CENTENNIAL TRENDS OF CARBON SOURCES AND SINKS IN PERIALPINE LAKES REVEALED BY SEDIMENT ARCHIVES AND PROCESS-BASED MODELING

Lakes play a dual role in the global carbon cycle, acting both as emitters of GHG and as long-term sedimentary carbon sinks. Yet these two fluxes are rarely assessed together over centennial scales, largely due to the scarcity of monitoring data. Here we combine sediment archives with process-based models to reconstruct carbon flux trajectories since 1850 CE in four large perialpine lakes that underwent eutrophication followed by reoligotrophication.Using high-resolution paleolimnological approaches, we show that organic carbon burial has more than doubled since the late 19th century, with no sign of decline despite major reductions in nutrient inputs. This persistent increase is attributed to both the maintenance of relatively high lake primary productivity and a shift toward the decline of deep-water oxygen conditions that increased: respiration rates are now up to four times higher than in pre-eutrophication conditions, reinforcing hypoxia and enhancing carbon preservation.To assess emissions, we calibrated a 1D thermal (GLM) model using multi-decadal monitoring data from the OLA observatory (RMSE < 1.5 °C). Simulations show altered mixing and water-column warming, enabling the reconstruction of past GHG fluxes. These model-based estimates are curently validated through monthly field campaigns in 2025 and 2026.Together, these results suggest that reoligotrophicated perialpine lakes may act as increasingly efficient long-term carbon sinks, raising the question of whether cumulative burial can partially or fully offset GHG emissions over decadal-to-centennial timescales.