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Climate of the Past An interactive open-access journal of the European Geosciences Union
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Preprints
https://doi.org/10.5194/cp-2020-111
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/cp-2020-111
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  30 Sep 2020

30 Sep 2020

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This preprint is currently under review for the journal CP.

Cosmogenic isotope measurements from recently deglaciated bedrock as a new tool to decipher changes in Greenland Ice Sheet size

Nicolás E. Young1, Alia J. Lesnek2, Josh K. Cuzzone3, Jason P. Briner4, Jessica A. Badgeley5, Alexandra Balter-Kennedy1, Brandon L. Graham4, Allison Cluett4, Jennifer L. Lamp1, Roseanne Schwartz1, Thibaut Tuna6, Edouard Bard6, Marc W. Caffee7,8, Susan R. H. Zimmerman9, and Joerg M. Schaefer1 Nicolás E. Young et al.
  • 1Lamont-Doherty Earth Observatory, Columbia University, Palisades NY, 10964, USA
  • 2Department of Earth Sciences, University of New Hampshire, Durham NH, 03824, USA
  • 3Department of Earth System Science, University of California Irvine, Irvine CA, 92697, USA
  • 4Department of Geology, University at Buffalo, Buffalo NY, 14260, USA
  • 5Department of Earth and Space Sciences, University of Washington, Seattle WA, 98195, USA
  • 6CEREGE, Aix-Marseille University, CNRS, IRD, INRAE, Collège de France, Technopôle del’Arbois, Aix-en-Provence, France
  • 7Department of Physics and Astronomy, PRIME Lab, Purdue University, West Lafayette IN, 47907, USA
  • 8Department of Earth, Atmospheric, and Planetary Sciences, Purdue University, West Lafayette IN, 47907, USA
  • 9Center for Accelerator Mass Spectrometry, Lawrence Livermore National Laboratory, Livermore CA, 94550, USA

Abstract. During the middle to late Holocene (8.2 ka BP to present), the Greenland Ice Sheet (GrIS) was smaller than its current configuration. Determining the exact dimensions of the Holocene ice-sheet minimum and the duration that the ice margin rested inboard of its current position remains challenging. Contemporary retreat of the GrIS from its historical maximum extent in southwestern Greenland is exposing a landscape that holds clues regarding the configuration and timing of past ice-sheet minima. To quantify the duration of the time the GrIS margin was near its modern extent we develop a new technique on Greenland that utilizes in situ cosmogenic 10Be-14C-26Al in bedrock samples that have become ice free only in the last few decades by the retreating ice-sheet margin at Kangiata Nunaata Sermia (n = 12 sites; KNS), southwest Greenland. To maximize the utility of this approach, we refine the deglaciation history of the region with stand-alone 10Be measurements (n = 49) and traditional 14C ages from sedimentary deposits contained in proglacial-threshold lakes. We combine our reconstructed ice-margin history in the KNS region with additional geologic records from southwestern Greenland and recent model simulations of GrIS change, to constrain the timing of the GrIS minimum in southwest Greenland, the magnitude of Holocene inland GrIS retreat, and explore the regional climate history influencing Holocene ice-sheet behavior. Our 10Be-14C-26Al measurements reveal that 1) KNS retreated behind its modern margin just before 10 ka, but likely stabilized near the present GrIS margin for several thousand years before retreating farther inland, and 2) pre-Holocene 10Be detected in several of our sample sites is most easily explained by several thousand years of surface exposure during the Last Interglaciation. Moreover, our new results indicate that the minimum extent of the GrIS likely occurred after ~ 5 ka, and the GrIS margin may have approached its eventual historical maximum extent as early as ~ 2 ka. Recent simulations of GrIS change are able to match the geologic record of ice-sheet change in regions dominated by surface mass balance, but produce a poorer model-data fit in areas influenced by oceanic and dynamic processes. Simulations that achieve the best model-data fit suggest that inland retreat of the ice margin driven by early to middle Holocene warmth may have been mitigated by increased precipitation. Triple 10Be-14C-26Al measurements in recently deglaciated bedrock provide a new tool to help decipher the duration of smaller-than-present ice over multiple timescales. Modern retreat of the GrIS margin in southwest Greenland is revealing a bedrock landscape that was also exposed during the migration of the GrIS margin towards its Holocene minimum extent, but has yet to tap into a landscape that remained ice covered throughout the entire Holocene.

Nicolás E. Young et al.

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Nicolás E. Young et al.

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Short summary
Retreat of the Greenland Ice Sheet (GrIS) margin is exposing a bedrock landscape that holds clues regarding the timing and extent of past ice-sheet minima. We present cosmogenic nuclides measurements from recently deglaciated bedrock surfaces (the last few decades), combined with a refined chronology of southwestern Greenland deglaciation and model simulations of GrIS change. Results suggest that inland retreat of the southwestern GrIS margin was likely minimal in the middle to late Holocene.
Retreat of the Greenland Ice Sheet (GrIS) margin is exposing a bedrock landscape that holds...
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