Surface Melting Drives Fluctuations in Airborne Radar Penetration in West Central Greenland

Inès N Otosaka,Peter Kuipers Munneke,Alessandro Di Bella,Tânia G D Casal,Sebastian B Simonsen,Alex Coccia,Karlus Macedo,Sine M Hvidegaard,Anna E Hogg,Henriette Skourup,Malcolm Davidson,Andrew Shepherd,Adriano Lemos,Veit Helm,Louise Sandberg Sørensen,Tommaso Parrinello,Xavier Fettweis,René Forsberg

doi:10.1029/2020gl088293

Abstract

AbstractGreenland Ice Sheet surface melting has increased since the 1990s, affecting the rheology and scattering properties of the near‐surface firn. We combine firn cores and modeled firn densities with 7 years of CryoVEx airborne Ku‐band (13.5 GHz) radar profiles to quantify the impact of melting on microwave radar penetration in West Central Greenland. Although annual layers are present in the Ku‐band radar profiles to depths up to 15 m below the ice sheet surface, fluctuations in summer melting strongly affect the degree of radar penetration. The extreme melting in 2012, for example, caused an abrupt 6.2 ± 2.4 m decrease in Ku‐band radar penetration. Nevertheless, retracking the radar echoes mitigates this effect, producing surface heights that agree to within 13.9 cm of coincident airborne laser measurements. We also examine 2 years of Ka‐band (34.5 GHz) airborne radar data and show that the degree of penetration is half that of coincident Ku‐band.

Highlights

IntroductionIn recent decades, increased melting at the surface of the Greenland Ice Sheet (van den Broeke et al, 2016) has had a marked impact on rates of runoff (Enderlin et al, 2014; van Angelen et al, 2014) and glacier flow (van de Wal et al, 2008), and has affected the structure of the near‐surface firn owing to the redistribution and refreezing of surface meltwater (de la Peña et al, 2015; Machguth et al, 2016)
In recent decades, increased melting at the surface of the Greenland Ice Sheet has had a marked impact on rates of runoff (Enderlin et al, 2014; van Angelen et al, 2014) and glacier flow, and has affected the structure of the near‐surface firn owing to the redistribution and refreezing of surface meltwater
We measured a total of 40 cm of ice from the firn core while IMAU‐ and Modèle Atmosphérique Régional (MAR)‐FDM simulated a total of 188 and 294 cm of ice in the corresponding firn column, indicating that the firn ice content is overestimated in the lower section of the Expéditions Glaciologiques Internationales au Groenland (EGIG) line (Figure S1a)

Summary

Introduction

In recent decades, increased melting at the surface of the Greenland Ice Sheet (van den Broeke et al, 2016) has had a marked impact on rates of runoff (Enderlin et al, 2014; van Angelen et al, 2014) and glacier flow (van de Wal et al, 2008), and has affected the structure of the near‐surface firn owing to the redistribution and refreezing of surface meltwater (de la Peña et al, 2015; Machguth et al, 2016).

Results

Discussion

Conclusion