Seasonal Variation of Underwater Noise in North-east Pacific

Abstract

BEFORE marine seismic and other systems that rely on the detection of acoustic signals can be successfully designed, variation of ambient acoustic levels in the oceans throughout the year must be determined. Here I report measurements of ambient noise over a 1 yr period made recently at three sites in the North-east Pacific (Fig. 1). Remote instrument packages designed for a maximum water depth of 670 m, as previously used in relatively shallow Arctic waters¹, were placed near the summits of seamounts Bowie (summit depth about 40 m)², Union (∼320 m)² and Cobb (∼34 m)³. The package on Bowie was placed in a saddle—at the north-east end of the approximately 4 mile long ridge-like summit at a depth of 220 m. On Union the package was placed within 0.5 mile of a dome-like summit at a depth of 340 m and on Cobb the package was placed on a gently sloping terrace some 2 mile to the east of the summit, at a depth of 224 m. Acoustic measurements were limited to the frequency band 150 to 300 Hz. The data yield, although limited by equipment malfunction, was sufficient to reveal seasonal variations.