Ocean Coupling Limits Rupture Velocity of Fastest Observed Ice Shelf Rift Propagation Event

The Antarctic ice sheet is buttressed by floating ice shelves that calve icebergs along large fractures called rifts. Despite the significant influence exerted by rifting on ice shelf geometry and buttressing, the scarcity of in situ observations of rift propagation contributes considerable uncertainty to understanding rift dynamics. Here, we report the first-ever seismic recording of a multiple-kilometer rift propagation event. Remote sensing and seismic recordings reveal that a rift in the Pine Island Glacier Ice Shelf extended 10.53 km at a speed of 35.1 m/s, the fastest known ice fracture at this scale. We simulate ocean-coupled rift propagation and find that the dynamics of water flow within the rift limit the propagation rate, resulting in rupture two orders of magnitude slower than typically predicted for brittle fracture. Using seismic recordings of the elastic waves generated during rift propagation, we estimate that ocean water flows into the rift at a rate of at least 2,300 m(3)/s during rift propagation and causes mixing in the subshelf cavity. Our observations support the hypotheses that large ice shelf rift propagation events are brittle, hydrodynamically limited, and exhibit sensitive coupling with the surrounding ocean. Plain Language Summary The flow rate of glaciers in Antarctica is regulated by floating bodies of ice called ice shelves. Ice shelves contain huge cracks called rifts that extend for many kilometers. On many ice shelves, these rifts grow until they disconnect a large iceberg from the rest of the ice shelf. In this study, we use satellite data and seismic recordings to observe over 10 km of rift growth at Pine Island Glacier, an important glacier in West Antarctica. The rift growth event we report is the fastest instance of rift growth ever observed. Using a computer simulation, we model the rift growth process. We find that the ice shelf interacts with the ocean as it cracks, and this interaction determines how quickly rifts can grow. Our observations and simulation also suggest that rift growth causes mixing in the ocean underneath the floating ice shelf.