Near-total loss of buttressing stresses observed on Pine Island Ice Shelf, West Antarctica.

Ice shelves, the floating extensions of the Antarctic Ice Sheet, provide critical buttressing stresses that resist the seaward flow of ice and help set the position of the grounding line, where the ice goes afloat. As buttressing stresses are diminished by thinning or fracturing and collapse of the ice shelf, glaciers tend to accelerate. Here, we focus on the response of Pine Island Ice Shelf (PIIS) in West Antarctica to multiple calving events and the disintegration of the lateral shear margins. Using observed time-series of the surface velocity fields between 2015 and 2024, we show multiple episodes of acceleration in ice flow and a marked reduction in the buttressing stresses. These observations show that PIIS experienced a significant reduction of its buttressing capacity during the observational record. We then investigate how a model glacier responds to loss in margin buttressing, and are able to broadly reproduce observations. By linking model simulations to observations, we recreate a timeline of buttressing loss on PIIS. These losses likely foreshadow a period of grounding line retreat and acceleration of Pine Island Glacier's contribution to global mean sea level rise.