INSIGHTS INTO GEOCHEMICAL WEATHERING AND ATMOSPHERIC CO2 DRAWDOWN IN PROGLACIAL RIVERS (BANFF AND JASPER NATIONAL PARKS, CANADA)

A landmark study was recently published showing that carbonate and silicate weathering of comminuted sediments of subglacial origin, that were exposed and washed downstream upon glacial retreat, were responsible for proglacial freshwaters being carbon dioxide (CO₂) sinks in a Canadian High Arctic watershed. Geochemical weathering-driven CO₂ drawdown had been previously identified subglacially, though this was the first study to demonstrate its presence in the headwaters of proglacial rivers. However, this study was seasonal, isolated to a High Arctic region, and focused on a few lake-terminating glacial rivers, which restricted how far downstream the researchers could study this phenomenon.

To address these limitations, we investigated the prevalence of geochemical weathering-driven CO₂ drawdown in the Canadian Rockies in Banff and Jasper National Parks. Here, we conducted year-round detailed water quality surveys in the proglacial headwaters of three large glacier-fed watersheds (Athabasca, North Saskatchewan, and Bow). As expected, geochemical weathering-driven CO₂ drawdown was most pronounced closest to a glacier, but there was evidence of geochemical weathering up to 100 kilometers downstream of glacier termini. Weathering rates were highest in the summer when glacial melt peaked, confirming the source of the comminuted sediments driving geochemical weathering reactions were of glacial origin. Weathering cations (Ca, Mg, Na, K), and particulate and dissolved inorganic carbon concentrations and stable isotope data confirmed the presence of weathering in these watersheds, while small dissolved organic carbon concentrations and other bioindicator parameters indicated biological contributions to CO₂ drawdown/production were minimal. Taken together, our data suggest that proglacial rivers in this mid-latitude alpine region have a similar capacity for CO₂ drawdown as those in the High Arctic, despite originating from glaciers with different thermal regimes and underlying geologies. This study thus demonstrates the importance of continued research in the conjunct fields of biogeochemistry, glaciology, and limnology, as geochemical weathering reactions in glacial meltwaters could have important implications for carbon cycling in glacierized regions.