Impact of Ice Topography, Basal Channels and Subglacial Discharge on Basal Melting Under the Floating Ice Tongue of 79N Glacier, Northeast Greenland

• Published in: Journal of advances in modeling earth systems Vol. 17; no. 9
• Main Authors: Mohammadi‐Aragh, Mahdi, Zeising, Ole, Reinert, Markus, Klingbeil, Knut, Humbert, Angelika, McPherson, Rebecca, Morlighem, Mathieu, Timmermann, Ralph, Wekerle, Claudia, Burchard, Hans
• Format: Journal Article
• Language: English
• Published: Washington John Wiley & Sons, Inc 01.09.2025; American Geophysical Union (AGU)
• Subjects: Algorithms; basal channel; Drag coefficient; Drainage; Eddy flux; Exchange coefficients; Floating ice; Glacier tongues; Glaciers; Greenland; Heat transfer; Ice effects; Ice sheets; ice shelf; Ice shelves; melt rate; Oceanic heat flux; plume model; Plume models; Spatial variability; Spatial variations; Thinning; Topographic effects; Topography; Turbulence models
• ISSN: 1942-2466; 1942-2466
• DOI: 10.1029/2024MS004735

The floating ice tongue of the 79N Glacier in Northeast Greenland has been thinning over the past two decades, with warning signs of a potential onset of disintegration. While previous studies primarily attribute the thinning of the ice shelf to oceanic heat flux, limited attention has been given to the significant role of ice shelf plume dynamics as a mechanism for distributing the heat beneath the ice shelf. Here, we develop a horizontal two‐dimensional plume model to assess the effects of key factors influencing plume dynamics and, consequently, the estimation of a high‐resolution basal melt rate. We examine the effect of ice basal topography roughness and the presence of basal channels, that is extreme roughness of the base in the hinge zone, as well as the impact and pathways of subglacial discharge on melt rates. Our model results show good agreement with observation‐based melt rate estimates and indicate that basal channels in the hinge zone are the dominant control on the ice shelf's basal melt rates. In combination with subglacial discharge, the melt rate is increased to 150myr−1 $150\,\mathrm{m}\,\mathrm{y}{\mathrm{r}}^{-\mathrm{1}}$ at the grounding line, intensifying the channelized melt rate pattern created by basal channels and increasing spatial variability. Additionally, our results indicate that incorporating wet‐dry algorithms and calculating a variable drag coefficient are crucial for accurately estimating melt rates during low subglacial discharge season, as well as for determining friction and turbulent exchange coefficients. Plain Language Summary Ice shelves are floating extensions of polar ice sheets, and control how fast glaciers flow into the ocean. Many of them are rapidly thinning, primarily due to basal melting, thereby reducing their ability to slow down ice flow. Accurately estimating basal melt rates improves the reliability of sea level predictions. However, existing modeling efforts have predominantly focused on large‐scale processes. This study employs a suite of simulations to investigate the role of narrow basal channels under the ice and the effect of freshwater discharge where the ice starts to float. Our sensitivity analysis focuses on the floating ice tongue of the 79N Glacier, in northeast Greenland, which has been experiencing thinning over the past few decades. The results highlight that narrow basal channels significantly increase both the variability and spatial mean melt rates where the ice starts to float, further amplified by subglacial discharge near the grounding line. Key Points Basal channels regulate the melt rate of 79N Glacier, making their modeling crucial for estimating the melt rate of ice shelves influenced by warm water A new drying and flooding algorithm solves the issue of plume water velocity divergence Subglacial discharge primarily affects melt rate in the hinge zone, with minimal variation in the calving zone