Chevron Rosebank SERPENT final report

This report presents the results from the SERPENT project collaborative research with Chevron at the Rosebank deep-water exploration site. SERPENT visited the Stena Carron drill ship in the Faroe Shetland Channel (FSC) to investigate megafaunal diversity at the seabed (1124m depth) and determine the effects of disturbance resulting from the drilling activities on the seabed and benthic organisms. The Magnum 156 remotely operated vehicle (ROV), was used to take eight video transects of at least 100m in length which were used to assess visually the extent of drill cuttings and to determine megafaunal densities. Sediment samples were also collected using ROV operated push cores at 250 and 400m from the well to determine heavy metal concentrations, total organic matter and particle size distribution. These methods suggested disturbance was variable depending on heading but drill cuttings completely covered the seabed 70m from the well and there was partial coverage to approximately 100m. Analysis of the sediment showed elevated Barium concentration in surface sediments close to the well. These physical changes were associated with significant reductions in megafaunal abundance and changes in the megafaunal community structure, with very few animals observed in a 60m radius of the well. In addition, specimens of the characteristic megafauna were collected and physical data from the water column was logged. An experiment was carried out to investigate bioturbation rate in disturbed and undisturbed sediment. Luminophore tracer particles were added to the sediment surface in corrals which were either controls or treated with a sedimentation disturbance event. The sediment was later sampled and sectioned for subsequent analysis.