• absorption
• CDOM
• dissolved organic matter
• DOC
• DOM
• fluorescence
• heterotrophic prokaryotes
• Mediterranean Sea
• microbial loop
• optical properties
• PARAFAC
• parallel multifactorial analysis
• thermoaline circulation

A different functioning of DOM dynamics and microbial loop has been observed in the western and eastern Mediterranean Sea.
DOM is a complex mixture of organic compounds that passes through a 0.2 μm filter.
A fraction of DOM (CDOM) is capable to absorb light in the visible and UV wavelengths. A fraction of CDOM emits part of the absorbed light in the form of fluorescence. DOM is mostly consumed by heterotrophic prokaryotes, starting the “microbial loop”, that can function as a link or a sink of C to the food web. Biological lability of DOM is defined by the time needed by heterotrophic prokaryotes to use it. Labile DOM compounds are immediately consumed; recalcitrant DOM compounds escape rapid microbial degradation and can therefore accumulate and be transported by water masses circulation.
The main results of these thesis suggested that the different DOM dynamics in the two basins of the Med Sea could be due to a change in DOM quality. DOM quality was investigated through DOM optical properties (absorption and fluorescence), which confirmed a change in DOM pool in the two basins. It has been observed a change in phytoplankton communities, which could be the responsible of the production of DOM with different chemical composition. Physical parameters are also involved in the different DOM dynamics in the two basins. In particular, photodegradation could transform DOM labile compounds into the recalcitrant ones, resulting in DOM accumulation in the eastern basin.