Effects of pacific summer water layer variations and ice cover on Beaufort Sea underwater sound ducting

Abstract

A one-year fixed-path observation of seasonally varying subsurface ducted sound propagation in the Beaufort Sea is presented. The ducted and surface-interacting sounds have different time behaviors. To understand this, a surface-forced computational model of the Chukchi and Beaufort Seas with ice cover is used to simulate local conditions, which are then used to computationally simulate sound propagation. A sea ice module is employed to grow/melt ice and to transfer heat and momentum through the ice. The model produces a time- and space-variable duct as observed, with Pacific Winter Water (PWW) beneath a layer of Pacific Summer Water (PSW) and above warm Atlantic water. In the model, PSW moves northward from the Alaskan coastal area in late summer to strengthen the sound duct, and then mean PSW temperature decreases during winter and spring, reducing the duct effectiveness, one cause of a duct annual cycle. Spatially, the modeled PSW is strained and filamentary, with horizontally structured temperature. Sound simulations (order 200 Hz) suggest that ducting is interrupted by the intermittency of the PSW (duct gaps), with gaps enabling loss from ice cover (set constant in the sound model). The gaps and ducted sound show seasonal tendencies but also exhibit random process behavior.