Dynamics and impacts of oil spills from seabed releases in the Faroe-Shetland channel

Oil and gas exploration are well-established in the Faroe-Shetland Channel (FSC) and gradually moving into deeper waters. The FSC is a complex physical system, host to strong currents, mesoscale variability, internal waves and tides, and a unique stratification structure. This thesis explores how these hydrodynamic features influence oil plume dynamics and the subsequent far-field transport, by using the Oil Spill Contingency and Response (OSCAR) modelling system. The operational hydrodynamic model commonly used as part of UK spill response (AMM7) is compared against CTD observations. AMM7 is poor at representing ocean stratification, because mid-water-column property gradients are too weak and there are large same-depth differences in temperature (order 5 ◦C) and salinity (order 0.2 gkg−1). Model-observation differences are then quantified and used to guide idealised plume modelling using the DeepBlow component of OSCAR. Plume trapping almost always occurs below the thermocline, irrespective of non-hydrodynamic parameters or the stratification and current structures. When oil is released from 1000 m, AMM7 will estimate the trapping depth to be too deep by order 100 m. Most oil (85–90%) will eventually surface and be advected north-eastward towards the Norwegian Sea. Four-fifths of the remaining submerged oil will instead be advected westward into the open North Atlantic. Regional spill modelling shows that the coasts of Shetland and Norway are at risk of contamination by a spill originating from the FSC, depending on the time of year and the release location. Compared to a deep (> 1000 m) release, a shelf (< 200 m) release increases the risk of coastline contamination but prevents the south-westward advection of oil. Simulating a spill using a finer resolution hydrodynamic model (AMM15) suggests that mesoscale processes act to recirculate and contain oil within the central FSC, but also act to increase the difficulty of a clean-up operation