Hannes Wagner

• Cold-water corals (CWC) occur throughout the world’s oceans, with the reef building coral Lophelia pertusa forming giant reefs and mounds in the Northeast Atlantic. Several important issues regarding CWC reefs remain not well understood. These include the relative contribution of different food sources to CWC ecosystem nutrition, the influence of hydrodynamic processes on reef nutrition, as well as the contribution of CWC ecosystems to benthic carbon turnover along continental margins. Within this PhD project, these issues were addressed at the Tisler cold-water coral reef (Norway) in a succession of field campaigns between 2007 and 2009, using a variety of methodological approaches. These consisted, amongst others, of the collection of CTD and chlorophyll profiles, the sampling and analyses of particulate organic matter (POM), the deployment of sediment traps, as well as the deployment of current meters, temperature sensors and oxygen sensors for time-series measurements. The environmental conditions at the Tisler Reef were found to be highly dynamic in terms of temperature and flow. Downwelling periodically delivered warmer, fresher and chlorophyll richer water masses down to the benthic boundary layer (BBL) of the downstream reef side. Particulate organic carbon (POC) content in the BBL was significantly depleted across the reef. Biodeposition was calculated to be 459 mg POC m-2 d-1 on average. Dissolved oxygen concentration within the reef structure decreased rapidly during short phases of stagnant or near stagnant flow. A community respiration rate of 981 mg C m-2 d-1 was estimated. Vertical POC fluxes measured with sediment traps supplied only ~25% of the estimated community respiration, indicating the presence of other carbon supplying mechanisms to the coral community such as biodeposition and feeding on zooplankton. These data on biodeposition, vertical carbon fluxes and respiration suggest that CWC reefs could play an important role in carbon cycling along continental margins.