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The Cryosphere An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/tc-2019-301
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/tc-2019-301
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 27 Jan 2020

Submitted as: research article | 27 Jan 2020

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This preprint is currently under review for the journal TC.

The contrasting response of outlet glaciers to interior and ocean forcing

John Erich Christian1, Alexander Robel2, Cristian Proistosescu3,4,5, Gerard Roe1, Michelle Koutnik1, and Knut Christianson1 John Erich Christian et al.
  • 1Department of Earth and Space Sciences, University of Washington, Seattle, Washington, USA
  • 2School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, Georgia, USA
  • 3Joint Institute for the Study of the Atmosphere and the Ocean, University of Washington, Seattle, Washington, USA
  • 4Department of Atmospheric Sciences, University of Illinois, Urbana-Champaign, Illinois, USA
  • 5Department of Geology, University of Illinois, Urbana-Champaign, Illinois, USA

Abstract. The dynamics of marine-terminating outlet glaciers are of fundamental interest in glaciology, and affect mass loss from ice sheets in a warming climate. In this study, we analyze the response of outlet glaciers to different sources of climate forcing. We find that outlet glaciers have a characteristically different transient response to surface-mass-balance forcing applied over the interior than to oceanic forcing applied at the grounding line. A recently developed reduced model represents outlet glacier dynamics via two widely-separated response timescales: a fast response associated with grounding-zone dynamics, and a slow response of interior ice. The reduced model is shown to emulate the behavior of a more complex numerical model of ice flow. Together, these models demonstrate that ocean forcing first engages the fast, local response, and then the slow adjustment of interior ice, whereas surface-mass-balance forcing is dominated by the slow interior adjustment. We also demonstrate the importance of the timescales of stochastic forcing for assessing the natural variability of outlet glaciers, highlighting that decadal persistence in ocean variability can affect the behavior of outlet glaciers on centennial and longer timescales. Finally, we show that these transient responses have important implications for: attributing observed glacier changes to natural or anthropogenic influences; the future change already committed by past forcing; and the impact of past climate changes on the preindustrial glacier state, against which current and future anthropogenic influences are assessed.

John Erich Christian et al.

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John Erich Christian et al.

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Short summary
We use simple, physics-based models to compare how marine-terminating glaciers respond to changes at their marine margin vs. inland surface melt. Initial glacier retreat is more rapid for ocean changes than for inland changes, but in both cases, glaciers will continue responding for millennia. We analyze several implications of these differing pathways of change. In particular, natural ocean variability must be better understood to correctly identify the anthropogenic role in glacier retreat.
We use simple, physics-based models to compare how marine-terminating glaciers respond to...
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