An International Polar Year aerogeophysical investigation of the high interior of East Antarctica reveals widespread freeze-on that drives substantial mass redistribution at the bottom of the ice sheet. Although the surface accumulation of snow remains the primary mechanism for ice sheet growth, beneath Dome A, 24% of the base by area is frozen-on ice. In some places, up to half of the ice thickness has been added from below. These ice packages result from the conductive cooling of water ponded near the Gamburtsev Subglacial Mountain ridges and the supercooling of water forced up steep valley walls. Persistent freeze-on thickens the ice column, alters basal ice rheology and fabric, and upwarps the overlying ice sheet, including the oldest atmospheric climate archive, and drives flow behavior not captured in present models.

Accurate quantification of surface snow accumulation overAntarctica is a key constraint for estimates of the Antarctic mass balance, as well as climatic interpretations of ice-core records 1,2 . Over Antarctica, near-surface winds accelerate down relatively steep surface slopes, eroding and sublimating the snow. This wind scour results in numerous localized regions (≤200 km 2 ) with reduced surface accumulation 3-7 . Estimates of Antarctic surface mass balance rely on sparse point measurements or coarse atmospheric models that do not capture these local processes, and overestimate the net mass input in wind-scour zones 3 . Here we combine airborne radar observations of unconformable stratigraphic layers with lidar-derived surface roughness measurements to identify extensive wind-scour zones over Dome A, in the interior of East Antarctica. The scour zones are persistent because they are controlled by bedrock topography. On the basis of our Dome A observations, we develop an empirical model to predict wind-scour zones across the Antarctic continent and find that these zones are predominantly located in East Antarctica. We estimate that ∼2.7-6.6% of the surface area of Antarctica has persistent negative net accumulation due to wind scour, which suggests that, across the continent, the snow mass input is overestimated by 11-36.5 Gt yr −1 in present surface-massbalance calculations.Over the interior of East Antarctica, significant spatial variability in snow accumulation results from the temperature inversion and gravity-driven katabatic winds interacting with ice surface topography 1,3,7,8 . These katabatic winds erode and sublimate both drifting snow and snow layers on the ground 1 . Extensive regions of wind-induced zero or near-zero surface mass balance (SMB) have been identified by airborne ice-penetrating radars 6 , satellite remote sensing 3 and ground traverses 1,4,[9][10][11][12][13][14] . A small fraction of the eroded snow over these regions is redeposited downslope forming dunes or infilling topographic depressions and the rest is sublimated 13,14 . Evaluating this complex deposition process over a low accumulation area such as the interior of East Antarctica is important for improving SMB estimates and annual accumulation from ice cores.Where the winds completely remove the annual snowfall over the scour zones, increased absorption of short-wave solar radiation and enhanced vapour transport facilitate grain growth and metamorphosis of the near-surface firn layers 3,[14][15][16] . In radar stratigraphy, these buried, metamorphosed layers form

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