Multi-Scale Spatial Heterogeneity In Ice-Wedge Permafrost Degradation

Abstract

Common methods of mapping ice-wedge degradation use surface water in remotely sensed imagery as a proxy for ice-wedge degradation; this method consistently underestimates total degradation and ice-wedge extents as surface hydrology in ice-wedge troughs is temporally variable and only a portion of all ice wedges are flooded. More accurate remote sensing methods for detecting ice-wedge degradation stages – that depict ice wedges in all undegraded, degraded, and stabilized stages – will better allow us to monitor and predict Arctic landscape change. We characterized ice-wedge degradation stages using a novel approach that leverages the unique spectral and spatial properties of differing degradation stages. In particular, we used sub-meter commercial satellite imagery to map 366 km2 of ice-wedge terrain along the Dalton highway near Prudhoe Bay, Alaska. We validated the resulting maps of ice-wedge terrain with field observations, airborne LIDAR, and drone multispectral surveys.

The mapping of ice-wedge degradation stages highlighted distinct patterns in permafrost degradation at a regional scale. We assessed this spatial heterogeneity in ice-wedge degradation through clustering: areas with significantly similar trough widths and flooding stage were grouped into hydrogeomorphic clusters. These clusters identify parts of the landscape where most ice-wedge troughs have the same degradation stage. This mapping revealed that ice-wedge degradation is heterogeneous across both meter and kilometer scales. The meter-scale heterogeneity in ice-wedge degradation stage implies that any given ice-wedge landscape has a wide range of factors controlling the degradation and stabilization of each individual trough, working both in concert across the landscape and individually on each ice wedge. Examining spectral and topographic trends across the site revealed that kilometer-scale heterogeneity is linked to spatial patterns in relative elevation. Relative elevation likely dictates the long-term evolution of ice-wedge degradation in tandem with large-scale, millennial geomorphic processes in this low-gradient landscape.