The life history of sea ice is written in its basal morphology. Sea ice progresses through several stages during its lifecycle, including frazil, nilas and pancake ice, until it bonds into a near-continuous sheet known as first-year (FY) ice. If this ice survives the summer melt-season, it becomes multiyear (MY) ice (Weeks & Ackley 1986). Both FY and MY sea ice have significant morphological variability, ranging from undeformed, level ice to heavily deformed or ridged ice. These variations lead to a complex, highly heterogeneous ice topography. Profiling the underside of Arctic sea ice was first performed by nuclear submarines (e.g. Wadhams 1988, 2000); however, since the end of the Cold War, military submarine transits of the Arctic have become less frequent and are insufficient to understand climate-induced trends. Therefore, deployment of autonomous underwater vehicles (AUVs) equipped with upward-looking multibeam sonar represents an important innovation.
Description
Sea ice is not a homogeneous medium. It occurs in a wide variety of forms due to the various thermodynamic and dynamic forces it undergoes during its lifecycle of growth, decay and deformation. The greatest variability is associated with deformed ice in the form of ridges: long, quasi-linear features composed of blocks of ice, piled both above and below the relatively level ice surface. Ridge sails may be up to several metres in height above the sea surface and keels may reach depths of >40 m. These morphological variations lead to a complex, highly heterogeneous sea-ice topography that varies on scales from <1 metre to 100s …
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