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 Lau deria 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 photosyn thetic rate that depends on the weighted light history of the cell. Th e 2 new parameters introduced in this formulation were found to be rob ust, i.e. they did not change for a variety of data sets. The photores ponse model was incorporated into a simple Lagrangian model of wind-dr iven vertical mixing. It was found that the modelled photoresponse can lead to enhanced vertically integrated photosynthesis under certain c onditions of light extinction and wind mixing. In particular, phytopla nkton in wind-mixed coastal regions may experience an increase in inte grated photosynthesis per cell under strong incident irradiance.