Permanent fast flow versus cyclic surge behaviour: numerical simulations of the Austfonna ice cap, Svalbard

Dunse, Thorben; Greve, Ralf; Schuler, Thomas; Hagen, Jon Ove

doi:10.3189/002214311796405979

Cited by 32 publications

(71 citation statements)

References 71 publications

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“…About one-third of the ice base is grounded below sea level down to a maximum depth of ∼ 150 m within an overdeepening in the central terminus region (Fig. 1b;Dowdeswell et al, 1986;Dunse et al, 2011). A previous velocity map based on satellite radar interferometry from data acquired in the mid-1990s revealed an ice stream in the northern (Dowdeswell et al, 2008).…”

Section: Austfonna Basin-3mentioning

confidence: 82%

Glacier-surge mechanisms promoted by a hydro-thermodynamic feedback to summer melt

et al. 2015

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Abstract. Mass loss from glaciers and ice sheets currently accounts for two-thirds of the observed global sea-level rise and has accelerated since the 1990s, coincident with strong atmospheric warming in the polar regions. Here we present continuous GPS measurements and satellite synthetic-aperture-radar-based velocity maps from Basin-3, the largest drainage basin of the Austfonna ice cap, Svalbard. Our observations demonstrate strong links between surface-melt and multiannual ice-flow acceleration. We identify a hydro-thermodynamic feedback that successively mobilizes stagnant ice regions, initially frozen to their bed, thereby facilitating fast basal motion over an expanding area. By autumn 2012, successive destabilization of the marine terminus escalated in a surge of Basin-3. The resulting iceberg discharge of 4.2 ± 1.6 Gt a −1 over the period April 2012 to May 2013 triples the calving loss from the entire ice cap. With the seawater displacement by the terminus advance accounted for, the related sea-level rise contribution amounts to 7.2 ± 2.6 Gt a −1 . This rate matches the annual ice-mass loss from the entire Svalbard archipelago over the period [2003][2004][2005][2006][2007][2008], highlighting the importance of dynamic mass loss for glacier mass balance and sea-level rise. The active role of surface melt, i.e. external forcing, contrasts with previous views of glacier surges as purely internal dynamic instabilities. Given sustained climatic warming and rising significance of surface melt, we propose a potential impact of the hydro-thermodynamic feedback on the future stability of ice-sheet regions, namely at the presence of a cold-based marginal ice plug that restricts fast drainage of inland ice. The possibility of large-scale dynamic instabilities such as the partial disintegration of ice sheets is acknowledged but not quantified in global projections of sea-level rise.

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Section: Austfonna Basin-3mentioning

confidence: 82%

Glacier-surge mechanisms promoted by a hydro-thermodynamic feedback to summer melt

et al. 2015

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“…The Nordaustlandet ice caps were also the target of an expedition in the International Geophysical Year (IGY) during 1957-1958 when ice cap geometry, temperatures, mass balance and ice thickness were measured (Schytt, 1964). More recently, Austfonna has been visited by expeditions led by University of Oslo (Dunse et al, 2009(Dunse et al, , 2012(Dunse et al, , 2011. The research area is presented in Fig.…”

Section: Research Sitementioning

confidence: 99%

Sensitivity of basal conditions in an inverse model: Vestfonna ice cap, Nordaustlandet/Svalbard

et al. 2012

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Abstract. The dynamics of Vestfonna ice cap (Svalbard) are dominated by fast-flowing outlet glaciers. Its mass balance is poorly known and affected dynamically by these fast-flowing outlet glaciers. Hence, it is a challenging target for ice flow modeling. Precise knowledge of the basal conditions and implementation of a good sliding law are crucial for the modeling of this ice cap. Here we use the full-Stokes finite element code Elmer/Ice to model the 3-D flow over the whole ice cap. We use a Robin inverse method to infer the basal friction from the surface velocities observed in 1995. Our results illustrate the importance of the basal friction parameter in reproducing observed velocity fields. We also show the importance of having variable basal friction as given by the inverse method to reproduce the velocity fields of each outlet glacier -a simple parametrization of basal friction cannot give realistic velocities in a forward model. We study the robustness and sensitivity of this method with respect to different parameters (mesh characteristics, ice temperature, errors in topographic and velocity data). The uncertainty in the observational parameters and input data proved to be sufficiently small as not to adversely affect the fidelity of the model.

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“…the Devon Island Ice Cap in Arctic Canada or the Academy of Sciences Ice Cap in the Russian Arctic (Dowdeswell et al, 2002). Model results suggest that the large ice thickness within these valleys allows for temperate basal conditions, and hence, basal motion as the dominant mechanism of ice flow (Dunse et al, 2011). Several basins are known to have surged in the past; Etonbreen and Bråsvellbreen in the 1930s and Basin-3 around 1850-1870 (Schytt, 1969;Lefauconnier and Hagen, 1991).…”

Section: The Austfonna Ice Capmentioning

confidence: 99%

“…Where GPR measurements are lacking, bedrock elevations are interpolated utilizing additional information from a bedrock map at 1 km horizontal resolution (Dunse et al, 2011). A detailed description of the methodology is provided in Appendix A.…”

Section: Additional Datamentioning

confidence: 99%

Seasonal speed-up of two outlet glaciers of Austfonna, Svalbard, inferred from continuous GPS measurements

et al. 2012

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Abstract.A large part of the ice discharge from ice caps and ice sheets occurs through spatially limited flow units that may operate in a mode of steady flow or cyclic surge behaviour. Changes in the dynamics of distinct flow units play a key role in the mass balance of Austfonna, the largest ice cap on Svalbard. The recent net mass loss of Austfonna was dominated by calving from marine terminating outlet glaciers. Previous ice-surface velocity maps of the ice cap were derived by satellite radar interferometry (InSAR) and rely on data acquired in the mid-1990s with limited information concerning the temporal variability. Here, we present continuous Global Positioning System (GPS) observations along the central flowlines of two fast flowing outlet glaciers over [2008][2009][2010]. The data show prominent summer speedups with ice-surface velocities as high as 240 % of the presummer mean. Acceleration follows the onset of the summer melt period, indicating enhanced basal motion due to input of surface meltwater into the subglacial drainage system. In 2008, multiple velocity peaks coincide with successive melt periods. In 2009, the major melt was of higher amplitude than in 2008. Flow velocities appear unaffected by subsequent melt periods, suggesting a transition towards a hydraulically more efficient drainage system. The observed annual mean velocities of Duvebreen and Basin-3 exceed those from the mid-1990s by factors two and four, respectively, implying increased ice discharge at the calving front. Measured summer velocities up to 2 m d −1 for Basin-3 are close to those of Kronebreen, often referred to as the fastest glacier on Svalbard.

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Permanent fast flow versus cyclic surge behaviour: numerical simulations of the Austfonna ice cap, Svalbard

Cited by 32 publications

References 71 publications

Glacier-surge mechanisms promoted by a hydro-thermodynamic feedback to summer melt

Glacier-surge mechanisms promoted by a hydro-thermodynamic feedback to summer melt

Sensitivity of basal conditions in an inverse model: Vestfonna ice cap, Nordaustlandet/Svalbard

Seasonal speed-up of two outlet glaciers of Austfonna, Svalbard, inferred from continuous GPS measurements

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