Modern bryomol-sediments in a cool-water, high-energy setting: the inner shelf off Northern Brittany

Abstract

The inner shelf off Roscoff/North Brittany, France situated in the Western English Channel, provides a unique facility for studying modern cold water BRYOMOL-carbonate deposits in the North Atlantic. High tidal gauge with extreme strong tidal currents, which effect the well-mixed water column throughout the year, and strong, seasonal storms characterize the conditions of the area. The shelf is seperated in two carbonate production zones: Boulder fields and sand fields. The main production areas are the sand fields with an intensive epifaunal and infaunal colonization by bivalves and the bryozoan thickets ofCellaria spp. and their associated epifauna. The most beneficial and dominant strategies of the sessile benthos are erect flexible and encrusting growth habits. The study area is partitioned in two zones: (1) the coarse sediment blanket typified by active sediment generation and little accumulation, and (2) the shell dune Trezen ar Skoden, characterized by accumulated sediments. Sediment transport and distribution of facies areas are controlled by the strong semidiurnal tidal current regime and episodically severe storms. As a result of these high energy processes of redeposition the autochthonous sediment particles are physically reworked and redeposited while in calmer periods deposition and biological destruction of the components occur. The Holocene development of the sea level has been of crucial influence to the costal morphology and the establishment of different carbonate production centers. The benthic communities produce with their carbonate skeletons the first biogenic sediment and provide substrates for colonization of epi- and endofauna. Changes in the current patterns and the morphology of the sea bottom resulted in the origin of the shell dune Trezen ar Skoden.