PICE talk by Nicolaj Krog Larsen

(Globe Institute, KU)

Title: Tracking the long-term history of the Greenland Ice Sheet – a complex puzzle with few pieces

Abstract: As the ongoing melting of the Greenland Ice Sheet has large societal implications there is a growing focus on determining how much it contributed to global sea level rise during past interglacial periods when it was warmer than present. However, as the geological archives to record these changes mainly are hidden beneath the present ice sheet this task is challenging. One exception is the present interglacial – the Holocene where recent years research has provided a good understanding about the ice marginal variations. In this talk, I will present how we have constrained the Holocene ice marginal variations of the Greenland Ice Sheet and local glaciers and ice caps using a multiproxy approach including cosmogenic exposure dating, proglacial threshold lakes, and isolation basins. We generally find that the last deglaciation was fast and driven by a combination of atmospheric and ocean warming. However, the timing may vary from fjord to fjord because of local topographic effects. In most areas the GrIS was smaller than present during the Holocene Thermal Maximum ~8-5 cal. ka BP where our models suggest that it contributed ~16 cm to the global sea level. In the same period, local glaciers and ice caps completely melted in southern Greenland whereas they survived in northern Greenland due to increased precipitation. Overall, our results show that the Greenland Ice Sheet has been rather stable during the Holocene and this may be perceived as a paradox as it has been less stable and significantly smaller during other interglacial periods where it only was slightly warmer than present. This potential paradox will be discussed in the last part of the talk.