Late-glacial and Holocene deglaciation chronology of the northeast Icelandic Ice Cap

Close to the Arctic front, Iceland with its ice sheet is a strategic accessible natural laboratory to study past and modern climate changes. Like in Greenland the Icelandic Ice Sheet (IIS) provides freshwater to the North Atlantic and modifies the circulation of its thermohaline currents. While the IIS margins are relatively well constrained offshore by marine or coastal evidences, little is known about its onshore characteristics and its rates of recession during the Holocene warmer periods. This study aims at filling this chronological gap of the IIS inland during the late Quaternary deglaciation using cosmogenic nuclides dating in northeast Iceland. Terrestrial evidences of the ice sheet past margins such as moraines, glacial outwash and kame terraces have been identified north of Vatnajökull where two complementary and independent cosmogenic exposure isotopes (36Cl and 3He) will be used to date these morphological markers of the IIS retreat. In doing so, we will constrain the chronology of the ice margins and test ice-sheet deglaciation models. The cosmogenic sampling strategy will consist of complementary surface boulders and 36Cl depth profiles of amalgamated cobbles originating from common lava flows and embedded in the morphological markers. All surface samples will be dated by both 36Cl and 3He surface exposure ages from Ca-rich plagioclases and from cogenetic pyroxene phenocrysts, respectively. The double dating with 36Cl and 3He and a control of the production mechanisms with the associated depth profiles will ensure that the cosmogenic ages are sound and effective in providing age constraints of the IIS deglaciation. Improved understanding of the IIS behaviour during periods of known rapid climate change will provide new tie-points for the calibration of the IIS models and will allow a better assessment of the volume and timing of terrestrial meltwater flux to the North Atlantic. This work will contribute to a better understanding of climate evolution in the North Hemisphere over the last 20 ka and, to a better understanding of the evolution of modern Ice sheets using analogue from the past.