Microbial biogeography and decomposition of terrigenous carbon compounds in the gradients of the Baltic Sea - Cruise No. M86/1ab - November 4 - December 5, 2011 - Bremerhaven (Germany) - Rostock (Germany) (English)

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In order to examine whether salinity-related phylogenetic shifts in microbial communities imply relevant functional changes it was planned to assess the structure and (selected) functions of pelagic prokaryotic communities (Bacteria, Archaea) along the whole lateral Baltic salinity gradient between the Skagerrak and the Bothnian Bay. This will provide the general background for the more specific question of decomposition dynamics of imported terrigenic organic compounds. The decomposition capacity for organic matter, particularly the degradation potential for introduced terrestrial dissolved organic matter (tDOM) was investigated both along the horizontal salinity and the vertical oxygen gradient of the Baltic Sea. The identification of microbial key organisms and the relation to functional characteristics in the vertical pelagic oxygen gradients of the central Baltic (Gotland Basin, Landsort Deep) includes the investigation of suboxic and anoxic conditions on organic matter degradation, specific processes within the nitrogen cycle, and an assessment of the general physico-chemical profiles, including nutrients and trace metals. Additionally, the significance of the newly identified groups of crenarchaea and epsilonproteobacteria for the nitrogen cycle (coupled nitrification/denitrification) and the carbon cycle were investigated. Finally, the historic, climate-driven shift of decomposition dynamics in the central basins, which is highly dependent on the temporal variability of bottom water inflow events, was accounted for by respective geological studies.