Multiple thermo-erosional episodes during the past six millennia: Implications for the response of Arctic permafrost to climate change

Anthropogenic warming may promote rapid permafrost thaw in the Arctic and alter the global carbon cycle. Although several studies suggest increased thermo-erosion as a result of recent warming, a long-term context is necessary to assess the linkages of thermokarst processes with climate variability. We analyzed sediment cores from two lakes on the Alaskan North Slope (USA), one with (Lake NE14) and one without (Perch Lake) watershed thermo-erosion. Distinct geochemical and lithological characteristics provide evidence for sedimentary input from carbonate-rich permafrost soils associated with past retrogressive thaw slumping at Lake NE14 but not at Perch Lake. These characteristics include increases in Ca:Sr, Ca:K, carbonate:[feldspar + clay minerals], percent CaCO3, and delta C-13, and decreases in Sr-87:Sr-86. At least ten episodes of thermo-erosion occurred over the past 6000 yr at Lake NE14. Most of these episodes coincided with periods of elevated summer temperatures, but moisture variation and geomorphic factors likely played a role in driving their occurrence. Our results suggest that positive feedbacks facilitate reactivation of thermo-erosion in ice-rich terrain, adding to the growing body of evidence that these Arctic landscapes are unstable in a changing climate.