Deformation of an ice pack influenced by waves and topographic enhancement of tidal motion near Hopen Island in the Barents Sea

Abstract

Understanding the physical mechanisms behind the deformation of pack ice floes is important for understanding the dynamics of the local ice regime, and for the calibration and validation of ice dynamics models. In April 2017, six Iridium satellite-tracking beacons were deployed on six pack ice floes in the Barents Sea south of Svalbard in the Norwegian Arctic. The ice tracker deployment was performed as part of an offshore research expedition carried out onboard the Research Vessel (RV) Polarsyssel to characterize the local sea ice environment. In addition to the ice tracker deployments, an anemometer beacon, a wave beacon, and an Acoustic Doppler Current Profiler (ADCP) were deployed on a drifting ice floe to which the vessel was moored for nearly three days, and extensive thickness, salinity, and density measurements were made. The wave beacon recorded the vertical acceleration of the floe so that wave forcing on the floe drift could be estimated. The in-situ wind, ocean current, wave, and ice thickness and density measurements permitted the estimation of met-ocean forcings on the acceleration of the ice floe. On April 28, two days after the last ice tracker was deployed on April 26, the six tracked ice floes rapidly dispersed just to the west-southwest of Hopen Island. The dispersion of the ice floes was dominated by strong shearing within the local ice pack, coinciding with a rapid increase in the speeds of the local tidal currents, which was soon followed by a rapid increase in the wave energy. Each of the six tracked ice floes increased their observed drift speeds in sync with the increase in the local tidal current speeds at different times for each floe, but at approximately the same decrease in water depth as they reached the northern edge of Spitsbergen Bank. The rapid increase in the tidal currents was linked to the topographic enhancement of tidal motion near Hopen Island in the shallower waters of Spitsbergen Bank. The wind and wave measurements made by the anemometer and wave beacons and ice tracker left on the ice floe to which the vessel was moored allowed for an estimate of the relative strength of the wind, tidal, and wave forcings on the local ice field. The results showed that the tidal currents initially dominated the dynamic response of the local ice field compared to the wind, which led to the conclusion that the enhanced tidal current was ultimately the dominant cause of the initial dispersion of the local pack ice field on April 28, and the dispersion was then further enhanced by the increase in wave energy.