Abstract
Abstract. Floating ice shelves can exert a retentive and hence stabilizing force onto the inland ice sheet of Antarctica. However, this effect has been observed to diminish by the dynamic effects of fracture processes within the protective ice shelves, leading to accelerated ice flow and hence to a sea-level contribution. In order to account for the macroscopic effect of fracture processes on large-scale viscous ice dynamics (i.e., ice-shelf scale) we apply a continuum representation of fractures and related fracture growth into the prognostic Parallel Ice Sheet Model (PISM) and compare the results to observations. To this end we introduce a higher order accuracy advection scheme for the transport of the two-dimensional fracture density across the regular computational grid. Dynamic coupling of fractures and ice flow is attained by a reduction of effective ice viscosity proportional to the inferred fracture density. This formulation implies the possibility of non-linear threshold behavior due to self-amplified fracturing in shear regions triggered by small variations in the fracture-initiation threshold. As a result of prognostic flow simulations, sharp across-flow velocity gradients appear in fracture-weakened regions. These modeled gradients compare well in magnitude and location with those in observed flow patterns. This model framework is in principle expandable to grounded ice streams and provides simple means of investigating climate-induced effects on fracturing (e.g., hydro fracturing) and hence on the ice flow. It further constitutes a physically sound basis for an enhanced fracture-based calving parameterization.
Highlights
The contemporarily observed sea-level change (Cazenave and Llovel, 2010; Church et al, 2011; Gregory et al, 2012) as well as the expected long-term sea-level commitment (Levermann et al, 2013) underpin the role of the contributions of the large polar ice sheets of Greenland and Antarctica (Van den Broeke et al, 2011; Rignot et al, 2011b; Shepherd et al, 2012; Hanna et al, 2013)
Fracture processes play a fundamental role in the dynamics of ice streams and ice shelves, in addition to ocean melt (Pritchard et al 2012; Rignot et al, 2013), and in interaction with external drivers, such as surface melt induced by atmospheric warming (MacAyeal and Sergienko, 2013)
In this study we present a simplified framework of continuum damage evolution based on ideas by Pralong and Funk (2005) and Borstad et al (2012), which we named “fracture density”, adapted to the finite-difference Parallel Ice Sheet Model (Bueler and Brown, 2009; Winkelmann et al, 2011, based on PISM v.05; see documentation: www.pism-docs. org)
Summary
The contemporarily observed sea-level change (Cazenave and Llovel, 2010; Church et al, 2011; Gregory et al, 2012) as well as the expected long-term sea-level commitment (Levermann et al, 2013) underpin the role of the contributions of the large polar ice sheets of Greenland and Antarctica (Van den Broeke et al, 2011; Rignot et al, 2011b; Shepherd et al, 2012; Hanna et al, 2013). Fracture processes play a fundamental role in the dynamics of ice streams and ice shelves, in addition to ocean melt (Pritchard et al 2012; Rignot et al, 2013), and in interaction with external drivers, such as surface melt induced by atmospheric warming (MacAyeal and Sergienko, 2013). Fractures are mostly found as elongated structures of fragments or sequences of troughs and open crevasses, visible at the ice surface. These fracture bands are aligned along the ice flow with origin in the wake of topographic features such as ice rises, ice rumples or along ice stream inlets and usually extend the whole distance towards the calving front. On that journey along the stream, prevailing stresses can change
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