This report is a contribution to the Strategic Environmental Assessment (SEA6) conducted by the Department of Trade and Industry (now Department of Energy and Climate Change). This report reviews the many different sources of underwater noise, both natural and anthropogenic, that combine to provide the background noise levels in which marine organisms need to survive throughout the SEA6 region. The sources of sound combine together in a complex manner resulting in significant spatial and temporal variations in the noise field. A map of the dominant noise sources in the Irish Sea is shown, indicating that man-made noise is the dominant source of noise over about 70% of the area. Shipping noise is likely to be dominant across large parts of the SEA6 area.

To fully characterise the ambient noise field in the SEA6 area would require multiple measurements at a large number of locations over a period of a year. However, a considerably lower cost approach would be to characterise each sound source and to use this with occurrence statistics for each source to model the ambient noise field across the region. The advantages and disadvantages of the acoustic modelling approach are discussed.