Phytoplankton competition during the spring bloom in four Plankton Functional Type Models

• Main Authors: Hashioka, Taketo, Vogt, Thomas, Yamanaka, Yasuhiro, Le Quéré, Corinne, Buitenhuis, E.T., Aita-Noguchi, Maki, Alvain, Séverine, Bopp, Laurent, Hirata, Takafumi, Lima, Ivan, Sailley, Sévrine, Doney, Scott C.
• Format: Report
• Language: English
• Published: Copernicus 2012
• Subjects: North Atlantic
• Online Access: https://hdl.handle.net/20.500.11850/60387; https://doi.org/10.3929/ethz-b-000060387

We investigated the mechanisms of phytoplankton competition during the spring bloom,one of the most dramatic seasonal events in lower-trophic level ecosystems, in fourstate-of-the-art Plankton Functional Type (PFTs) models: PISCES, NEMURO, Plank-TOM5 and CCSM-BEC. In particular, we investigated the relative importance of dif-5ferent ecophysiological processes on the determination of the community structure,focusing both on the bottom-up and the top-down controls. The models reasonablyreproduced the observed global distribution and seasonal variation of phytoplanktonbiomass. The fraction of diatoms with respect to the total phytoplankton biomass in-creases with the magnitude of the spring bloom in all models. However, the governing10mechanisms differ between models, despite the fact that current PFT models repre-sent ecophysiological processes using the same types of parameterizations. The in-creasing trend in the percentage of diatoms with increasing bloom magnitude is mainlycaused by a stronger nutrient dependence of photosynthesis for diatoms compared tonanophytoplankton (bottom-up control). The difference in the maximum photosynthesis rate plays an important role in NEMURO and PlankTOM5 and determines the abso-lute values of the percentage of diatoms during the bloom. In CCSM-BEC, the lightdependency of photosynthesis plays an important role in the North Atlantic and theSouthern Ocean. The grazing pressure by zooplankton (top-down control), however,strongly contributes to the dominance of diatoms in PISCES and CCSM-BEC. The re-20gional differences in the percentage of diatoms in PlankTOM5 are mainly determinedby top-down control. These differences in the mechanisms suggest that the responseof marine ecosystems to climate change could significantly differ among models, evenif the present-day ecosystem is reproduced to a similar degree of confidence. For fur-ther understanding of plankton competition and for the prediction of future change in marine ecosystems, it is important to understand the relative ...