The objective of this study was to determine the levels, characteristics, and range dependence of underwater and in-air sounds produced during the open-water seasons of 2000–2003 by the Northstar oil development, located in nearshore waters of the Alaskan Beaufort Sea. Specifically, sounds originating at the island itself (from construction, drilling, and oil production activities) were compared with sounds produced by vessels performing island support. Sounds were obtained with boat-based recordings (at distances up to 37km from Northstar), a cabled hydrophone (distance ∼450m), and with autonomous seafloor recorders (distance ∼22km). Vessels (crew boat, tugs, self-propelled barges) were the main contributors to the underwater sound field and were often detectable underwater as much as ∼30km offshore. Without vessels, broadband island sounds reached background values at 2–4km. Island sound levels showed more variation (lower min, higher max) during construction than during drilling and production. In-air broadband measurements were not affected by the presence of vessels and reached background values 1–4km from Northstar. However, one airborne tone (81Hz) believed to originate at Northstar was still detectable in the spectrum 37km away.

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