Early Career Scientist Prize

The IACS 2016 Early Career Scientist Prize
is jointly awarded to

Dr Thorben Dunse
University of Oslo

for his paper

Glacier-surge mechanisms promoted by a
hydro-thermodynamic feedback to summer melt
T Dunse, T. Schellenberger, J. O. Hagen, A. Kääb, T. V. Schuler &
C.H. Reijmer
The Cryosphere, 9(1), 197–215 (2015); doi:10.5194/tc-9-197-2015

(Citation Abstract Fig. 1A Fig. 2A)

Ms Rachel Tilling
University College London

for her paper

Increased Arctic sea ice volume
after anomalously low melting in 2013
R. L. Tilling, A. Ridout, A. Shepherd & D. J. Wingham
Nature Geoscience 8(8), 643–646 (2015); doi:10.1038/ngeo2489

(Citation Abstract Fig. 1B Fig. 2B)

The Selection Panel, Regine Hock (Chair), Tómas Jóhannesson, Olga Solomina, and Christine Schøtt Hvidberg expressed their pleasure at the very high standard of the nominated 16 entries. The Prize will be awarded again in 2019.

Citation for Dr Dunse by the 2016 Selection Panel:
"Thorben Dunse and colleagues analyze unique field observations of ice velocity during the onset and development of a surge in one of the drainage basins of the Austfonna ice cap in Svalbard. The data set provides new insights into the yet poorly understood mechanisms of surging glaciers. The authors propose a hydro-thermodynamic feedback that mobilizes stagnant ice initially frozen to the bed, thus leading to fast basal motion and surge initiation. The possibility of such instabilities caused by warming initially cold marginal ice resisting fast drainage may have major implications for ice sheet stability."


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 2003–2008, 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.


Flow velocities along the centreline of the fast-flow region of Basin-3, Austfonna, between May 2008 and May 2013. GPS stations are numbered from 1 at the lowest elevation to 5 at the highest (Fig. 1). Red bars (upper panel) indicate potential melt days and cumulative positive-degree days (PDD) for each summer, inferred from the temperature record of an automatic weather station. [doi:10.5194/tc-9-197-2015]


Surface velocity fields of Basin-3, Austfonna, derived from TerraSAR-X feature tracking: (a) April/May 2012, (b) August, (c) October, and (d) January/February 2013. Red circles represent mean position of GPS receivers over the particular repeat-pass period; fill colour according to colour coding of receivers in Fig. 2. The red arrows indicate associated GPS velocity vectors. Glacier elevation contours plotted in grey at 100m intervals; front position at time of repeat pass in orange. [doi:10.5194/tc-9-197-2015]

Creative Commons License
doi:10.5194/tc-9-197-2015 licensed under a CC Attribution 3.0 License


Citation for Ms Tilling by the 2016 Selection Panel:
"Rachel Tilling and her colleagues assessed variations in Northern Hemisphere sea-ice thickness and volume between 2010 and 2014, and analyzed the drivers of these changes. Results reveal complex spatio-temporal patterns and indicate that Arctic sea-ice is sensitive to modest environmental changes. A pronounced increase in sea-ice volume following a cool summer indicates a resilience in Arctic sea-ice previously not anticipated."


Abstract: Changes in Arctic sea ice volume affect regional heat and freshwater budgets and patterns of atmospheric circulation at lower latitudes. Despite a well-documented decline in summer Arctic sea ice extent by about 40% since the late 1970s, it has been dicult to quantify trends in sea ice volume because detailed thickness observations have been lacking. Here we present an assessment of the changes in Northern Hemisphere sea ice thickness and volume using five years of CryoSat-2 measurements. Between autumn 2010 and 2012, there was a 14% reduction in Arctic sea ice volume, in keeping with the long-term decline in extent. However, we observe 33% and 25% more ice in autumn 2013 and 2014, respectively, relative to the 2010–2012 seasonal mean, which oset earlier losses. This increase was caused by the retention of thick sea ice northwest of Greenland during 2013 which, in turn, was associated with a 5% drop in the number of days on which melting occurred—conditions more typical of the late 1990s. In contrast, springtime Arctic sea ice volume has remained stable. The sharp increase in sea ice volume after just one cool summer suggests that Arctic sea ice may be more resilient than has been previously considered. [doi:10.1038/ngeo2489]


Observed and modelled Northern Hemisphere sea ice volume, from 2010–2014. Cryosat-2 estimates of total (red stars), first-year (green diamonds) and multi-year (blue triangles) sea ice volume are shown, as well as model estimates of volume from PIOMAS. To estimate uncertainties in CryoSat-2 monthly sea ice volume, we account for uncertainties in the sea ice density, snow density, snow depth and the measurement of sea ice freeboard. [doi:10.1038/ngeo2489]


The relationship between Arctic sea ice volume and summer melting. (a) Time series of PIOMAS model Arctic sea ice volume for autumn 1980–2014 (solid line) and spring 1981–2014 (dashed line). CryoSat-2 volume estimates (red stars) are plotted for 2010–2014. (b) Time series of average melting degree days (MDD) across the Arctic Ocean for 1980–2014 (solid purple line), and CryoSat-2 autumn ice volume for 2010–2014 (red stars). The MDD time series mean (solid black line) and standard deviation (dashed black lines) are shown. The purple dashed line is a linear fit to the data. (c) Relationship between anomalies of CryoSat-2 autumn ice volume and the number of MDD during the preceding year, for first-year ice (green diamonds and green dashed line; r2=0.12), multi-year ice (blue triangles and blue dashed line; r2=0.78) and total ice (red stars and red dashed line; r2=0.75). [doi:10.1038/ngeo2489]