Preprints
https://doi.org/10.5194/tc-2021-63
https://doi.org/10.5194/tc-2021-63

  23 Feb 2021

23 Feb 2021

Review status: a revised version of this preprint was accepted for the journal TC and is expected to appear here in due course.

Upstream flow effects revealed in the EastGRIP ice core using a Monte Carlo inversion of a two-dimensional ice-flow model

Tamara Annina Gerber1, Christine Schøtt Hvidberg1, Sune Olander Rasmussen1, Steven Franke2, Giulia Sinnl1, Aslak Grinsted1, Daniela Jansen2, and Dorthe Dahl-Jensen1,3 Tamara Annina Gerber et al.
  • 1Section for the Physics of Ice, Climate and Earth, The Niels Bohr Institute, University of Copenhagen, Copenhagen, Denmark
  • 2Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Bremerhaven, Germany
  • 3Centre for Earth Observation Science, University of Manitoba, Winnipeg, Canada

Abstract. The Northeast Greenland Ice Stream (NEGIS) is the largest active ice stream on the Greenland Ice Sheet (GrIS) and a crucial contributor to the ice-sheet mass balance. To investigate the ice-stream dynamics and to gain information about the past climate, a deep ice core is drilled in the upstream part of the NEGIS, termed the East Greenland Ice-Core Project (EastGRIP). Upstream flow effects introduce non-climatic bias in ice cores and are particularly strong at EastGRIP due to high ice-flow velocities and the location inside an ice stream on the eastern flank of the GrIS. Understanding and ultimately correcting for such effects requires information on the source area and the local atmospheric conditions at the time of ice deposition. We use a two-dimensional Dansgaard–Johnsen model to simulate ice flow along three approximated flow lines between the summit of the ice sheet (GRIP) and EastGRIP. Model parameters are determined using a Monte Carlo inversion by minimizing the misfit between modelled isochrones and isochrones observed in radio-echo-sounding (RES) images. We calculate backward-in-time particle trajectories to determine the source area of ice found in the EastGRIP ice core and present estimates of surface elevation and past accumulation rates at the deposition site. Our results indicate that increased accumulation in the upstream area is predominantly responsible for the constant annual layer thicknesses observed in the upper part of the ice column at EastGRIP. Inverted model parameters suggest that the imprint of basal melting and sliding is present in large segments along the flow profiles and that most internal ice deformation happens in the lower half of the ice column. The results of this study act as a basis for applying upstream corrections to a variety of ice-core measurements, and the model parameters are useful constraints for more sophisticated modelling approaches in the future.

Tamara Annina Gerber et al.

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on tc-2021-63', Anonymous Referee #1, 30 Mar 2021
    • AC1: 'Reply on RC1', Tamara Annina Gerber, 21 May 2021
  • RC2: 'Comment on tc-2021-63', Anonymous Referee #2, 08 Apr 2021
    • AC2: 'Reply on RC2', Tamara Annina Gerber, 21 May 2021

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on tc-2021-63', Anonymous Referee #1, 30 Mar 2021
    • AC1: 'Reply on RC1', Tamara Annina Gerber, 21 May 2021
  • RC2: 'Comment on tc-2021-63', Anonymous Referee #2, 08 Apr 2021
    • AC2: 'Reply on RC2', Tamara Annina Gerber, 21 May 2021

Tamara Annina Gerber et al.

Tamara Annina Gerber et al.

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Short summary
We simulate the ice flow in the onset region of the Northeast Greenland Ice Stream to determine the source area and past accumulation rates of ice found in the EastGRIP ice core. This information is required to correct for non-climatic bias introduced by upstream effects. Our results reveal that increasing accumulation rates in the upstream area lead to constant annual layer thicknesses in the upper 900 m of the ice core and suggest that the ice stream has been active during the past 8000 years.