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Changing carbon-to-nitrogen ratios of organic-matter export under ocean acidification


Ocean acidification (OA) will affect marine biotas from the organism to the ecosystem level. Yet, the consequences for the biological carbon pump and thereby the oceanic sink for atmospheric CO2 are still unclear. Here we show that OA considerably alters the C/N ratio of organic-matter export (C/Nexport), a key factor determining efficiency of the biological pump. By synthesizing sediment-trap data from in situ mesocosm studies in different marine biomes, we find distinct but highly variable impacts of OA on C/Nexport, reaching up to a 20% increase/decrease under partial pressure of CO2 (\(p_{{\rm{CO}}_{2}}\)) conditions projected for 2100. These changes are driven by \(p_{{\rm{CO}}_{2}}\) effects on a variety of plankton taxa and corresponding shifts in food-web structure. Notably, our findings suggest a pivotal role of heterotrophic processes in controlling the response of C/Nexport to OA, thus contradicting the paradigm of primary producers as the principal driver of biogeochemical responses to ocean change.

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Fig. 1: Mesocosm experiment locations and design.
Fig. 2: Impact of simulated OA on C/N ratios of sinking particulate matter in the different in situ mesocosm studies.
Fig. 3: The role of plankton communities in shaping OA impacts on the C/N ratio of organic-matter export.
Fig. 4: Change in C/N of sinking particles and its response to OA.

Data availability

The raw data of the mesocosm studies are archived in the World Data Centre MARE/PANGAEA ( and can be found using the keyword ‘KOSMOS’. In addition, the data supporting the findings of this study are available from the corresponding author upon reasonable request.


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This study was supported by the German Federal Ministry of Science and Education (BMBF) in the framework of the projects BIOACID III (Biological Impacts of Ocean Acidification, FKZ 03F0728) and SOPRAN III (Surface Ocean Processes in the ANthropocene, FKZ 03F0662). Funding for the different mesocosm studies was also provided by the European Project on Ocean Acidification (EPOCA, grant no. 211384) from the European Community’s Seventh Framework Programme (FP7/2007–2013), the EU project MESOAQUA (grant no. 228224), as well as BIOACID II (FKZ 03F06550) and SOPRAN II (03F0611). Furthermore, we thank all participating scientists and technicians for their huge effort in realizing the different studies. We also thank the staff of the marine biological stations in the different study locations for providing logistics, technical assistance and support at all times. We also thank the captains and crews of R/V Viking Explorer, M/V Esperanza of Greenpeace, R/V Håkon Mosby (2011609), R/V Alkor (AL376, AL394, AL397, AL406, AL420), R/V Heincke (HE360), R/V Poseidon (POS463) and R/V Hesperides (29HE20140924) for support during transport, deployment and recovery of the mesocosm facilities.

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Authors and Affiliations



J.T., L.T.B. and M.S. conceived and designed the meta-analysis. J.T., T.B., P.S., L.T.B., A.J.P. and U.R. coordinated and implemented the mesocosm experiments, including data acquisition. J.T. was responsible for data analysis, data processing and visualization. J.T. wrote the manuscript, with editing by all co-authors.

Corresponding author

Correspondence to Jan Taucher.

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Extended data

Extended Data Fig. 1 Impact of elevated CO2 concentrations on cumulative probability distributions of C:Nexport.

Shown are ambient conditions (blue) and ocean acidification (red) with shaded areas denoting standard deviation. Data used for analysis is identical with that in Fig. 2, but computed as cumulative values, thereby depicting the visual representation of a Kolmogorov-Smirnov test. Non-overlapping probability distributions indicate statistically significant differences in C:N between ambient and OA conditions. Note different scaling of x-axes due to large variations in baseline C:N among study regions.

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Supplementary Information

Supplementary Tables 1–4, and Figs. 1 and 2.

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Taucher, J., Boxhammer, T., Bach, L.T. et al. Changing carbon-to-nitrogen ratios of organic-matter export under ocean acidification. Nat. Clim. Chang. 11, 52–57 (2021).

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