Abstract Rock weathering influences Earth’s atmosphere and climate. The dissolution of silicate minerals draws down atmospheric CO2 while sulfide oxidation coupled with carbonate dissolution releases CO2. Alpine glacier rock weathering causes high sulfide oxidation and carbonate dissolution. This influence on weathering suggests a potential negative climate feedback where ice growth leads to CO2 release, warming, and limitations on ice extent. However, the role continental ice sheets play in this feedback remains unclear. Here, we investigate global measurements of proglacial meltwater and find that ice sheets favor silicate weathering over sulfide oxidation and carbonate dissolution. This contrast in weathering mode from alpine glaciers and ice sheets means that the proportion of discharge coming from each determines their net effect on the carbon cycle, which has likely varied across Pleistocene glacial interglacial timescales. Additionally, we find that the influence of glacial weathering reactions is greatest during periods of increased ice loss.