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Permafrost thaw slumping in lakes in the Mackenzie Delta region

Permafrost thaw slumping in lakes in the Mackenzie Delta region

by Charlie West

Charlie West sampling lakes in Yellowknife, Northwest Territories

The Mackenzie Delta region is the largest Arctic delta in North America and the second-largest in the circumpolar North. Located in the northern Northwest Territories, the Mackenzie Delta region is part of the traditional territories of the Gwich’in and Inuvialuit peoples. The region is almost entirely underlain with ice-rich permafrost, meaning the effects of thawing permafrost can have significant impacts on the landscape because of instability caused by melting ground ice. One such impact is the formation of retrogressive thaw slumps, a thermoerosional feature.

Thaw slumps form on the sloping shorelines of lakes. They occur when warming and wave action destabilizes the ice-rich permafrost soils of a slope and triggers the sediments to move downslope. Sediment debris from the thaw slump is then deposited into the adjacent lake waters. The large input of sediments from thaw slumps causes changes to the water quality of the lake, including increases in pH, conductivity, and the levels of some heavy metals, as well as decreases in nutrient levels and dissolved organic carbon.

Thaw slump. Photo credit: Josh Thienpont

In lieu of long-term monitoring, which is sparse for most Arctic regions, paleolimnological techniques can be used to ascertain the ecological changes that occur as a result of thaw slump disturbances and to track the long-term ecological trajectory of lakes in this rapidly warming region. Paleolimnology is the study of the past conditions of lakes and rivers through the analysis of deposited sediments. Through time, sediments are deposited on the bottom of water bodies, preserving the different physical, chemical, and biological conditions that existed in the system at the time of sediment deposition. This creates an environmental archive where the deeper you go in the sediment core, the further back in time you go.

For my research, I am measuring algal pigments preserved in sediment cores from three lakes in the Mackenzie Delta region that span a gradient of thaw slump disturbance. This includes a lake with a long history of polycyclic cycles of thaw slumping, stabilization, and slump reinitiation, a lake with a recent slump history starting in ~1990, and a reference lake with no history of thaw slumping. Algal pigments will tell me how the phytoplankton community has changed over time because different phytoplankton groups produce unique pigment signatures. Phytoplankton forms the base of the lake food web and is important for lake ecosystem health.