Enhanced thermodynamic ice growth by sea-ice deformation

Abstract

Sca-icc drift and deformation were measured with an array of drifting buoys during a 1995 winter experiment off the East Antarctic continental shelf south of the Antarctic Divergence. The buoys were configured so that deformation of the icefield could be monitored on a range of spatial scales from 2 to 130 km. The mean hourly drift rate during the 3 week-long experiment was 0.21 m s−1, and the mean daily translation of the field was 17.3 km. Differential kinematic parameters calculated from the data show a very high short-term variance, indicating that high-frequency processes are dominant. Spectral analysis of the velocity data shows a major peak of the energy spectrum at the frequency of passage of synoptic weather systems, and a second peak at the inertial frequency. A major storm event occurred during the experiment. Net divergence over this phase of the experiment, as measured by a five-buoy array, is small compared to the short-period variance. This alternating divergence and convergence has a marked effect on the net ice growth. Intense freezing and rapid new ice formation occurs in the open water areas formed during divergence, and this is thickened by rafting and ridge-building during the subsequent convergence. New open water areas equivalent to 10% of the total area formed during the first phase of the experiment. A one-dimensional multilayer thermodynamic model of ice growth shows that this led to an increase of 2.8 cm in the area-averaged ice growth over a 7 day interval, which is equivalent to 40-50% of the total estimated ice growth over the region.