Complex upper ocean sound–speed structure measured by gliders in the Canada Basin

The Canada Basin's upper ocean structure is undergoing swift changes with the intrusion of warmer Pacific waters and sea ice loss with profound implications for sound propagation in this region. Two Seagliders measured high-resolution transects of temperature, salinity, and pressure across fronts and eddies, providing estimates of the spatial sound-speed variability in the upper ocean along transmission paths of an acoustic tomography array during the summer months of 2016 and 2017. The spatial analysis highlights the importance of placing the results within the context of the structure of the Beaufort Gyre. The measured profiles are used to quantify the depth-dependent contributions of internal waves, halocline eddies, and spice on sound-speed fluctuations. Results support and complement measurements from a sub-surface distributed vertical line array mooring and extend observations into the mixed layer. In the upper 100 m, spice is found to be the major driver of sound-speed fluctuations with a maximum of 3 m/s rms at 23 m, which corresponds to the bottom of the mixed layer. Fluctuations from the vertical displacement of isopycnals driven by halocline eddies and internal waves have three distinct peaks at 25, 60, and 270 m, with values of 0.73, 0.43, and 0.2 m/s rms respectively.