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(Copepoda) from a deep sediment-trap; Abundance and implications for ecological and biogeochemical studiesIkenoue, Takahito*; Otosaka, Shigeyoshi*; Honda, Makio*; Kitamura, Minoru*; Mino, Yoshihisa*; Narita, Hisashi*; Kobayashi, Takuya
Frontiers in Marine Science (Internet), 9, p.884320_1 - 884320_11, 2022/05
Times Cited Count：0 Percentile：0.01(Environmental Sciences)We studied seasonal variations of the mesozooplankton swimmer community collected by a sediment trap moored at 873 m in the Kuroshio & Oyashio Transition region off the east coast of Japan from 5 August 2011 to 23 June 2013. The total flux of mesozooplankton swimmers varied between 0 and 11.1 individuals m-2 d-1, with a mean of 3.1 individuals m-2 d-1 during the sampling period. Among the Copepoda, Neocalanus cristatus was the most dominant taxon. The species composition of the swimmers closely reflected the mid-depth mesozooplankton of the Oyashio region. The fluxes of Neocalanus species reflected ontogenetic vertical migration, but may have been overestimates of active fluxes if they included dormant individuals that accidentally entered the sediment trap.
Otosaka, Shigeyoshi*; Suzuki, Takashi; Tsuruta, Tadahiko; Misono, Toshiharu; Mino, Yoshihisa*; Sukigara, Chiho*; Ito, Yukari*; Shirai, Kotaro*; Sugihara, Naoko*
no journal, ,
In order to clarify the transport process of suspended radiocesium from the coast to the offshore area, which is one of the processes that change the concentration of radiocesium in sediments off Fukushima, a time-series sediment trap was deployed from October 2017 to June 2018 at a station located in southeast of the Fukushima Daiichi Nuclear Power Plant. Sinking particles of 39 periods were collected by this experiment. 
Cs was detected from sinking particles throughout the observation period, and the concentration showed clear seasonal variation. The maximum Cs concentration was an order of magnitude higher than that in the surface sediment (0-1 cm layer) at the station. On the other hand, the observed annual sinking flux of Cs was less than 1% of the Cs inventory in the seabed column. From these results, it can be concluded that the transport of Cs-bound particles from the coastal area has a relatively small effect of changing the abundance of radiocesium in sediments.
Otosaka, Shigeyoshi*; Suzuki, Takashi; Tsuruta, Tadahiko; Misono, Toshiharu; Dohi, Terumi; Mino, Yoshihisa*; Sukigara, Chiho*; Ito, Yukari*; Kanda, Jota*; Ishimaru, Takashi*
no journal, ,
A time-series sediment trap was deployed from October 2017 to June 2018 at a station located in southeast of the Fukushima Daiichi Nuclear Power Plant to clarify the transport process of suspended radiocesium from the coast to the offshore area. Sinking particles of 39 periods were collected by this experiment. Radiocesium was detected from sinking particles throughout the observation period, and the concentration showed clear seasonal variation. The observed flux of radiocesium showed maxima in winter (December-January) and spring (March-April). From detailed analysis of physical and chemical characteristics of sinking particles, it was found that sinking particles were composed of biological particles with relatively low degradation in winter and fine-grained terrestrial particles in spring. Especially in spring, high radiocesium flux was observed, and it was presumed due to lateral transport of radiocesium-bound lithogenic particles from the coastal area to the offshore. However, the effect of redistribution of radiocesium in seabed sediments by this process is considered to be limited.
