Search for: All records

Abstract. Radio-echo sounding (RES) has revealed an internal architecture within Antarctica’s ice sheets that records their depositional, deformational and melting histories. Crucially, spatially-widespread RES-imaged internal-reflecting horizons, tied to ice-core age-depth profiles, can be treated as isochrones that record the age-depth structure across the Antarctic ice sheets. These enable the reconstruction of past climate and ice-dynamical processes on large scales, which are complementary to but more spatially-extensive than commonly used proxy records across Antarctica. We review progress towards building a pan-Antarctic age-depth model from these data by first introducing the relevant RES datasets that have been acquired across Antarctica over the last six decades (focussing specifically on those that detected internal-reflecting horizons), and outlining the processing steps typically undertaken to visualise, trace and date (by intersection with ice cores, or modelling) the RES-imaged isochrones. We summarise the scientific applications to which Antarctica’s internal architecture has been applied to date and present a pathway to expanding Antarctic radiostratigraphy across the continent to provide a benchmark for a wider range of investigations: (1) Identification of optimal sites for retrieving new ice-core palaeoclimate records targeting different periods; (2) Reconstruction of surface mass balance on millennial or historical timescales; (3) Estimates of basal melting and geothermal heat flux from radiostratigraphy and comprehensively mapping basal-ice units, to complement inferences from other geophysical and geological methods; (4) Advancing knowledge of volcanic activity and fallout across Antarctica; (5) The refinement of numerical models that leverage radiostratigraphy to tune time-varying accumulation, basal melting and ice flow, firstly to reconstruct past behaviour, and then to reduce uncertainties in projecting future ice-sheet behaviour. 

Abstract. The crystal orientation fabric (COF) of ice sheets records the past history ofice sheet deformation and influences present-day ice flow dynamics. Though notwidely implemented, coherent ice-penetrating radar is able to detect bulkanisotropic fabric patterns by exploiting the birefringence of ice crystals atradar frequencies, with the assumption that one of the crystallographic axesis aligned in the vertical direction. In this study, we conduct a suite ofquad-polarimetric measurements consisting of four orthogonal antennaorientation combinations near the Western Antarctic Ice Sheet (WAIS) Divideice core site. From these measurements, we are able to quantify the azimuthalfabric asymmetry at this site to a depth of 1400 m at abulk-averaged resolution of up to 15 m. Our estimates of fabricasymmetry closely match corresponding fabric estimates directly measured fromthe WAIS Divide ice core. While ice core studies are often unable to determinethe absolute fabric orientation due to core rotation during extraction, we areable to identify and conclude that the fabric orientation is depth-invariantto at least 1400 m, equivalent to 6700 years BP (years before1950) and aligns closely with the modern surface strain direction at WAISDivide. Our results support the claim that the deformation regime at WAISDivide has not changed substantially through the majority of theHolocene. Rapid polarimetric determination of bulk fabric asymmetry andorientation compares well with much more laborious sample-based COFmeasurements from thin ice sections. Because it is the bulk-averaged fabricthat ultimately influences ice flow, polarimetric radar methods provide anopportunity for its accurate and widespread mapping and its incorporation intoice flow models.