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Abstract

The Shallow Ice Approximation (SIA) is commonly introduced in ice-sheet models to simplify the equations describing ice dynamics. However, the SIA is not applicable in fast flowing regions where basal sliding operates. To overcome this limitation, recent studies have introduced heuristic, hybrid combinations of the SIA and the Shelfy Stream Approximation. Here, we implement four different hybrid schemes into a model of the Antarctic Ice Sheet in order to compare their performance under a realistic scenario. For each scheme, the model is calibrated using an iterative technique to infer the spatial variability in basal sliding parameters. Model results are validated against topographic and velocity data. Our analysis shows that the calibration compensates for the differences between the schemes, producing similar ice sheet configurations through quantitatively different parameter distributions. Despite this, we observe a robust agreement in the reconstructed patterns of hard vs. soft basal conditions. We use averaged and swapped parameter distributions to demonstrate that the results of the model calibration cannot be straightforwardly transferred to models based on different approximations of ice dynamics. However, this requirement for internal consistency can be fulfilled through the implementation of easily adaptable calibration techniques, as shown in this study.