Bragg scattering of surface gravity waves by periodic "roll" structure on Arctic ice shelves

The few ice shelves remaining in the Arctic are found primarily along the northern coast of Ellesmere Island in the Nunavut region of Canada. These ice shelves are remnants of what was once the largest contiguous ice shelf in the Arctic, which formed from multiyear sea ice that thickened and rumpled against the coast. The remarkable feature of this ice shelf, uncovered in 1906 by American polar explorer Robert Peary and still evident in its present-day remnants the Ward Hunt and Milne ice shelves, are the wave-like rolls which furrow its surface (e.g., Coffee et al., 2022). We hypothesize that these rolls (and their basal expression) preserve the integrity of the ice shelf by deflecting incident wave energy from the Arctic Ocean. By scattering incoming surface waves, these periodic rolls prevent waves from flexing and breaking the shelf. Using numerical models, we compute the eigenmodes of the coupled ice shelf-ocean system obeying physical conservation laws. Our results reveal "band gaps" in the frequency spectrum of the eigenmodes, implying that the ice shelf reflects incoming waves with frequencies within these gaps. Moreover, these band gaps are sensitive to the physical dimensions of the ice shelf, such as thickness, water depth, and wavelength and amplitude of the surface rolls. We speculate that roll morphology provides a "fitness" for survival that explains why this phenomenon is only observed in the oldest and thickest multiyear sea ice of the Arctic. Understanding this phenomenon will help to reveal natural mechanisms of ice shelf resistance to calving, which can have widespread impacts for international commerce and climate change.

Figure caption: Digital Elevation Model (from Arctic DEM, by Polar Geospatial Center, U. Minnesota) of present-day remnant of the Ward Hunt Ice Shelf showing surface elevation rolls. Inset: photograph of Ward Hunt Ice Shelf from aircraft (courtesy of Denis Sarrazin, Centre d'etudes nordiques, U. Laval, Canada). Amplitude of surface rolls varies from 1 - 5 m, wavelength varies from 200 m to 500 m.

Coffey, N., MacAyeal, D., Copland, L., Mueller, D., Sergienko, O., Banwell, A., & Lai, C. (2022). Enigmatic surface rolls of the Ellesmere Ice Shelf. Journal of Glaciology, 1-12. doi:10.1017/jog.2022.3