Abstract
Due to seasonal ice cover, acoustics can provide a unique means for Arctic undersea communication, navigation, and remote sensing. This study seeks to quantify the annual cycle of the thermohaline structure in the Beaufort Sea and characterize acoustically relevant oceanographic processes such as eddies, internal waves, near-inertial waves (NIWs), and spice. The observations are from a seven-mooring, 150-km radius acoustic transceiver array equipped with oceanographic sensors that collected data in the Beaufort Sea from 2016 to 2017. Depth and time variations of the sound speed are analyzed using isopycnal displacements, allowing a separation of baroclinic processes and spice. Compared to lower latitudes, the overall sound speed variability is small with a maximum root mean square of 0.6 m/s. The largest source of variability is spice, most significant in the upper 100 m, followed by eddies and internal waves. The displacement spectrum in the internal wave band is time dependent and different from the Garret-Munk (GM) spectrum. The internal wave energy varied with time averaging 5% of the GM spectrum. The spice sound-speed frequency spectrum has a form very different from the displacement spectrum, a result not seen at lower latitudes. Because sound speed variations are weak, observations of episodic energetic NIWs with horizontal currents up to 20 cm/s have potential acoustical consequences.
Highlights
The Arctic Ocean is of considerable interest in the context of its changing processes such as currents, thermohaline structure, and sea ice extent
The thermohaline and current structures of the Beaufort Sea are studied from the yearlong moored Canada Basin Acoustic Propagation Experiment (CANAPE) data and ship CTD observations (e.g., Fig. 2)
Water masses of Arctic surface water (ASW), Pacific summer water (PSW), Pacific winter water (PWW), and Atlantic water (AW) were characterized by temperature and salinity properties, and two haloclines were observed
Summary
The Arctic Ocean is of considerable interest in the context of its changing processes such as currents, thermohaline structure, and sea ice extent. Using observations from the 2016–2017 Canada Basin Acoustic Propagation Experiment (CANAPE), this paper seeks to quantify the effects of these changes and important ocean processes, such as eddies, internal waves, internal tides, and temperature/salinity variability, along isopycnals (spice) on Arctic sound speed and current structure. NIWs can originate from sea ice motion and winds at the surface in the Arctic Ocean (D’Asaro, 1985; Dosser and Rainville, 2016; Rigby, 1976) and typically generate currents of the order of tens of centimeters per second These waves are of interest to Arctic acoustics because sound-speed fluctuations due to eddies and internal wave displacements are of the order of several tens of centimeters per second.
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