• Energy Research

AbstractNumerous acoustic Doppler current profiler (ADCP) surveys were performed in the Inner Sound of the Pentland Firth, a channel between the Orkney Islands and the northern coast of Scotland connecting the Atlantic Ocean to the west and the North Sea to the east. The Pentland Firth has the highest tidal streams of the British Isles, and one of the highest that can be found around the globe. Here, the tidal energy industry is in its demonstration phase, but not many real current measurements are in the public domain. The authors present real current data, measured during different phases of the tidal cycle, using a vessel-mounted ADCP. The tidal changes can be rapid, and because the underway measurements take time, the apparent spatial patterns are affected by temporal variation. A method is described that estimated and corrected this temporal distortion using a hydrodynamic model. It appeared that ebb and flood streams did not fully overlap, and that the tidal streams were more complicated, turbulent, and variable than existing models suggest. The data were analyzed for characteristics pertinent to practical tidal stream energy exploitation, and two favorable sites in the Inner Sound are identified. All original current data are available from the British Oceanographic Data Centre (BODC).

Sediment banks within a fast-flowing tidal channel, the Inner Sound in the Pentland Firth, were mapped using multi-frequency side-scan sonar. This novel technique provides a new tool for seabed sediment and benthic habitat mapping. The sonar data are supplemented by sediment grab and ROV videos. The combined data provide detailed maps of persistent sand and shell banks present in the Sound despite the high energy environment. Acoustic Doppler Current Profiler (ADCP) data and numerical model predictions were used to understand the hydrodynamics of the system. By combining the hydrodynamics and sediment distribution data, we explain the sediment dynamics in the area. Sediment particle shape and density, coupled with persistent features of the hydrodynamics, are the key factors in the distribution of sediment within the channel. Implications for tidal energy development planned for the Sound are discussed.

Abstract Marine plastic debris floating on the ocean surface is a major environmental problem. However, its distribution in the ocean is poorly mapped, and most of the plastic waste estimated to have entered the ocean from land is unaccounted for. Better understanding of how plastic debris is transported from coastal and marine sources is crucial to quantify and close the global inventory of marine plastics, which in turn represents critical information for mitigation or policy strategies. At the same time, plastic is a unique tracer that provides an opportunity to learn more about the physics and dynamics of our ocean across multiple scales, from the Ekman convergence in basin-scale gyres to individual waves in the surfzone. In this review, we comprehensively discuss what is known about the different processes that govern the transport of floating marine plastic debris in both the open ocean and the coastal zones, based on the published literature and referring to insights from neighbouring fields such as oil spill dispersion, marine safety recovery, plankton connectivity, and others. We discuss how measurements of marine plastics (both in situ and in the laboratory), remote sensing, and numerical simulations can elucidate these processes and their interactions across spatio-temporal scales.