Roughness and storage capacity of freshwater ice in the Straits of Mackinac

Abstract

In the event of a maritime oil spill in winter conditions, the fate of oil released under ice presents considerable difficulties with respect to detection, containment and recovery compared to spills that form slicks in open water. This study presents the first quantification of roughness and associated storage capacity of the ice-water interface for freshwater ice in the Laurentian Great Lakes in North America. Ground Penetrating Radar (GPR) observations are used to retrieve ice thicknesses every 2.5 cm on a grid over ice ranging between 0.26 and 0.48 m in the Straits of Mackinac to derive a digital elevation model of the ice bottom. The root mean square of height deviations of the ice underside is observed to be 0.03 m (over a correlation length of approximately 20 m) with a storage capacity of 0.03 m3/m2. The observed physical characteristics relevant to oil entrainment at the ice underside are similar to those reported for first year sea ice and may store similar quantities of oil during the initial spill. However, the difference in the physical structure between first year ice (with brine channels) and freshwater ice (consolidated ice cap) may result in a disparity in the timing of oil appearance, and require considerably different remediation treatment.