Glacier Bay Underwater Noise - August 2000 through August 2002

Kipple, Blair; Gabriele, Chris

Both manmade and naturally occurring underwater noise in lower Glacier Bay was studied using almost 10,000 hourly noise samples obtained during 20 months between August 2000 and August 2002. The primary contributor of natural noise was wind generated surface noise, which averaged 84 dB re 1 microPa at 1 kHz and ranged from 67 to a maximum of 102 dB. Average monthly wind noise levels were not widely variable by season. Noise from rainfall was present in an average of 2.1 out of 24 samples per day and was not especially prevalent in winter versus other seasons. Rain noise levels at 16 kHz averaged 91 dB and ranged as high as 110 dB. Humpback whales were the most common source of biologic noise. These sounds included various grunts, whoops, and squeaks as well as songs. They were most common from August through November. Sixty-percent of all humpback songs were logged in October 2000. Marine vessel noise was the only identifiable source of manmade noise that was observed. On average it was present in 7.7 out of 24 samples per day, but it ranged from a low of 1.7 samples per day in December 2000 to a high of 16.5 per day in August 2000. Not surprisingly, vessel noise was most common in summer. Peak vessel noise levels averaged 94 dB, 10 dB greater than the average wind noise level. The highest vessel level recorded was 129 dB, but only about 5% of the peak vessel noise levels exceeded 110 dB at the hydrophone. Medium sized vessels were the most prevalent vessel type at all times of year. They constituted 68% of all vessel types observed. At most, large ships were observed in 4 samples per day. Noise from small craft was most common from May to August. The average large vessel noise level was 2 dB higher than the average small vessel level and 7 dB higher than the average medium craft level. Vessel noise levels were lower during periods when a 10-knot speed limit was in effect, especially for large and small vessels. On average, a heavy rolling transient noise was observed in 75% of the samples acquired per day in June and July. The source of this noise was not identified, but its presence was strongly dependent on season.

Glacier Bay Underwater Noise - August 2000 through August 2002

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