IMPACTS OF ICE ON THE GEOMORPHOLOGY OF COLD-CLIMATE COASTS

Approximately 30% of the world's coastlines have cold climates and are impacted by ice. As global climate warms, cold coasts will be disproportionately affected by rising atmospheric and water temperatures. Areas that were once permanently or seasonally frozen will transition to a shortened shore ice season or multiple nearshore ice construction and breakup events. This alteration in the relative importance and timing of shore ice processes will have ramifications for nearshore sediment budgets and long-term geomorphic evolution of cold-climate coasts because nearshore sediment transport mechanisms (i.e., alongshore and cross-shore transport) are altered by the presence of ice. The Western Laurentian Great Lakes of North America are located between approximately 41.4 to 48.5 degrees north latitude and provide a natural setting to study the impacts of reduced ice-cover on nearshore processes. Winter ice conditions include continuous seasonal cover in Lake Superior, multiple cycles of ice formation and break up in central Lake Michigan, and no ice cover in some years in southern Lake Michigan. Here we present the results of photographic surveys of near-shore ice complex break-up, pre-and post-ice bathymetric surveys, novel ring-shear and wave tank laboratory experiments, and XBeach-Surfbeat numerical simulations. Combined, these demonstrate that ice can have large impacts on coastal geomorphology. Ring shear studies have shown that ice can entrain large volumes of sediment and that the mechanics between grounded debris laden ice and the underlying unfrozen sediment govern the stability of shore fast portions of ice. Thermal conditions dominate ice breakup and mechanical processes expedite the process. Most importantly, the formation of nearshore ice ridges can redirect incoming wave energy and push sediments offshore, potentially beyond the depth of closure. These winter processes are a crucial component of the annual sediment budget along cold coasts that are vulnerable to climate change.