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The Cryosphere An interactive open-access journal of the European Geosciences Union
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Volume 12, issue 7 | Copyright
The Cryosphere, 12, 2249-2266, 2018
https://doi.org/10.5194/tc-12-2249-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 12 Jul 2018

Research article | 12 Jul 2018

Simulated retreat of Jakobshavn Isbræ since the Little Ice Age controlled by geometry

Nadine Steiger1, Kerim H. Nisancioglu2,3, Henning Åkesson2,a, Basile de Fleurian2, and Faezeh M. Nick4 Nadine Steiger et al.
  • 1Geophysical Institute, University of Bergen and the Bjerknes Centre for Climate Research, Bergen, Norway
  • 2Department of Earth Science, University of Bergen and the Bjerknes Centre for Climate Research, Bergen, Norway
  • 3Centre for Earth Evolution and Dynamics, University of Oslo, Oslo, Norway
  • 4Department of Arctic Geology, University Centre in Svalbard, Longyearbyen, Norway
  • anow at: Department of Geological Sciences, Stockholm University, Bolin Centre for Climate Research, Stockholm, Sweden

Abstract. Rapid retreat of Greenland's marine-terminating glaciers coincides with regional warming trends, which have broadly been used to explain these rapid changes. However, outlet glaciers within similar climate regimes experience widely contrasting retreat patterns, suggesting that the local fjord geometry could be an important additional factor. To assess the relative role of climate and fjord geometry, we use the retreat history of Jakobshavn Isbræ, West Greenland, since the Little Ice Age (LIA) maximum in 1850 as a baseline for the parameterization of a depth- and width-integrated ice flow model. The impact of fjord geometry is isolated by using a linearly increasing climate forcing since the LIA and testing a range of simplified geometries.

We find that the total length of retreat is determined by external factors – such as hydrofracturing, submarine melt and buttressing by sea ice – whereas the retreat pattern is governed by the fjord geometry. Narrow and shallow areas provide pinning points and cause delayed but rapid retreat without additional climate warming, after decades of grounding line stability. We suggest that these geometric pinning points may be used to locate potential sites for moraine formation and to predict the long-term response of the glacier. As a consequence, to assess the impact of climate on the retreat history of a glacier, each system has to be analyzed with knowledge of its historic retreat and the local fjord geometry.

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We use an ice flow model to reconstruct the retreat of Jakobshavn Isbræ since 1850, forced by increased ocean warming and calving. Fjord geometry governs locations of rapid retreat: narrow and shallow areas act as intermittent pinning points for decades, followed by delayed rapid retreat without additional climate warming. These areas may be used to locate potential moraine buildup. Evidently, historic retreat and geometric influences have to be analyzed individually for each glacier system.
We use an ice flow model to reconstruct the retreat of Jakobshavn Isbræ since 1850, forced by...
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