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Ref.: Global OCEANS MTS/IEEE, San Diego/Porto, October 2021
Marine seismic sources use extremely powerful sound pulses to penetrate the ocean bottom, which in consequence
may be harmful for numerous marine species in the surrounding area. During the last decade the Portuguese
Government has granted rights for oil and gas exploration in several offshore slots along the SW coast.
In contrast to what happens in deep water seismic surveying, which is well studied and described, shallow water
surveying effects, that usually rely on light seismic techniques, are under-investigated. Numerous cetaceans
sightings along that coast denote a rich ecosystem, which may be subject to marine life harmful noise levels
resulting from light seismic techniques and which may have acute, cumulative and chronic effects on marine
organisms. The results suggest that there is an important contribution of the bathymetry transition from
offshore to inshore for the propagation of the noise resulting from seismic sources. Indeed, it was observed
that the continental platform works as a natural barrier precluding the sound resulting from offshore sources
(located at more than 50km from the shore) to propagate towards land. It was also shown that sound level of
sources located near the shore attenuate more rapidly than those offshore, even though high sound exposure
levels may be reached due to shore proximity.
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