An abyssal topographic experiment

Observations have been made of the flow field and density structure surrounding a small isolated hill 20 × 5 km × 500 m on the Iberian Abyssal Plain in 5340-m depth. Typical flows far from the hill were from the west and south, and of the order of 2.5 cm s ^-1 at the level of the hill top. Near the hill the currents at this level were accelerated on the western flank and reduced to the east by an anticyclonic flow perturbation giving a velocity difference across the hill of 3 to 5 cm s ^-1. CTD (conductivity-temperature-depth) profiles showed a doming of isotherms over the hill and potential temperatures on top of the hill that were as low as on the abyssal plain 500 m below. The profiles also revealed that topographically induced density perturbations penetrated to approximately 2.5 times the height of the hill above the abyssal plain. The observations compare reasonably with a theoretical stratified Taylor column model.