The extreme yet transient nature of glacial erosion

Abstract

Ice can sculpt extraordinary landscapes, yet the efficacy of, and controls governing, glacial erosion on geological timescales remain poorly understood and contended, particularly across Polar continental shields. Here, we assimilate geophysical data with modelling of the Eurasian Ice Sheet — the third largest Quaternary ice mass that spanned 49°N to 82°N — to decipher its erosional footprint during the entire last ~100 ka glacial cycle. Our results demonstrate extreme spatial and temporal heterogeneity in subglacial erosion, with rates ranging from 0 to 5 mm a−1 and a net volume equating to ~130,000 km3 of bedrock excavated to depths of ~190 m. A hierarchy of environmental controls ostensibly underpins this complex signature: lithology, topography and climate, though it is basal thermodynamics that ultimately regulates erosion, which can be variously protective, pervasive, or, highly selective. Our analysis highlights the remarkable yet fickle nature of glacial erosion — critically modulated by transient ice-sheet dynamics — with its capacity to impart a profound but piecemeal geological legacy across mid- and high latitudes.

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

“…8d,h) in a variety of empirical glacial erosion 'laws' (Cook et al, 2020;Herman et al, 2015;Koppes et al, 2015) gives expected erosion rates on the order of ~2 mm/yr within the valleys. The latter value is also more consistent with the typical range associated with alpine/polar glaciers (Koppes & Montgomery, 2009;Patton et al, 2022). Moreover, MIS 11 simulations suggest that while the GrIS was much-diminished, basal ice remained below the pressure melting point across much of the remaining ice cap (Robinson et al, 2017), helping to preserve the landscape at GISP2 beneath cold-based, non-erosive ice (Bierman et al, 2014).…”

Morphometric analysis of ice scour lakes in Iceland: A proxy for ice sheet dynamics

“…Ice divide migration in the Cordilleran Ice Sheet is documented by Dulfer et al (2022) as well. These studies combined with our results from Iceland suggest that ice scour lakes may be the result of time‐transgressive processes and agrees with the model of transient glacial erosion as suggested by Patton et al (2022).…”

“…Similar to our findings, Rice et al (2020) document high lake density at high elevations in northeastern Quebec and interpret more areal scouring during multiple ice flow phases of the Laurentide Ice Sheet. In addition, Patton et al (2022) show an increase in erosion on high‐elevation plateaus during phases of deglaciation of the Eurasion Ice Sheet similar to Vestfirðir and illustrate the transient nature of glacial erosion.…”

Proglacial methane emissions driven by meltwater and groundwater flushing in a high Arctic glacial catchment

“…Ultimately, while some methanogenesis is potentially occurring in the subglacial environment of Vallåkrabreen, we hypothesize that any microbially-produced methane in the drainage system is supplemented largely by thermogenic methane sourced from the rocks over which the glacier has flowed. The physical processes related to glacial advance-such as the excavation of large depths of bedrock through glacial erosion and geological faulting induced by glacial loading-can encourage the migration of deep-seated hydrocarbons to the surface where they may be introduced to the subglacial drainage system (Patton et al, 2022;Vachon et al, 2022). Alternatively, pressurized subglacial water may route through the fractured bedrock beneath the glacier, extracting methane along its flowpath-effectively inducing a natural 'glacial fracking' process.…”