Can multi-glacier moraine analysis constrain paleoclimate reconstructions? Evidence from 3D glacier modeling in the Cordillera Real, Bolivia

Abstract. Glacier moraines are widely used as proxies for past climate, as they are interpreted to reflect near-equilibrium glacier extents. However, a single glacier geometry can arise from multiple temperature–precipitation combinations and their quantification relies on glacier modeling that introduce additional uncertainties. Here, we investigate how this non-uniqueness can be constrained from a 3D full-Stokes ice-flow model (Elmer/Ice), applied to neighboring coeval glaciers in the Zongo–Charquini area of the Bolivian Cordillera Real. Using synthetic experiments, in which Temperature-Precipitation (T-P) anomaly curves are derived from several glacier extents generated under prescribed climate conditions, we show that differences in glacier geometry and hypsometry cannot be used to distinguish between temperature and precipitation conditions. However, we also show that glacier thickness may provide a way to dissociate temperature and precipitation but with a limited sensitivity that would require highly accurate past volume estimates to be useful in practice, which is often not feasible. Using real moraine records, our results show that single-glacier reconstructions are strongly influenced by both, methodological choice (melt model), and site-specific uncertainties, resulting in a range of T-P anomaly curves describing the same climate. In this context, using a multi-glacier framework allows to better assess the temperature-precipitation condition and its associated uncertainties. Using this approach combined with independent tree-ring and hydrological lake-balance precipitation reconstruction in the region, we estimate temperature anomalies of -0.8+-0.3°C for the Little Ice Age and -1.3+-0.4°C for the Early Holocene (∼10 ka BP), relative to a present-day reference climate (1950–2023).