Japan Geoscience Union Meeting 2015

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Oral

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

[M-IS26] Biogeochemistry

Thu. May 28, 2015 11:00 AM - 12:45 PM 104 (1F)

Convener:*Muneoki Yoh(Tokyo University of Agriculture and Technology), Shibata, Hideaki(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:Yoshinori Takano(Japan Agency for Marine-Earth Science and Technology (JAMSTEC)), Seiya Nagao(Institute of Nature and Environmental Technology, Kanazawa University), Izumi Watanabe(Graduate School of Agriculture, Tokyo University of Agriculture and Technology), Yoriko Yokoo(同志社大学理工学部)

11:30 AM - 11:45 AM

[MIS26-10] Sources of dissolved organic nitrogen in the ocean indicated by nitrogen isotopic analysis of amino acids

*Yasuhiko T. YAMAGUCHI1, Taylor A. B. Broek1, Matthew D. McCarthy1 (1.University of California, Santa Cruz)

Keywords:Dissolved Organic Matter, Nitrogen Cycle, Amino Acids, Isotopes, North Pacific Subtropical Gyre, Gulf of Mexico

Estimating sources of marine dissolved organic matter (DOM) is one of crucial steps for mechanistic understanding of marine biogeochemical cycles. Bacteria have been suggested as important sources of marine DOM, but nature of the source Bacteria (e.g., heterotrophic v.s. autotrophic) currently remains uncertain. While compound-specific isotope analysis of amino acids (CSI-AA) can be a powerful tool for elucidation of the source of marine DOM, it has been difficult due to the large analytical errors of CSI-AA associated with the complexity of marine DOM. Here we developed a new method for precise d15N-AA analysis of marine DOM by coupling HPLC purification and GC-IRMS, and then applied the method to high-molecular-weight (HMW) DOM samples collected at the Gulf of Mexico and the North Pacific Subtropical Gyre. d15N-AA values and patterns of the HMW-DOMs were significantly different between the surface and the mesopelagic depths, indicating that their sources are different. Especially, the d15N-AA signatures of the mesopelagic HMW-DOMs suggest that they are product of resynthesis by heterotrophic Bacteria, rather than remnant of DOM produced by autotrophic Bacteria.