Abstract
AbstractObservations show that the Greenland ice sheet has been losing mass at an increasing rate over the past few decades, which makes it a major contributor to sea-level rise. Here we use a three-dimensional higher-order ice-flow model, adaptive mesh refinement and inverse methods to accurately reproduce the present-day ice flow of the Greenland ice sheet. We investigate the effect of the ice thermal regime on (1) basal sliding inversion and (2) projections over the next 100 years. We show that steady-state temperatures based on present-day conditions allow a reasonable representation of the thermal regime and that both basal conditions and century-scale projections are weakly sensitive to small changes in the initial temperature field, compared with changes in atmospheric conditions or basal sliding. We conclude that although more englacial temperature measurements should be acquired to validate the models, and a better estimation of geothermal heat flux is needed, it is reasonable to use steady-state temperature profiles for short-term projections, as external forcings remain the main drivers of the changes occurring in Greenland.
Highlights
Recent observations show an accelerated ice loss of the Greenland ice sheet (Velicogna, 2009; Rignot and others, 2011) during the past few decades, attributed to both changes in surface mass balance and ice dynamics (Howat and others, 2007; Rignot and others, 2011)
We rely on four different initial ice thermal regimes: (1) steady-state temperatures calculated from the initial velocities; (2) a linear variation from 38C at the bed to 08C at the surface added to the steady-state temperatures (EXP1); (3) a warm model, where the temperature varies linearly between the surface temperature and the pressure-melting point at the base (EXP2); and (4) a cold-ice model, where the temperature is equal to the surface temperature for the entire ice column (EXP3)
Additional inversions were performed with different initial guesses of basal friction and led to similar results, demonstrating the limited influence of the initial value
Summary
Recent observations show an accelerated ice loss of the Greenland ice sheet (Velicogna, 2009; Rignot and others, 2011) during the past few decades, attributed to both changes in surface mass balance and ice dynamics (Howat and others, 2007; Rignot and others, 2011). To better understand the behavior of the Greenland ice sheet, several large-scale ice-flow numerical models have been employed to simulate the evolution of the ice sheet over the coming centuries (Greve, 1997a; Ritz and others, 2001; Greve and others, 2011; Gillet-Chaulet and others, 2012; Seddik and others, 2012) These models rely on different iceflow approximations, parameterizations of physical processes and initialization procedures. Most ice-flow models rely on simplified first-order approximations of the momentum balance equations, such as the shallow-ice approximation (SIA; Hutter, 1982), the shelfy-stream approximation (SSA; MacAyeal, 1989; Greve and others, 2011; Aschwanden and others, 2012a) or a combination of SIA and SSA (Bueler and Brown, 2009; Pollard and DeConto, 2009) Initialization of these numerical models generally consists of running paleoclimate spin-ups over at least the last glacial cycle, in order to obtain a suitable present-day configuration (Greve and others, 2011; Aschwanden and others, 2012a). Previous studies (Ritz and others, 2001; DeConto and Pollard, 2003; Pollard and DeConto, 2009; Applegate and others, 2012; Rogozhina and others, 2012) illustrated the ability of these simplified models to improve our understanding of ice-sheet paleoclimate, as well as to evaluate the effect of different model parameters
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