Over recent decades, Greenland ice sheet surface melt has shown an increase both in intensity and spatial extent. Part of this water probably reaches the bed and can enhance glacier speed, advecting a larger volume of ice into the ablation area. In the context of a warming climate, this mechanism could contribute to the future rate of thinning and retreat of land-terminating glaciers of Greenland. These changes in ice flow conditions will in turn influence surface crevassing and thus the ability of water to reach the bed at higher elevations. Here, using a coupled basal hydrology and prognostic ice flow model, the evolution of a Greenland-type glacier subject to increasing surface melt is studied over a few decades. For different scenarios of surface melt increase over the next decades, the evolution of crevassed areas and the ability of water to reach the bed is inferred. Our results indicate that the currently observed crevasse distribution is likely to extend further upstream which will allow water to reach the bed at higher elevations. This will lead to an increase in ice flux into the ablation area which, in turn, accelerates the mass loss of land-terminating glaciers.
Read more: Gagliardini O. and M. Werder, 2018. Influence of increasing surface melt over decadal timescales on land-terminating Greenland-type outlet glaciers, Journal of Glaciology, 1-11, doi:10.1017/jog.2018.59.
The Wordie Ice Shelf–Fleming Glacier system in the southern Antarctic Peninsula has experienced a long-term retreat and disintegration of its ice shelf in the past 50 years. What is responsibe for this massive loss of ice? The work - consisting of two articles - presented here uses Elmer/Ice to investigate the dynamics of the retreat of the glacier front during the period from 2008 until 2015. From inversions based on a multi-cycle spin-up scheme to reduce the influence of the initial approximated englacial temperatures (detailed in part 1 of this paper series), part 2 shows that the grounding line of the fully grounded Fleming glacier in 2008, which was the main tributary to the shelf, has retreated by about 9 km land inward until 2015. This position virtually coincides with the last known grounding line position in 2014 . How strong the influence on this retreat was split between the acting Marine Ice Sheet Instability (MISI), ocean forcing or an increase in the observed drastic change in bed lubrication further upstream the Fleming glacier remains to be subject of further investigations.
Zhao, C., R. M. Gladstone, R. C. Warner, M. A. King, T. Zwinger, and M. Morlighem, 2018. Basal friction of Fleming Glacier, Antarctica – Part 1: Sensitivity of inversion to temperature and bedrock uncertainty, The Cryosphere 12, 2637-2652, doi:10.5194/tc-12-2637-2018.
Zhao, C., R. M. Gladstone, R. C. Warner, M. A. King, T. Zwinger, and M. Morlighem, 2018. Basal friction of Fleming Glacier, Antarctica – Part 2: Evolution from 2008 to 2015, The Cryosphere 12, 2653-2666, doi:10.5194/tc-12-2653-2018.
The amount of ice discharged by an ice stream depends on its width, and the widths of unconfined ice streams such as the Siple Coast ice streams in West Antarctica have been observed to evolve on decadal to centennial timescales. Thermally driven widening of ice streams provides a mechanism for this observed variability through melting of the frozen beds of adjacent ice ridges. This widening is driven by the heat dissipation in the ice stream margin, where strain rates are high, and at the bed of the ice ridge, where subtemperate sliding is possible. The inflow of cold ice from the neighboring ice ridges impedes ice stream widening. Determining the migration rate of the margin requires resolving conductive and advective heat transfer processes on very small scales in the ice stream margin, and these processes cannot be resolved by large-scale ice sheet models. Here, we exploit the thermal boundary layer structure in the ice stream margin to investigate how the migration rate depends on these different processes. We derive a parameterization of the migration rate in terms of parameters that can be estimated from observations or large-scale model outputs, including the lateral shear stress in the ice stream margin, the ice thickness of the stream, the influx of ice from the ridge, and the bed temperature of the ice ridge. This parameterization will allow the incorporation of ice stream margin migration into large-scale ice sheet models.