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

Abstract

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.

Multi-year surface velocities and sea-level rise contribution of the Basin-3 and Basin-2 surges, Austfonna, Svalbard

“…In this study, we closely follow the processing steps of Schellenberger et al (2015) and Dunse et al (2015) to derive glacier surface velocity of Basin-3 and Basin-2 by means of SAR offset and speckle tracking. The time-series of velocity maps from Table 1.…”

“…We used different methods to fill the remaining gaps. The velocity along 20 the fluxgate at the time steps t 3 and t 6 (Table A1 in Appendix A) were derived by scaling the remaining estimates as described in Dunse et al (2015).…”

“…We also extend the frontal ablation estimate and sea 30 level rise contribution of Basin-3 for the period 19 April 2012 -9 May 2013 of Dunse et al (2015) until 26 July 2016.…”

“…1). Dunse et al (2015) used ground penetrating radar to map the formation of 15 crevasses along two profiles in the accumulation area of Basin-3 between 2004 and 2012. They observed multiannual stepwise acceleration of GPS stations within a distinct flow unit in the north of Basin-3 since 2008.…”

Basal drag of Fleming Glacier, Antarctica, Part B: implications of evolution from 2008 to 2015

“…It arises from two main sources in polar regions: either surface melt water draining into the subglacial hydrologic system via crevasses or moulins or in-situ melting at the bed (Banwell et al, 2016;Dunse et al, 2015;Hoffman and Price, 2014). Hoffman and Price (2014) also found a positive feedback between the basal melt and basal sliding through 245 the frictional heating on an idealized mountain glacier using coupled subglacial hydrology and ice dynamics models.…”