Trends in low‐frequency deep ocean ambient noise levels: New results from old data.

Abstract

Concern about effects of anthropogenic sound generated by ships, seismic exploration, naval operations, and ocean acoustic research on marine life has stimulated new studies of marine animal bioacoustics. An underlying issue in assessing the noise impact establishes the present‐day background noise level and compares it to noise levels from previous times. The most generally accepted prediction of noise level trend at low frequencies (below 500 Hz) is due to Ross, who used noise levels from the 1950s and the mid‐1960s to predict an increase of about 3 dB/decade. This paper addresses the issue of the trend in low‐frequency ambient noise levels in the ocean and presents measurements taken in the intermediate years between the mid‐1960s and the present time. The measurements were made using a calibrated multi‐element volume array (MEVA) at deep ocean sites in the Northeast Pacific from 1978 to 1986. The array provided spectral noise levels and horizontal and vertical directionalities. Compared to the 1965 va...