Joint Inversion for Surface Accumulation and Geothermal Flux from Ice-Penetrating Radar Observations at Dome A, East Antarctica: Ice Sheet State and Analysis

Abstract:

Dome A is the highest, coldest, and slowest part of the East Antarctic Ice Sheet (EAIS). It is underlain by the rugged Gamburtsev Subglacial Mountains (GSM). Despite the cold and slow conditions at the surface, the rugged topography underneath produce a complex basal hydrological system featuring basal melt, water transport and storage, and freeze-on. In a companion paper (Wolovick and Moore, in prep), we used an inverse model to infer the spatial distributions of geothermal flux and accumulation rate that best fit radar observations of subglacial water, freeze-on, and internal layers in this region. Here, we present and analyze the best-fit state of the ice sheet predicted by that model in detail. Our modelled thermal structure and basal hydrology agree well with the observed water bodies and freeze-on structures, while also predicting a significant amount of unobserved water and suggesting a change in stratigraphic interpretation that reduces the volume of the freeze-on units. Our ice sheet flow field predicts that a weak Raymond effect underneath the ice divide has been mostly masked by the high-amplitude variability in the layers produced by draping over subglacial topography. Our model age field agrees well with observations, and we predict- assuming that the ice divide has been stable over time- that there will be two distinct patches of old ice greater than 1 Ma suitable for ice coring underneath the divide. Our best-fit accumulation rate pattern contains a pronounced precipitation shadow aligned with the modern-day ice divide, suggesting that divide migration has been minimal for the last one and a half glacial cycles, a hopeful but not a definitive sign for ice core siting. Finally, we analyze our best-fit geothermal flux field in the context of East Antarctic geology. Our geothermal flux estimate is substantially higher than previous estimates for this region. While our estimate may have been biased high because water observations are preferentially located in narrow valleys not fully captured by the gridded topography, correcting for this bias still leaves our result in the high end of past estimates, with substantial local anomalies that are hotter still. Fundamentally, the observational evidence of a complex basal hydrological system is inconsistent with a simple picture of a uniformly cold East Antarctic craton.