<title>Spatial variations of photosynthetic parameters in equatorial Pacific: forcing by vertical mixing and light penetration</title>

Abstract

Laboratory experiments already showed that the most significant photoacclimation strategy deployed by Prochiorococcus sp. would consist of changing the number of photosynthetic units per cell' and, thereby, the minimal turnover time for in vivo electron transport from water to CO2 (t). As a result, the saturation parameter Ek, would tightly covary with growth irradiance. Also, because the zeaxanthin cellular content in Prochiorococcus sp. is quite stable, the ratio of zeaxanthin-to-dv-chl a would also covary with irradiance. A study in the Atlantic Ocean already showed that, to some extent (i.e. by a factor of 3), the maximum quantum yield of carbon fixation, , is proportional to the ratio of nonphotosynthetic pigments (mostly zeaxanthin) to all phytoplankton pigments (hereafter denoted the "non-photosynthetic pigment index; NPP index)2. In turn, the NNP index is linearly correlated with the mean irradiance in the mixed layer. The present study aims at documenting the above mentioned relationships in the equatorial and sub-equatorial Pacific, where prokaryotic photoautrotrophs dominate the phytoplankton community.