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Title: The role of diatoms in the global carbon cycle
Author: Chollet, Sophie Francoise
Awarding Body: University of East Anglia
Current Institution: University of East Anglia
Date of Award: 2011
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The Dynamic Green Ocean Model PlankTOM5.3 is a global ocean biogeochemical model representing interactions between planktonic organisms, ocean and atmosphere. The plankton is divided into five Plankton Functional Types (PFTs), each playing a specific role in carbon and nutrient cycling and in the trophic chain. The growth parameters for each PFT are now being derived in order to represent their dependence on environmental conditions, including climate change. Here we present our work on diatoms, a phytoplankton group of major importance. We reviewed published data on the temperature dependence of diatom growth rate. By applying a quantile regression we calculate the upper-edge of the maximum growth rate. Exponential and optimal curves both have a higher intercept (0.99 and 0.96 d-1) than Eppley’s (1972) curve (0.59 d-1). However, the rates at high temperature are over-estimated by the exponential function. Both average and maximal diatom community growth rate up to 37°C are better represented by an optimal function. Photosynthesis experiments were carried out with an Oxygraph on four diatom species acclimated to different irradiances. PI curve parameters αChl, θm, Pm and Rd were calculated. Compared to the literature, θm values are low, resulting in high αChl values. Values for αChl and θm differs also between polar and temperate species. Optimisation of the model (Buitenhuis and Geider, 2010) give similar θm and lower αChl values than those we calculated. Finally, we applied the optimal temperature-dependence function and our values of αChl and θm to the model PlankTOM5.3. The sensitivity of the ecosystem to each parameter is studied by changing one parameter at a time, in eight different simulations. Primary production varies from 47.28 to 50.44 Pg C yr-1. Changes of PFTs abundance are highest for mixed-phytoplankton and coccolithophores. Meso-zooplankton, mixed-phytoplankton and diatom abundances are more sensitive to changes in temperature-dependence, while coccolithophores respond more to photosynthesis parameters.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available