Inferring Holocene variations in ice-flow patterns and accumulation gradients at Hercules Dome from radar measurements of internal layering and englacial velocity profiles with 2D ice-flow modeling

Abstract:

Hercules Dome (86S, 105W) sits at the intersection of the West and East Antarctic ice sheets. The internal layering retains information about the history of ice flow and accumulation in the region, although deciphering unique histories is challenging. Here we use accumulation rate histories inferred from geophysical data (ice-penetrating radar and GPS) and 2D modeling across the ice divide to determine whether the modern spatial and temporal patterns have been consistent throughout the Holocene. Geophysical data collected in the 18-19 and 19-20 field seasons provide the primary constraints. The modeling seeks to match the internal stratigraphy imaged with impulse radar and dated by connecting with data from the US ITASE traverse between Herc Dome and South Pole. An important additional data set is automated phase-sensitive radar (ApRES) measurements of the vertical velocities at 8 locations along two transects. On one transect, the vertical velocities suggest a Raymond effect – more near-surface vertical strain due to the non-linearity of ice deformation – is operating within an ice-thickness of the present ice divide; however, a Raymond arch is not readily discernable. This could either be because the divide position has varied through time or because the bedrock beneath the divide is elevated and rough enough to obscure a Raymond arch. We force the model with variations in the accumulation rate and pattern indicated by the radar data and with variations in the boundary flux which causes divide migration; then we quantify the fit to the dated internal layers. While we anticipate a range of forcings will fit the internal layers adequately, we expect that some scenarios will be excluded providing insight into the stability of Hercules Dome throughout the Holocene as it responded to broader changes in both the West and East Antarctic ice sheets.

Hercules Dome is a site for a future deep ice core to bedrock but a specific drill location has not yet been selected. While many of the goals of the ice core project are for ice older than the Holocene, the Holocene stability is nonetheless important for selecting the ice core location. A stable divide position likely indicates the best location to drill is beneath the present divide, while past migration may indicate locations to be avoided due to past flow along rough bedrock topography.