At low frequencies (5 to 500 Hz), commercial shipping is the major contributor to noise in the world’s
oceans. Distant ships contribute to the background noise over large geographic areas. The sounds of
individual vessels are often spatially and temporally indistinguishable in distant vessel traffic noise. Noise
from vessel traffic at high latitudes is particularly efficient at propagating over large distances because in
these regions the oceanic sound channel (zone of most efficient sound propagation) reaches the ocean
surface