DOI: 10.5285/cfafb639-991a-422f-9caa-7793c195d316
title: Dated radar stratigraphy between Dome A and South Pole, East Antarctica, derived from AGAP North PASIN (2008-2009) and PolarGAP PASIN2 (2015-2016) surveys

description: This dataset contains the position and depth (ice thickness) of three spatially-extensive Internal Reflecting Horizons (IRHs) mapped from ice-penetrating radar data acquired with the British Antarctic Survey's PASIN and PASIN2 ice radar systems across central East Antarctica. The dataset extends geographically from Dome A to South Pole. Using previous dated IRHs from Winter et al (2019), an independent validation of IRH ages from the South Pole ice-core chronology and a 1-D steady-state model, we assigned ages to our three IRHs: (H1) 38.5 +/- 2.2 ka, (H2) 90.4 +/- 3.57, and (H3) 161.9 +/- 6.76 ka.

This study was motivated by the AntArchitecture Action Group of the Scientific Committee for Antarctic Research (SCAR). The project was supported by the National Environmental Research Council (NERC)-funded ONE Planet Doctoral Training Partnership (NE/S007512/1), hosted jointly by Newcastle and Northumbria Universities. The authors thank the BAS science and logistics teams for acquiring both the AGAP PASIN and PolarGAP PASIN2 data which is fully available on the Polar Airborne Geophysics Data Portal of the UK Polar Data Center (https://www.bas.ac.uk/project/nagdp/). BedMachine (version 2) data are available at https://doi.org/10.5067/E1QL9HFQ7A8M.
description: Instrumentation and Processing:
The primary radar dataset used (AGAP North) was acquired with the British Antarctic Survey's PASIN system. The AGAP survey was flown over the Gamburtsev Province and the interior of East Antarctica in the 2008/9 Antarctic field season (Bell et al. 2011; Corr et al. 2021). Radar data were collected using the PASIN ice penetrating radar system mounted on the BAS Twin Otter aircraft 'VP-FBL'. The operating centre frequency was 150 MHz, and the system used two interleaved pulses: a 4-microseconds, 10 MHz bandwidth linear chirp for deep sounding and a 0.1-microseconds unmodulated pulse for shallow sounding. Further details of the processing applied can be found at Corr et al. (2021) and Fremand et al. (2022).

The second radar dataset used was acquired with the British Antarctic Survey's PASIN2 system. Data were acquired during the ESA PolarGAP survey (PolarGap: 'Filling the GOCE polar gap in Antarctica and ASIRAS flight around South Pole' https://doi.org/10.5270/esa-8ffoo3e, Ferraccioli et al 2021), flown during the austral summer of 2015/2016, which increased ice-penetrating radar data coverage south of 83.5degS. PolarGAP covered an area from the South Pole to the Recovery Subglacial Lakes, encompassing Support Force, Foundation, Academy and Recovery Glaciers. Radar data were acquired using the PASIN-2 radar echo sounding system mounted on the BAS Twin Otter aircraft 'VP-FBL'. Operating in full polarimetric mode, with a centre frequency of 150 MHz, the system used a 4-microseconds, 13 MHz bandwidth linear chirp for deep sounding. Further details of the processing applied can be found at Ferraccioli et al. (2021) and Fremand et al. (2022). 
For the purposes of increasing IRH traceability, we applied a natural-log filter and a 10-trace horizontal average to both the AGAP North and PolarGAP radar data to reduce incoherent noise. For both the AGAP North and PolarGAP data, we removed the air-to-ice two-way travel time and shifted the surface elevation to time zero, prior to exporting the data to standard 2-D SEG-Y format for data interpretation.
We conducted our IRH tracing in the freely available Opendtect Seismic Interpretation Software using a semi-automated maximum-amplitude layer picker.

Methodology and Results:
Three prominent Internal Reflecting Horizons (IRHs) were identified (H1-3) in a subset of the AGAP North and PolarGAP radar data. We initially identify the three IRHs along a single 'control' survey line (i.e. AGAP N flightline A10B) because the englacial reflections in the data for that flight were characterised by high spatial continuity and visibility. The IRHs were then propagated outwards across the remainder of the data used. Crossovers between radar profiles were used as calibration points to trace the IRHs. The diagnostic character of the IRHs was used when tracing the layers from crossover intersection points (see Sanderson et al., 2024, for more details).
All IRHs were converted from the time domain to ice thickness using a value for the speed of electromagnetic waves through ice of 168.5 m/microseconds, and the application of a 12 m spatially-invariant firn correction. All ice thickness measurements are given in depth below the surface (set at 0 m).

The maximum vertical depth uncertainty for all the traced layers from the two radar datasets is +/- 17 m for H1, +/- 21 m for H2, and +/- 27 m for H3. More details on how these uncertainties were calculated can be found in Sanderson et al. (2024). The IRHs were dated using intersection with previously dated IRH from East Antarctica (Winter et al 2019), independently verified using the South Pole ice-core and a steady-state 1-D vertical-strain model.
description: The data were collected as part of the AGAP North survey (PASIN): season 2008-2009 and PolarGAP PASIN2 survey: season 2015-2016
description: Uncertainties in IRH depths can be found in the Lineage section and in the paper. Where the PASIN radar did not sound the full ice thickness (i.e. there was no identifiable reflection from the ice base), we used BedMachine v2 to constrain full ice thickness (i.e. from surface to ice base), and subsequently 'fractional depth' of the IRHs.