Three-dimensional modelling of the dynamics of Johnsons Glacier, Livingston Island, Antarctica

Abstract

A new three-dimensional finite-element model of the steady-state dynamics of temperate glaciers has been developed and applied to Johnsons Glacier, Livingston Island, Antarctica, with the aim of determining the velocity and stress fields for the present glacier configuration. It solves the full Stokes system of differential equations without recourse to simplifications such as those involved in the shallow-ice approximation. Rather high values of the stiffness parameter B (∼0.19–0.23MPaa1/3) are needed to match the observed ice surface velocities, although these results do not differ much from those found by other authors for temperate glaciers. Best-fit values of the coefficient k in the sliding law (*2.2–2.7 x 103m a–1MPa–2) are also of the same order of magnitude as those found by other authors. The results for velocities are satisfactory, though locally there exist significant discrepancies between computed and observed ice surface velocities, particularly for the vertical ones. This could be due to failures in the sliding law (in particular, the lack of information on water pressure), the use of an artificial down-edge boundary condition and the fact that bed deformation is not considered. For the whole glacier system, the driving stress is largely balanced by the basal drag (80% of the driving stress). Longitudinal stress gradients are only important in the divide areas and near the glacier terminus, while lateral drag is only important at both sides of the terminal zone.

The Potsdam Parallel Ice Sheet Model (PISM-PIK) – Part 1: Model description

“…Three-dimensional models which solve the complete Stokes stress balance (e.g., Martín et al, 2004;Jarosch and Gudmundsson, 2007;Pattyn, 2008) cannot be used for largescale, long-term, high resolution modeling because they are computationally too demanding. The same constraint generally applies to intermediate, so-called higher order models (e.g., Blatter, 1995;Pattyn, 2003).…”

A 14-year dataset of in situ glacier surface velocities for a tidewater and a land-terminating glacier in Livingston Island, Antarctica

“…However, this is still insufficient to study velocity variations on scales shorter than the seasonal one. For this reason, perhaps the highest interest of the dataset presented is its use for tuning the free parameters of numerical models of glacier dynamics (Martín et al, 2004;Otero et al, 2010), since these models represent averaged velocities on time-step scales, which are often of the order of weeks (especially for steady-state models such as those cited, in which a limited time evolution is applied to get the model to reach a steady-state configuration). But even for transient models, weekly time steps are usual (e.g.…”

“…These islands, located off the north-western tip of the Antarctic Peninsula, previously had a scarce record of in situ velocity observations, which included measurements in the late 1980s on Nelson Island (Ren Jiaven et al, 1995), earlier measurements in the late 1990s on Johnsons Glacier (Ximenis et al, 1999), and measurements in the Arctowski Icefield, the Bellingshausen Dome, and the Central Dome of King George Island between 1999and 2008/09 (Blindow et al, 2010Rückamp et al, 2010Rückamp et al, , 2011. Such in situ velocity measurements are critical for the validation of the estimates of remote-sensor-based studies of ice discharge in the region such as those by Osmanoglu et al (2013Osmanoglu et al ( , 2014 for King George and Livingston islands (the present dataset has in fact been used in the latter paper with such purposes), as well as for tuning free parameters of glacier dynamics models, as done by Martín et al (2004) and Otero et al (2010) using an earlier (and shorter) version of the dataset presented. An added interest of the presented velocity record is that it corresponds to both a tidewater glacier and a landterminating glacier, two glacier types that are typical in this region but very different in dynamical behaviour.…”

“…Some models have treated these coefficients as constant in space (e.g. Hanson, 1995;Martín et al, 2004;Otero et al, 2010). Recently, it is becoming more and more common to establish the viscosity and/or the basal friction coefficients as functions of position.…”

Semi-brittle rheology and ice dynamics in DynEarthSol3D

“…In the past 5 years numerical models have largely risen to the challenge of simulating the continent-scale, steady-state viscous flow of ice, leading to the development of the latest class of ice sheet models that represent ice physics across many flow regimes and in three spatial dimensions. These are often nonlinearly viscous, thermo-mechanical models that solve the so-called full-Stokes (FS) equations (e.g., Martin et al, 2004;Larour et al, 2012). Models based on shallow ice (SIA) and shallow shelf (SSA) approximations of the FS equations are also in wide use and simulate ice flow well in most areas (e.g., Winkelmann et al, 2011;Lipscomb et al, 2013).…”