Reply on RC2

Abstract

Antarctica’s ice shelves resist the flow of grounded ice towards the ocean through “buttressing” arising from their contact with ice rises, rumples, and lateral margins. Ice shelf thinning and retreat reduces buttressing, leading to increased delivery of mass to the ocean that adds to global sea level. Ice shelf response to large annual cycles in atmospheric and oceanic processes provide opportunities to examine how environmental changes affect dynamics of both ice shelves and the buttressed grounded ice. Here, we explore whether seasonal variability of sea surface height (SSH) can explain observed seasonal variability of ice velocity. We investigate this hypothesis using several time series of ice velocity from Ross Ice Shelf (RIS), satellite-based estimates of SSH seaward of the RIS front, ocean models of SSH under and near RIS, and a viscous ice sheet model. The observed annual changes in RIS velocity are of order 1–10 metres per year (roughly 1 % of mean flow). The ice sheet model, forced by the observed and modelled range of SSH of about 10 cm, reproduces the observed velocity changes when visco-elastic effects near the grounding line are parameterized in our viscous model. The model response is dominated by grounding line migration, but with a significant contribution from SSH-induced tilt of the ice shelf. Improvements in measurements and models of SSH, including under ice shelves, combined with additional long-term GNSS records of ice shelf velocities, will provide further insights into longer term ice shelf and ice sheet response to future changes in sea level.