Processes of sedimentation in Gollum Channel, Porcupine Seabight: submersible observations and sediment analyses

Abstract

AbstractManned submersible dives were conducted in the submarine canyon channel system of Porcupine Seabight, NE Atlantic Ocean. Visual observations were made, and sediment samples collected and analysed to elucidate the nature of the sedimentary regime. In the upper part of the canyon (480-940 m water depth) sediments consisted of a mixture of terrigenous quartz rich silts and sands, skeletal carbonate of benthonic and planktonic origin and minor clay minerals and authigenic dolomite. There were localised Lophelia pertusa coral thickets on both the flanks and floor of the canyon. Sedimentary structures and physical measurements revealed there to be active transport of sediments in the canyon down to a depth of at least 940 m, effected by (?tidal) reversing currents and bioturbation. In these parts of the canyon, deposits around glacial dropstones and coral thickets indicate that there has been a maximum of 0-1 m of net sediment accumulation since the last glacial period. At 3000 m water depth, in the channel system, the sediments were fine calcareous ooze with a drape (up to 0-3 m thick) of flocculant phytoplankton detritus. At these depths, there was no evidence for present-day sediment resuspension by currents.