Increased Subglacial Sediment Discharge in a Warming Climate: Consideration of Ice Dynamics, Glacial Erosion, and Fluvial Sediment Transport

We evaluate changes to subglacial sediment discharge during glacier retreat by considering ice dynamics, bedrock erosion, and sediment transport processes. Coupling these components together within a single framework, we simulate sediment discharge from synthetic alpine glaciers experiencing accelerated glacier melt for 100 years. We find that sediment discharge increases by about 8 times the steady glacier values by the end of the simulation. The enhanced sediment discharge persists through peak water discharge and despite annual bedrock erosion volumes decreasing by approximately 30% from the initial value. The greater sediment discharge results from increased melt at the glaciers' higher region, where transport was limited prior to glacier retreat. These findings suggest that large increases in sediment discharge may occur as glaciers retreat. The magnitude of the sediment discharge increase primarily depends on the quantity of sediment stored subglacially. Plain Language Summary Changes to sediment discharge from glaciers can dramatically impact downstream communities and ecosystems. We account for two primary processes that largely control to sediment discharge from glaciers: (1) bedrock erosion, which creates sediment below the glacier and (2) the ability of meltwater below the glacier to carry this sediment. To understand the potential changes in sediment discharge as glaciers retreat, we link numerical models of both processes and run them in a scenario that complies with ongoing climate warming. In the scenario, we find that sediment discharge increases dramatically, despite smaller quantities of sediment being produced by bedrock erosion. This is because more meltwater higher on the glaciers increases sediment transport in these upper regions. Results here suggest that future subglacial sediment discharge depends on the amount of sediment that already exists below glaciers. Large increases in subglacial sediment discharge are possible.