Nitrogen cycle in the surface ocean

2015 Fiscal Year Final Research Report

• Project/Area Number: 25281013
• Research Category: Grant-in-Aid for Scientific Research (B)
• Allocation Type: Partial Multi-year Fund
• Section: 一般
• Research Field: Environmental dynamic analysis
• Research Institution: Japan Agency for Marine-Earth Science and Technology
• Principal Investigator: Ogawa Nanako O. 国立研究開発法人海洋研究開発機構, 生物地球化学研究分野, 主任技術研究員 (80359174)
• Co-Investigator(Kenkyū-buntansha): YOSHIKAWA Chisato 国立研究開発法人海洋研究開発機構, 生物地球化学研究分野, 技術研究員 (40435839)
• Project Period (FY): 2013-04-01 – 2016-03-31
• Keywords: クロロフィル / 光合成 / 窒素同位体比 / 硝酸態窒素 / 化合物レベル同位体比 / 海洋窒素循環

Outline of Final Research Achievements

In this study, nitrogen isotopic compositions of chlorophyll and substrate nitrate were determined to investigate the nitrogen cycle in the photic zone, from two Pacific sites (Station K2 and Station S1). Samples were collected during summer blooms in 2012, 2013, 2014, and 2015 (MR12-02, MR13-04, MR14-04, KH15-J01). The observed nitrogen isotopic compositions of chlorophyll at the stations K2 and S2 were -10.5 to +1.9‰ and -0.5 to +2.3‰, respectively. It was suggested that the nitrogen isotopic distribution of chlorophyll can be explained by either (1) large isotopic fractionation during nitrate assimilation by phytoplankton, or (2) significant contribution of ammonia as a substrate for the photosynthetic nitrogen assimilation, at Station K2. By applying a quantitative nitrogen cycle model in the surface ocean (Yoshikawa et al., 2005), it was concluded that there was a large (>50%) contribution of ammonia as a substrate for the phytoplankton.

Free Research Field

生物地球化学