A dynamic model of the cellular carbon to chlorophyll ratio applied to a batch culture and a continental shelf ecosystem

Mark E. Baird, Peter J. Ralph, Farhan Rizwi, Karen Wild-Allen and Andrew D. L. Steven

Limnol. Oceanogr., 58(4), 2013, 1215-1226 | DOI: 10.4319/lo.2013.58.4.1215

ABSTRACT: A novel parameterization of the dynamical relationship between cellular carbon (C) and chlorophyll (Chl) is developed using a Chl synthesis term that includes the physiological status of the cell and the effect of packaging of pigments within cells. The geometric derivation highlights the non-linear relationship between Chl content and absorption due to the package effect. When parameterized for a generic 3 µm radius phytoplankton cell, the model reproduces the magnitude and daily variations of C : Chl and C : nitrogen ratios of the diatom Skeletonema costatum in published laboratory experiments. The parameterization is then applied in a three-dimensional biogeochemical model containing three phytoplankton classes in the coastal waters off southeast Tasmania, Australia, which demonstrates the behavior of the dynamic Chl parameterization over a range of light- and nutrient-limiting environments for phytoplankton of different sizes and growth rates. The model produces C : Chl ratios of ∼ 12–20 (weight : weight) and ∼ 60–80 for phytoplankton communities dominated by fast-growing small and fast-growing large cells, respectively, close to the ratios of 17 and 76 observed at two sampling stations during periods with diatom- and flagellate-dominated communities. Throughout the simulation, community C : Chl ratios generally vary between 12 and 200, which is similar to the range observed globally. In the new parameterization, C : Chl ratios are most influenced by the package effect for light-limited, slow-growing large microalgae, with physiological processes becoming important for smaller, nutrient-limited, fast-growing microalgae.

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