Radar isochrones as constraints on paleo–ice-sheet model simulations in two off-divide regions of East Antarctica

Abstract. Radio-echo sounding of polar ice masses has revealed extensive isochrones that have primarily been used to constrain paleo-accumulation rates, geothermal heat flux, and changes in ice-sheet dynamics in stable regions of the ice sheet. However, isochrones remain under-utilised for calibrating ice-sheet models over large spatial scales, particularly in areas far from the stable ice divide where isochrones are typically more disrupted and models likely perform less accurately. Here, we illustrate the utility of isochrones for constraining paleo-ice-sheet simulations in two off-divide areas of the East Antarctic Ice Sheet; the Wilkes Subglacial Basin (WSB) and the Dronning Maud Land (DML) regions. Using airborne radio-echo sounding data from both legacy and newly acquired surveys, and the three-dimensional, thermo-mechanically coupled Parallel Ice-Sheet Model (PISM), we show that traced and dated isochrones are essential for calibrating model simulations in faster-flowing regions of the ice sheet. Associated with this paper are two datasets of nine and seven newly traced isochrones spanning the Holocene and Last Interglacial (∼ 4.8–128.4 ka) across the WSB and DML sectors, respectively, which may be used in future modelling studies to assess the paleo-evolution of the East Antarctic Ice Sheet. Using a commonly traced isochrone dated at ∼ 91 ka across both sectors, we simulate its modelled equivalent along two off-divide transects and discuss its utility for constraining the model. We highlight the influence of paleo-climate forcing and model parameterisation, which can lead to widely different model representations of isochrones despite producing reasonable present-day ice-sheet geometries that are consistent with observations. This study demonstrates that achieving a good present-day match in ice-sheet geometries in off-divide areas does not necessarily translate to an appropriate transient ice-sheet evolution in the model and thus emphasises the need to incorporate isochrones as boundary conditions in paleo-ice-sheet model simulations.