Modeling Sediment Fluxes From Debris‐Rich Basal Ice Layers

• Published in: Journal of geophysical research. Earth surface 2024-10, Vol.129 (10), p.n/a
• Main Authors: Pierce, Ethan, Overeem, Irina, Jouvet, Guillaume
• Format: Article
• Language: English
• Subjects: alpine glaciers; basal ice; Climatic conditions; Debris; Detritus; dispersed ice; Downstream; Earth surface; Ecosystems; Entrainment; Erosion processes; Evolution; Fluxes; frozen fringe; Glacial drift; Glaciation; Glacier flow; Glacier ice; Glacier melting; Glaciers; Ice; Ice cover; Ice formation; Ice sheets; Lakes; Landscape; Landscape preservation; Mathematical models; Meltwater; Numerical models; Numerical simulations; Nutrients; Parameter sensitivity; Rivers; Sediment; sediment entrainment; Sediment transport; Sediments; Soil erosion; Spatial distribution; Stratigraphy; Thickness
• ISSN: 2169-9003; 2169-9011
• DOI: 10.1029/2024JF007665

Sediment erosion, transport, and deposition by glaciers and ice sheets play crucial roles in shaping landscapes, provide important nutrients to downstream ecosystems, and preserve key indicators of past climate conditions in the geologic record. While previous work has quantified sediment fluxes from subglacial meltwater, we also observe sediment entrained within basal ice, transported by the flow of the glacier itself. However, the formation and evolution of these debris‐rich ice layers remains poorly understood and rarely represented in landscape evolution models. Here, we identify a characteristic sequence of basal ice layers at Mendenhall Glacier, Alaska. We develop a numerical model of frozen fringe and regelation processes that describes the co‐evolution of this sequence and explore the sensitivity of the model to key properties of the subglacial sedimentary system, using the Instructed Glacier Model to parameterize ice dynamics. Then, we run numerical simulations over the spatial extent of Mendenhall Glacier, showing that the sediment transport model can predict the observed basal ice stratigraphy at the glacier's terminus. From the model results, we estimate basal ice layers transport between 23,300 m3 ${\mathrm{m}}^{3}$ a−1 ${\mathrm{a}}^{-1}$ and 39,800 m3 ${\mathrm{m}}^{3}$ a−1 ${\mathrm{a}}^{-1}$ of sediment, mostly entrained in the lowermost ice layers nearest to the bed, maximized by high effective pressures and slow, convergent flow fields. Overall, our results highlight the role of basal sediment entrainment in delivering eroded material to the glacier terminus and indicate that this process should not be ignored in broader models of landscape evolution. Plain Language Summary Glaciers shape landscapes by eroding mountain ranges and moving the eroded sediment downstream to the lakes, fjords, and other ecosystems near the terminus. To quantify this supply of sediment, and thus understand the evolution of high alpine landscapes, we often use numerical models to simulate the processes of erosion and transport. Previous work has focused on the role of meltwater channels underneath glaciers to transport sediment, analogous to how rivers move sediment across much of Earth's surface, but we also know from field observations that a portion of the underlying sediment is picked up and incorporated into the ice itself. Here, we develop a new model to simulate where and how sediment is incorporated into ice beneath the glacier, and how those debris‐ric