Modelling interactions between kelp cultures and the ocean carbon system

There is a surge of interest in how and to what extent macroalgal farming delivers positive ecosystem services and contributes to atmospheric CO₂ sequestration. Recent results indicate that there may be significant positive contributions in both cases, but there is also due concern that there may be negative impacts of macroalgal farming at large extent and high intensities. We will highlight environmental and climate interactions of sugar kelp (Saccharina latissima) farming in Norway by using a high resolution coupled physics-biogeochemical-kelp ocean model system. The system takes into account two-way feedback between all its variables and includes forcing by atmospheric pCO2. Specifically, we will present simulation results on the interactions of the kelp cultures with the ocean carbon system. We will consider uptake of CO₂ and production of O₂ by the kelp cultures over the season and how this impacts on pH and alkalinity locally. We will also discuss new empirical results on vertical transport of particulate matter shredded from Saccharina latissima cultures, as well as the shredding rates, in the context of numerical modelling. The new results allow us to provide better estimates of the carbon export potential from Saccharina cultures. This research is funded by SINTEF's Climate fund (Seaweed CDR) and the project "The Norwegian Continental Shelf: A Driver for Climate-Positive Norway" (NCS C+) funded by the Research Council of Norway (328715) under the green platform program.