Japan Geoscience Union Meeting 2014

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Oral

Symbol M (Multidisciplinary and Interdisciplinary) » M-IS Intersection

[M-IS21_28AM1] Biogeochemistry

Mon. Apr 28, 2014 9:00 AM - 10:45 AM 511 (5F)

Convener:*Muneoki Yoh(Tokyo University of Agriculture and Technology), Hideaki Shibata(Field Science Center fot Northern Biosphere, Hokkaido University), Naohiko Ohkouchi(Japan Agency for Marine-Earth Science and Technology), Youhei Yamashita(Faculty of Environmental Earth Science, Hokkaido University), Chair:Taichi Yokokawa(Center for Marine Environmental Studies, Ehime University), Hidetaka Nomaki(Institute of Biogeosciences, Japan Agency for Marine-Earth Science and Technology), Yoshinori Takano(Institute of Biogeosciences, Japan Agency for Marine-Earth Science and Technology (JAMSTEC)), Seiya Nagao(Institute of Nature and Environmental Technology, Kanazawa University)

10:15 AM - 10:30 AM

[MIS21-06] Nitrogen isotopic record of chlorophylls as a tool for understanding of nitrogen dynamics in the oceanic photic zone

*Nanako O. OGAWA1, Chisato YOSHIKAWA1, Hisami SUGA1, Naohiko OHKOUCHI1 (1.JAMSTEC)

Keywords:nitrogen isotope, oceanic photic zone, nitrogen dynamics, photosynthetic pigments, nitrate

Nitrogen isotope record of chlorophylls has a large potential as a tool for reconstructing the nitrogen cycle and its dynamics in the photic zone. In this study, we determined the nitrogen isotopic compositions of chlorophyll a (δ15Nchl) and pheophytin a (δ15NPhe) as well as nitrate (δ15NNO3) collected from two sites (S1 and K2) in the northwest Pacific as a case study. Both chlorophyll a and pheophytin a were extracted from the particulate organic matter (POM) and purified by the fraction collector of high-performance liquid chromatography. The nitrogen isotopic composition of the isolated chlorophylls was determined by our ultra-sensitive elemental analyzer / isotope ratio mass spectrometry. The estimated isotopic fractionation associated with the chlorophyll synthesis is -7.9‰ to -13.1‰, confirming the previous studies. However, the δ15N of POM is not consistent with those of chlorophylls, suggesting that the POM from both sites is a mixture of phytoplankton and other materials like detritus of zooplankton. The δ15Nchl value provides pure δ15N signature of phytoplankton, which is crucial for better understanding of nitrogen dynamics in the surface ocean. Chlorophylls are also buried and preserved in the sediments for long, and thus useful for the reconstruction of nitrogen cycle in the surface ocean in the geological past. In this presentation, we will summarize the evidence and discuss advantages and pitfalls of this tool for the future use in the oceanography and paleoceanography.