TY - JOUR
T1 - Dissolved Organic Nitrogen Cycling in the South China Sea From an Isotopic Perspective
AU - Zhang, Run
AU - Wang, Xingchen T.
AU - Ren, Haojia
AU - Huang, Jie
AU - Chen, Min
AU - Sigman, Daniel M.
N1 - Funding Information:
This work was supported by the National Nature Science Foundation of China (42076042, 41721005, 41676174), China Ministry of Science and Technology (2017FY201403), the Foundation of China Ocean Mineral Resources R&D Association (DY135‐E2‐2‐03), and China Scholarship Council. D. M. S. and the isotopic analysis facilities at Princeton were supported by the U.S. NSF through grant OCE‐0960802 to D. M. S. and grant OCE‐1136345 to B. B. Ward and D. M. S.; support was also provided by the Grand Challenges Program of Princeton University. Samples were collected onboard R/V “” implementing the open research cruise NORC2015‐07 supported by NSFC Shiptime Sharing Project. Thanks are due to M. Zheng, Y. Qiu, X. J. Wang, S. Chen, and D. Li for help of sampling and measurements. We would like to thank W. Zhuang, X. Liu, and X. L. Li for constructive discussions. The manuscript benifited from the comments raised by the reviewers and editor. The software Ocean Data View was used for making plots (Schlitzer, R., Ocean Data View, https://odv.awi.de , 2018). SHIYAN 3
Funding Information:
This work was supported by the National Nature Science Foundation of China (42076042, 41721005, 41676174), China Ministry of Science and Technology (2017FY201403), the Foundation of China Ocean Mineral Resources R&D Association (DY135-E2-2-03), and China Scholarship Council. D. M. S. and the isotopic analysis facilities at Princeton were supported by the U.S. NSF through grant OCE-0960802 to D. M. S. and grant OCE-1136345 to B. B. Ward and D. M. S.; support was also provided by the Grand Challenges Program of Princeton University. Samples were collected onboard R/V ?SHIYAN 3? implementing the open research cruise NORC2015-07 supported by NSFC Shiptime Sharing Project. Thanks are due to M. Zheng, Y. Qiu, X. J. Wang, S. Chen, and D. Li for help of sampling and measurements. We would like to thank W. Zhuang, X. Liu, and X. L. Li for constructive discussions. The manuscript benifited from the comments raised by the reviewers and editor. The software Ocean Data View was used for making plots (Schlitzer, R., Ocean Data View, https://odv.awi.de, 2018).
Publisher Copyright:
©2020. American Geophysical Union. All Rights Reserved.
PY - 2020/12
Y1 - 2020/12
N2 - Dissolved organic nitrogen (DON) is the dominant form of fixed nitrogen in most low and middle latitude ocean surface waters. Here, we report measurements of DON isotopic composition (δ15N) from the west South China Sea (SCS), with the goal of providing new insight into DON cycling. The concentration of DON in the surface ocean is correlated (r = 0.70, p < 0.0001) with chlorophyll a concentration, indicating DON production in these surface waters. The concentration and δ15N of DON fall in a relatively narrow range in the surface ocean (4.6 ± 0.1 μM and 4.3 ± 0.2‰ vs. air, respectively; ±SD), similar to other ocean regions. The mean DON δ15N above 50 m (4.5 ± 0.3‰) is similar to the δ15N of nitrate in the “shallow subsurface” (i.e., immediately below the euphotic zone; 4.6 ± 0.2‰) but is higher than the δ15N of suspended particles in the surface ocean (~2.3‰). This set of isotopic relationships has been observed previously (e.g., in the oligotrophic North Atlantic and North Pacific) and can be explained by the cycling of N between particulate organic nitrogen (PON), DON, and ammonium, in which an isotope effect associated with DON degradation preferentially concentrates 15N in DON. Consistent with this view, a negative correlation (r = 0.70) between the concentration and the δ15N of DON is observed in the upper 75 m, suggesting an isotope effect of ~4.9 ± 0.4‰ for DON degradation. Comparing the DON δ15N data from the SCS with other regions, we find that the δ15N difference between euphotic zone DON and shallow subsurface nitrate δ15N (Δδ15N(DON-NO3)) rises from ocean regions of inferred net DON production to regions of net DON consumption, with the SCS representing an intermediate case.
AB - Dissolved organic nitrogen (DON) is the dominant form of fixed nitrogen in most low and middle latitude ocean surface waters. Here, we report measurements of DON isotopic composition (δ15N) from the west South China Sea (SCS), with the goal of providing new insight into DON cycling. The concentration of DON in the surface ocean is correlated (r = 0.70, p < 0.0001) with chlorophyll a concentration, indicating DON production in these surface waters. The concentration and δ15N of DON fall in a relatively narrow range in the surface ocean (4.6 ± 0.1 μM and 4.3 ± 0.2‰ vs. air, respectively; ±SD), similar to other ocean regions. The mean DON δ15N above 50 m (4.5 ± 0.3‰) is similar to the δ15N of nitrate in the “shallow subsurface” (i.e., immediately below the euphotic zone; 4.6 ± 0.2‰) but is higher than the δ15N of suspended particles in the surface ocean (~2.3‰). This set of isotopic relationships has been observed previously (e.g., in the oligotrophic North Atlantic and North Pacific) and can be explained by the cycling of N between particulate organic nitrogen (PON), DON, and ammonium, in which an isotope effect associated with DON degradation preferentially concentrates 15N in DON. Consistent with this view, a negative correlation (r = 0.70) between the concentration and the δ15N of DON is observed in the upper 75 m, suggesting an isotope effect of ~4.9 ± 0.4‰ for DON degradation. Comparing the DON δ15N data from the SCS with other regions, we find that the δ15N difference between euphotic zone DON and shallow subsurface nitrate δ15N (Δδ15N(DON-NO3)) rises from ocean regions of inferred net DON production to regions of net DON consumption, with the SCS representing an intermediate case.
KW - South China Sea
KW - dissolved organic nitrogen
KW - isotopic composition
KW - upper ocean N cycle
UR - http://www.scopus.com/inward/record.url?scp=85097997206&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=85097997206&partnerID=8YFLogxK
U2 - 10.1029/2020GB006551
DO - 10.1029/2020GB006551
M3 - Article
AN - SCOPUS:85097997206
SN - 0886-6236
VL - 34
JO - Global Biogeochemical Cycles
JF - Global Biogeochemical Cycles
IS - 12
M1 - e2020GB006551
ER -