- 1GEOMAR Helmholtz Centre for Ocean Research Kiel, Kiel, Germany
- 2Institute of Oceanography, National Taiwan University, Taipei, Taiwan (cchien308@ntu.edu.tw)
During the Last Glacial Maximum (LGM), atmospheric pCO2 was approximately 90 ppm lower than in the pre-industrial era. Several hypotheses have been proposed to explain this decrease, including changes in nutrient supply, increased iron input to the ocean, and variations in overturning circulation strength driven by differences in wind stress and moisture diffusivity. Current modeling approaches that simulate LGM marine biogeochemistry typically use parameter sets calibrated under pre-industrial boundary conditions, introducing uncertainty due to the imperfect knowledge of the values that can be assigned to the parameters for the LGM environment. The extent to which this uncertainty affects the simulated LGM marine biogeochemistry remains unclear. In this study, we employ an optimality-based non-Redfield plankton ecosystem model coupled with a 3D Earth system model to simulate LGM conditions. We conduct sensitivity analyses with 24 combinations of biogeochemical parameters (reduced benthic denitrification rate, decreased sedimentary iron input, higher PO4 levels, and increased atmospheric iron deposition) and physical boundary conditions (changes in wind stress pattern and increased meridional moisture diffusivity over the Southern Ocean). For each scenario, we perform 20 simulations using 20 biogeochemical parameter sets selected out of 600—each representing pre-industrial biogeochemistry and evaluated based on the misfit between observations and model outputs—resulting in a total of 480 simulations. Our results show that iron input exerts the most profound influence on LGM marine biogeochemistry and atmospheric pCO2, while changes in major nutrient supplies have minor effects. Additionally, the impact of physical conditions on biogeochemical tracers varies, depending on the specific biogeochemical settings. Compared to pre-industrial reference conditions, atmospheric pCO2 under full LGM conditions decreases by 36 to 58 ppm across the 20 simulations. The difference between the maximum and minimum pCO2 changes amounts to 50% of the 43 ppm average decrease. These findings highlight that, although the 20 parameter sets effectively reproduce pre-industrial marine biogeochemistry, significant cross-model variance in pCO2 responses and marine biogeochemical changes persists under LGM conditions.
How to cite: Chien, C.-T., Pahlow, M., Schartau, M., Somes, C., and Oschlies, A.: Simulating marine biogeochemistry and atmospheric pCO2 for the Last Glacial Maximum using an ensemble of calibrated parameter sets, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17858, https://doi.org/10.5194/egusphere-egu25-17858, 2025.