The importance of the permanent thermocline to the cold water coral carbonate mound distribution in the NE Atlantic
A prominent feature of the NW European continental slope is the presence of numerous cold water coral carbonate mounds that are clustered in a number of provinces. These provinces occupy a relatively narrow depth range along the continental slope: 95% of all coral carbonate mounds identified on the Irish seabed have their mound bases between 500 and 1000. m water depths, with a peak in distribution at ~650 m water depth. The distribution in mound base depths is skewed with a tail extending from the maximum at 650. m to deeper depths. This distribution brackets the depth of the permanent thermocline in the NE Atlantic (600-1000. m) formed below the base of the winter mixed layer. It is shown that the permanent thermocline is associated with the strongest residual near seabed current flow, with typical residual current speeds up to 2-3 times larger at the thermocline depth compared to other depths. The strong vertical density gradient associated with the permanent thermocline, together with the steep continental slope at those depths, also enhances the energy of certain periodic motions such as internal waves and baroclinic tidal currents. These dynamic conditions favour mound growth through the promotion of significant along-slope sediment transport and also provide large across-slope sediment movement and organic matter fluxes. The stability of the thermocline structure is likely the key in providing favourable conditions over long time scales that allow mound growth through sediment baffling processes. © 2010 Elsevier B.V.