Thawing of high-latitude permafrost is modifying the delivery of acids and oxidants to subsurface chemical weathering reactors. While enhanced weathering of carbonate and silicate minerals removes atmospheric carbon dioxide, mitigating the effects of modern climate change, oxidation of sulfide minerals fuels further landscape degradation. This work employs historical data and an inversion model to quantify solute sources to the Yukon River and Mackenzie River and finds that, despite changes in dissolved chemistry, the impact of chemical weathering in these large catchments on atmospheric carbon dioxide has been invariant over the last 40 years.