Abstract
Abstract. We have determined the photosynthetic production of dissolved (DOCp) and particulate organic carbon (POCp) along a longitudinal transect in the Mediterranean Sea during the summer stratification period. The euphotic layer-integrated rates of DOCp and POCp ranged between approximately 50–130 and 95–210 mgC m−2 d−1, respectively, and showed an east to west increasing trend. For the whole transect, the relative contribution of DOCp to total, euphotic layer-integrated primary production (percentage of extracellular release, PER) averaged ~37% and did not show any clear longitudinal pattern. In spite of the relatively high PER values, the measured DOCp rates were much lower than the estimated bacterial carbon demand, suggesting a small degree of coupling between phytoplankton exudation and bacterial metabolism. Our results, when compared with previous measurements obtained with the same methods in several ecosystems of contrasting productivity, support the view that the relative importance of DOCp increases under strong nutrient limitation.
Highlights
The production of dissolved organic carbon (DOCp), or dissolved primary production, is the fraction of the recently fixed carbon that is released to the extracellular medium in dissolved form
The results we report must be regarded as net DOC production rates
The Mediterranean Sea is often described as a system with a characteristic transition from oligotrophic conditions in the western basin to ultraoligotrophic conditions in the eastern basin
Summary
The production of dissolved organic carbon (DOCp), or dissolved primary production, is the fraction of the recently fixed carbon that is released to the extracellular medium in dissolved form. DOCp can result from an active process that takes place when cells experience high light and nutrient stress Under these conditions, phytoplankton tend to maintain their full photosynthetic capacity and, as a result, prevent photochemical damage and maximize their growth rate by eliminating any lag period for resuming carbon fixation when nutrients became available (Fogg, 1983; Wood and Van Valen, 1990). Phytoplankton tend to maintain their full photosynthetic capacity and, as a result, prevent photochemical damage and maximize their growth rate by eliminating any lag period for resuming carbon fixation when nutrients became available (Fogg, 1983; Wood and Van Valen, 1990) This latter mechanism could be relevant in surface waters of oligotrophic regions.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
