21 Sep 2022
21 Sep 2022
Status: this preprint is currently under review for the journal TC.

Holocene history of 79° N ice shelf reconstructed from epishelf lake and uplifted glacimarine sediments

James A. Smith1, Lousie Callard2, Michael J. Bentley3, Stewart S. R. Jamieson3, Maria Luisa Sánchez-Montes4, Timothy P. Lane5, Jeremy M. Lloyd3, Erin L. McClymont3, Christopher M. Darvill6, Brice R. Rea7, Colm O'Cofaigh3, Pauline Gulliver8, Werner Ehrmann9, Richard S. Jones10, and David H. Roberts3 James A. Smith et al.
  • 1British Antarctic Survey, High Cross, Madingley Road, Cambridge, CB3 0ET, UK
  • 2School of Geography, Politics and Sociology, Newcastle University, Newcastle upon Tyne, NE1 7RU, UK
  • 3Department of Geography, Durham University, Durham, DH1 3LE, UK
  • 4INSTAAR – Institute of Arctic and Alpine Research, University of Colorado Boulder, Boulder, CO 80309-0450, USA
  • 5School of Biological and Environmental Sciences, Liverpool John Moores University, Liverpool, L3 3AF, UK
  • 6Department of Geography, University of Manchester, Manchester, M13 9PL, UK
  • 7School of Geosciences University of Aberdeen, Aberdeen, AB24 3TU, UK
  • 8NERC Radiocarbon Facility, East Kilbride, G75 0QF, UK
  • 9Institute for Geophysics & Geology, University of Leipzig, Leipzig 04103, Germany
  • 10School of Earth Atmosphere and Environment, Monash University, Clayton, Victoria, Australia

Abstract. Nioghalvfjerdsbrae, or 79° N Glacier, is the largest marine-terminating glacier draining Northeast Greenland Ice Stream (NEGIS). In recent years, it’s ~70 km-long fringing ice shelf (hereafter referred to as 79° N ice shelf) has thinned, and a number of small calving events highlight its sensitivity to climate warming. With the continued retreat of 79° N ice shelf and the potential for accelerated discharge from NEGIS, which drains 16 % of the Greenland Ice Sheet (GrIS), it has become increasingly important to understand the long-term history of the ice shelf in order to put the recent changes into perspective and to judge their long-term significance. Here we reconstruct the Holocene dynamics of 79° N ice shelf by combining radiocarbon dating of marine mollusc from isostatically uplifted glacimarine sediments with a multi-proxy investigation of two sediment cores recovered from Blåsø, a large epishelf lake 2–13 km from the current grounding line of 79° N Glacier. Our reconstructions suggest that the ice shelf retreated between 8.5 and 4.4 cal. ka. BP, which is consistent with previous work charting grounding line and ice shelf retreat to the coast, and open marine conditions in Nioghalvfjerdsbrae. Ice shelf retreat followed a period of enhanced atmospheric and ocean warming in the Early Holocene. Based on our detailed sedimentological, microfaunal and biomarker evidence the ice shelf reformed at Blåsø after 4.4 cal. ka BP, reaching a thickness similar to present by 4.0 cal. ka BP. Reformation of the ice shelf coincides with decreasing atmospheric temperatures, increased dominance of Polar Water, a reduction in Atlantic Water and (near) perennial sea-ice cover on the adjacent continental shelf. Together with available climate archives our data indicate that 79° N ice shelf is susceptible to collapse when mean atmospheric and ocean temperatures are ~2 °C warmer than present, which could be achieved by the middle of this century under some climate model scenarios. Finally, the presence of ‘marine’ markers in the uppermost part of the Blåsø sediment cores could record modern ice shelf thinning, although the significance and precise timing of these changes requires further work.

James A. Smith et al.

Status: open (until 16 Nov 2022)

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James A. Smith et al.

James A. Smith et al.


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Short summary
The Greenland Ice Sheet is melting at an accelerating rate. To understand the significance of these changes we reconstruct the history of ones its fringing ice shelves, known as 79° N ice shelf. We show that the ice shelf disappeared 8,500 years ago, following a period of enhanced warming. An important implication of our study is that 79° N ice shelf is susceptible to collapse when atmospheric and ocean temperatures are ~2 °C warmer than present, which could occur by the middle of this century.