Glacier thickness, thermal regime, and subjective uncertainty from ground-penetrating radar of 25 Svalbard glaciers

Erik Schytt Mannerfelt , Ursula Enzenhofer, Satu Innanen, Jogscha Miriam Abderhalden, Karlijn Ploeg, Johannes Brunner, Mette Kusk Gillespie, Gabrielle Emma Kleber, Jonathan Kolar, Geir Moholdt, Solveig Solem, Andrew Jonathan Hodson

Glacier thickness and thermal regime control glacier dynamics and long-term evolution, but observations are sparse at regional scales. Both can be measured using ground-penetrating radar (GPR), which requires manual or automated interpretation. Interpretation often depends on more than signal waveform analysis alone, and this subjectivity has not been thoroughly quantified before. We present 699 km of ground-based GPR data from 25 glaciers in Svalbard, after crowd-sourcing glacier bed and cold-temperate transition surface (CTS) interpretations from 41 contributors. We find that subjective uncertainty is usually smaller than instrument-related uncertainties for the glacier bed, though notable exceptions exist from off-nadir reflections or occlusion by temperate ice. CTS interpretations have higher spreads and show qualitative disagreement in the required amount of scatter to be considered as temperate ice. Our thermal regime consensus estimates reveal a wide diversity in temperate ice extent and distribution between glaciers, as well as insights into the thermal structure of glaciers with surge-related histories. Our thickness consensus agrees with previous measurements, and we show that thickness inversion model performance varies with thermal regime. All data are available to enable novel applications and automated bed/CTS detection methods that acknowledge interpretation uncertainty.