2,- 1School of Oceanograpahy, Shanghai Jiao Tong University, Shanghai, China (liqian00@sjtu.edu.cn)
- 2School of Ocean Science and Engineering, Southern University of Science and Technology, Shenzhen, China (mark@sustech.edu.cn)
Recent studies investigating the biological responses to ocean alkalinity enhancement (OAE) have produced varying results. Some research suggests that the impact on microbial communities is overall insignificant, while other studies indicate that certain phytoplankton, such as diatoms and nitrogen-fixing species, can benefit from OAE due to the release of biominerals. Factors including the method of OAE and especially whether it constitutes an equilibrated or unequilibrated addition of alkalinity to the ocean may be critical in determining biological responses.
Two mesocosms experiments in Guangdong to date suggested no significant microbial effects to an unequilibrated alkalinity addition of 100-200 µmol kg-1. However, these experiments were short in duration (<1 month) in lined ponds with no benthic interactions or higher trophic levels (e.g. fish). In our forthcoming project, we will conduct longer-term (months to over a year) mesocosm experiments at million litre scale to monitor the responses of microbial and planktonic communities to an ocean alkalinity gradients under more environmentally realistic conditions than is possible in smaller incubations. Our main focus will be on prokaryotes, eukaryotes, and viruses, which encompass primary producers, grazers, decomposers, and parasites—essentially the main functional groups that mediate elemental cycles within the microbial and biological carbon pump.
We plan to sample and analyze crucial ecological parameters, including primary production, carbon fixation rates, trophic strategies, particle production and transportation rates, as well as aggregation and disaggregation processes. Additionally, we will examine community composition and biodiversity indices, while also conducting chemical measurements of inorganic carbon and biominerals, such as calcium carbonate and biogenic silica to close carbon and nutrient budgets. Finally, data collected by our collaborators will be synthesized and analyzed to address two main questions: whether OAE can lead to significant biological effects and whether side-effects alter the overall efficiency of the OAE concept with respect to altering the carbon budget.
How to cite: Li, Q., Hopwood, M., Wang, X., and Wang, Y.: Assessing the Benefits and Risks of Ocean Alkalinity Enhancement for Carbon Sequestration: Biological and Microbial Impacts, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-840, https://doi.org/10.5194/oos2025-840, 2025.
