A Resilient Greenland Ice Sheet More Than 900,000 Years Old.

Abstract:

The Greenland Ice Sheet (GRIS) has the potential of causing a 7.36 m global sea level rise (GSLR) if it were to melt away. To properly assess risk of future melting, it is crucial to understand the formation and growth of the GRIS during past climate regimes. However, despite decades of research, it remains debated when and in what environment GRIS got established and to what extent GRIS changed in size during past warm interglacials, such as MIS 5e some 130 kyr BP. Here, we present results from analyses of environmental DNA, ¹⁰Be/³⁶Cl, ²³⁴U/²³⁸U, single grain optically stimulated luminescence (OSL), palaeomagnetics, macrofossils and molecular clock dating of basal ice from the Camp Century ice core in north western Greenland and the Kap København Formation in North Greenland. We combine these with results from the DYE 3 and GRIP ice cores from southern and central Greenland to evaluate the evolution of the GRIS. We find evidence that the present GRIS formed quickly some time before 900 kyr BP in a largely forested Greenland and that it has changed by only 30-40% of its present volume since it was established. Our DNA findings of boreal forest imply that warming of more than 10^oC is needed to have an ice-free Greenland. This threshold is higher than earlier predictions and the corresponding palaeo-calibration of the GRIS contribution to sea level changes suggests a sensitivity of 0.3-0.5 m GSLR per degree Celsius of warming over Greenland. Ice core data from the deep Greenland ice cores can be used to reconstruct the size of the ice sheet during the present interglacial (the Holocene) and the last interglacial (the Eemian). Reconstructions based on stable water isotopes and gas content is used to validate the resilience of the GRIS.