Model dependences of the deactivation of phytoplankton pigment excitation energy on environmental conditions in the sea**Support for this study was provided by the project ‘Satellite Monitoring of the Baltic Sea Environment - SatBałtyk’ funded by European Union through European Regional Development Fund contract No. POIG 01.01.02-22-011/09.

A semi-empirical, physical models have been derived of the quantum yield of the deactivation processes (fluorescence, photosynthesis and heat production) of excited states in phytoplankton pigment molecules. Besides some already known models (photosynthesis and fluorescence), this novel approach incorporates the dependence of the dissipation yield of the excitation energy in phytoplankton pigment molecules on heat. The quantitative dependences of the quantum yields of these three processes on three fundamental parameters of the marine environment are defined: the chlorophyll concentration in the surface water layer Ca(0) (the basin trophicity), the irradiance PAR(z) and the temperature temp(z) at the study site. The model is complemented with two other relevant models describing the quantum yield of photosynthesis and of natural Sun-Induced Chlorophyll a Fluorescence (SICF) in the sea, derived earlier by the author or with her participation on the basis of statistical analyses of a vast amount of empirical material. The model described in the present paper enables the estimation of the quantum yields of phytoplankton pigment heat production for any region and season, in waters of any trophicity at different depths from the surface to depths of ca 60m. The model can therefore be used to estimate the yields of these deactivation processes in more than half the thickness of the euphotic zone in oligotrophic waters and in the whole thickness (and deeper) of this zone in mesotrophic and eutrophic waters. In particular these relationships may be useful for a component analysis of the budget of light energy absorbed by phytoplankton pigments, namely, its utilization in fluorescence, photochemical quenching and nonphotochemical radiationless dissipation – i.e. direct heat production