Underwater Noise Thematic Assessment

Activities producing underwater noise

Sound sources are categorised as continuous or impulsive. Continuous sounds are long lasting without pulse characteristics. Impulsive sounds are of short duration, with rapid onset. High-frequency sounds propagate less well in the marine environment than low- frequency sounds, which can travel far in waters that are sufficiently deep. Most anthropogenic sound sources considered in this assessment are low-frequency, but may have high frequency components, for example, shipping, seismic airguns, pile driving, and detonation of unexploded ordnance. Higher frequency sources include sonar, some acoustic deterrent devices (ADDs), and some geophysical surveys.

Human activities producing continuous noise

Shipping is the main source of anthropogenic continuous noise in the OSPAR Maritime Area. Between 75% and 90% of the EU’s external trade and one third of intra-EU trade involve maritime transport. The Greater North Sea, Celtic Seas, and the Bay of Biscay and Iberian Coast have a particularly high amount of shipping, with the highest densities in the English Channel, the Southern and Eastern North Sea, and the entrance to the Mediterranean. The OSPAR Maritime Area includes three of the twenty leading container ports globally, and ten of the twenty largest ports in Europe.

In 2018, the overall weight of goods handled and passenger numbers in OSPAR ports were little changed from 2008. Annual reviews by the United Nations Conference on Trade and Development (UNCTAD) anticipate some increase in global shipping in the future, but note that this could be affected by factors such as slow economic growth, trade tensions, or more regionalised trade flows. Shipping routes and their usage could also change somewhat – for example, due to rerouting of cargo vessels away from wind farms, increased traffic related to wind farms or increases in shipping, including cruise ships, via Arctic Waters. This could add to the pressure from noise in previously less disturbed areas. Fleet composition may also change, including more larger ships, more energy-efficient ships and, potentially, alternative fuels.

Dredging activities associated with shipping also generate noise. Special-purpose vessels, used in a variety of activities, often have dynamic positioning systems which generate noise at higher frequencies than those from propulsion machineries or pumps.

Tourism and recreation generate continuous noise. Recreational boating (including jet skis, motor boats and power boats) can be a significant source of mid- to high-frequency underwater noise in shallow coastal waters. This is not currently included in noise assessment models as these craft do not have the automatic identification systems (AIS) used in the models, and noise propagation in shallow coastal waters, in particular tidal waters, is more difficult to model and predict (Hermannsen et al., 2019). OSPAR intends to include this source in future modelling, although how data is obtained needs further consideration.

Fishing contributes to underwater noise from vessel movements, and from bottom trawls dragging the seabed.

The offshore oil and gas industry is a source of continuous noise from drilling equipment and production platforms. The number of wells drilled increased over the period from 2009 to 2019; most wells drilled are development wells rather than exploration and appraisal wells.

Renewable energy produced from operational offshore wind turbines is a source of low-frequency underwater noise. While noise from individual turbines is low compared with noise from ships, the high projected increase in offshore wind farms means that the cumulative contribution of wind farms to the underwater soundscape requires assessment (Tougaard et al., 2020).

Extraction of aggregates (sand and gravel), notably in the Greater North Sea, produces continuous noise (through extraction, material passing through pumps and pipes, and vessel movements).

Human activities producing impulsive noise

Impulsive noise is produced by several sources. OSPAR’s Common Indicator on the Pressure from Impulsive Noise categorises these as seismic airgun surveys, pile driving, explosions, sonar and acoustic deterrents, and generic, which includes sources such as non-airgun seismic surveys (e.g. sub-bottom profilers). Some of the loudest and most potentially damaging sources of underwater impulsive noise, in terms of severity of injuries, are caused by explosives.

Seismic surveys, using seismic airguns, are used in the oil and gas industry in discovering and defining new hydrocarbon reservoirs, assessing the extent and depletion of those reservoirs, and for characterising and monitoring geological structures for the storage of carbon dioxide. The oil and gas industry also carries out non-airgun seismic surveys (sub-bottom profilers). It uses explosives for cutting (e.g. casing and tubing, or in decommissioning) or for perforating well casings. Infrastructure installation activities in the oil and gas industry involve underwater hammer piling.

Renewable energy development, through percussive pile driving during the installation of offshore wind turbines, as well as through site surveys, is an increasing source of impulsive noise. Offshore wind capacity in the North-East Atlantic increased substantially between 2009 and 2019, from 1,9 GW to over 22 GW. The Greater North Sea had 77% of this capacity and the Irish Sea 13%. Offshore wind installation in other OSPAR regions was very small in comparison. At present, the majority of turbines use impact-driven monopile foundations.

Planned growth in offshore wind energy is ambitious: in 2020, the European Commission envisaged an expansion in offshore wind in the EU 27 from 12 GW to at least 60 GW by 2030 and 300 GW by 2050, and the United Kingdom Government set out plans for a fourfold increase to 40 GW by 2030. Under a maximum scenario developed by the wind industry, 212 GW could be installed in the North Sea by 2050, with 85 GW in the Atlantic and Irish Sea off France, Ireland and the United Kingdom. Initially, most new capacity will be bottom-fixed installations requiring pile driving, although floating offshore wind, which uses less noisy techniques for anchoring installations, is also expected to develop further. Other low-noise foundations such as suction bucket or gravity base foundations are infrequently used at present.

Shipping and ports development generates pile driving noise in inshore waters as a result of construction works for ports, and noise from explosives used for cutting purposes in activities including ship repair, harbour works and salvage or removal of shipwrecks and cargos.

Military activity is a source of impulsive noise but is outside the remit of OSPAR to regulate. Military activity is a source of impulsive noise from sonar. It could generate explosions, either operationally or for training. Explosions mainly arise from the detonation of unexploded ordnance, such as mines or ammunition, left undetonated or dumped after the World Wars. Detonation is necessary for health and safety reasons (e.g. before offshore construction activities begin).

In aquaculture, acoustic deterrent devices (ADDs) producing loud, mid-frequency sound are used to deter seals from approaching fish farms. These can have unintended consequences for non-target species, particularly cetaceans. While newer generation ADDs reduce sound outputs at frequencies most likely to disturb cetaceans, more research and development concerning their possible use is still required, including if the noise produced is impulsive or continuous (Marine Scotland, 2021).

Seismic surveys are also used to gather data for academic and governmental needs, for example seabed surveys or analysis of geological features below the seabed.

Other sources of impulsive noise include echosounders, underwater communication systems and measurement instruments, although as high-frequency sources, their effects are likely to be localised.