Contributions of airgun activity to the ice-free ambient noise environment of the shallow Beaufort Sea between 2007 and 2011

Abstract

Every year since 2007 a collection of at least 35 “Directional Autonomous Seafloor Acoustic Recorders” (DASARs) have been deployed across a 280 km swath of the Beaufort Sea continental shelf, in water depths between 15 and 50 m. The ability of these instruments to estimate the arrival azimuth of transient signals has facilitated the development of an automated algorithm for the detection of airgun activity. This algorithm has been applied to five seasons of data, and in this presentation the contributions of this activity to the overall ambient noise background of the ice-free shallow-water Beaufort environment will be quantified with a variety of metrics, in terms of both level (peak-to-peak, rms, sound exposure level), frequency, and time (intervals and fraction of time present). During some years, up to four airgun operations could be detected simultaneously, and a random one-second time sample yielded a 40% chance of containing an airgun signal, but the levels detected are generally within the bounds of natural wind-driven ambient noise levels. This dataset provides useful empirical insight into discussions about the cumulative effects of anthropogenic activity on an environment extensively used by several marine mammal species. [Work sponsored by the Shell Exploration and Production Company.]