Large-scale ice-shelf calving events follow prolonged amplifications in flexure

The retreat of Antarctic ice shelves due to calving and the subsequent reduction in buttressing of the Antarctic Ice Sheet are of major concern for future sea-level rise. Sudden, widespread calving of weakened ice shelves has been linked to fracture amplification forced by ocean swell following regional sea-ice losses, but increases in the magnitudes and durations of swell-induced ice-shelf flexure in the lead-ups to calving events have not been tracked. Here we present 7-year datasets of sea-ice-barrier lengths and shelf-front flexural stress that encompass large-scale calving events for the Wilkins and Voyeykov ice shelves. We find that the ice shelves exhibit similar preconditioning patterns, characterized by prolonged amplifications in flexure and the collapse of adjoining fast-ice barriers. We propose a conceptual model for the swell–sea-ice–shelf-front conditions that lead to calving events, show that it fits other major calving events and discuss the likely importance of sea-ice loss for the future of ice shelves. The loss of sea ice enhances swell-induced flexural stress in Antarctic ice shelves before large-scale calving events, according to satellite observations and swell-induced flexural stress modelling.