A Greenland-wide empirical reconstruction of paleo ice-sheet retreat informed by ice extent markers: PaleoGrIS version 1.0
Authors: Leger Tancrède P. M. , Clark Christopher D. , Huynh Carla , Jones Sharman , Ely Jeremy C. , Bradley Sarah L. , Diemont Christiaan , Hughes Anna L. C. 
Published: July 2023

Abstract. The Greenland Ice Sheet is a large contributor to global sea-level rise, and current mass losses are projected to accelerate. However, model projections of future ice-sheet evolution are limited by the fact that the ice sheet is not in equilibrium with present-day climate, but is still adjusting to past changes that occurred over thousands of years. Whilst the influence of such committed adjustments on future ice-sheet evolution remains unquantified, it could be addressed by calibrating numerical ice sheet models over larger timescales and, importantly, against empirical data on ice margin positions. To enable such paleo data-model interactions, we need Greenland-wide empirical reconstructions of past ice-sheet extent that combine geomorphological and geochronological evidence. Despite an increasing number of field studies producing new chronologies, such a reconstruction is currently lacking in Greenland. Furthermore, a time-slice reconstruction can help: i) answer open questions regarding the rate and pattern of ice margin evolution in Greenland since the glacial maximum, ii) develop a standardised record of empirical data, and iii) identify understudied sites for new field campaigns. Based on these motivations, we here present PaleoGrIS 1.0, the first Greenland-wide isochrone reconstruction of ice-sheet extent evolution through the Late-Glacial and early-to-mid Holocene informed by both geomorphological and geochronological markers. Our isochrones have a temporal resolution of 500 years and span ~7.5 kyr from approximately 14 to 6.5 kyr BP. We here describe the resulting reconstruction of the shrinking ice sheet and conduct a series of ice-sheet wide and regional analyses to quantify retreat rates, areal extent change, and their variability across space and time. During the Late-Glacial and early-to-mid Holocene, we find the Greenland Ice Sheet has lost about one third of its areal extent (0.89 million km2). Between ~14 and ~8.5 kyr BP, it experienced a near constant rate of areal extent loss of 170 ± 27 km2 yr-1. We find the ice-sheet-scale pattern of margin retreat is well correlated to atmospheric and oceanic temperature variations, which implies a high sensitivity of the ice sheet to deglacial warming. However, during the Holocene, we observe inertia in the ice-sheet system that likely caused a centennial to millennial-scale time lag in ice-extent response. At the regional scale, we observe highly heterogeneous deglacial responses in ice-extent evident in both magnitude and rate of retreat. We hypothesise that non-climatic factors, such as the asymmetrical nature of continental shelves and onshore bed topographies, play important roles in determining the regional-to-valley scale dynamics. PaleoGrIS 1.0 is an open-access database designed to be used by both the empirical and numerical modelling communities. It should prove a useful basis for improved future versions of the reconstruction when new geomorphological and geochronological data become available.