07 Nov 2023
 | 07 Nov 2023
Status: this preprint is open for discussion.

Subglacial valleys preserved in the highlands of south and east Greenland record restricted ice extent during past warmer climates

Guy J. G. Paxman, Stewart S. R. Jamieson, Aisling M. Dolan, and Michael J. Bentley

Abstract. The Greenland Ice Sheet is a key contributor to contemporary global sea level rise, but its long-term history and response to episodes of warming in Earth’s geological past remain uncertain. The terrain covered by the ice sheet comprises ~79 % of Greenland and ~1.1 % of the Earth’s land surface and contains geomorphological records that may provide valuable insights into past ice-sheet behaviour. Here we use ice surface morphology and radio-echo sounding data to identify ice-covered valleys within the highlands of southern and eastern Greenland and use numerical ice-sheet modelling to constrain the climatological and glaciological conditions responsible for valley incision. Our mapping reveals intricate subglacial valley networks with morphologies that are indicative of substantial glacial modification of an inherited fluvial landscape, yet many of these valleys are presently situated beneath cold-based, slow-moving (i.e., non-erosive) ice. We use the morphology of the valleys and our simple ice-sheet model experiments to infer that incision likely occurred beneath erosive mountain valley glaciers during one or more phases of Greenland’s glacial history when ice was restricted to the southern and eastern highlands, and Greenland’s contribution to barystatic sea level was up to +7 metres relative to today. We infer that this valley incision primarily occurred prior to the growth of a continental-scale ice sheet, most likely during the late Miocene (ca. 7–5 Ma) and/or late Pliocene (ca. 3.6–2.6 Ma). Our findings therefore provide new data-based constraints on early Greenland Ice Sheet extent and dynamics that can serve as valuable boundary conditions in models of regional and global palaeoclimate during past warm periods that are important analogues for the 21st Century and beyond.

Guy J. G. Paxman et al.

Status: open (until 04 Jan 2024)

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  • RC1: 'Comment on egusphere-2023-2502', Anonymous Referee #1, 20 Nov 2023 reply

Guy J. G. Paxman et al.

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Subglacial valleys preserved in the highlands of south and east Greenland record restricted ice extent during past warmer climates: Datasets Guy Paxman, Stewart Jamieson, Aisling Dolan, Mike Bentley

Guy J. G. Paxman et al.


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Short summary
This study maps the topography of the mountains of eastern Greenland hidden beneath the ice sheet. We find that the landscape once hosted river networks that were later eroded by valley glaciers when ice first began to grow on Greenland. Computer models of ice flow indicate that this landscape likely formed during warmer climates several million years ago, when local air temperatures were at least 4 °C higher than today and ice coverage in Greenland was restricted to areas of high topography.