A New Digital Elevation Model for Hercules Dome, Antarctica from CryoSat-2 Altimetry - Toward Site Selection for the Next Antarctic Deep Ice Core

Hercules Dome (86.50S; 1080W) has been identified as a possible site for a new ice core in Antarctica because the ice here likely contains an isotopic and geochemical record of the drawdown of the West Antarctic Ice Sheet during the last interglacial. An interpretable climate record from the Eemian is likely preserved here because: 1) the deep ice is situated in a depression that may be enclosed; 2) the ice has a relatively simple flow history with likelihood of only minor disturbances in internal stratigraphy; and 3) coupled high-resolution atmosphere/ice-sheet models indicate that this region would not have been deglaciated during the Eemian, even under the most aggressive warm climate scenarios. A ground-based geophysical survey is, however, necessary to confirm the presence of intact, interpretable Eemian ice. Before commencing such a survey, it is critical to have an accurate digital elevation model (DEM) that characterizes the surface topography, which will allow precise site selection and inform preliminary ice-dynamics modeling of putative Raymond bumps identified in previous ground-based ice-penetrating radar surveys. The existing DEM (Bamber, 2009) relies on extrapolation of radar and laser altimetry data from ERS-1 (limit -81.50) and ICESat (limit -860), and is known to be inaccurate in the region of Hercules Dome through comparison with ground-based GPS data. We constructed a new DEM from Cryosat-2 radar altimetry (LRM) data with approximately 26.5 million surface elevation measurements over a region of 600 x 600 km. These points were interpolated to a 1km grid and subsequently smoothed with a search radius of 3 km to produce the DEM. Comparison of the map elevations with surface-based GPS measurements along the US-ITASE traverse show an RMS difference of about 2 m in the region of the dome. Further comparison with another new DEM made from World View stereo imagery of the region immediately around the dome also shows excellent agreement. Rather than a simple two-dimensional ice divide or dome, our DEM models Hercules Dome as an asymmetric 60 m rise in topography near the center of a broad plateau at 2550 m elevation.