Observations of Surface Wave Dispersion in the Marginal Ice Zone

This study presents the most comprehensive set of in situ and remote sensing measurements of wave number, and hence the dispersion relation, in ice to date. A number of surface-following buoys were deployed in sea ice from the R/V Sikuliaq, which also hosted an X-band marine radar, during the ONR Arctic Sea State field experiment. The heave-slope-correlation method was used to estimate the root-mean-square wave number from the buoys. The method was highly sensitive to noise, and extensive quality control measures were developed to isolate real signals in the estimated wave number. The buoy measurements were complemented by shipboard marine X-band radar dispersion measurements, which are limited to lower frequencies (<0.32 Hz). Overall, deviation from the linear open water dispersion relation was not significant, and matched the open water relation nearly exactly for the range 0.10-0.30 Hz. Isolating a subset of data during the strongest wave event showed evidence of increased wave numbers at frequencies greater than 0.30 Hz. The ice conditions and deviation from linear open water dispersion were qualitatively consistent with predictions from the mass loading model. However, the dispersion curves did not exactly follow the contours of the mass loading model, suggesting either measurement error or other processes at play. Plain Language Summary The relationship between wavelength and wave period is known as the dispersion relation. The dispersion relation is well known for waves on the open ocean. The relationship is altered by shallow water and by changing currents at the surface, but we do not know if it is altered by ice cover. In this study, we present measurements of the dispersion relation in the marginal ice zone, the transition zone between open areas of ocean and areas dominated by ice cover. The measurements were tricky, so there is a good deal of uncertainty involved. We found that dispersion of long period waves were not affected by ice in this zone, but under certain circumstances, the short period waves were slightly reduced in wavelength. This reduction in wavelength was consistent with a theory which adjusts dispersion for the added weight of the ice.