| Summary: | The conditions under which ice fractures and calves icebergs from Antarctic ice shelves are poorly understood due largely to a lack of relevant observations. Though previous studies have estimated the stresses at which ice fractures in the laboratory and through sparse observations, there remains significant uncertainty in the applicability of these results to naturally deforming glacier ice on larger scales. Here, we aim to better constrain the stresses under which ice fractures using remote sensing data by identifying large-scale fractures on Antarctic ice shelves, calculating the principal stresses from the observed strain rates, and comparing the stresses of unfractured and fractured areas. Using the inferred stresses, we evaluate five common fracture criteria: Mohr-Coulomb, von Mises, strain energy, Drucker-Prager, and Hayhurst. We find the tensile strength of ice ranges from 202 to 263 kPa assuming the viscous stress exponent n=3, narrowing the range produced by previous observational studies. For n=4, we find tensile strengths of 423-565 kPa, bringing our inferences closer to alignment with laboratory experiments. Importantly, we show that crevassed and uncrevassed areas in the four largest ice shelves are distinct in principal stress space, suggesting our results apply to all ice shelves and the broader ice sheet.
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