Mineral Weathering and the Permafrost Carbon‐Climate Feedback

Abstract

Permafrost thaw in the Arctic enables the biogeochemical transformation of vast stores of organic carbon into carbon dioxide (CO 2 ). This CO 2 release has significant implications for climate feedbacks, yet the potential counterbalance from CO 2 fixation via chemical weathering of minerals exposed by thawing permafrost is entirely unstudied. We show that thermokarst in the western Canadian Arctic can enable rapid weathering of carbonate tills, driven by sulfuric acid from sulfide oxidation. Unlike carbonic acid-driven weathering, this caused significant and previously undocumented CO 2 production and outgassing in headwater streams. Increasing riverine solute fluxes correspond with long-term intensification of thermokarst and reflect the regional predominance of sulfuric acid-driven carbonate weathering. We conclude that thermokarst-enhanced mineral weathering has potential to profoundly disrupt Arctic freshwater carbon cycling. While thermokarst and sulfuric acid-driven carbonate weathering in the western Canadian Arctic amplify CO 2 release, regional variation in sulfide oxidation will moderate the effects on the permafrost carbon-climate feedback.Plain Language Summary In the Arctic, perennially frozen ground (permafrost) in previously glaciated regions stores abundant minerals and is often ice-rich. Therefore, this permafrost can rapidly thaw and collapse, resulting in thermokarst and exposing minerals to breakdown by chemical weathering. Mineral weathering by carbonic acid fixes CO 2 , making it less likely to enter the atmosphere. However, the effect of thermokarst on mineral weathering, carbon cycling, and rising atmospheric CO 2 levels is unknown. We show thermokarst enhances weathering in streams in the western Canadian Arctic can rapidly produce significant and previously undocumented CO 2 because carbonate weathering in this region is driven by sulfuric acid (from weathering of sulfide minerals) instead of carbonic acid. Long-term river chemistry reveals that this weathering is intensifying as thermokarst accelerates. Across the Arctic, increasing thermokarst will profoundly impact freshwater carbon cycling, yet the influence of weathering on climate feedbacks will depend on regional variation in the mineral composition of permafrost soils. À

Thermokarst Effects on Carbon Dioxide and Methane Fluxes in Streams on the Peel Plateau (NWT, Canada)

“…Common geochemical controls of p CO 2 and p CH 4 were significantly affected by RTS activity. Compared to upstream, RTS runoff and downstream had significantly higher concentrations of DIC, SO 4 2– , and DIN and showed lower values of SUVA 254 and DO (Tables and ; see also Kokelj et al, ; Littlefair et al, ; Zolkos et al, ). DOC concentrations were also significantly lower downstream than upstream (Table ).…”

“…The Peel Plateau is predominantly composed of glacial till, glaciofluvial, and glaciolacustrine deposits (Duk‐Rodkin & Hughes, ; Kokelj, Tunnicliffe, et al, ) emplaced at the western margin of the Laurentide Ice Sheet (LIS). These deposits contain carbonates and sulfides (Zolkos et al, ) that were likely incorporated into the basal ice and diamicton by the LIS during its westward expansion across regional carbonate and shale bedrock (Norris, ; Stott, ). Following retreat of the LIS, rapid climate warming during the early Holocene (12–8.5 kybp) resulted in regional thermokarst, including an increase in thaw depth and an acceleration of thaw slumping (Lacelle et al, ), enabling mineral weathering and the accumulation of solutes and organic matter (Burn, ; Lacelle, ; Malone et al, ).…”

Atmospheric change as a driver of change in the Canadian boreal zone1

“…(e.g., Trudeau et al 2014;Humphreys et al 2014;Pelletier et al 2014;Strachan et al 2016). In permafrost regions, thawing-induced changes in riverine CO 2 emissions depend on the underlying lithology of the terrain (Zolkos et al 2018). Thawenhanced mineral weathering driven by carbonic acid can sequester carbon.…”

Spatiotemporal Variability and Sources of DIC in Permafrost Catchments of the Yangtze River Source Region: Insights From Stable Carbon Isotope and Water Chemistry

“…Permafrost thaw is likely to increase the DIC export in permafrost watersheds (Prokushkin et al, ; Striegl et al, ; Tank, Raymond, et al, ). Permafrost thaw across the Alaskan Arctic has been shown to change stream water chemistry through increased flow paths (Keller et al, ) and enhance H 2 SO 4 ‐driven carbonate weathering (Zolkos et al, ) and bicarbonate export (Striegl et al, ). These different sources and processes are key regulators for δ 13 C‐DIC.…”

“…Carbonate rocks and minerals typically have δ 13 C values around 0‰ (Clark & Fritz, 1997;Marwick et al, 2015). Carbonate weathering by carbonic acid produces δ 13 C-DIC values between the δ 13 C values of carbonate rock and soil CO 2 , while sulfuric acid weathering of carbonate minerals (Zolkos et al, 2018) yields the same δ 13 C-DIC value as the carbonate rock. Biogenic DIC, in contrast, comes from vegetation and soil-respired CO 2 , with a typical δ 13 C value close to −27‰ for C3 plants or −11‰ for C4 plants (Clark and Fritz, 1997;Marwick et al, 2015).…”