Environmental control on cold-water carbonate mounds development

Cold-water coral reefs are very abundant along the European continental margin in intermediate water depths and are able to build up large mound structures. These carbonate mounds particularly occur in distinct mound provinces on the Irish and British continental margins. Previous investigations resulted in a better understanding of the cold-water coral ecology and the development of conceptual models to explain carbonate mound build-up. Two different hypotheses were evoked to explain the origin and development of carbonate mounds, external versus internal control (e.g., Freiwald et al. 2004 versus e.g. Hovland 1990). Several short sediment cores have been obtained from Propeller Mound, Northern Porcupine Seabight, indicating that cold-water corals grew during interglacial and warm interstadial periods of the Late Pleistocene controlled by environmental and climatic variability supporting the external control hypothesis (e.g. Dorschel et al. 2005, Rüggeberg et al. 2007). The recent discovery of Dullo et al. (2008) highlights the impact and importance of the external (environmental) control hypothesis with coral growth and distribution following the structure of seawater density, i.e. the potential density anomaly sigma-theta. This study evidences that all studied living coral reef sites of the NE Atlantic are occurring in water masses with a specific density window of sigma-theta = 27.5 ± 0.15 kg/m3, whereas dead reefs are outside this density range. In order to transfer this idea to the paleo-record, we used the method of Lynch-Stieglitz (2001) and others for the determination of paleo-densities using stable oxygen isotope measurement