[M-TT37] Frontiers in Geochemistry

[MTT37-P05] Challenges in quantifying triple oxygen isotopic compositions of nitrate in subtropical surface oceans

*Peng Weiqing¹, Yoshiumi Matsumoto¹, Chiho Sukigara¹, Masanori Ito¹, Fumiko Nakagawa¹, Urumu Tsunogai¹ (1.Graduate School of Environmental Studies, Nagoya University)

Keywords:nitrate, triple oxygen isotopic compositions, surface seawater, subtropical ocean

In this study, we challenged to quantify triple oxygen isotopic composition (¹⁷O-excess) of nitrate in nutrient-poor subtropical surface seawater. ¹⁷O-excess of low level nitrate in the water sample has been determined by adding nitrate standard of already-known oxygen isotopic compositions in each sample. By using this internal standard method, we successfully determined the ¹⁷O-excess of dissolved nitrate in surface seawater with its concentration ranging from 0.1 to 0.5 μmol/L and observed high ¹⁷O-excess of +4.7±2‰ in dissolved nitrate of surface seawater samples collected in the western north pacific. The result indicates that atmospheric nitrate deposited on the surface seawater account for 10%~25% of the total dissolved nitrate in the samples.