Rapid carbonation of silicate minerals drives atmospheric CO2 drawdown in glacier-fed stream waters

Glacierized landscapes produce abundant fine-grained reactive minerals that play a pivotal role in high-altitude inorganic carbon cycling, mainly through geochemical weathering. However, our understanding of the relationship between glacially comminuted mineral dissolution, precipitation of secondary phases and inorganic carbon cycling in the world’s glacier-fed streams (GFSs) remains elusive. Here, we investigate first-order relationships between suspended sediment mineralogy, streamwater solute chemistry and CO ₂ saturation across 170 GFSs draining Earth’s most prominent mountain ranges and the periphery of the Greenland Ice Sheet. The sampled GFSs span the major global climate belts, including cool-continental (50%), polar-alpine (20%), temperate-subtropical (20%), and tropical (10%) environments, and drain catchments dominated by felsic lithologies (69%) including minor shield crystalline terrains, mafic rocks (19%), and carbonous, including mixed carbonate-felsic systems (13%). We find that the majority (74%) of the studied GFSs are undersaturated in CO ₂ relative to atmospheric equilibrium. Our analysis, based on streamwater geochemistry, end-member inversion mixing modeling, calcite saturation state, Ca-Mg-Na-Sr systematics, and suspended sediment mineralogy, reveals widespread evidence for carbonate precipitates enriched in Mg, Si, Fe, and other transition metals on sediment grains. This process can explain CO ₂ removal from waters and undersaturation of many GFS, even in settings where sulfide mineral weathering would be expected to result in low pH waters and CO ₂ release. These findings show for the first time how carbonation of silicate minerals in GFSs can result in CO ₂ drawdown, making the transient storage and fate of these poorly understood sedimentary carbonate phases key to understanding the net impacts on carbon cycling over centennial to millennial timescales.