Observing Beaufort Sea conditions with sound

A combination of acoustic observations, in situ observations, and modeling of the ocean state and sound has improved our knowledge of the Arctic Ocean north of Alaska. This area features the anti-cyclonic Beaufort Gyre and a strong upper ocean halocline enabled by low Arctic diapycnal mixing rates. Here, the input of two types of Pacific waters (warm and cold, summer and winter) beneath the low-salinity near surface layer is balanced by turbulent diffusive loss sustaining the Beaufort Sea sound duct. Observations of sound propagation in this duct, and its layered temperature and salinity variations, may provide an integrated measurement of the net upper-ocean heat content. This heat has a seasonal cycle, and has strong spatial variability, so it is difficult to sense with point sensors, making a wave propagation-based measure attractive. However, the spatial variability of the layering also complicates a propagation-based measure, with stochastic mode coupling complicating acoustic signals. In addition, the seasonal nature of the surface-flux related near surface temperature maximum causes a normally double-ducted situation to become triple-ducted. A summary will be presented of what has been learned from high-resolution ocean modeling, acoustic simulation, and acoustic and physical parameter in situ data analysis. [Work supported by ONR.]