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Distribution and sources of organic matter in surficial sediments on the shelf and slope off Tokachi, western North Pacific, inferred from C and N stable isotopes and C / N ratios

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Title: Distribution and sources of organic matter in surficial sediments on the shelf and slope off Tokachi, western North Pacific, inferred from C and N stable isotopes and C / N ratios
Authors: Usui, Toshihiro1 Browse this author
Nagao, Seiya Browse this author
Yamamoto, Masanobu Browse this author
Suzuki, Koji Browse this author
Kudo, Isao Browse this author →KAKEN DB
Montani, Shigeru Browse this author →KAKEN DB
Noda, Atsushi Browse this author
Minagawa, Masao Browse this author
Authors(alt): 碓井, 敏宏1
Keywords: Carbon isotope
Nitrogen isotope
C/N ratio
Sediment
Suspended particle
Grain size
Issue Date: Feb-2006
Publisher: Elsevier B.V.
Journal Title: Marine Chemistry
Volume: 98
Issue: 2-4
Start Page: 241
End Page: 259
Publisher DOI: 10.1016/j.marchem.2005.10.002
Abstract: Organic carbon (C) and total nitrogen (N) contents and corresponding isotope ratios were determined in surficial sediment (0–3 cm) at 94 stations ranging from 21 to 1995 m water depth off Tokachi, Hokkaido, Japan, to elucidate the distribution and source of sedimentary organic matter. Suspended particulate organic matter (POM) in the seawater and suspended POM and sediment in the Tokachi River were also examined. δ13C, δ15N and C / N ratios of the samples in the Tokachi River suggest that the spring snowmelt is an important process for the transport of terrestrial organic matter to the coastal waters. δ13C values of suspended POM in the surface seawater were higher in May and November than in August, while δ15N values of the POM were higher in May and August than in November. These changes are attributed to seasonal changes in phytoplankton growth rate and nitrate availability. δ13C and δ15N values in the sediments off Tokachi were lowest near the Tokachi River mouth, and increased offshore to constant values that persisted from 134 to 1995 m water depth. The spatial variation in C / N ratios in the sediment mirrored those of δ13C and δ15N. Comparison of δ13C, δ15N and C / N ratios in the sediments off Tokachi with those in the Tokachi River and seawater indicates that about half of the organic matter in the sediment was of terrestrial origin near the Tokachi River mouth, and the sedimentary organic matter from 134 to 1995 m water depth was of marine origin. The organic C content in the sediment was high near the Tokachi River mouth, and also around 1000 m water depth. The C content was significantly correlated with silt plus clay content, with different regression lines for those stations shallower and deeper than 134 m, owing to several stations of higher C content with the elevated C / N ratio on the inner shelf. These results suggest that transport and deposition of organic-rich fine sediment particles by hydrodynamic processes were major factors controlling C content off Tokachi. In addition, the supply of a fraction of terrestrial organic matter with high C / N probably also affected C content on the inner shelf.
Relation: http://www.sciencedirect.com/science/journal/03044203
Type: article (author version)
URI: http://hdl.handle.net/2115/4871
Appears in Collections:環境科学院・地球環境科学研究院 (Graduate School of Environmental Science / Faculty of Environmental Earth Science) > 雑誌発表論文等 (Peer-reviewed Journal Articles, etc)

Submitter: 碓井 敏宏

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