Canada’s Carbon Emission Conundrum

Weathering rates of rocks in the Canadian Arctic are increasing over time due to rising temperatures, resulting in a feedback loop whereby increasing amounts of carbon dioxide are released into the atmosphere, according to researchers from the University of Oxford’s Department of Earth Sciences.

The team investigated the temperature sensitivity of sulfide oxidation in the permafrost zones of the Mackenzie River Basin in Northern Canada over a period of 60 years (1960–2020). They found that sulfate (SO₄^2-) concentrations in the Mackenzie River Basin increased by 45 percent, suggesting a corresponding rise in sulfide oxidation.

“These fools gold (sulfide) minerals are particularly important, because they can make acid, which dissolves other stable carbon stores in rocks, releasing the carbon as the greenhouse gas carbon dioxide,” say co-authors Ella Walsh and Robert Hilton. “Altogether, we find that over the last few decades, these reactions and the carbon release have increased dramatically.”

The largest fluxes observed were in catchments with high bare rock cover and physical weathering processes, such as frost cracking and thermokarst, which expose sulfide-rich minerals to oxidation. These processes contribute to a faster rate of CO₂ release as reactive mineral surfaces are exposed by thawing permafrost.

To analyze these processes, the team used a combination of ion chromatography, flux modeling, and geospatial analysis. The results were formed using the “Weighted Regressions on Time, Discharge, and Season” (WRTDS) model to estimate SO₄^2- fluxes across 23 catchment sites. They also used gridded climate data from the ERA5 reanalysis to assess temperature changes and future projections under various emissions scenarios from the CMIP6 climate models.

“The larger geospatial analysis was interesting – this involved processing and organizing datasets of river geochemistry, in space and time, which is always a complex task,” say Walsh and Hilton. “Thinking then how to link with climate data was also a challenge – questions about data products, their resolution and uncertainty. But we solved this through trial and error – and perseverance.”

The researchers’ findings highlight concerns for the future of the Canadian Arctic if action isn’t taken to address permafrost thaws caused by rising global temperatures. Surface air temperatures are currently increasing up to four times greater than the global average in the Arctic. And, according to their estimations, the authors suggest that the estimated CO₂ release from sulfide oxidation “could double by 2,100 across the Mackenzie River basin.” 

“While the fluxes are much lower than other carbon feedbacks (like from warming soils), which is some good news, they are large enough that regional carbon budgets are being impacted,” say Walsh and Hilton. “Over hundreds of years, these processes will mean a longer recovery from global warming than we might have previously expected.” The researchers believe more research is needed here to establish these trends using carbon cycle and climate models. 

When asked about plans for further research in this area, Walsh and Hilton shared details of their new project funded by the UK Natural Environment. “It is looking more at the exact mechanisms which are happening, so we can better predict and understand the changes occurring with rock weathering,” they say. “We are also taking a global view across other landscapes undergoing rapid change – for example in high mountain areas outside the Arctic.”