Spatiotemporal patterns in CO₂ fluxes and geochemical weathering in mountain glacial rivers

Abstract. Despite low temperatures that slow chemical reactions, geochemical weathering can be pronounced in glacial rivers due to large quantities of fresh comminuted sediments (glacial flour). We assessed the types and magnitude of geochemical weathering across multiple seasons and years in three proglacial rivers (Sunwapta-Athabasca, North Saskatchewan, and Bow) on the eastern slopes of the Canadian Rocky Mountains, as they meandered from their alpine glacial origins to the montane altitudinal life zone up to 100 kms downstream. To overcome the inherent ecological complexity of our study region, multiple lines of evidence were used to quantify geochemical weathering along river transects and across seasons. Carbon dioxide (CO₂) was highly undersaturated and instantaneous CO₂ fluxes mostly net consumptive at sampling sites nearest source glaciers. Basic geochemical parameters and a large suite of isotopes (⁸⁷Sr/⁸⁶Sr, δ³⁴S-SO₄, δ¹⁸O-SO₄, δ¹³C-PIC, δ¹³C-DIC, and Δ¹⁴C-DIC) were used to dissect general trends in weathering geochemistry. These trends were supported by an inversion model and an inorganic-organic carbon mass balance model, which together found that while carbonate weathering dominated at all sampling sites and times, silicate weathering and organic carbon contributions to the dissolved inorganic carbon pool increased with distance downriver of glaciers regardless of season. Globally, we suspect these spatiotemporal patterns in the type and magnitude of geochemical weathering are common across glacierized watersheds. Therefore, as glaciers continue to retreat, we can expect to see an encroachment of downriver altitudinal life zones concurrent with glacier mass loss and an evolution of in-river geochemical weathering processes, with direct implications for present-day regional and global carbon budgets.