It is not known how much additional carbon can be stored by a total increase in the living biomass of the oceans — but all the oceans only contain about 6 GtC in the form of living biomass, whereas we need to sequester more than 190 GtC to get back to historically safe atmospheric CO2 levels.
The notion of enhancing oceanic biomass to sequester more carbon and mitigate climate change is compelling. However, with the world's oceans holding approximately 6 gigatons of carbon (GtC) in the form of living biomass, addressing the need to sequester more than 190 GtC to achieve historically safe atmospheric CO2 levels seems impractical. Several biological, ecological, and logistical factors make this approach insufficient for the massive scale of carbon sequestration required. This article explores these limitations and examines why increasing ocean biomass alone cannot be relied upon as a solution to the climate crisis.
Current Ocean Biomass and Carbon Content
The total living biomass in the world's oceans is estimated to contain about 6 gigatons of carbon (GtC). This biomass encompasses all marine life, from microscopic phytoplankton to large marine mammals. While these organisms play a vital role in the carbon cycle through processes like photosynthesis and respiration, the total amount of carbon they sequester is relatively small compared to the carbon we need to manage. The current biomass simply cannot address the vast amounts of carbon required for significant climate impact.[^1][^2]
Scale of the Carbon Problem
To return atmospheric CO2 levels to historically safe levels, it is estimated that we need to sequester more than 190 GtC.[^3] This figure dwarfs the current carbon content of all oceanic biomass. Expecting the ocean's biomass to increase to levels capable of sequestering such vast amounts of carbon is unrealistic for several reasons:
Biological Limits
Marine ecosystems are already operating near their biological limits. The growth and biomass of marine organisms are constrained by factors such as nutrient availability, light, temperature, and ecological interactions. Rapidly increasing biomass beyond these natural limits could disrupt existing ecosystems and lead to unintended consequences. [^4]
Nutrient Limitation
Phytoplankton, the primary producers in the ocean, require nutrients like nitrogen, phosphorus, and iron to grow. These nutrients are often limited in many parts of the ocean, particularly in regions known as "ocean deserts" where nutrient levels are too low to support large populations of phytoplankton. Artificially increasing nutrient levels to boost biomass can lead to harmful algal blooms and other ecological disruptions. [^5]
Ecological Balance
Drastically altering the biomass of marine organisms could upset the delicate ecological balance of the ocean. Predators, prey, and symbiotic relationships would be affected, potentially leading to cascading effects throughout marine ecosystems. Maintaining biodiversity and ecosystem health is essential for the stability and resilience of the oceans.[^6]
Conclusion
Increasing the ocean's living biomass to sequester more carbon is an interesting concept, but it is not a practical or sufficient solution to address the scale of carbon sequestration needed to mitigate climate change. The biological, ecological, and practical limitations make it unlikely that we could achieve the necessary increase in biomass to sequester more than 190 GtC. Other approaches, such as reducing emissions, protecting and restoring natural carbon sinks on land, and exploring advanced carbon capture technologies, are more feasible and effective strategies for addressing the climate crisis.
[^1] Bar-On, Y. M., Phillips, R., & Milo, R. (2018). The biomass distribution on Earth. Proceedings of the National Academy of Sciences, 115(25), 6506-6511. https://doi.org/10.1073/pnas.1711842115
[^2] Ritchie, H. (2019). Oceans, land, and deep subsurface: How is life distributed across environments? Our World in Data. https://ourworldindata.org/life-by-environment
[^3] Stocker, T. F., et al. (Eds.). (2013). Summary for policymakers. In Climate change 2013: The physical science basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press. https://doi.org/10.1017/CBO9781107415324.004
[^4] Moore, C. M., Mills, M. M., Arrigo, K. R., Berman-Frank, I., Bopp, L., Boyd, P. W., Galbraith, E. D., Geider, R. J., Guieu, C., Jaccard, S. L., et al. (2013). Processes and patterns of oceanic nutrient limitation. Nature Geoscience, 6(9), 701-710. https://www.nature.com/articles/ngeo1765
[^5] Bristow, L. A., Mohr, W., Ahmerkamp, S., & Kuypers, M. M. M. (2017). Nutrients that limit growth in the ocean. Current Biology, 27(11), R474-R478. https://doi.org/10.1016/j.cub.2017.03.030
[^6] Stachowicz, J. J., Bruno, J. F., & Duffy, J. E. (2007). Understanding the effects of marine biodiversity on communities and ecosystems. Annual Review of Ecology, Evolution, and Systematics, 38(1), 739-766. https://doi.org/10.1146/annurev.ecolsys.38.091206.095659