Glaciological processes under ice sheets provide sustainable ecosystems for microbes, forming an aquatic environment through basal melting, and providing nutrients and energy from bedrock. Microbes facilitate solute production in most Earth surface environments, but the balance of biotic and abiotic weathering in subglacial environment is presently unknown. This study demonstrates an up to eightfold increase in dissolved major cations in biotic relative to abiotic weathering experiments using glacial sediments and meltwater. This conclusion greatly expands our view of Earth’s biogeochemically active weathering zone by incorporating the large wet-based portions of glaciated continents, both at present and during Earth’s history. The profound environmental significance is that microbial processes have the ability to maintain terrestrial chemical weathering rates in cooling climates during glacial advance.