We analyzed a large dataset of simultaneous measurements of phytoplankton pigments, spectral specific absorption coefficient for phytoplankton [a*(l)], and photosynthesis versus irradiance (P versus E) curve parameters to examine the possible relationships between phytoplankton community structure and photophysiological properties at large spatial scales. Data were collected in various regions, mostly covering the trophic gradient encountered in the world's open ocean. The community composition is described in terms of biomass of three phytoplankton classes, determined using specific biomarker pigments. We present a general empirical model that describes the dependence of algal photophysiology on both the community composition and the relative irradiance within the water column (essentially reflecting photoacclimation). The application of the model to the in situ dataset enables the identification of vertical profiles of photophysiological properties for each phytoplankton class. The class-specific a*(l) obtained are consistent with results from the literature and with previous models developed for small and large cells, both in terms of the absolute values and the vertical patterns. Similarly, for the class-specific P versus E curve parameters, the magnitude and vertical distribution obtained with this method are coherent with previous observations. Large cells (mainly diatoms) may be more efficient in carbon storage than smaller cells, whereas their yield of light absorption is lower. We anticipate that such photophysiological parameterizations can improve primary production models by providing estimates of primary production that are specific to different phytoplankton classes on large scale.Estimates of marine primary production on large to global scales rely on the use of primary production models (e.g., Longhurst et al. 1995;Antoine et al. 1996;Behrenfeld et al. 2002a). Such models typically incorporate: (1) an estimate of the phytoplankton biomass, usually in the form of the chlorophyll a concentration ([Chl a], mg m 23 ); (2) the photosynthetically available irradiance (from 400 to 700 nm; PAR [mmol quanta m 22 s 21 ]); and (3) a relationship expressing changes in photosynthetic efficiency as a function of incident or absorbed irradiance. Although the mathematical description varies from one model to another (Behrenfeld and Falkowski 1997a), all models aim at parameterizing the primary production rate (P, mg C m 22 h 21 ) as followswhere a* is the chlorophyll-specific absorption coefficient of phytoplankton [m 2 (mg Chl a) 21 ], W c (PAR) is the irradiance-dependent quantum yield of carbon fixation [mol C (mol quanta) 21 ], and 12000 enables the conversion of moles of quanta into milligrams of carbon. Equation 1 includes two photophysiological variables: a* and W c (PAR). The relationship between their product, i.e., a* W c (PAR), and the incident PAR is often expressed by a photosynthesis versus irradiance (P vs. E) curve that can be represented by various mathematical formulations (see, for exa...