Chinese Journal of Polar Research

Chinese Journal of Polar Research ›› 2025, Vol. 37 ›› Issue (4): 658-667.DOI: 10.13679/j.jdyj.20240023

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Concentrations of nitrate and its dual isotopes in Bering Sea sediments reveal nitrate transformation processes

CHEN Jiaqin1, CHEN Ling1, ZHUANG Yanpei 2, REN Jian1, JI Zhongqiang1, BAI Youcheng1, YANG Zhi1, LI Yangjie1, CHEN Jianfang1,3,4, JIN Haiyan1,3,5,6   

  1. 1 Key Laboratory of Marine Ecosystem Dynamics, Second Institute of Oceanography, Ministry of Natural Resources, Hangzhou 310012, China;
    2 Polar and Marine Research Institute, Jimei University, Xiamen 361021, China;
    3 School of Oceanography, Shanghai Jiaotong University, Shanghai 200240, China;
    4 State Key Laboratory of Satellite Ocean Environment Dynamics, Hangzhou 310012, China;
    5 Southern Marine Science and Engineering Guangdong Laboratory (Zhuhai), Zhuhai 5190823, China;
    6 Donghai Laboratory, Zhoushan 316000, China
  • Received:2024-03-06 Revised:2024-05-09 Online:2025-12-30 Published:2026-01-12

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Abstract:

Simultaneous nitrification and denitrification processes happened in marine sediments affect the nitrate (NO3–) cycling in the Ocean. Studies of nitrogen (N) transformation processes occurring in Bering Sea sediments are crucial for improving our understanding of the N cycling in polar and subpolar marine regions. In this study, we conducted preliminary analyses of nitrate and its stable nitrogen and oxygen isotopes (d15N-NO3–, d18O-NO3–) in the sediment pore water in Bering Sea sediments. Samples were extracted from sediment cores collected during the 5th Chinese Arctic Research Expedition from the Bering Sea Basin (BL-10) and the 7th Chinese Arctic Research Expedition from the Bering Sea shelf (B12). The results show that: (1) at BL-10 station, nitrate concentration in pore water was 0.61~22.52 μmol·L–1, d15N-NO3– was 3.6‰~17.8‰, and d18O-NO3– was 10.5‰~20.9‰, suggesting coupling between nitrification-denitrification process. (2) At B12 station, the nitrate concentration in sediment pore water was 0.20~1.61 μmol·L–1, in 0~2 cm d15N-NO3– was 10.3‰~16.4‰, d18O-NO3– was 13.2‰~19.7‰, which was significantly lower than that in bottom sea (18.60 μmol·L–1). This indicates intense denitrification in the surface sediment pore water. (3) Denitrification appears to be more intense in shelf than in basin sediments because of the combined influence of water depth, primary productivity, and sediment organic carbon content.


Key words: nitrate, nitrogen and oxygen isotopes, sediment pore water, transformation process, Bering Sea