Dr. Manfredi Manizza to speak in the EAPS-PAOC Sack Lunch Seminar Series. Abstract: The top part of the Arctic Ocean is strongly influenced by an extraordinary amount of freshwater discharged by rivers along the entire basin (~10 % of the global freshwater although the Arctic is only 1 % of global ocean volume). This remarkable freshwater discharge is also associated with a large input of dissolved organic carbon (DOC, 35-40 Tera gC/year) that is produced by the surrounding terrestrial ecosystems. The abundance and spatial distribution of DOC in the Arctic Ocean is controlled by the interplay between the ocean circulation and mircobial degradation. Due to these two processes, salinity and DOC load become distinct signatures of water masses of different origin (coastal vs off-shore) and their relationship strongly depends on the rate of DOC microbial degradation superimposed on surface ocean circulation. By combining both numerical tools and theoretical models I will show : (1) how and why I can realistically model the DOC-Salinity relationship matching field data and (2) how important is the riverine DOC input (due to its conversion into inorganic carbon) for the air-sea fluxes of CO2 at basin scale. In the same context, I will also provide a general outlook on the recent and evident trend of Arctic sea-ice loss and its implications for the ocean CO2 sink of this region.