Hydrodynamic conditions in a cold-water coral mound area on the Renard Ridge, southern Gulf of Cadiz

Near-bed hydrodynamic conditions obtained by bottom landers on the Renard Ridge are presented complemented with a data set from repeated CTD casts. On the Renard Ridge cold-water coral mounds were discovered in the last 10 years. Unlike cold-water coral habitats known from the Norwegian and Irish margins, these mounds are not covered with living corals. Mounds are located near the boundary between North Atlantic Central Water and Antarctic Intermediate Water. Mediterranean Water was present at greater depth, but was not observed in the vicinity of the Renard Ridge. Near-bed temperature and current speed reflect a baroclinic semi-diurnal tidal motion, causing vertical watermass movements up to 100 m and temperature fluctuations up to 1.2 °C. Average current speed was 8.8 cm s− 1, while occasionally peak current speeds up to 30 cm s− 1 occurred on top of the Renard Ridge. Tidal currents force the formation of up to 300 m thick bottom nepheloid layers. Near-bed hydrodynamic conditions around the mounds fit in the range for cold-water coral occurrences as described in literature. However, at present coral growth seems restricted by the low near-bed current speeds, the low surface productivity in a well stratified water column and the high near-bed load of fine sediment particles.

► First long-term near-bed hydrodynamic measurements recorded in the southern Gulf of Cadiz.
► Semi-diurnal tidal cycle is present on the Renard Ridge, causing daily temperature and current speed fluctuations.
► Tidal currents force the formation of nepheloid layers.
► Cold-water coral mounds occur at the boundary of two water masses.
► At present cold-water coral growth is limited by low current speeds, low productivity and high near-bed particle load.