New Constrains on the History of the Greenland Ice Sheet from Krypton-81 Age Estimates

Understanding Greenland Ice Sheet (GrIS) variability over million-year timescales is critical for assessing its long-term stability and sensitivity to climate change. This study presents a synthesis of published evidence on past ice-free and ice-covered conditions in Greenland, integrating multiple paleoclimatic methods and datasets to provide a coherent overview of GrIS evolution. This outline highlights key intervals of changes in ice cover, such as warm and interglacial periods that are older than the last interglacial but remain less explored. Special attention is given to the Mid-Pleistocene Transition (MPT), when global glacial cycles shifted from 41 kyr to 100 kyr periodicity, potentially forming the basis for the present-day ice sheet geometry and state. Plausible scenarios for the GrIS respond to these periods will be explored and discussed based on the outline of evidence.

In addition to the synthesis, new age constraints from the Green2Ice project refine the existing picture. Novel krypton-81 dating of deep ice from the GRIP core reveals ice as old as 856 (+35/-33) ka, indicating persistent ice cover in central Greenland for nearly one million years. This finding provides a key point for evaluating model simulations and assessing physically meaningful scenarios for GrIS. Furthermore, these new results help test the hypotheses of significant ice sheet reorganization during the MPT.

By comparing evidence of ice-cover and ice-free conditions across methods and locations, this work explores areas of strong coherence and remaining uncertainties in Greenland’s long-term history. These insights not only improve our understanding of past GrIS behaviour but also inform projections of its future response under ongoing climate change.