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Abstract Frontal ablation processes at marine‐terminating glaciers are challenging to observe and difficult to represent in numerical ice flow models, yet play critical roles in modulating ice sheet mass balance. Current ice sheet models typically rely on simple iceberg calving models to prescribe either terminus positions or iceberg calving rates, but the relative accuracies and uncertainties of these calving models remain largely unconstrained at the ice sheet scale. Here, we evaluate six published iceberg calving models against spatially and temporally diverse observations from 50 marine‐terminating outlet glaciers in Greenland. We seek the single model that best reproduces observed conditions across all glaciers, at all observation times, and with low sensitivity to calibration uncertainty. Five of six calving models can produce unbiased estimates of calving position or calving rate at the ice sheet scale. However, time series analysis reveals that, when using a single, optimized model parameter, rate‐predicting calving models frequently yield calving rate errors in excess of 10 m d⁻¹. In comparison, terminus position‐predicting calving models more accurately track observed changes in terminus position (remaining within ~1 km of the observed grounded terminus position). Overall, our results indicate that the crevasse depth calving model provides the best balance of high accuracy and low sensitivity to imperfect parameter calibration. While the crevasse depth model appears unlikely to capture the true controls on crevasse penetration, numerically, it reproduces observed terminus dynamics with high fidelity and should be considered a leading candidate for use in models of the Greenland Ice Sheet. 

Abstract. Crevasses are affected by and affect both the stresses and the surfacemass balance of glaciers. These effects are brought on through potentiallyimportant controls on meltwater routing, glacier viscosity, and icebergcalving, yet there are few direct observations of crevasse sizes andlocations to inform our understanding of these interactions. Here we extractdepth estimates for the visible portion of crevasses from high-resolutionsurface elevation observations for 52 644 crevasses from 19 Greenlandglaciers. We then compare our observed depths with those calculated usingtwo popular models that assume crevasse depths are functions of localstresses: the Nye and linear elastic fracture mechanics (LEFM) formulations.When informed by the observed crevasse depths, the LEFM formulation produceskilometer-scale variations in crevasse depth, in decent agreement withobservations. However, neither formulation accurately captures smaller-scalevariations in the observed crevasse depths. Critically, we find thatalong-flow patterns in crevasse depths are unrelated to along-flow patternsin strain rates (and therefore stresses). Cumulative strain rate ismoderately more predictive of crevasse depths at the majority of glaciers.Our reliance on lidar limits the inference we can make regarding fracture depths. However, given the discordant patterns in observed and modeled crevasses, we recommend additional in situ and remote sensing analyses before Nye and LEFM models are considered predictive. Such analyses should span extensional and compressive regions to better understand the influence of advection on crevasse geometry. Ultimately, such additional study will enable more reliable projection of terminus position change and supraglacial meltwater routing that relies on accurate modeling of crevasse occurrence.