Yi Hou , Jotis Baronas, Preston Cosslett Kemeny, Julien Bouchez, Áslaug Geirsdóttir, Gifford Miller, Mark Albert Torres 

How glaciation affects CO2 drawdown by chemical weathering sets the strength of the weathering-climate feedback, which controls the exogenic carbon cycle and planetary habitability (Kump et al., 2000). However, the exact role of glaciers remains elusive as glaciation alters multiple factors controlling weathering, the net effect of which is ambiguous even in directionality. While illustrative, modern observations have limited ability to constrain time-dependent behavior, which is thought to be important to glacial weathering (Vance et al., 2009; Kemeny et al., 2021). To isolate and quantify the effect of glaciers over millennial timescales, we developed a novel multi-proxy system for constraining catchment-scale fluxes in the past. This approach utilizes the correlation between Ge/Si and Si isotope ratios in modern rivers, which sensitively tracks weathering processes, and the preservation of these signals in biogenic silica in lake sediments. We report changes in weathering fluxes in two catchments with different glacial histories during the past ten thousand years from two lacustrine records in Iceland. We find that the chemical weathering fluxes are an order of magnitude higher in the same catchment when glaciated compared to when ice free. The synchronous variations in weathering fluxes with the expansion and contraction of glaciers indicate a rapid effect of glaciation that may amplify climatic variations via a positive feedback.