Preprints
https://doi.org/10.5194/os-2021-74
https://doi.org/10.5194/os-2021-74

  19 Aug 2021

19 Aug 2021

Review status: this preprint is currently under review for the journal OS.

Carbon and nitrogen dynamics in the coastal Japan Sea inferred from 15 years of measurements of stable isotope ratios of Calanus sinicus

Ken-ichi Nakamura1,a, Atsushi Nishimoto2, Saori Yasui-Tamura1,b, Yoichi Kogure1, Misato Nakae1, Naoki Iguchi1, Haruyuki Morimoto1, and Taketoshi Kodama3 Ken-ichi Nakamura et al.
  • 1Fisheries Resources Institute, Japan Fisheries Research and Education Agency, Niigata, 951-8121, Japan
  • 2Fisheries Technology Institute, Japan Fisheries Research and Education Agency, Yokohama, 236-8648, Japan
  • 3Fisheries Resources Institute, Japan Fisheries Research and Education Agency, Yokohama, 236-8648, Japan
  • apresent address: Kokusai Kogyo Co. Ltd., Tokyo, 102-0085, Japan
  • bpresent address: Department of Ocean Sciences, Tokyo University of Marine Science and Technology, Tokyo, 108-8477, Japan

Abstract. Human activities have caused sometimes dramatic changes to the marine environment globally and locally during the last half century. We hypothesized that the carbon and nitrogen stable isotope ratios (δ13C and δ15N) of the copepod Calanus sinicus, one of the dominant secondary producers of North Pacific coastal waters, would record anthropogenic impacts on the coastal environment of the Japan Sea. We monitored these isotope ratios during the spring at four stations in the Japan Sea from 2006 to 2020. The δ13C values ranged from −24.7 ‰ to −15.0 ‰ and decreased from the spring bloom (February/March) to the post-bloom (June/July). This monthly variation was attributed to changes in both the physiology of C. sinicus and phytoplankton δ13C. The negative correlation between the δ13C values of C. sinicus and their carbon:nitrogen ratios reflected lipid accumulation by the copepods; high δ13C values were associated with high sea surface chlorophyll a concentrations. The δ15N values ranged from 2.8 ‰ to 8.8 ‰. The tendency of the δ15N values to increase from the bloom to post-bloom was attributable to an increase of the δ15N of the phytoplankton associated with nitrate depletion and Rayleigh fractionation. These monthly changes were synchronized among the four stations, but δ13C and δ15N differed significantly between stations. Interannual variations were statistically significant, but there were no significant monotonic trends. Interannual variations differed between δ13C and δ15N as well as among stations. These results suggest that local conditions rather than global-scale trends were the primary determinants of elemental cycles in this coastal ecosystem.

Ken-ichi Nakamura et al.

Status: open (until 14 Oct 2021)

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  • RC1: 'Comment on os-2021-74', Anonymous Referee #1, 16 Sep 2021 reply

Ken-ichi Nakamura et al.

Ken-ichi Nakamura et al.

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Short summary
The Japan Sea surrounding Russia, Korean Peninsula and Japanese Archipelago, is one of the most rapidly changing sea all over the world. We measured carbon and nitrogen isotope ratio of zooplankton. We had thought changes of the ratios have tendency because nitrogen input to this sea is increasing through the atmospheric pollution. However, changes did not have tendency. This result suggested that the local ecosystem prevails, and local studies are necessary for achievement of the SDG 14 Goal.