Abstract
AbstractStreaming ice accounts for a major fraction of global ice flux, yet we cannot yet fully explain the dominant controls on its kinematics. In this contribution, we use an anisotropic full-Stokes thermomechanical flow solver to characterize how mechanical anisotropy and temperature distribution affect ice flux. For the ice stream and glacier geometries we explored, we found that the ice flux increases 1–3% per °C temperature increase in the margin. Glaciers and ice streams with crystallographic fabric oriented approximately normal to the shear plane increase by comparable amounts: an otherwise isotropic ice stream containing a concentrated transverse single maximum fabric in the margin flows 15% faster than the reference case. Fabric and temperature variations independently impact ice flux, with slightly nonlinear interactions. We find that realistic variations in temperature and crystallographic fabric both affect ice flux to similar degrees, with the exact effect a function of the local fabric and temperature distributions. Given this sensitivity, direct field-based measurements and models incorporating additional factors, such as water content and temporal evolution, are essential for explaining and predicting streaming ice dynamics.
Highlights
The extent of continental ice plays a large role in environmental systems, from the direct effect on sea level to changes in surface albedo, to controlling fresh water resources in mountain communities
One study from the Whillans ice stream margin found a multiple maximum fabric varying to a single maximum with a cone angle ∼40° (Jackson, 1999)
Complementing laboratory and theoretical studies, we show that crystallographic fabrics in streaming ice can inhibit or enhance flow, with the magnitude of strengthening or weakening depending on the concentration, orientation and location of the fabric, as well as the geometry and boundary conditions of the system
Summary
The extent of continental ice plays a large role in environmental systems, from the direct effect on sea level to changes in surface albedo, to controlling fresh water resources in mountain communities. With only medium confidence at present in predicting ice discharge (Vaughan and others, 2013), due in large part to the uncertainty in the viscous constitutive laws, improvement in describing ice dynamics can have a strong impact on overall predictions of the mass balance of ice sheets and glaciers. Since the 1950s (Nye, 1953; Glen, 1955) the glaciology community has had reasonable constraints on the bulk flow of effectively isotropic ice. Flow laws developed with some modification (e.g., Barnes and others, 1971; Ashby and Duval, 1985; Goldsby and Kohlstedt, 2001; Treverrow and others, 2012), have approximated the kinematics that prevail over much of the ice sheets. Glen’s flow law, which is valid for low-strain, isotropic ice, falls short of representing flow changes in regions of high strain (Alley, 1992; Thorsteinsson and others, 2003; Martín and others, 2009, 2014; Ma and others, 2010; Budd and others, 2013; Minchew and others, 2018)
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