Long-Term Impacts of Boreal Wildfire on Carbon Cycling Dynamics In Interior Alaska
Media Type: Video
Distribution Contact(s):
  • Alaska Fire Science Consortium
Date: December 4, 2013

Cataloging Information

  • AFSC - Alaska Fire Science Consortium
  • boreal fire
  • carbon cycling
  • carbon release
  • climate change
  • organic carbon
  • paleolimnology
  • permafrost
  • sediment chronology
  • thermokarst
Record Maintained By:
Record Last Modified: August 6, 2019
FRAMES Record Number: 16460


Wildland fire is a major disturbance in the boreal forest, and warming climate will likely increase the frequency and severity of burning. Fires trigger thermokarst, the thawing of permafrost (perennially frozen ground), which can release large amounts of ancient carbon to the atmosphere. But how vulnerable is the organic carbon stored in permafrost in the boreal forest to a changing fire regime? Paleolimnological records can tell us how the landscape actually responded during prehistoric fires and provide a valuable perspective on future events. Here we present a whole-watershed summary of terrestrial and aquatic carbon dynamics during multiple fire and thermokarst disturbances over the last millennia. We use laminated lake sediments laid down in an anoxic, thermokarst lake basin in Interior Alaska (Ace Lake) to decipher the impacts of wildfires on permafrost carbon release from the surrounding watershed. Sediment chronologies based on layer counts, lead and cesium dating, and radiocarbon dating of plant macrofossils, provide decadal resolution of environmental changes over the last 100 years. Charcoal accumulation rates quantified from sediment thin-sections and fire-scarred spruce trees constrain the timing of fires. The variability of permafrost carbon release before and after fires was investigated by analyzing several geochemical indices including radiocarbon dating on the sediment organic matter directly above and below charcoal layers in the sediment stack. Carbon isotopes of sediment organic matter provide a time-series of permafrost C released from watershed soils through the respiration of organic matter, which gets taken up by algae that are then deposited as sediment. The difference between a sediment layer's "true" age of deposition based on layer counts and the apparent radiocarbon age on the same bulk sediment material (radiocarbon age offset) is then used as a prozy for the relative age of this permafrost carbon release. Fires are not the only triggers of permafrost-C release. Thermokarst caused by shoreline erosion triggered by some combination of fires, beaver dams that raise the lake levels, and chance events complicate the larger watershed signal of C release.

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