Modeling silicate–nitrate–ammonium co-limitation of algal growth and the importance of bacterial remineralization based on an experimental Arctic coastal spring bloom culture study

• Published in: Biogeosciences
• Main Authors: Vonnahme, Tobias R., Leroy, Martial, Thoms, Silke, van Oevelen, Dick, Harvey, H. Rodger, Kristiansen, Svein, Gradinger, Rolf, Dietrich, Ulrike, Völker, Christoph
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: 2021
• Subjects: Arctic; Phytoplankton
• Online Access: https://epic.awi.de/id/eprint/53845/; https://epic.awi.de/id/eprint/53845/1/Vonnahme21BG.pdf; https://doi.org/10.5194/bg-18-1719-2021; https://hdl.handle.net/10013/epic.de0584de-7c5c-4d69-9390-295bbb3008ab

Arctic coastal ecosystems are rapidly changing due to climate warming. This makes modeling their produc- tivity crucially important to better understand future changes. System primary production in these systems is highest dur- ing the pronounced spring bloom, typically dominated by di- atoms. Eventually the spring blooms terminate due to sili- con or nitrogen limitation. Bacteria can play an important role for extending bloom duration and total CO2 fixation through ammonium regeneration. Current ecosystem mod- els often simplify the effects of nutrient co-limitations on al- gal physiology and cellular ratios and simplify nutrient re- generation. These simplifications may lead to underestimations of primary production. Detailed biochemistry- and cell- based models can represent these dynamics but are difficult to tune in the environment. We performed a cultivation experiment that showed typical spring bloom dynamics, such as extended algal growth via bacterial ammonium remineralization, reduced algal growth and inhibited chlorophyll synthesis under silicate limitation, and gradually reduced nitrogen assimilation and chlorophyll synthesis under nitrogen limitation. We developed a simplified dynamic model to represent these processes. Overall, model complexity in terms of the number of parameters is comparable to the phytoplankton growth and nutrient biogeochemistry formulations in common ecosystem models used in the Arctic while improv- ing the representation of nutrient-co-limitation-related processes. Such model enhancements that now incorporate in- creased nutrient inputs and higher mineralization rates in a warmer climate will improve future predictions in this vulnerable system.