Reconstruction of the formation history of the Darwin Mounds, N Rockall Trough: How the dynamics of a sandy contourite affected cold-water coral growth

Cold-water coral mounds, formed through a feed-back process of cold-water coral growth and sediment baffling, have been studied all along the NE Atlantic continental margin. However, major questions remain concerning their formation history, especially their initiation and early development in relation to the surrounding sediment dynamics. For the first time, two small mounds located in a sandy contourite have been cored from the top to mound base: here, the formation history of the Darwin Mounds, located in the Northern Rockall Trough was investigated and reconstructed from two piston cores using a multidisciplinary approach. This consisted of CT-scanning for quantifying coral density changes with depth, grain-size analysis to obtain the hydrodynamic trends and radiocarbon and U-series dating to place the results into a wider paleoceanographic context. The results show that the Darwin Mounds formed during the early Holocene (~ 10 ka BP) through sediment baffling, mainly by Lophelia pertusa. The initiation of both mounds shows a similar pattern of increased current velocities resulting in coarser sediment deposition and a relatively high coral density with a peak of 23 vol%. The mound growth was rapid between ~ 10-9.7 ka BP (up to 277 cm ka− 1 in one of the mounds), with further vibrant growth periods around ~ 8.8 ka BP, 6.5 ka BP and 3.4 ka BP. The demise of the mounds ca. ~ 3 ka BP was likely caused by an intensification in bottom current velocities causing a hostile environment for coral growth in the contourite setting. In a wider context, the development of the Darwin Mounds appears to have responded to the relative strength and position of the Subpolar Gyre, which affected food supply to the corals, sedimentation rates, current speeds and other water mass properties in the area.