The concept of glaciers as active ecosystems is strongly supported by evidence of significant contributions to global carbon and macronutrient cycles by extant glaciers. Regrettably, the roles of glacial ecosystems in past glaciations are generally overlooked. Therefore we reconstructed glacial habitats and carbon fluxes on the last glaciers of north Wales at their maximum extent during the Younger Dryas chronozone glaciation. Net uptake of 30-180 kg C of CO2 and emissions of 265-1591 g C CH4 per annum are estimated for the palaeoglaciers. This emphasises the hitherto unexplored potential for the last Welsh glaciers as actors in biogeochemical cycles; however our understanding could be extended by linking our knowledge of contemporary glacial ecosystems with analyses of sedimentary biomarkers and thermomechanical models of Devensian ice mass dynamics.