Recent changes in the flow of the Ross Ice Shelf, West Antarctica

- Patterns of velocity and thickness change on the Ross Ice Shelf are investigated.
- Ice-mechanical causes of velocity and thickness transients are investigated.
- Transients reflect hundreds of years of changing boundary conditions.
- A recent change in basal traction on the Whillans Ice Stream ice plain is inferred.

Comparison of surface velocities measured during the Ross Ice Shelf Geophysical and Glaciological Survey (RIGGS, 1973 to 1978) and velocities measured via feature tracking between two Moderate-resolution Imaging Spectroradiometer (MODIS) mosaics (compiled from 2003/4 and 2008/9 images) reveals widespread slowing and minor areas of acceleration in the Ross Ice Shelf (RIS) over the approximately 30 year interval. The largest changes (−13 ma−2) occur near the Whillans and Mercer Ice Streams grounding line in the southernmost part of the ice shelf. Speed has increased over the interval (up to 5 ma−2) between the MacAyeal Ice Stream grounding line and the shelf front, and along the eastern shelf front. Changes in ice thickness computed using ICESat laser altimetry are used together with a well-tested model of the ice shelf to investigate underlying causes of change in the flow of the ice shelf over time. The observed transients represent a combination of recent forcings and ongoing response to ice stream discharge variations over the past millennium. While evidence of older events may be present, the modern signal is dominated by shorter time scale events, including the stagnation of Kamb Ice Stream about 160 years ago, recent changes in basal drag on the Whillans Ice Stream ice plain and, perhaps, iceberg calving. Details in embayment geometry, for example the shallow sea floor below Crary Ice Rise, modulate the spatial pattern of ice shelf response to boundary condition perturbations.