Skip to main content
SpringerLink
Log in

Nitrate isotope dynamics in the lower euphotic-upper mesopelagic zones of the western South China Sea

  • Published:
Acta Oceanologica Sinica Aims and scope Submit manuscript

Abstract

The dual isotopes (N and O) of nitrate were measured using a denitrifier bacterial method in the western South China Sea (WSCS) during September 2015 to elucidate key information during N transformation in the lower euphotic zone (LEZ)-upper mesopelagic zone (UMZ, down to 500 m in this study) continuum, which is a vital sub-environment for marine N cycle and sequestration of atmospheric CO2 as well. The N isotopic composition (δ15N) of nitrate generally decreased from 500 m toward the base of the euphotic zone (∼100 m), reaching a value of ∼4.6‰ (vs. air N2) at the base of the LEZ, suggesting the imprint of remineralization (nitrification) of isotopically light N from atmospheric source. The δ15N and δ18O of nitrate only generally conform to a 1:1 line at 50 m and 75 m, suggesting that nitrate assimilation is a dominant process to shape nitrate isotope signature in this light-limited and relatively N-replete lower part of the euphotic zone. The fractionation factors of N and O isotopes during nitrate fractionation (15εASSIM, 18εASSIM) using a steady-state model were estimated to be 4.0‰±0.39‰ and 5.4‰±0.39‰, respectively. The occurrence of nitrification at the base of the LEZ and most of the UMZ is corroborated by the decoupling of δ15N and the oxygen isotopic composition (δ18O) of nitrate. Our results will provide insights for better understanding N cycle in the South China Sea from a perspective of present and past.

This is a preview of subscription content, log in via an institution to check access.

Access this article

Log in via an institution

Price excludes VAT (USA)
Tax calculation will be finalised during checkout.

Instant access to the full article PDF.

Institutional subscriptions

Similar content being viewed by others

References

  • Bai Peng, Yang Jingling, Zhang Shuwen, et al. 2019. Upwelling off the west coast of Hainan Island: sensitivity to wave-mixing. Acta Oceanologica Sinica, 38(11): 11–19, doi: https://doi.org/10.1007/s13131-019-1494-3

    Article  Google Scholar 

  • Braman R S, Hendrix S A. 1989. Nanogram nitrite and nitrate determination in environmental and biological materials by vanadium (III) reduction with chemi luminescence detection. Analytical Chemistry, 61(24): 2715–2718, doi: https://doi.org/10.1021/ac00199a007

    Article  Google Scholar 

  • Buchwald C, Casciotti K L. 2013. Isotopic ratios of nitrite as tracers of the sources and age of oceanic nitrite. Nature Geoscience, 6(4): 308–313, doi: https://doi.org/10.1038/ngeo1745

    Article  Google Scholar 

  • Cai Pinghe, Chen Weifang, Dai Minhan, et al. 2008. A high-resolution study of particle export in the southern South China Sea based on 234Th: 238U disequilibrium. Journal of Geophysical Research: Oceans, 113: C04019

    Article  Google Scholar 

  • Casciotti K L. 2016a. Nitrite isotopes as tracers of marine N cycle processes. Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 374(2081): 20150295

    Article  Google Scholar 

  • Casciotti K L. 2016b. Nitrogen and oxygen isotopic studies of the marine nitrogen cycle. Annual Review of Marine Science, 8: 379–407, doi: https://doi.org/10.1146/annurev-marine-010213-135052

    Article  Google Scholar 

  • Casciotti K L, Buchwald C, Santoro A E, et al. 2011. Assessment of nitrogen and oxygen isotopic fractionation during nitrification and its expression in the marine environment. Methods in Enzymology, 486: 253–280

    Article  Google Scholar 

  • Casciotti K L, Sigman D M, Hastings M G, et al. 2002. Measurement of the oxygen isotopic composition of nitrate in seawater and freshwater using the denitrifier method. Analytical Chemistry, 74(19): 4905–4912, doi: https://doi.org/10.1021/ac020113w

    Article  Google Scholar 

  • Chen Yangjun, Bardhan P, Zhao Xiufeng, et al. 2021. Nitrite cycle indicated by dual isotopes in the northern South China Sea. Journal of Geophysical Research: Biogeosciences, 126(7): e2020JG006129

    Google Scholar 

  • Chen Yuh-ling Lee, Chen Houng-Yung, Tuo Sing-how, et al. 2008. Seasonal dynamics of new production from Trichodesmium N2 fixation and nitrate uptake in the upstream Kuroshio and South China Sea basin. Limnology and Oceanography, 53(5): 1705–1721, doi: https://doi.org/10.4319/lo.2008.53.5.1705

    Article  Google Scholar 

  • Chen Fajin, Lao Qibin, Zhang Shuwen, et al. 2020. Nitrate sources and biogeochemical processes identified using nitrogen and oxygen isotopes on the eastern coast of Hainan Island. Continental Shelf Research, 207: 104209, doi: https://doi.org/10.1016/j.csr.2020.104209

    Article  Google Scholar 

  • Coale K H, Bruland K W. 1987. Oceanic stratified euphotic zone as elucidated by 234Th: 238U disequilibria. Limnology and Oceanography, 32(1): 189–200, doi: https://doi.org/10.4319/lo.1987.32.1.0189

    Article  Google Scholar 

  • Craig H, Gordon L. 1964. Deuterium and Oxygen 18 Variations in the Ocean and Marine Atmosphere. Pisa: Laboratorio di Geologia Nucleare, 277–374

    Google Scholar 

  • Deman F, Fonseca-Batista D, Roukaerts A, et al. 2021. Nitrate supply routes and impact of internal cycling in the North Atlantic Ocean inferred from nitrate isotopic composition. Global Biogeochemical Cycles, 35(4): e2020GB006887

    Article  Google Scholar 

  • Dore J E, Karl D M. 1996. Nitrification in the euphotic zone as a source for nitrite, nitrate, and nitrous oxide at Station ALOHA. Limnology and Oceanography, 41(8): 1619–1628, doi: https://doi.org/10.4319/lo.1996.41.8.1619

    Article  Google Scholar 

  • Dore J E, Letelier R M, Church M J, et al. 2008. Summer phytoplankton blooms in the oligotrophic North Pacific Subtropical Gyre: Historical perspective and recent observations. Progress in Oceanography, 76(1): 2–38, doi: https://doi.org/10.1016/j.pocean.2007.10.002

    Article  Google Scholar 

  • Du Chuanjun, Liu Zhiyu, Kao Shuh-Ji, et al. 2017. Diapycnal fluxes of nutrients in an oligotrophic oceanic regime: The South China Sea. Geophysical Research Letters, 44(22): 11510–11518, doi: https://doi.org/10.1002/2017GL074921

    Article  Google Scholar 

  • Eppley R W, Peterson B J. 1979. Particulate organic matter flux and planktonic new production in the deep ocean. Nature, 282(5740): 677–680, doi: https://doi.org/10.1038/282677a0

    Article  Google Scholar 

  • Fawcett S E, Ward B B, Lomas M W, et al. 2015. Vertical decoupling of nitrate assimilation and nitrification in the Sargasso Sea. Deep-Sea Research Part I: Oceanographic Research Papers, 103: 64–72, doi: https://doi.org/10.1016/j.dsr.2015.05.004

    Article  Google Scholar 

  • Fripiat F, Martínez-García A, Fawcett S E, et al. 2019. The isotope effect of nitrate assimilation in the Antarctic Zone: Improved estimates and paleoceanographic implications. Geochimica et Cosmochimica Acta, 247: 261–279, doi: https://doi.org/10.1016/j.gca.2018.12.003

    Article  Google Scholar 

  • Granger J, Sigman D M, Needoba J A, et al. 2004. Coupled nitrogen and oxygen isotope fractionation of nitrate during assimilation by cultures of marine phytoplankton. Limnology and Oceanography, 49(5): 1763–1773, doi: https://doi.org/10.4319/lo.2004.49.5.1763

    Article  Google Scholar 

  • Granger J, Sigman D M, Rohde M M, et al. 2010. N and O isotope effects during nitrate assimilation by unicellular prokaryotic and eukaryotic plankton cultures. Geochimica et Cosmochimica Acta, 74(3): 1030–1040, doi: https://doi.org/10.1016/j.gca.2009.10.044

    Article  Google Scholar 

  • Kao Shuh-Ji, Yang Jin-Yu Terence, Liu Kon-Kee, et al. 2012. Isotope constraints on particulate nitrogen source and dynamics in the upper water column of the oligotrophic South China Sea. Global Biogeochemical Cycles, 26(2): GB2033

    Article  Google Scholar 

  • Karl D M, Letelier R M, Bidigare R R, et al. 2021. Seasonal-to-decadal scale variability in primary production and particulate matter export at Station ALOHA. Progress in Oceanography, 195: 102563, doi: https://doi.org/10.1016/j.pocean.2021.102563

    Article  Google Scholar 

  • Karl D, Letelier R, Tupas L, et al. 1997. The role of nitrogen fixation in biogeochemical cycling in the subtropical North Pacific Ocean. Nature, 388(6642): 533–538, doi: https://doi.org/10.1038/41474

    Article  Google Scholar 

  • Karsh K L, Granger J, Kritee K, et al. 2012. Eukaryotic assimilatory nitrate reductase fractionates N and O isotopes with a ratio near unity. Environmental Science & Technology, 46(11): 5727–5735

    Article  Google Scholar 

  • Karsh K L, Trull T W, Lourey M J, et al. 2003. Relationship of nitrogen isotope fractionation to phytoplankton size and iron availability during the Southern Ocean Iron Release Experiment (SOIREE). Limnology and Oceanography, 48(3): 1058–1068, doi: https://doi.org/10.4319/lo.2003.48.3.1058

    Article  Google Scholar 

  • Kemeny P C, Weigand M A, Zhang R, et al. 2016. Enzyme-level interconversion of nitrate and nitrite in the fall mixed layer of the Antarctic Ocean. Global Biogeochemical Cycles, 30(7): 1069–1085, doi: https://doi.org/10.1002/2015GB005350

    Article  Google Scholar 

  • Lao Qibin, Chen Fajin, Liu Guoqiang, et al. 2019. Isotopic evidence for the shift of nitrate sources and active biological transformation on the western coast of Guangdong Province, South China. Marine Pollution Bulletin, 142: 603–612, doi: https://doi.org/10.1016/j.marpolbul.2019.04.026

    Article  Google Scholar 

  • Li Denghui, Zhou Meng, Zhang Zhaoru, et al. 2018. Intrusions of Kuroshio and shelf waters on northern slope of South China Sea in summer 2015. Journal of Ocean University of China, 17(3): 477–486, doi: https://doi.org/10.1007/s11802-018-3384-2

    Article  Google Scholar 

  • Liang Wenzhao, Tang Danling, Luo Xin. 2018. Phytoplankton size structure in the western South China Sea under the influence of a ‘jet-eddy system’. Journal of Marine Systems, 187: 82–95, doi: https://doi.org/10.1016/j.jmarsys.2018.07.001

    Article  Google Scholar 

  • Liu Kon-Kee, Atkinson L, Quiñones P R, et al. 2010. Carbon and Nutrient Fluxes in Continental Margins: A Global Synthesis. Berlin, Heidelberg: Springer, 423–493

    Book  Google Scholar 

  • Loick N, Dippner J, Doan H N, et al. 2007. Pelagic nitrogen dynamics in the Vietnamese upwelling area according to stable nitrogen and carbon isotope data. Deep-Sea Research Part I: Oceanographic Research Papers, 54(4): 596–607, doi: https://doi.org/10.1016/j.dsr.2006.12.009

    Article  Google Scholar 

  • Mariotti A, Germon J C, Hubert P, et al. 1981. Experimental determination of nitrogen kinetic isotope fractionation: Some principles; illustration for the denitrification and nitrification processes. Plant and Soil, 62(3): 413–430, doi: https://doi.org/10.1007/BF02374138

    Article  Google Scholar 

  • Montoya J P, Carpenter E J, Capone D G. 2002. Nitrogen fixation and nitrogen isotope abundances in zooplankton of the oligotrophic North Atlantic. Limnology and Oceanography, 47: 1617–1628

    Article  Google Scholar 

  • Moore C M, Mills M M, Arrigo K R, et al. 2013. Processes and patterns of oceanic nutrient limitation. Nature Geoscience, 6(9): 701–710, doi: https://doi.org/10.1038/ngeo1765

    Article  Google Scholar 

  • Needoba J A, Harrison P J. 2004. Influence of low light and a light: Dark cycle on NO −3 uptake, intracellular NO −3 , and nitrogen isotope fractionation by marine phytoplankton. Journal of Phycology, 40: 505–516

    Article  Google Scholar 

  • Peters B D, Lam P J, Casciotti K L. 2018. Nitrogen and oxygen isotope measurements of nitrate along the US GEOTRACES Eastern Pacific Zonal Transect (GP16) yield insights into nitrate supply, remineralization, and water mass transport. Marine Chemistry, 201: 137–150, doi: https://doi.org/10.1016/j.marchem.2017.09.009

    Article  Google Scholar 

  • Rafter P A, DiFiore P J, Sigman D M. 2013. Coupled nitrate nitrogen and oxygen isotopes and organic matter remineralization in the Southern and Pacific Oceans. Journal of Geophysical Research: Oceans, 118(10): 4781–4794, doi: https://doi.org/10.1002/jgrc.20316

    Article  Google Scholar 

  • Rafter P A, Sigman D M. 2016. Spatial distribution and temporal variation of nitrate nitrogen and oxygen isotopes in the upper equatorial Pacific Ocean. Limnology and Oceanography, 61(1): 14–31, doi: https://doi.org/10.1002/lno.10152

    Article  Google Scholar 

  • Ren Haojia, Chen Yichi, Wang Xingchen T, et al. 2017. 21st-century rise in anthropogenic nitrogen deposition on a remote coral reef. Science, 356(6339): 749–752, doi: https://doi.org/10.1126/science.aal3869

    Article  Google Scholar 

  • Shang Shaoling, Lee Z, Wei Guomei. 2011. Characterization of MODIS-derived euphotic zone depth: Results for the China Sea. Remote Sensing of Environment, 115(1): 180–186, doi: https://doi.org/10.1016/j.rse.2010.08.016

    Article  Google Scholar 

  • Sigman D M, Altabet M A, McCorkle D C, et al. 1999. The δ15N of nitrate in the Southern Ocean: Consumption of nitrate in surface waters. Global Biogeochemical Cycles, 13(4): 1149–1166, doi: https://doi.org/10.1029/1999GB900038

    Article  Google Scholar 

  • Sigman D M, DiFiore P J, Hain M P, et al. 2009. The dual isotopes of deep nitrate as a constraint on the cycle and budget of oceanic fixed nitrogen. Deep-Sea Research Part I: Oceanographic Research Papers, 56(9): 1419–1439, doi: https://doi.org/10.1016/j.dsr.2009.04.007

    Article  Google Scholar 

  • Sigman D M, Fripiat F. 2019. Nitrogen isotopes in the ocean. In: Cochran J K, Bokuniewicz H J, Yager P L, eds. Encyclopedia of Ocean Sciences. 3rd ed. Oxford: Academic Press, 263–278

    Chapter  Google Scholar 

  • Sigman D M, Granger J, DiFiore P J, et al. 2005. Coupled nitrogen and oxygen isotope measurements of nitrate along the eastern North Pacific margin. Global Biogeochemical Cycles, 19(4): GB4022

    Article  Google Scholar 

  • Sigman D M, Hain M P, Haug G H. 2010. The polar ocean and glacial cycles in atmospheric CO2 concentration. Nature, 466(7302): 47–55, doi: https://doi.org/10.1038/nature09149

    Article  Google Scholar 

  • Stephens B M, Wankel S D, Beman J M, et al. 2020. Euphotic zone nitrification in the California Current Ecosystem. Limnology and Oceanography, 65(4): 790–806, doi: https://doi.org/10.1002/lno.11348

    Article  Google Scholar 

  • Voss M, Bombar D, Loick N, et al. 2006. Riverine influence on nitrogen fixation in the upwelling region off Vietnam, South China Sea. Geophysical Research Letters, 33(7): L07604

    Article  Google Scholar 

  • Wan Xianhui Sean, Sheng Huaxia, Dai Minhan, et al. 2018. Ambient nitrate switches the ammonium consumption pathway in the euphotic ocean. Nature Communications, 9: 915, doi: https://doi.org/10.1038/s41467-018-03363-0

    Article  Google Scholar 

  • Ward B B. 2005. Temporal variability in nitrification rates and related biogeochemical factors in Monterey Bay, California, USA. Marine Ecology Progress Series, 292: 97–109, doi: https://doi.org/10.3354/meps292097

    Article  Google Scholar 

  • Wong G T F, Tseng Chun-Mao, Wen Liang-Saw, et al. 2007. Nutrient dynamics and N-anomaly at the SEATS station. Deep-Sea Research Part II: Topical Studies in Oceanography, 54(14–15): 1528–1545

    Article  Google Scholar 

  • Wu Jingfeng, Chung Shi-Wei, Wen Liang-Saw, et al. 2003. Dissolved inorganic phosphorus, dissolved iron, and Trichodesmium in the oligotrophic South China Sea. Global Biogeochemical Cycles, 17(1): 1008

    Article  Google Scholar 

  • Wu Jinhui, Lao Qibin, Chen Fajin, et al. 2021. Water mass processes between the South China Sea and the western Pacific through the Luzon Strait: insights from hydrogen and oxygen Isotopes. Journal of Geophysical Research: Oceans, 126(8): e2021JC 017484

    Google Scholar 

  • Xiao Hongwei, Xiao Huayun, Luo Li, et al. 2018. Stable carbon and nitrogen isotope compositions of bulk aerosol samples over the South China Sea. Atmospheric Environment, 193: 1–10, doi: https://doi.org/10.1016/j.atmosenv.2018.09.006

    Article  Google Scholar 

  • Xu Chao. 2021. Nitrogen and oxygen isotopic compositions of nitrate in the South China Sea and the western North Pacific (in Chinese) [dissertation]. Xiamen: Xiamen University

    Google Scholar 

  • Yang Zhi, Chen Jianfang, Chen Min, et al. 2018. Sources and transformations of nitrogen in the South China Sea: insights from nitrogen isotopes. Journal of Oceanography, 74(1): 101–113, doi: https://doi.org/10.1007/s10872-017-0443-z

    Article  Google Scholar 

  • Yang Jin-Yu Terence, Kao Shuh-Ji, Dai Minhan, et al. 2017. Examining N cycling in the northern South China Sea from N isotopic signals in nitrate and particulate phases. Journal of Geophysical Research: Biogeosciences, 122(8): 2118–2136, doi: https://doi.org/10.1002/2016JG003618

    Article  Google Scholar 

  • Yool A, Martin A P, Fernández C, et al. 2007. The significance of nitrification for oceanic new production. Nature, 447(7147): 999–1002, doi: https://doi.org/10.1038/nature05885

    Article  Google Scholar 

  • Zakem E J, Al-Haj A, Church M J, et al. 2018. Ecological control of nitrite in the upper ocean. Nature Communications, 9: 1206, doi: https://doi.org/10.1038/s41467-018-03553-w

    Article  Google Scholar 

  • Zhang Run, Chen Min, Yang Qing, et al. 2015. Physical-biological coupling of N2 fixation in the northwestern South China Sea coastal upwelling during summer. Limnology and Oceanography, 60(4): 1411–1425, doi: https://doi.org/10.1002/lno.10111

    Article  Google Scholar 

  • Zhang Run, Wang Xingchen T, Ren Haojia, et al. 2020. Dissolved organic nitrogen cycling in the South China Sea from an isotopic perspective. Global Biogeochemical Cycles, 34(12): e2020GB 006551

    Article  Google Scholar 

  • Zhu Yifan, Liu Jing, Mulholland M R. 2021. Dynamics of ammonium biogeochemistry in an oligotrophic regime in the South China Sea. Marine Chemistry, 237: 104040

    Article  Google Scholar 

Download references

Author information

Authors and Affiliations

  1. College of Ocean and Earth Sciences, Xiamen University, Xiamen, 361102, China

    Zixuan Li, Chao Xu, Minfang Zheng, Mengya Chen, Yusheng Qiu, Hantao Zhou, Min Chen & Run Zhang

Authors
  1. Zixuan Li
    View author publications

    You can also search for this author in PubMed Google Scholar

  2. Chao Xu
    View author publications

    You can also search for this author in PubMed Google Scholar

  3. Minfang Zheng
    View author publications

    You can also search for this author in PubMed Google Scholar

  4. Mengya Chen
    View author publications

    You can also search for this author in PubMed Google Scholar

  5. Yusheng Qiu
    View author publications

    You can also search for this author in PubMed Google Scholar

  6. Hantao Zhou
    View author publications

    You can also search for this author in PubMed Google Scholar

  7. Min Chen
    View author publications

    You can also search for this author in PubMed Google Scholar

  8. Run Zhang
    View author publications

    You can also search for this author in PubMed Google Scholar

Corresponding author

Correspondence to Run Zhang.

Additional information

Foundation item

The National Natural Science Foundation of China under contract Nos 42076042 and 41721005; the Science and Technology Basic Resources Investigation Program of China under contract No. 2017FY201403.

Rights and permissions

Reprints and permissions

About this article

Check for updates. Verify currency and authenticity via CrossMark

Cite this article

Li, Z., Xu, C., Zheng, M. et al. Nitrate isotope dynamics in the lower euphotic-upper mesopelagic zones of the western South China Sea. Acta Oceanol. Sin. 42, 1–11 (2023). https://doi.org/10.1007/s13131-022-2091-4

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI: https://doi.org/10.1007/s13131-022-2091-4

Key words

Search

Navigation