Ocean-Driven Seasonal Velocity Variability of Ross Ice Shelf, Antarctica

Ice shelves play a critical role in the dynamic mass loss from the grounded portion of the Antarctic Ice Sheet, regulating the ice sheet's contribution to sea level rise. In this study, we focus on potential for changes in buttressing of Antarctica's largest ice shelf, the Ross Ice Shelf, with a total area of about 480,000 km². In November 2015, we installed an array of 13 high-rate GNSS stations, which operated until November 2016. Overall, we found good agreement between the GPS time-averaged velocities and the MEaSUREs satellite- based Antarctic ice velocity field. The largest discrepancies were at the ice front, which we attribute toa combination of extrapolation from the actual GPS positions to the nearest MEaSUREs locationand, potentially, widening of the rift near the Nascent Iceberg . After removing the long-term trends at each GPS site, the intra-annual transient motion at all stations is spatially coherent, and the flow-parallel velocity anomaly has a seasonal pattern: upstream during the austral summer and downstream during the austral winter. The amplitude of this transient motion varies along flow, ranging from almost 5 m/yr near the front to 0.3 m/yr at the southernmost site (about 430 km from the ice front). We hypothesize that the measured seasonal variability of ice shelf velocities is related to seasonal variability in ice shelf mass loss by ocean-driven basal melting. To explore this hypothesis, we used time-varying ice shelf melt rates along the shelf front (output from the Regional Ocean Modeling System) to force a shallow shelf model of Ross Ice Shelf and its basin catchments. Our simulation recreates the seasonal flow velocity variability in the GPS observations, suggesting that future increases in summer upper-ocean heating near the ice front could accelerate thinning and associated flow of the Ross Ice Shelf and its tributary glaciers.