Internal Waves in the Arctic: Influence of Ice Concentration, Ice Roughness, and Surface Layer Stratification

• Published in: Journal of geophysical research. Oceans Vol. 123; no. 8; pp. 5571 - 5586
• Main Authors: Cole, Sylvia T., Toole, John M., Rainville, Luc, Lee, Craig M.
• Format: Journal Article
• Language: English
• Published: Washington Blackwell Publishing Ltd 01-08-2018
• Subjects: Annual variations; Arctic; Arctic ice; Density stratification; Energy; Energy levels; Evolution; Floating ice; Fractures; Geophysics; Glaciation; Ice; ice concentration; Ice cover; Ice environments; ice roughness; Ice sheets; Influence; Interactions; Internal wave generation; Internal waves; Mathematical models; near‐inertial; Numerical models; Ocean currents; Ocean models; Oceans; Profilers; Profiles; Roughness; Sea currents; Sea ice; Seasonal variation; Seasonal variations; Stratification; Surface boundary layer; Surface layers; Topography; Topography (geology); Velocity; Vertical mixing; Water properties; Wave generation; Wave propagation; Wave properties; Arctic Ocean; Canada; Arctic region
• ISSN: 2169-9275; 2169-9291
• DOI: 10.1029/2018JC014096

The Arctic ice cover influences the generation, propagation, and dissipation of internal waves, which in turn may affect vertical mixing in the ocean interior. The Arctic internal wavefield and its relationship to the ice cover is investigated using observations from Ice‐Tethered Profilers with Velocity and Seaglider sampling during the 2014 Marginal Ice Zone experiment in the Canada Basin. Ice roughness, ice concentration, and wind forcing all influenced the daily to seasonal changes in the internal wavefield. Three different ice concentration thresholds appeared to determine the evolution of internal wave spectral energy levels: (1) the initial decrease from 100% ice concentration after which dissipation during the surface reflection was inferred to increase, (2) the transition to 70–80% ice concentration when the local generation of internal waves increased, and (3) the transition to open water that was associated with larger‐amplitude internal waves. Ice roughness influenced internal wave properties for ice concentrations greater than approximately 70–80%: smoother ice was associated with reduced local internal wave generation. Richardson numbers were rarely supercritical, consistent with weak vertical mixing under all ice concentrations. On decadal timescales, smoother ice may counteract the effects of lower ice concentration on the internal wavefield complicating future predictions of internal wave activity and vertical mixing.
Plain Language Summary
This study addresses how seasonal changes in the Arctic Ocean's floating sea ice influence the ocean's small‐scale, high‐frequency currents. These motions can influence the distribution of heat and other water properties in the Arctic Ocean but are not resolved in numerical models and so need to be parameterized. Observations from the 2014 Marginal Ice Zone experiment are used to collectively analyze over 8,500 profiles of temperature and salinity, and over 5,000 profiles of velocity in the upper 250 m of the Arctic Ocean's Canada Basin. These observations began in March beneath a contiguous ice sheet; by fall the measurement domain included regions of low ice concentration as well as open water. The ocean's high‐frequency currents changed abruptly in response to changes in the ice cover, with the lowest energy observed beneath a fractured ice cover and the largest energy in open water. The under‐ice topography also influenced the ocean's high‐frequency currents, with smoother topography corresponding to weaker ocean currents. The primary implication is that contrasts between smoother versus rougher under‐ice topography and a fractured versus continuous ice cover are critical for understanding the interactions between the ocean and sea ice, now and in the future.
Key Points
Ice roughness influenced internal wave properties for ice concentrations greater than approximately 70‐80%
Internal wave energy levels transitioned abruptly at three ice concentrations: the initial decrease from 100%, 70‐80%, and 0%
Internal wave amplitudes were 80% larger in open water than beneath full ice cover