Abstract
AbstractAs part of the Ross Ice Shelf Geophysical and Glaciological Survey (RIGGS), ice velocities were measured on the Ross Ice Shelf (RIS) during 1973–78. Comparisons of these with velocity estimates at the same locations derived from RADARSAT synthetic aperture radar (SAR) measurements in 1997 and 2009 show velocity reduction in the southeast quadrant of the ice shelf by almost 200 m a−1, with deceleration rates increasing with time. Large areas of ice shelf in this region are lightly grounded, forming an ‘ice plain’ that increases local buttressing of the ice streams. ICESat measurements show this ice plain to be thickening. The observed decrease in ice-shelf velocities implies a total reduction in the mass of ice flowing into the RIS from the West Antarctic ice sheet (WAIS) by ∼23 Gt a−1, shifting the mass balance of the WAIS drainage basin from strongly negative in the 1970s to strongly positive in 2009. The resulting decrease in ice advection should lead to ice-shelf thinning further seaward of the ice plain. This thinning would reduce the lateral drag and back-stress of the shelf ice, further contributing to thinning through an increase in spreading rate. ICESat measurements show recent thinning of most of the freely floating ice shelf.
Highlights
The Ross Ice Shelf (RIS) is fed by large glaciers and ice streams flowing from both East and West Antarctica, by snow falling on its surface and, to a lesser extent, by basal freezing
Our analysis of Ross Ice Shelf Geophysical and Glaciological Survey (RIGGS) and Interferometric SAR (InSAR) measurements shows continued slowing of Ice Streams A and B flowing into the southeast part of the Ross Ice Shelf, sufficient to shift the balance of the western part of the West Antarctic ice sheet (WAIS) from –14 Gt a–1 in 1975 to growth by 9 Gt a–1 in 2009
Ice discharge into the RIS from East Antarctica totals $50 Gt a–1, and showed no significant change between 1975 and 2009
Summary
The Ross Ice Shelf (RIS) is fed by large glaciers and ice streams flowing from both East and West Antarctica, by snow falling on its surface and, to a lesser extent, by basal freezing. It loses ice by basal melting and the calving of icebergs from its seaward ice front. Shabtaie and Bentley (1987) used the RIGGS measurements to infer a negative mass balance of $20 Gt a–1 for the catchment regions of these ice streams They showed the inland ice to be more extensive than previously mapped, and that it includes a large, weakly grounded ‘ice plain’ in the southeast corner of the ice shelf that was thickening quite rapidly (Thomas, 1976). Between 2003 and 2009, NASA’s Ice, Cloud and land Elevation Satellite (ICESat) made accurate measurements of surface elevation over most of the Earth, including Antarctica, and we use these measurements to confirm recent thickening of the WAIS drainage basin, and slow thinning of much of the RIS
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