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Scientists Don’t Know or Agree How Much Carbon is Stored Permanently or Semi-Permanently by Oceans—But It Is Probably a Very Small Share of the Total Carbon Flow

The global carbon cycle is a complex and dynamic system, with the oceans playing a critical role in the storage and sequestration of atmospheric carbon dioxide (CO₂). However, the scientific community has yet to reach a consensus on the exact magnitude and nature of carbon storage in the oceans1.

Recent studies have shed light on the complexities involved in quantifying ocean carbon uptake and storage23456. The benthic (seafloor) ecosystems, for instance, have been identified as potentially significant carbon sinks, with their biodiversity and habitat integrity directly linked to the capacity for long-term carbon sequestration. At the same time, there remains significant uncertainty surrounding the biological carbon pump and its efficiency in transporting organic carbon to the deep ocean where it can be stored for extended periods7.

The ocean is estimated to absorb nearly 30% of anthropogenic CO2 emissions, with the Southern Ocean being a particularly important carbon sink8. However, the precise mechanisms and rates of carbon uptake and storage within the oceans are not fully understood.

The 1990s saw the development of several approaches to estimating the global inventory of anthropogenic carbon in the ocean interior, with most analyses suggesting a total inventory of around 120 Pg C in the mid-1990s3.

Rates of permanent carbon sequestration on the ocean floor remain a key knowledge gap, with the efficiency of biological and physical carbon pumps subject to ongoing research. Continued monitoring of ocean carbon dynamics through dedicated observation networks will be crucial to better constrain the role of the oceans in the global carbon cycle and improve our understanding of long-term carbon storage23.

The share of the total carbon flow that is stored permanently or semi-permanently by the oceans is likely to be relatively small, given the complex nature of ocean carbon cycling9101112.

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Footnotes​

  1. Jiao, N., Luo, T., Chen, Q., Zhao, Z., Xiao, X., Liu, J., Jian, Z., Xie, S., Thomas, H., Herndl, G. J., Benner, R., Gonsior, M., Chen, F., Cai, W.-J., & Robinson, C. (2024). The microbial carbon pump and climate change. Nature Portfolio, 22(7), 408-419. https://doi.org/10.1038/s41579-024-01018-0 ↩

  2. Feely, R. A., Sabine, C. L., Takahashi, T., & Wanninkhof, R. (2001). Uptake and storage of carbon dioxide in the ocean: The global CO2 survey. Oceanography Society, 14(4), 18-32. https://doi.org/10.5670/oceanog.2001.03 ↩ ↩2

  3. Álvarez, M., & Tanhua, T. (2009). Estimation of anthropogenic CO2 inventories in the Ocean. https://oceanrep.geomar.de/1872/ ↩ ↩2 ↩3

  4. [No author]. (2023). [No title]. http://digital.csic.es/bitstream/10261/52596/1/Sabine_Science-2004.pdf ↩

  5. Khatiwala, S., Tanhua, T., Mikaloff Fletcher, S. E., Gerber, M., Doney, S. C., Graven, H., Gruber, N., McKinley, G. A., Murata, A., Ríos, A. F., & Sabine, C. L. (2013). Global ocean storage of anthropogenic carbon. Copernicus Publications, 10(4), 2169-2191. https://doi.org/10.5194/bg-10-2169-2013 ↩

  6. Wanninkhof, R., Park, G.-H., Takahashi, T., Sweeney, C., Feely, R. A., Nojiri, Y., Gruber, N., Doney, S. C., McKinley, G. A., Lenton, A., Le Quéré, C., Heinze, C., Schwinger, J., Graven, H., & Khatiwala, S. (2013). Global ocean carbon uptake: magnitude, variability and trends. Copernicus Publications, 10(3), 1983-2000. https://doi.org/10.5194/bg-10-1983-2013 ↩

  7. Martin, P., Rutgers van der Loeff, M. M., Cassar, N., Vandromme, P., d'Ovidio, F., Stemmann, L., Rengarajan, R., Soares, M. A., González, H. E., Ebersbach, F., Lampitt, R. S., Sanders, R., Barnett, B. A., Smetacek, V., & Naqvi, S. W. A. (2013). Iron fertilization enhanced net community production but not downward particle flux during the Southern Ocean iron fertilization experiment LOHAFEX. Global Biogeochemical Cycles, 27(3), 871-881. https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1002/gbc.20077 ↩

  8. Jin, D., Hoagland, P., & Buesseler, K. O. (2020). The value of scientific research on the ocean's biological carbon pump. Science of The Total Environment, 749, 141357. https://doi.org/10.1016/j.scitotenv.2020.141357 ↩

  9. Regnier, P., Resplandy, L., Najjar, R. G., & Ciais, P. (2022). The land-to-ocean loops of the global carbon cycle. Nature, 603(7901), 401-410. https://doi.org/10.1038/s41586-021-04339-9 ↩

  10. Onyemachi, D. I., Eze, W. U., Musa, M. A., Okolo, V. N., Kalip, A. D., Paulleo, P., Igiri, B. E., & John, A. (2022). Carbon sequestration in the ocean-an escape route. Environmental Problems, 7(1), 23-33. https://doi.org/10.23939/ep2022.01.023 ↩

  11. Fano, G. (2010). A primer on the carbon cycle. American Journal of Physics, 78(4), 367-376. https://doi.org/10.1119/1.3298429 ↩

  12. Christopher L. Sabine et al. ,The Oceanic Sink for Anthropogenic CO2.Science305,367-371(2004). https://www.science.org/doi/10.1126/science.1097403 ↩