Preliminary Study on the Ocean Ambient Noise in Central Bering Sea

With the increase of human activities in the Arctic, it is necessary to study the characteristics of ocean ambient noise in the Bering Sea for it is the only way to enter the Arctic Ocean from Pacific. From September 11, 2018 to April 5, 2019 (local time), an underwater signal recorder (USR) measured ocean ambient noise in the central Bering Sea at 357 m depth for 2 min per hour, and the central Bering Sea was ice-free during the experiment. It is found that there are a large number of transient sounds in the ocean ambient noise from September to November 2018. These transient sounds are inferred as anthropogenic underwater noise, but it needs to be further studied to specify the noise sources. The correlation coefficients of noise spectrum level and sea surface wind speed are greater than 0.71 in frequencies from 160 Hz to 5 kHz. However, it is decreased rapidly with decreasing frequency when the frequency is less than 160 Hz, and it is only 0.45 at 125 Hz. During the experiment, the average sea surface wind speed is 10.7 m/s and the corresponding Beaufort wind force is about level 5 to level 6. At this wind speed, the mean value of noise spectrum level is about 70.3 dB at 1 kHz in this paper. However, it is about 66 dB in the Wenz curves. The mean value of noise spectrum level in this paper is greater than that in the Wenz curves under the same Beaufort wind force. It should be attributed to the long-time high wind speeds during the experiment, especially the wind speeds are greater than 8 m/s over 67% of the time. The sea waves will grow more fully and the wave breaking will be intensified for the long-time of high wind speeds, so the wind-driven noise spectrum levels may be increased and higher although at the same Beaufort wind force. In the frequency range of 500Hz to 5kHz and wind speed range of 4 m/s to 16 m/s, the attenuation slope of noise spectrum level with increasing frequency, and the increment of noise spectrum level with the doubling of wind speed, are also compared with Wenz's results.