Enhanced Erosion Across a Transition From Continuous to Discontinuous Permafrost in Alaska

Abstract

Permafrost degradation is expected to accelerate over the next century, with potentially important consequences for Arctic hillslope stability, channel erosion, sediment mobilization, water quality, and carbon release from previously frozen soils. However, the extent to which changes in permafrost cover alter the intensity and dominant mechanisms of catchment‐scale erosion remains poorly constrained. This study uses sediments from 12 Alaskan lakes across two regions to compare the intensity of hillslope and channel physical erosion in small catchments between areas with continuous and discontinuous permafrost cover. Sediment‐based erosion rates computed from dated lake sediment cores spanning the middle Holocene to present, combined with a Landscape Evolution Model suggest that (a) a simple model accounts for most of the variance in sediment‐based erosion rates between lakes, (b) diffusive (primarily hillslope) processes are more significant than advective (primarily fluvial) processes, and (c) the average intensity of diffusive processes is ∼2.1 to ∼3.0 times higher in areas of discontinuous compared to continuous permafrost landscapes. Additional processes, including shoreline wave action and thaw slumping, may also contribute to the variability in erosion rates among lakes. Overall, these results suggest that warming‐driven shifts from continuous to discontinuous permafrost could more than double the intensity of erosional processes; however, the limited data and associated uncertainties underscore the need for more data to better constrain the impacts of permafrost thaw on catchment‐scale erosion.