| Summary: | Ongoing, centennial-scale flow variability within the Ross ice streams of West Antarctica suggests that the present-day positive mass balance in this region may reverse in the future. Here, we use a three-dimensional ice-sheet model to simulate ice flow in this region over 250 years. The flow responds to changing basal properties, as a subglacial till layer interacts with water transported in an active subglacial hydrological system. We show that a persistent weak bed beneath the tributaries of the dormant Kamb Ice Stream is a source of internal ice-flow instability, which reorganizes all ice streams in this region, leading to a reduced (positive) mass balance within decades and a net loss of ice within two centuries. This hitherto unaccounted for flow variability could raise sea-level by 5mm this century. Better constraints on future sea-level change from this region will require improved estimates of geothermal heat flux and subglacial water transport. This work was carried out with support from the Isaac Newton trust, Cecil H. and Ida M. Green Foundation and Natural Environment Research Council (grants NE/E005950/1 and NE/J005800/1). SFP was supported by the U.S. Department of Energy Office of Science, Biological and Environmental Research program. ST acknowledges support from National Science Foundation (grant #0338295). SPC was supported by funding from the Cryospheric Sciences program of NASA and HAF was supported by funding from NSF (grant ANT-0838885 (Fricker)). The source code for the results presented can be obtained by contacting the corresponding author directly This is the final version of the article. It first appeared from Wiley via http://dx.doi.org/10.1002/2015GL065782
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