6:15 PM - 7:30 PM
[HTT31-P12] Stable isotope analysis of food-web system in subarctic to subtropical region of western North Pacific
Keywords:nitrogen stable isotope, carbon stable isotope, food web, isotope fractionation
Biota were collected in eight depths (0-50, 50-100, 100-150, 150-200, 200-300, 300-500, 500-750, 750-1000m) at both sites using IONESS from February 2010 to July 2011. We also collected water samples from seasonal and vertical (~1,000m depth) profiles in δ15N (NO3+ + NO2-) together with zooplankton δ15N at K2 and S1 in special reference to nitrogen cycles. Biota samples were freeze-dried on board immediately after the sampling, and dried one day and delipidated before the analysis. The δ15N and δ13C values of zooplankton ware determined at SI Science and Research Institute for Humanity and Nature, whereas the δ15N ratio of nitrate ions (NO3-+NO2-) in the water was determined using denitrifying method (Casciotti et al., 2002; Sigman et al., 2001) at Tokyo University of Agriculture and Technology and the University of California, Davis.
The δ15N and δ13C values of amphipods and copepod, omnivorous zooplankton in the surface ocean, showed a large seasonal variation. The δ15N values of zooplankton and nitrate ions in the water at the S1 site tended to be lower than those at the K1 site, indicating that the basic food-web is affected by nitrogen fixation. We further compared the trophic fractionation of carbon and nitrogen isotopes (Δδ13C, Δδ15N) at these two sites statistically with previously databases for food chains in four marine environments of the Antarctic Ocean, gulf of Alaska, Oyashio, and Kuroshio. It is observed that a simple relationship exists in the Δδ15N/Δδ13C regardless of species and ecosystems. This result demonstrates that the Δδ15N/Δδ13C, which is an isotope fractionation in the baiting process of food-web system, is determined by energy metabolism mainly driven by amino-acids and decarbonation. This contention suggests an unified regularity is maintained in the lower to higher trophic level in the marine ecosystem.