GLACIER AND ICE SHEET WEATHERING FEEDBACKS

Rock weathering influences Earth's climate and can increase or decrease atmospheric CO₂ depending on the dominance of sulfide oxidation paired with carbonate weathering (source) and silicate weathering by carbonic acid (sink). Glaciers and ice sheets influence Earth's energy balance and respond to changes in atmospheric CO₂. Additionally, research demonstrating that glaciers enhance sulfide oxidation and carbonate weathering suggest that they may serve as a self-limiting feedback preventing runaway glaciation under oxygenated atmospheric conditions (ca. 2.4 Ga onwards). We investigate the mechanics of this feedback by estimating weathering related CO₂ fluxes at the last glacial maxima (LGM 20 kya) and performing a sensitivity analysis under varying weathering regimes and runoff conditions with steady state, ice gain, and ice loss scenarios. We utilize an inverse geochemical mixing model and a compilation of alpine glacier, Greenland, and Antarctica stream chemistry to determine the dominant weathering reactions associated with glaciers and ice sheets. Combining the outputs of the mixing model with the hydrologic analysis yields a range of possible CO₂ fluxes from weathering reactions under LGM ice extents. We find that glacier and ice sheets promote different weathering reactions. As a result, assuming alpine-glacier-style weathering supports atmospheric CO₂ increases whereas assuming Greenland- or Antarctica-style weathering enables atmospheric CO₂ drawdown from LGM to present. Additionally, the melting of ice sheet and glaciers provides additional runoff that magnifies weathering-related pCO₂ changes. This research demonstrates that weathering under ice sheets and glaciers may serve as a feedback regulating Earth's climate, and that the proportion of ice sheets and alpine glaciers over geologic time can be an important lever of the direction of the feedback.