Ocean Alkalinity Enhancement (OAE) stands as a promising, nature-based CO2 removal technology. Within the deployment catalogue, dissolved, CO2 non-equilibrated addition is considered realistic, but causes water chemistry perturbations. Among mineral alkalinity sources, carbonates and silicates are recurrently proposed, but can fertilize. As such, research is needed on the effects these can have on ecosystem integrity and services. With food security as a pressing global challenge, the service of food production is of relevance. We studied responses of a temperate zooplankton community and their value as food for fish to different CO2 non-equilibrated OAE scenarios. To do so, large mesocosms were deployed in a Norwegian fjord between May and July 2022. Two OAE gradients, ranging from ambient to delta TA of 600 micromol per L, were established for each of the two minerals, silicates and carbonates. Across the TA range, gradients in pCO2, pH and omega aragonite emerged, with silicate-based OAE entailing an increase in this nutrient. Such changes will likely have direct and indirect effects, through shifts in phytoplankton composition and nutritional value, on zooplankton. To assess the integrity of the community, we analyzed zooplankton diversity and trophic length. Effects on their value as food for fish were addressed via zooplankton biomass, functional composition, CN stoichiometry, population size structure and per capita size. On this basis, we provide a first insight on OAE impacts on the continuity of the service of food production in a temperate community.

Primary Presenter: Nicolas Smith Sanchez, GEOMAR Helmholtz Centre for Ocean Research Kiel (nsanchez@geomar.de)

Authors:

Nicolas Sanchez, GEOMAR Helmholtz Centre for Ocean Research Kiel  ()

Silvan Goldenberg, GEOMAR Helmholtz Centre for Ocean Research Kiel  ()

Synne Spjelkavik, Centre for Gelatinous Plankton Ecology & Evolution, Technical University of Denmark (DTU Aqua)  ()

Cornelia Jaspers, Centre for Gelatinous Plankton Ecology & Evolution, Technical University of Denmark (DTU Aqua)  ()

Jacqueline Haussmann, GEOMAR Helmholtz Centre for Ocean Research Kiel  ()

Jonas Blendl, GEOMAR Helmholtz Centre for Ocean Research Kiel  ()

Amrita Bhaumik, Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung  ()

Maria Couret, Instituto de Oceanografía y Cambio Global, IOCAG, Universidad de Las Palmas de Gran Canaria, Unidad Asociada ULPGC-CSIC  ()

Ulf Riebesell, GEOMAR Helmholtz Centre for Ocean Research Kiel  ()