MB FUTURE SCIENCE BRIEF 
TODAY'S OCEAN 
S50UNDSCAPE 
Eurapean a 
MARINE BOARD jenes?” 
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ANTHROPOGENIC SOURCES 
ACOUSte deteTent devices 
Yshing vessch 
Recreatlanal v=&ssels 5 
Truise ships 10 
Tommercial shipping we 
"Wfshore al & 9a5 
Seismilc airgun suruays 
Military 5 cdwillan sonar 
Mishore renewabhle energy 
Jnderweter explostons 
*arstnuctlon and pile-driving 
NATURAL SCURCES 
Waues 
Wind 
Ralrı 
Marine mammaks 
Current 
N 
Underwater kandshdes, 
volcanos and ecrnthguakes 
Pirhes 
Invertebrates 
Figure 3. Today’s Ocean soundscape including anthropogenic and natural sound sources, labelled anti-clockwise 
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2.2 Today’s Ocean soundscape 
Today’s Ocean soundscape comprises many different sound sources 
of both natural and anthropogenic origin. Natural sources include 
geophysical events such as wind-generated waves, wave breaking, 
earthquakes, rainfall, thermal agitation ofthe seawater and cracking 
ice, as well as biological phenomena such as shrimp snapping, 
whale song, dolphin clicks and fish vocalizations. Anthropogenic 
sources are also diverse and range from small recreational crafts to 
supertankers, and from acoustic deterrent devices to seismic surveys 
(see Figure 3). Most human activities in the marine environment 
generate sound, either intentionally for a specific purpose 
(e.g.seismicairgun surveys for mappingof deep geological structures, 
sonar for detection and localization of objects, acoustic deterrent 
devices), or unintentionally as a by-product of their activities 
(e.g. shipping, offshore construction). 
A description of sound sources is a very important part of the 
risk assessment framework. Underwater sounds are commonly 
classified into ’impulsive’ if they are of short duration or 
'continuous’ if they occur without a pause. Impulsive sounds can 
occur individually, irregularly or as part of a repeating pattern. In 
many cases impulsive sounds (e.g. seismic airgun pulses) have 
higher intensity than continuous sounds, such as those recorded 
from shipping. However, these definitions are not unambiguous 
and are contingent on circumstances. For example, pulses from 
an airgun can merge at larger distances from the source and thus 
become continuous. On the other hand, some continuous sources 
can be very powerful e.g. supertankers (Hildebrand, 2005; Southall 
et al., 2007; Southall et al., 2019). Figure 4 presents an overview of 
the respective frequency ranges for sound sources, which are split 
into natural and anthropogenic, with the latter split further into 
continuous and impulsive. 
Boyd et al, (2008) concluded that the uncertainty around 
characteristics of natural and anthropogenic sound sources was 
noderate’, which reflected the relatively good level of understanding 
of the characteristics of natural and anthropogenic sound sources, 
which was summarized in EMB Position Paper N° 13. However, with 
ncreased research in the past decade, particularly with respect to 
new’ sound sources such as offshore wind farm construction and 
operation, it is useful to summarize the current state of knowledge, 
noting in particular where progress has been made since EMB 
Position Paper N° 13. The consensus in the scientific literature is that