A Simple New Formulation for Phytoplankton Photoresponse and an Application in a Wind-Driven Mixed-Layer Model

We present a simple new formulation of photoresponse in the diatom Lauderia borealis. This formulation assumes time-dependence in the value of P-max, the maximal photosynthetic rate. The rate of change of P-max is nonlinearly dependent on the present irradiance, giving a photosynthetic rate that depends on the weighted light history of the cell. The 2 new parameters introduced in this formulation were found to be robust, i.e. they did not change for a variety of data sets. The photoresponse model was incorporated into a simple Lagrangian model of wind-driven vertical mixing. It was found that the modelled photoresponse can lead to enhanced vertically integrated photosynthesis under certain conditions of light extinction and wind mixing. In particular, phytoplankton in wind-mixed coastal regions may experience an increase in integrated photosynthesis per cell under strong incident irradiance.