Entwicklung, Analyse und Implementierung von rechnereffizienten Modellen zur Auflösung der Zell- und Artzusammensetzung von Plankton
Ökologie und Biodiversität der Pflanzen und Ökosysteme
Zusammenfassung der Projektergebnisse
Phytoplankton play an important role in biogeochemical cycling of carbon and nutrients. However, their representation in biogeochemical models are often too simple, ignoring their acclimative flexibilities and variable cellular composition. More detailed models do exist, however they are challenged with formidable computational costs. In this project, we elaborated a previously proposed instantaneous acclimation approach, which accounts for various acclimative flexibilities, but using a single state variable, which can lead to a higher computational efficiency in spatially explicit setups, because of the lower number of state variables that need to be transported. Specifically, our objectives were: 1. Understanding the the relevance of various acclimation processes to the vertical and horizontal distributions of Chl:C:N:P ratios. 2. Assessing the added value of resolving acclimation in terms of model skill and behavior. 3. Evaluating the portability of ecosystem models with and without acclimation capacities. To meet these objectives, we first built a model that can consistently emulate the instantaneous acclimation model, as well as an otherwise equivalent dynamic acclimation model that resolves N and C content of the cells explicitly by using an additional state variable, and a third, nonacclimative fixed-stoichiometry model. To facilitate its adoption and further testing, we implemented this model in a popular framework (FABM) in a modular fashion, where the phytoplankton component is isolated from the rest of the ecosystem model. By thoroughly comparing the behavior of these models in an idealized water column setup, we gained an improved understanding of the acclimative mechanisms responsible for the vertical distribution of Chl:C:N ratios across the water column, bloom formation and export fluxes, therefore meeting the first and partially the second objectives. We then applied this model in a realistic setup of two oceanic sites and rigorously tested the ability of the three variants of the models in reproducing the oceanic observations in a realistic setup, and found evidence for the relevance of photoacclimation in reproducing the deep-chlorophyll maxima phenomena, therefore meeting the second objective. These tests also showed that considering acclimative flexibilities in general, and stoichiometric variabilities in specific increased the portability of the models. Lastly, we extended the model with fluxes associated with changing nutrient quotas, for being able to achieve massconservation of both N and C, and demonstrated that the mass can be largely conserved, and the instantaneous and dynamic acclimation models behave, to a large extent, similarly, but that differences arise during seasonal transitions. The COVID-19 pandemic, and associated travel restrictions coincided with almost the entire project, which made it impossible to realize the planned research stays, and adversely affected the progression of the project. Scientifically the largest challenge we faced was the realization that the flux calculations associated with temporal changes in nutrient quota was not sufficient to conserve mass of multiple elements simultaneously in a spatially explicit setup, and that anologous flux calculations are necessary for the spatial changes in nutrient quota (e.g., due to differential diffusion and advection of C and N bound to phytoplankton). Future research may aim to generalize the model to achieve mass conservation in spatially explicit setups.
Projektbezogene Publikationen (Auswahl)
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Enhancing Ocean Biogeochemical Models With Phytoplankton Variable Composition. Frontiers in Marine Science, 8.
Anugerahanti, Prima; Kerimoglu, Onur & Smith, S. Lan
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FABM-NflexPD 1.0: assessing an instantaneous acclimation approach for modeling phytoplankton growth. Geoscientific Model Development, 14(10), 6025-6047.
Kerimoglu, Onur; Anugerahanti, Prima & Smith, Sherwood Lan
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FABM-NflexPD 2.0: testing an instantaneous acclimation approach for modeling the implications of phytoplankton eco-physiology for the carbon and nutrient cycles. Geoscientific Model Development, 16(1), 95-108.
Kerimoglu, Onur; Pahlow, Markus; Anugerahanti, Prima & Smith, Sherwood Lan
