Japan Geoscience Union Meeting 2019

Presentation information

[J] Oral

A (Atmospheric and Hydrospheric Sciences ) » A-CG Complex & General

[A-CG42] Biogeochemical linkages between the surface ocean and atmosphere

Wed. May 29, 2019 10:45 AM - 12:15 PM 102 (1F)

convener:Yuzo Miyazaki(Institute of Low Temperature Science, Hokkaido University), Jun Nishioka(Hokkaido University, Institute of low temperature sciences), Koji Suzuki(Hokkaido University), Yoko Iwamoto(Graduate School of Biosphere Science, Hiroshima University), Chairperson:Yuzo Miyazaki(Institute of low temperature science, Hokkaido University), Jun Nishioka(Institute of low temperature science, Hokkaido University)

11:30 AM - 11:45 AM

[ACG42-04] Very low δ15N of atmospheric nitrate found in the earstern equatorial Pacific and its implication to dynamic nitrogen recycle between ocean and lower atmosphere

*Shohei Hattori1, Kazuki Kamezaki1, Yoko Iwamoto2, Sakiko Ishino1, Mitsuo Uematsu3, Kazuhiko Miura4, Naohiro Yoshida1 (1.Department of Chemical Science and Engineering, School of Materials and Chemical Technology, Tokyo Institute of Technology, 2.Hiroshima University, 3.University of Tokyo, 4.Tokyo University of Science)

Keywords:Nitrate, Stable Isotopes, Pacific Ocean, Equatorial Pacific

Atmospheric nitrogen sources in the marine boundary layer of the remote ocean have been known to include long-range transport (LRT) of anthropogenic pollutants, and the LRT of anthropogenic atmospheric particulate nitrate (p-NO3) within the free troposphere has been observed in regions influenced by westerlies from the Asian continent over Pacific Ocean. This traditional paradigm that the ocean is considered a passive recipient of anthropogenic N deposition can be applied western north Pacific regions. However, for the equatorial Pacific under the influence of pristine air, the sources of such p-NO3 remain unresolved. To address this, we present δ15N of p-NO3 collected over the Pacific Ocean between 40°S and 68°N on two cruises, carried out by the Research Vessel Hakuho Maru, and estimated δ15N of source NOx of each sample. We categorized six marine regions within the Pacific Ocean, based on backward trajectory analysis to determine their source regions and various ion concentrations to assess whether anthropogenic or non-anthropogenic sources were dominant.

We found remarkably low δ15N(NOx) values for the equatorial Pacific regions compared to those in other regions over Pacific Ocean. These low source δ15N(NOx) values cannot be explained using conventional NOx apportionment. Given that the eastern equatorial Pacific is one of the biologically active ocean regions resulted from upwelling water, here we postulate the alternative biogenic nitrogen source (NH3 or alkyl nitrate) in this region. In the presentation, we will discuss important feature of self-recycle process of nitrogen between ocean and lower atmosphere in the eastern equatorial Pacific. We will also discuss its implication to nitrogen deposition for this region, which may contribute to new marine biological production and/or nitrous oxide emissions.