A revised and expanded deep radiostratigraphy of the Greenland Ice Sheet from airborne radar sounding surveys between 1993–2019

Abstract. Between 1993 and 2019, NASA and NSF sponsored 26 separate airborne campaigns that surveyed the thickness and radiostratigraphy of the Greenland Ice Sheet using successive generations of coherent VHF radar sounders developed and operated by The University of Kansas. Most of the ice-sheet’s internal VHF radiostratigraphy is composed of isochronal reflections that record its integrated response to past centennial-to-multi-millennial-scale climatic and dynamic events. We previously generated the first comprehensive dated radiostratigraphy of the Greenland Ice Sheet using the first 20 of these campaigns (1993–2013) and investigated its value for constraining the ice sheet’s history and modern boundary conditions. Here we describe the second major version of this radiostratigraphic dataset using all 26 campaigns, which includes substantial improvements in survey coverage and was mostly acquired with higher-fidelity systems. We incorporated several lessons learned from our previous efforts for improved quality control and accelerated tracing, including an automatic test for stratigraphic conformability, a cutoff length for semi-automatic tracing propagation, a thickness-normalized reprojection for radargrams, and automatic inter-segment reflection matching. We reviewed and augmented the 1993–2013 radiostratigraphy and applied an existing independently developed method for predicting radiostratigraphy to the previously untraced campaigns (2014–2019) to accelerate their semi-automatic tracing. The result is a more robust radiostratigraphy of the ice sheet that can validate the sensitivity of ice-sheet models to past major climate changes and constrain long-term boundary conditions (e.g., accumulation rate). Based on these results, we make several recommendations for how radiostratigraphy may be traced more efficiently and reliably in the future. This dataset is freely available at https://doi.org/10.5281/zenodo.14531734 (MacGregor et al., 2024). It includes all traced reflections at the spatial resolution of the radargrams and grids (5 km horizontal resolution) of the depths of isochrones between 3–115 ka and ages between 10–80 % of the ice thickness; associated codes are available at https://doi.org/10.5281/zenodo.14183061 (MacGregor, 2024a).