Diversity and function of microbial communities in the Arctic Ocean

The Arctic Ocean ecosystem is rapidly changing in response to climate warming. The ongoing decline of its sea-ice cover has raised many questions as to the ecological consequences on biodiversity, primary productivity, and the biological carbon pump. The diversity and function of bacterial communities in the Arctic Ocean has been little explored, despite their often important role in biogeochemical cycling. One objective of this thesis was therefore to improve the current knowledge of microbial community diversity in the most understudied region of the Arctic Ocean, the deep central Eurasian basin. As sea-ice reduction is altering primary productivity and biological transport processes from the surface ocean to the deep sea, another focus of this thesis was the identification of bacterial groups associated to freshly formed, sinking and deposited particulate organic matter. Finally, the underlying genomic features that deep-sea surface sediment bacteria use for carbon turnover were analyzed, as the degradation of organic matter by heterotrophic bacteria in deep-sea sediments regulates the efficiency of CO2 removal from the atmosphere over geological time scales