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https://doi.org/10.5194/egusphere-2026-1212
© Author(s) 2026. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/egusphere-2026-1212
© Author(s) 2026. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
23 Mar 2026
| 23 Mar 2026
Status: this preprint is open for discussion and under review for Biogeosciences (BG).
Impact of anticyclonic eddies on the spatial distribution and emission of non-methane hydrocarbons in the northern South China Sea
Abstract. Non-methane hydrocarbons (NMHCs) are important trace active gases that exert significant impacts on climate. Ubiquitous mesoscale eddies likely act as a key physical process regulating the marine emission of these gases, yet the underlying mechanisms remain poorly understood. Herein, we characterized the distributions and emissions of NMHCs in the South China Sea, with particular emphasis on the impacts of an anticyclonic eddy. Significantly lower NMHC concentrations were observed within the eddy-controlled region (201 ± 101 pmol L−1) relative to the reference sites (433 ± 62.5 pmol L−1). Downwelling in the anticyclonic eddy core reduced surface nutrient availability, suppressing the biological production and surface concentrations of alkanes and isoprene, whereas lower alkene levels were mainly driven by weakened photochemical production. NMHC sea-to-air fluxes dropped by 56 % within the eddy, which further diminished ozone and secondary organic aerosol generation by 59% and 60%, respectively. Overall, our findings elucidate the regulatory role of mesoscale eddies in NMHC dynamics, highlighting their critical function in shaping marine trace gas cycling and associated environmental consequences.
How to cite. Liu, Z.-F., Qiao, W.-Z., Yang, Z.-Y., Xu, F., Xu, G.-B., Wang, J., Qiao, H., Li, C.-S., and Zhang, H.-H.: Impact of anticyclonic eddies on the spatial distribution and emission of non-methane hydrocarbons in the northern South China Sea, EGUsphere [preprint], https://doi.org/10.5194/egusphere-2026-1212, 2026.
Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.
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Latest update: 01 May 2026
Zhen-Fei Liu
Frontiers Science Center for Deep Ocean Multispheres and Earth System, Key Laboratory of Marine Chemistry Theory and Technology, Ministry of Education, Ocean University of China, Qingdao 266100, China
Laoshan Laboratory, Qingdao 266237, China
Wen-Zhu Qiao
Weihai Institute of Product Quality Standard and Metrology Inspection, Weihai 264209, China
Ze-Yun Yang
Frontiers Science Center for Deep Ocean Multispheres and Earth System, Key Laboratory of Marine Chemistry Theory and Technology, Ministry of Education, Ocean University of China, Qingdao 266100, China
Frontiers Science Center for Deep Ocean Multispheres and Earth System, Key Laboratory of Marine Chemistry Theory and Technology, Ministry of Education, Ocean University of China, Qingdao 266100, China
Gao-Bin Xu
Frontiers Science Center for Deep Ocean Multispheres and Earth System, Key Laboratory of Marine Chemistry Theory and Technology, Ministry of Education, Ocean University of China, Qingdao 266100, China
Jian Wang
CORRESPONDING AUTHOR
Frontiers Science Center for Deep Ocean Multispheres and Earth System, Key Laboratory of Marine Chemistry Theory and Technology, Ministry of Education, Ocean University of China, Qingdao 266100, China
Hao Qiao
Frontiers Science Center for Deep Ocean Multispheres and Earth System, Key Laboratory of Marine Chemistry Theory and Technology, Ministry of Education, Ocean University of China, Qingdao 266100, China
Cheng-Shuai Li
Frontiers Science Center for Deep Ocean Multispheres and Earth System, Key Laboratory of Marine Chemistry Theory and Technology, Ministry of Education, Ocean University of China, Qingdao 266100, China
Hong-Hai Zhang
CORRESPONDING AUTHOR
Frontiers Science Center for Deep Ocean Multispheres and Earth System, Key Laboratory of Marine Chemistry Theory and Technology, Ministry of Education, Ocean University of China, Qingdao 266100, China
Laoshan Laboratory, Qingdao 266237, China
Short summary
Mesoscale eddies can influence the biogeochemistry of non‑methane hydrocarbons (NMHCs). Eddy‑induced downwelling reduces nutrient availability in the euphotic zone, thereby suppressing phytoplankton growth and the biological production of alkanes and isoprene, while limited dissolved organic carbon constrains the photochemical production of alkenes. As a result, NMHC emissions within eddies were substantially reduced, weakening their contribution to ozone and secondary organic aerosol formation.
Mesoscale eddies can influence the biogeochemistry of non‑methane hydrocarbons (NMHCs)....
General comments: This study was designed to investigate the impact of anticyclonic eddy systems on the distribution and oceanic efflux of an array of non-methane hydrocarbon compounds (NMHCs) and the projected atmospheric impact in the South China Sea. The measurements in this manuscript show that 1) the concentrations and oceanic emissions of NMHCs were significantly lower in eddy-influenced stations compared to the reference stations; 2) the photoproduction of NMHCs was slower in eddy-influenced waters compared to the reference waters. This work is of significance because the biogeochemical cycling of NMHCs and other volatile organic compounds (VOCs) has not been thoroughly studied in mesoscale eddies. However, the most critical issue with this work, in my opinion, is the lack of clarification on the method of statistical analysis on multiple occasions that has compromised the quality of this manuscript in telling a compelling story. That’s being said, statistical analyses must be performed throughout the manuscript to truly tell if these differences are significant, particularly when error propagation is involved in this work. Please see the texts below for the major and minor issues that I believe need to be addressed for the manuscript to be of a better quality. Overall, I think this work is well designed and carries significant scientific merits by providing new knowledge to the study of oceanic NMHCs in the system of mesoscale eddies. Thereby I believe it’s suited for publication in Biogeosciences after revision.
Major issues and recommendation: 1) This study relies on the comparison made for the measurements between eddy-impacted water and reference waters. However, the uncertainty associated with these measurements and the method of statistical analysis are missing on many occasions in the manuscript. For instance, in the Abstract (Lines 16-19), the authors claimed that the difference between the two means of NMHC concentrations was significant. What statistical analysis was performed that led to this conclusion? What is the sample number? Can authors clarify if the data are normally distributed? This is just an example. Authors should check through manuscripts and ensure proper statistical analyses are coupled with comparisons of means.
2) The authors should acknowledge that only four photochemical experiments were done in the field that a robust assessment cannot be made here in any capacity for the photoproduction rates of NMHCs between eddy-influenced and reference stations. I understand that field work is labor intense and it’s of great value to collect preliminary results. For future, 1) more photochemical experiments should be carried out; 2) I recommend authors think about what the rationales are that a difference is expected for their photoproduction in eddy vs reference stations; 3) Authors should also measure the CDOM absorbance in these waters to see if there is a difference in absorbance; 4) The most effective approach to study spectral dependence of a photochemical process is to determine wavelength-dependent apparent quantum yields. The crude spectral study, using optical treatments, is less valuable as it’s well known that marine photochemistry is a UV-controlled process particularly during field work at sea. I’d rather invest the valuable sea time in performing more photochemical experiments that would afford one a larger dataset.
Minor issues: The writing of this manuscript in English language could benefit from further polishing for a more concise and accurate communication of your research.
Specific comments:
Line 16: Get rid of “particular”
Line 17: Were these concentrations determined in water samples from the near-surface?
Lines 21-22: It’s not that the flux dropped by 56% in the eddies. I believe you meant that the flux in the eddies is 56% lower than reference sites. Please have this sentence rewritten if that’s true.
Line 29: Add a dot (•) to the side of OH to make a radical.
Line 74: Get rid of “systematically”, and I’d avoid this type of “empty” words in scientific writing.
Line 76: Get rid of “formation”.
Line 95: Add “photochemical” before incubation experiments.
Line 93: Can you clarify what that 0.5 m/s on the figure to the right shows?
Line 100: Just simply say “samples were collected in duplicate at 4 stations”.
Line 144: Change “light” to optical.
Line 145: To my knowledge, the term “visible light” rather than PAR is used more often in photochemical studies.
Lines 159-160: Are there any studies supporting this statement about photolysis of NMHCs in seawater? If so, provide the references. If not, get rid of this statement since it’s meaningless. I highly doubt any of these NMHCs photolyze in ambient seawater. What would be the photolysis mechanism(s)?
Line 211: Authors should take time to verify the scales on the y-axes of these plots. As an example, the scale for the DOC plot seems to be too broad if you look at the color scheme in the plot. There is no dark red in the plot.
Lines 218-219: please provide statistics for the DOC comparison like you did for Chl a. Are these two means truly statistically different?
Line 22, section 3.2: As a general comment, the concentration or standing stock of an NMHC species measured is always a net result of its production and removal. Are there any previous studies that investigated the impact of eddies on bacterial activity or more specifically on the consumption rates of NMHCs or any other biogenic products?
Lines 247-248: Make your writing concise by simply saying “In 0.2µm-filtered seawater”. In the method, you already clarified about the purpose of filtration.
Lines 252-254: what is the sample number n?
Lines 257-260: what is the sample number for eddy, eddy edge, and refence stations? Very important to show these information.
Line 266, Table 1: Change “natural light” to Full spectrum because that’s the comparison you are showing Full spectrum vs Specific spectral bands (e.g. UVB). Please clarify why there are these blank spaces. Experiments were not performed at these stations or data were problematic? Also, please provide the concentrations in your dark controls as it’s so important to know the level of [ ]s in the dark. You said that triplicate quartz tubes were irradiated. Can you provide the uncertainty associated with these measurements? Can you actually say with confidence that the production in PAR is significant since the production is so low?
Line 281: these differences in Chl a are statistically different? They are definitely not substantially different.
Line 298: It’s not entirely accurate to say “wavelength dependence” because the way you did in this work can only give you an idea of the crude spectral dependence. The best way to do it is using a monochromatic system or even a polychromatic system with narrower spectral range.