Mesoscale sea ice deformation in the East Greenland marginal ice zone

In this paper, mesoscale (10 km) ice kinematics data obtained during the drift phase of the 1983 Marginal Ice Zone Experiment are analyzed. The measurements were made with a microwave transponder system accurate to better than 1 m. From the point of view of granular media theory, the ice pack was close to ideal. Over the scale of the array the pack was quite regular, with floes of relatively uniform size closely packed together. The main external driving force for the ice was the ocean current. Simultaneous current measurements were made at three of the strain array sites. The ice behaved in a relatively rigid manner, with more shear than dilatation occurring. Least squares fits of the strain rate tensor showed the deformation field to be quite homogeneous. Superimposed on the rigid motion were smaller fluctuations with a spectrum falling off proportional to frequency to the power of −3/2 to −2. Close examination of individual strain lines showed rather discontinuous distance changes more representative of plastic slip rather than floe bumping. Although a substantial signal at the inertial period was present in the absolute drift, no clear peaks at this period occurred in the spectra of the strain rate tensor invariants. Analysis of the spatial variation of the underlying ocean currents revealed quite a different picture from that of the ice kinematics. In particular, the current field exhibited a much greater spatial variability than the ice motion, with considerable variance at the inertial period. Coherence between the ice and ocean differential velocity was small for all frequencies. Overall, the rigid interactive character of the compact ice cover prevented most of the differential ocean currents from being transferred to the differential ice motion.