Numerical modeling of glacial sediment production and transport during deglaciation

We aim to improve the understanding of sediment fluxes originating from ice sheet outlet glaciers in order to explain the evolution of sedimentary fjord fills. A numerical glacial erosion and sediment flux process model has been developed to quantify sediment generation and subglacial transport. Dynamic ice sheet cover is generated from topography and climate parameters, affecting the glacial net mass balance. Pressure, temperature and velocity characteristics of the ice sheet force erosion at the glacier bed. Bed erodability depends on bedrock hardness and potential shielding by sediment. After erosion, sediment is either stored at the bed, or transported either by meltwater or englacially (within basal ice). Model experiments show ice retreat is driven by valley topography: rapid retreat occurs in the flatter valley stretches and slower retreat in the steeper parts of a glacial valley. Distinct depocenters of exposed sediment develop during retreat. Predicted erosion rates in the glaciated valley range from 37 to 56 mm/yr for different climate scenarios, which is well within the range of reported field reconstructions. Erosion is significantly accelerated beneath warm-based ice and the effect of an enlarged warm-based footprint during warming compensates for decreasing ice mass. Topographic shielding of bedrock by previously eroded material in large areas constrains erosion by a factor 4. Simulated glacier retreat and melt water flux initially occur at a high rate and subsequently decelerate, while sediment delivery exhibits a distinct lagging of several thousands of years behind the meltwater flux. Upon the transition from glaciation to deglaciation, the subglacial system is in a sediment-starved state. Late-deglacial erosion and sub- and englacial sediment storage cause a lagging sediment delivery to downstream periglacial, fluvial and lacustrine domains. (C) 2012 Elsevier B.V. All rights reserved.