Glacially Enhanced Silicate Weathering Revealed by Holocene Lake Records

Abstract

How glaciation affects ${\text{CO}}_2$ drawdown by chemical weathering influences the weathering-climate feedback strength, which controls the exogenic carbon cycle and planetary habitability. However, the role of glaciers remains elusive as glaciation alters multiple factors controlling weathering, the net effect of which is ambiguous even in directionality. To isolate and quantify the effect of glaciers, we developed a novel multi-proxy system for constraining catchment-scale weathering fluxes in the past. This approach utilizes the correlation between Ge/Si and Si isotope ratios in modern rivers and the preservation of these signals in lacustrine sediments. Reconstructed weathering fluxes in two Icelandic catchments with different glacial histories during the past 10,000 years show that chemical weathering fluxes are roughly 10 times higher when a catchment is glaciated versus ice-free. The synchronous variations in weathering fluxes with the expansion and contraction of glaciers indicate that glaciation may rapidly amplify climatic variations via a positive feedback.