An Investigation into Arctic Sea-Ice Dynamics and Energetics

Sparse observational data impede understanding of the Arctic Ocean and the sea ice that drifts upon it. Quantifying the exchanges across the air-ice-ocean boundary layer and their representation in models are central research problems today. Focusing on the sea ice component of this system, we analyze data from 5 Ice-Tethered Profilers with Velocity (ITPV) systems deployed in support of the 2013-2015 Marginal Ice Zone program. Ice motion is examined in the time and frequency domains and characterized using the momentum and kinetic energy balance equations. Wind velocity data were obtained from Autonomous Weather Stations augmented by reanalysis data. The ITPVs directly measured the ocean velocity relative to the ice, while the ice velocities were derived from hourly GPS fixes by the ITPV surface buoys. The latter two data streams were combined to estimate absolute ocean velocity. The ITPV data also support direct covariance estimates of the turbulent vertical momentum flux about the ice-ocean interface. Spectral and coherence analyses of the ice, ocean and wind velocity data document significant coupling at subinertial frequency, with the characteristic offset of the velocity vector to the right between the wind and ice velocities and between the ice and ocean velocities. During summer months, rotary spectra of the ice and ocean velocities show clockwise peaks in energy density at the inertial frequency with high coherence and near zero phase. Wind spectra in contrast are red with no discernible peaks at any frequency. Analysis of individual terms in the sea ice momentum and kinetic energy balance equations reveals that the wind stress and the ocean drag on the ice constitute the dominant first order balance for major segments of the records. This analysis will help evaluate and guide models used to predict and characterize sea ice motion.