A Coupled Ice‐Sheet/Ice‐Shelf/Sediment Model Applied to a Marine‐Margin Flowline: Forced and Unforced Variations

Abstract

A standard large-scale ice-sheet model is extended by (i) adding ice stream-shelf flow using a combined set of scaled equations for sheet and shelf flow, and (ii) coupling with a deforming sediment model that predicts bulk sediment thickness. The combination of sheet and shelf flow equations is heuristic, but allows horizontal shear and longitudinal stretching without a priori assumptions about the flow regime, and a freely migrating grounding line. The sediment model includes bulk transport under ice assuming a weakly non-linear till rheology, and generation of till by glacial erosion. The combined model explicitly simulates off-shore sediment strata, taking one step towards the goal of direct comparisons with Cenozoic glacimarine sediments on Antarctic continental shelves.Preliminary 1-D flowline simulations are described on a linearly sloping domain, with simple prescribed spatial and temporal variations of surface ice mass balance. Each simulation is run for 10 million years, and the various patterns of offshore sediment strata built up over the course of each run are examined. A wide variety of sediment patterns is produced depending on uncertain model parameters, including unforced irregular oscillations in the absence of external forcing variations. The results are not conclusive, but illustrate the variety of possible interactions that may play a role as more definitive 3-D models become available to link Cenozoic climate variations with the Antarctic sediment record.

Ice flow models and glacial erosion over multiple glacial–interglacial cycles

“…(1), is based upon another assumption, and various other erosion laws tie the erosion rate to other powers of the sliding velocity (Hallet, 1979;Iverson, 1995;MacGregor et al, 2009), the ice flux (Kessler et al, 2008), or the basal shear stress (Pollard and Deconto, 2007), and a different choice would influence the patterns of erosion and the locations of maximum erosion rate. Comparing the magnitude of effects of erosion laws on developing topography can be difficult for a number of reasons: scaling factors and constants might vary; the ice physics, which can add further complications, determine the basal shear stress; and subglacial hydrology is still quite complicated.…”

“…Fluvial erosion processes are calculated from this discharge and the sediment supply, local topographic slope, and the channel width, all of which also are input into a linear sediment cover model (Braun and Sambridge, 1997). Hillslope processes are simulated from diffusion and a threshold landsliding algorithm when hillslopes steepen beyond a certain threshold (Burbank et al, 1996;Stolar et al, 2007). Within ICE-Cascade, the climate simulation is a combination of the inputs that govern the pattern of sea-level temperature and an orographic precipitation model (Yanites and Ehlers, 2012;Roe et al, 2003).…”

“…Within ICE-Cascade, the climate simulation is a combination of the inputs that govern the pattern of sea-level temperature and an orographic precipitation model (Yanites and Ehlers, 2012;Roe et al, 2003). The temperature and moisture content variations over all elevations is calculated using an input lapse rate and the Clausius-Clapeyron relation, and these values, along with inputs governing the wind speed and direction, are then used to calculate annual precipitation (Roe et al, 2003). When the temperature is below freezing, the precipitation takes the form of snow.…”

“…Hillslope processes are simulated from diffusion and a threshold landsliding algorithm when hillslopes steepen beyond a certain threshold (Burbank et al, 1996;Stolar et al, 2007). Within ICE-Cascade, the climate simulation is a combination of the inputs that govern the pattern of sea-level temperature and an orographic precipitation model (Yanites and Ehlers, 2012;Roe et al, 2003). The temperature and moisture content variations over all elevations is calculated using an input lapse rate and the Clausius-Clapeyron relation, and these values, along with inputs governing the wind speed and direction, are then used to calculate annual precipitation (Roe et al, 2003).…”

How do icebergs affect the Greenland ice sheet under pre-industrial conditions? – a model study with a fully coupled ice-sheet–climate model

“…Some models also differentiate between fast-and slow-flowing ice, such as ice shelves and grounded ice, respectively, to allow for a dynamic computation of the grounding line (e.g. Huybrechts, 1990;Huybrechts and de Wolde, 1999;Greve, 1995Greve, , 1997Ritz et al, 2001;Pollard and DeConto, 2007). These models are used, on the one hand, to predict the future development of the ice sheets and, on the other hand, to model their evolution during the past millennia and even millions of years.…”