Constraining the extent of the Greenland Ice Sheet during warmer climates of the Pliocene and Pleistocene: insights from subglacial geomorphology

The Greenland Ice Sheet is a key contributor to contemporary global sea-level rise, but its long-term history remains highly uncertain. The landscape covered by the ice sheet comprises ∼79% of Greenland and is one of the most sparsely mapped regions on Earth. However, sub-ice geomorphology offers a unique record of environmental conditions prior to and during glaciation, and of the ice sheet’s response to changing climate.

Here we use ice-surface morphology and radio-echo sounding data to identify, and quantify the morphology of, valley networks beneath the Greenland Ice Sheet. Our mapping reveals intricate subglacial valley networks beneath the ice-sheet interior that appear to have a fluvial origin. By contrast, in the southern and eastern coastal highlands, valleys have been substantially modified by glacial erosion. We use geomorphometric analysis and simple ice-sheet model experiments to infer that these valleys were incised 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.

These inferred early mountain ice masses contained ~0.5 metres of sea-level equivalent (compared to 7.4 metres in the modern Greenland Ice Sheet). We believe the most plausible time for the formation of this landscape was prior to the growth of a continental-scale ice sheet in the late Pliocene, with the possibility of further incision having occurred during particularly warm and/or long-lived Pleistocene interglacials. 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 climate change in the 21st century and beyond.