ALBERT

Description: Retrogressive thaw slump are among the most important carbon emitters along the Arctic coastline. Significant increases in their activity in the last 50 years has been demonstrated at multiple locations including Herschel Island. While distribution, size of retrogressive thaw slump and their respective change over time are assessed in a number of projects and publications at the moment, mechanics, spatial and temporal dynamics of retrogressive thaw slumps are still poorly understood. We have performed direct current (2D/3D) and capacitively coupled (2D) resistivity tomography, refraction seismics (2D) and ground penetrating radar (2D). Longitudinal, transverse and 3D measurements were systematically arranged on a series of mega (several hundred meters length) retrogressive thaw slumps. Using the ergodic principle, we compared thaw slumps in an initial, accelerating, climax and decelerating stage and compared them with sites with proven historical activity at 300 years B.P. and with undisturbed sites. We can rely on multiple validation measurements including exposed ice wedge profiling, chemical composition of ice, permafrost augering, ice wedge and tundra C14 dating and a 50 year sequence of air photography. The tomographies display remarkable spatial and temporal thaw slump dynamics in all development stages. Already in the initial stage, the tomographies show a large impact of the shoreline an associated warming at the toe of the slumps often extending several tens of meters inland. This could initiate a destabilisation dynamic starting from the toe rather than headwall of a slump, which contrasts previous hypothesis. In the climax stage, bimodal flows act to transport massive amounts of sediments to the shoreline. We can show that both, the accumulation of deep mud pools and the incision of the gully network has a decadal impact on permafrost distribution and mechanics of the thaw slumps. After the climax stage, deep reaching thermal patterns conditioned by bimodal flows and shoreline activity act to persist over hundreds of years and can be clearly distinct from undisturbed tundra slopes. The results are evaluated using the field evidence of ice wedge profiling, chemical ice data, permafrost augering, dating and air photography. Here we show how the 20-30 m deep reaching geophysical data and associated field surveys, profiles and laboratory data can help to create a better understanding of the temporal and spatial patterns of mega retrogressive thaw slumps and their response to atmospheric and marine forcing.

Description: Retrogressive thaw slumps (RTS) are spectacular lateral thermokarst features occurring in ice-rich permafrost regions. They develop along streams or coastlines and expand inland to form landslide-like U-shaped scars exceeding a kilometer size in selected locations. These slumps are a major source of sediment, organic carbon and nutrients that have a large effect on the aquatic environment. The consequences of the occurrence of RTS, which have been shown to occur at increased frequencies in the Arctic are not well understood, mostly because they have only been studied over the past ten years. The impact of RTS sediment delivery on coastal ecosystems is even less known, even though RTS contribute quantities of sediment sometimes greater than coastal erosion itself. In this study, we present the results of a systemic multidisciplinary study attempting to understand the structure, the evolution and the fate of RTS on Herschel Island, Yukon Territory, in the southern Canadian Beaufort Sea. Herschel Island for the exceptionally ice-rich nature of the permafrost and the occurrence of multiple RTS. We use information stemming from cryostratigraphic sampling in the ice headwall of the RTS, from cores collected above the headwall and in the slump floor, from sediment and water samples collected in the slump outflow, from timelapse photography, from outflow channel discharge measurements and from geophysics (mostly Direct Current and Capacitive Coupled Resistivity) to describe the structure of the slump. We emphasize the role of ground ice distribution, sea water vicinity and sensible and radiative heat input in dictating the pace at which slump initiate, stabilize and re-activate. We compare this information to past knowledge on slumps to emphasize the transient nature of slump occurrence in the arctic coastal zone and the existence of “pulses” of slump activity with potentially important impacts on the nearshore ecosystem.

Description: Retrogressive thaw slumps (RTS) are spectacular lateral thermokarst features occurring in ice-rich permafrost regions. They develop along streams or coastlines and expand inland to form landslide-like U-shaped scars exceeding a kilometer size in selected locations. These slumps are a major source of ediment, organic carbon and nutrients that have a large effect on the aquatic environment. The consequences of the occurrence of RTS, which have been shown to occur at increased frequencies in the Arctic are not well understood. The impact of RTS sediment delivery on coastal ecosystems is even less known, even though RTS contribute quantities of sediment sometimes greater than coastal erosion itself. In this study, we present the results of a systemic multidisciplinary study attempting to understand the structure, the evolution and the fate of RTS on Herschel Island, Yukon Territory, in the southern Canadian Beaufort Sea and to relate it to slump occurrence. We use information stemming from cryostratigraphic sampling in the ice headwall of the RTS, from cores collected above the headwall and in the slump floor and from geophysics (mostly Direct Current and Capacitive Coupled Resistivity) to describe the structure of the slump. We emphasize the role of ground ice distribution, sea water vicinity and sensible and radiative heat input in dictating the pace at which slump initiate, stabilize and re-activate. We compare this information to past knowledge on slumps to highlight the transient nature of slump occurrence in the arctic coastal zone and the existence of “pulses” of slump activity with potentially important impacts on the nearshore ecosystem.