Patterns of valley incision beneath the Greenland Ice Sheet revealed using automated mapping and classification

Subglacial valleys preserved in the highlands of south and east Greenland record restricted ice extent during past warmer climates

“…For this task, we used a recently assembled database of the locations of subglacial valleys visible in Operation IceBridge RES data (Fig. S1a) across the GrIS (Paxman, 2023). This dataset also contains quantitative metrics of valley cross-profile morphology, including depth, width, Vshapedness, and curvature, as well as classifications of valleys as either 'glacial' or 'fluvial' based on their morphological similarity to glacial or fluvial valleys observed elsewhere in the Northern Hemisphere.…”

“…This valley classification was accomplished using the random forest supervised machine learning algorithm (Breiman, 2001), which is a statistical method associated with uncertainty that is encapsulated in the classification 'score'. For the purposes of this analysis, we only examined valleys with a score of at least 0.75, indicating that the classification is associated with relatively high confidence or probability (for more information the reader is referred to Paxman, 2023).…”

“…2). Using the MODIS MoG image and the RES-derived subglacial valley database (Paxman, 2023), we digitised valley planform patterns within the highlands of southern and eastern Greenland visible in ice surface imagery, ground-truthed their locations using RES data, and extracted their cross-profile morphometrics.…”

“…The model domain includes the entirety of Greenland with a horizontal grid resolution of 10 km, which represents a compromise between computational efficiency and the ability to capture the larger valley networks present in the subglacial topography (cf. Paxman, 2023). Selected experiments were also performed at a higher resolution of 5 km, which reflects the average valley width in the eastern and southern highlands (Paxman, 2023), allowing us to examine the influence of valley topography on the simulated patterns of ice flow in greater detail.…”

Geologic Provinces Beneath the Greenland Ice Sheet Constrained by Geophysical Data Synthesis

“…Whether this subset of long, linear valleys formed by fluvial or subglacial processes remains unclear. Where they are intersected by airborne radar sounding data, the cross‐sectional morphology of these valleys shows a range of forms resembling both glacial and fluvial valleys elsewhere in the Northern Hemisphere, although definitively U‐shaped cross‐profiles are uncommon in the Greenlandic interior (Paxman, 2023). A fluvial origin is most likely given low long‐term glacial erosion rates in the vicinity of GISP2 in central Greenland (Bierman et al., 2014), although subglacial meltwater may have also contributed to valley incision where the bed is thawed (e.g., Kirkham et al., 2022).…”