15N and 13C abundances in the Antartic Ocean with emphasis on the biogeochemical structure of the food web

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公開日
1987-05
権利情報
  • https://www.elsevier.com/tdm/userlicense/1.0/
DOI
  • 10.1016/0198-0149(87)90039-2
公開者
Elsevier BV

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説明

Abstract Distributions of δ15N and δ13C for biogenic substances in the Antarctic Ocean were investigated to construct a biogeochemical framework for assessing the Antarctic ecosystem. Phytoplankton exhibited particularly low δ15N (0.5%) and 13C (-26.9%) values in pelagic plankton samples. High nitrate concentrations, and high PCO2 in the surface waters on the southern side of the polar front and the resulting slow growth rate of phytoplankton under low light intensity are suggested as possible factors in causing the low isotopic compositions. Mean fractionation factors of 1.029 and 1.006 were estimated for photosynthetic carbon fixation and for the assimilation of inorganic nitrogeneous compounds (ammonium plus nitrate) during algal growth, respectively. Enrichment of 15N with increasing trophic level was confirmed for Antarctic ecosystems: δ15Nanimal% = 3.3 (trophic level −1) + δ5Nalgae, whereas 13C content did not increase in the same manner. Differences in lipid content among animals may be the main factor in causing this δ13C anomaly. 15N and 13C abundance of sedimentary organic nitrogen differed from phytoplankton and settling particles. An exact mechanism for explaining the high δ15N (around 5%) is not known. The very high δ13C value of −20.5% at Sta. 3B may originate in ice algae that had grown under CO2-limited conditions. Particles collected by sediment traps gave characteristically low δ15N values (−3.0 to 0.9%), strongly suggesting a phytoplankton origin. The δ15N and δ13C values of settling material showed similar vertical profiles with depth which might arise from temporal variation of algal growth.

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