02 Nov 2023
 | 02 Nov 2023
Status: this preprint is open for discussion.

Mapping the vertical heterogeneity of Greenland’s firn from 2011–2019 using airborne radar and laser altimetry

Anja Rutishauser, Kirk Michael Scanlan, Baptiste Vandecrux, Nanna B. Karlsson, Nicolas Jullien, Andreas Peter Ahlstrøm, Robert S. Fausto, and Penelope How

Abstract. The firn layer on the Greenland Ice Sheet (GrIS) plays a crucial role in buffering surface meltwater runoff, which is constrained by the available firn pore space and impermeable ice layers that limit deeper meltwater percolation. Understanding these firn properties is essential for predicting current and future meltwater runoff and its contribution to global sea-level rise. While very high-frequency (VHF) radars have been extensively used for surveying the GrIS, their lower bandwidth restricts direct firn stratigraphy extraction. In this study, we use concurrent VHF airborne radar and laser altimetry data collected as part of Operation Ice Bridge (OIB) over the period 2011–2019 to investigate vertical offsets in the radar surface reflection (dz). Our results, corroborated by modelling and firn core analyses, show that a dz larger than 1 m is strongly related to the vertical heterogeneity of a firn profile, and effectively delineates between vertically homogeneous and vertically heterogeneous firn profiles. Temporal variations in dz align with climatic events and reveal an expansion of heterogeneous firn between 2011–2013 covering an area of ~338,450 km2, followed by firn replenishment over the years 2014–2019 spanning an area of ~664,734 km2. Our approach reveals the firn evolution of key regions on the Greenland Ice Sheet, providing valuable insights for detecting potential alterations in meltwater runoff patterns.

Anja Rutishauser et al.

Status: open (until 14 Dec 2023)

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  • RC1: 'Comment on egusphere-2023-2385', Anonymous Referee #1, 17 Nov 2023 reply

Anja Rutishauser et al.

Anja Rutishauser et al.


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Short summary
The Greenland Ice sheet interior is covered by a layer of firn, which is important for surface meltwater runoff and contributions to global sea-level rise. Here, we combine airborne radar sounding and laser altimetry measurements to delineate vertically homogeneous and heterogeneous firn. Our results reveal changes in firn between 2011–2019, aligning well with known climatic events. This approach can be used to outline firn areas primed for significantly changing future meltwater runoff.