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Origin and decomposition of sinking particulate organic matter in the deep water column inferred from the vertical distributions of its δN, δ and δ
Authors:Takeshi Nakatsuka  Nobuhiko Handa  Naomi Harada  Tatsuhiro Sugimoto  Shigemi Imaizumi
Institution:Instiute for Hydrospheric-Atmospheric Sciences, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-01, Japan;Now at Institute of Low Temperature Science, Hokkaido University, Kita-19 Nishi-8, Kita-ku, Sapporo 060, Japan;Now at Aichi Prefectural University, Takada-cho, Mizuho-ku, Nagoya 467, Japan;§Now at Japan Marine Science and Technology Center, Natsushima-cho, Yokosuka 327, Japan;Now at Bio-Laboratory, Toyota Motor Company, Toyota-cho, Toyota 237, Japan;Now at Governmental Office of Gifu Prefecture, Gifu, Japan
Abstract:Sinking particles were analyzed for their nitrogen isotopic ratio δ15N) of total particulate nitrogen (PN), stable carbon isotopic ratio (δ13C) and radioactive isotopic ratio (δ14C) of total particulate organic carbon (POC), at three different latitudinal (temperate, subpolar and equatorial) and geomorphological (trench, proximal abyssal plain and distal abyssal plain) sites in the western North Pacific Ocean using year-long time series sediment trap systems, to clarify the common vertical trends of the isotopic signals in deep water columns. Although the δ15N and δ13C values of sinking particulate organic matter (POM) were partly affected by the resuspension of sedimentary POM from the sea floor, especially in the trench, the changes in δ15N and δ13C values owing to the resuspension could be corrected by calculation of the isotopic mass balance from δ14C of sinking POC. After this correction, common downward decreasing trends in δ15N and δ13C values were obtained in the deep water columns, irrespective of the latitudes and depths. These coincidental isotopic signals between δ15N and δ13C values provide new constraints for the decomposition process of sinking POM, such as the preferential degradation of 15N- and 13C-rich compounds and the successive re-formation of the sinking particles by higher trophic level organisms in the deep water column.
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