SOPHY – Improved model parameterizations for Southern Ocean phytoplankton using laboratory data

• Applicant: Dr. Miriam Seifert
• Subject Area: Oceanography
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 541440679

Marine primary production constitutes an important component of the global carbon cycle as it eases the uptake of atmospheric CO2 by the ocean. Model projections of the present-day and future marine primary production, however, vary significantly between different models. In the Southern Ocean in particular, biological process description is one major source of uncertainty in the model estimations of the present-day air-sea CO2 flux during summer. Improved process description based on laboratory and observational data is one way to reduce model uncertainty. SOPHY aims to update, amend, and test parameterizations in a global ocean biogeochemistry model for Southern Ocean phytoplankton bottom-up and top-down drivers in order to improve projections of the Southern Ocean net primary production. In the first part of the project, model functions describing interactive effects between bottom-up drivers will be developed and implemented into an earth system model. The new model functions will be based on a collection of past and most recent laboratory data as well as new spearheading laboratory experiments, conducted by collaborators and explicitly designed to inform model functions. Simulations using a realistic climate scenario from present-day to end-of-century climate will be performed to investigate the effects of bottom-up driver interactions on the contemporary and future Southern Ocean biological carbon pump. The second part of SOPHY will focus on one of the main sources of uncertainty in ocean biogeochemistry models, i.e., the parameterization of grazers. A new zooplankton group of salps and corresponding fecal pellets characteristics will be implemented into an ocean-only model based on experimental data from collaboration partners. This development will allow to compare krill and salp-dominated systems in the Southern Ocean, and subsequent differences in fecal pellets sinking, remineralization and the effects of variable bioavailability of iron released from fecal pellets. Finally, various grazing functions currently in use in different ocean biogeochemistry models will be collated and systematically tested in the ocean-only model. The functions that best describe chlorophyll a observations in the Southern Ocean will be determined. In conclusion, SOPHY will contribute to the improvement of future projections of the Southern Ocean primary production in ocean biogeochemistry models.

• DFG Programme: Infrastructure Priority Programmes
• Subproject of: SPP 1158: Infrastructure area - Antarctic Research with Comparative Investigations in Arctic Sea Ice Areas
• International Connection: Switzerland, United Kingdom
• Cooperation Partners: Professorin Dr. Sinead Collins; Dr. Mridul K. Thomas