Sinking of organic particles from the ocean’s productive surface layers is a key component in the biological carbon pump, and essential to carbon sequestration by the ocean. Its regulation needs to be comprehended in order to accurately determine the oceans’ role in the global climate system. The impact of bacterial degradation on the fate of marine particles demands further study in order to significantly strengthen our understanding of oceanic carbon cycling. By investigating the prokaryotic community composition of suspended and sinking marine particles, the degradation activities of different prokaryotic groups, and colonisation of particles, BacPac will provide new knowledge elucidating the role of bacteria in vertical flux regulation.The project will use state-of-the-art molecular tools (DGGE, ARISA, and 454-pyrosequencing) to determine the prokaryotic community in ambient seawater, on marine particles (zooplankton faecal pellets, algal aggregates and marine snow), and on sinking particles collected by sediment traps. The main sampling activities in the Mediterranean Sea will be supplemented by field collections from North-Norwegian and European Arctic waters. The project combines the researcher’s expertise on vertical export and the host's expertise in marine microbial ecology in order to advance both disciplines.BacPac’s objectives are directly relevant to contemporary research in marine carbon cycling and microbiology, and will contribute to strengthening European scientific expertise in these fields. The proposed activities will advance both the scientific and complimentary skills of the researcher and will be an important step in his career development. The mobility (University of Tromsø, Norway, to the Marine Science Institute in Barcelona, Spain) will be beneficial to European research integration and will provide a network for future collaboration.