principal modes. One was a rapid sinking of radiocesium-bound particles (moderate mode). This mode was dominant especially in the early post-accident stage, and was presumed to establish the distribution of radiocesium in the offshore seabed. Another was the secondary transport of particles attributed to turbulence near the seabed and was observed in winter (turbulence mode). Although the latter process would not drastically change the distribution of sedimentary radiocesium, attention should be paid as this key process redistributing the accident-derived radiocesium may cumulatively affect the long-term distribution.
Suzuki, Takashi; Kitamura, Toshikatsu; Togawa, Orihiko; Amano, Hikaru
UTNST-SMP-12, p.116 - 121, 2003/12
no abstracts in English
Amano, Hikaru; Yabuuchi, Noriaki; Matsunaga, Takeshi
JAERI-Research 96-049, 125 Pages, 1996/10
JAERI-Research-96-049.pdf:4.04MB
no abstracts in English
; Haga, Kazuo
PNC TN9410 91-185, 62 Pages, 1991/05
Conceptual design of a 200kWe power source for a 6.5 km class research submersible was performed by using a sodium and a lithium cooled high temperature reactors and a closed Brayton cycle system. The SPECTRA, which had been already designed as a portable reactor, was employed in the conceptual design. A pressure hull, made of high strength steel containing 10 % Ni, had the shape of two spheres connected horizontally, which had the same inner diameter of 3 m. Heat removal from the reactor system was by heat transfer to the sea water after thermal conduction through the pressure hull. The conceptual design work confirmed the technical availability of this system as the power source for the deep sea research submersible.
; Haga, Kazuo
PNC TN9410 91-176, 51 Pages, 1991/05
Fast reactor power systems for deep sea research were studied to some types of usage. Two concepts were figured out to power sources for an uninhibited base (water level 8,020 m, 10kWe) and for a 10 km class research submersible (20 kWe), which are expected to be required in near future. Whereas the power conversion system of the uninhibited base adopted thermoelectric cells and a closed Brayton cycle, that of the submersible used a closed Brayton cycle. It is favorable that the power system for deep sea research is as light as possible. The calculated weight of these power sources showed that the total value including a a pressure shell container will be less than an objected value of 10 tons even in the 10 km class research submersible.
JAERI 4002, 49 Pages, 1957/03
no abstracts in English
Buesseler, K. O.*; German, C. R.*; Honda, Makio*; Otosaka, Shigeyoshi; Black, E. E.*; Kawakami, Hajime*; Manganini, S. M.*; Pike, S.*
no journal, ,
A three year time-series of particle fluxes is presented from sediment traps deployed at 500 and 1000 m at a site 115 km southeast of Fukushima Daiichi Nuclear Power Plant. Results show a high fraction of lithogenic material in sinking particles, suggesting a lateral source of sediments. From Cs/Pb ratio in sinking particles, it was inferred that accident-derived radiocesium associate with slope and shelf sediments were resuspended and transported laterally to the offshore regions in winter and typhoon seasons. Continuous observation of such transport processes of particulate radiocesium near the seabed would be significant for better understanding of the fate of accident-derived radiocesium.
Jeon, H.; Otosaka, Shigeyoshi; Yamashita, Yohei*; Ogawa, Hiroshi*
no journal, ,
The ocean is a huge reservoir of dissolved organic carbon that contains almost the same amount of carbon in the atmosphere. Radiocarbon signatures of dissolved organic carbon (DO
C) in seawater can provide useful information on how organic carbon is produced, transported, and ultimately sequestered in the ocean's interior. In order to measure radiocarbon contents of seawater samples, they should be processed with a specific preparation system consists of the custom quartz reactor, dedicated vacuum line and UV lamp followed by radiocarbon counting with an accelerator mass spectrometer. As the first step of the study, we developed the irradiation procedure using a low-pressure Hg lamp and an oxidation catalyst. We present here not only how the system is progressing but also what radiocarbon study in the central Pacific Ocean means for better understanding of oceanic carbon cycle.
Otosaka, Shigeyoshi
no journal, ,
Cesium and iodine are known to behave differently in the marine environment. However, in 2011, activity ratio of 
I/Cs in seabed sediment collected in the 160 km radius from the Fukushima Daiichi Nuclear Power Plant showed almost constant regardless of observation areas. This result indicated that initial deposition of I and Cs to the seafloor was not caused by gentle settling of biogenic particles, but by the contact of highly-contaminated seawater with the seafloor in a relatively short period of time. After that, the I/Cs ratio decreased in the coast and slightly increased in the offshore (water depth of 200 m to 500 m) regions. Such changes in the I/Cs ratio provide helpful information showing the transport of radionuclides near the seabed at the scale of several years.
