Evidence for an Ice-Covered Southern Greenland at Dye-3 during the Last Interglacial

Models estimate a wide range of surface and margin changes to the Greenland Ice Sheet (GIS) in response to a significant polar warming of ~3-5ºC during the last interglacial (~130 ka). Unfortunately, limited empirical data is available to constrain these model responses, especially from the temperature-sensitive southern GIS region. Here, we re-examine the Dye-3 ice core (southern Greenland) to provide insights as to whether the southern GIS survived the last interglacial period, a warming event that serves as an imperfect analogy to expected future polar warming. We present geochemical analyses of the trapped air from the basal ice of Dye-3 (1991-2035m depth) that characterize and date the ice. We analyzed the elemental and isotopic composition of O2, N2, and Ar (d15N, d38Ar/36Ar, d18O of O2, dAr/N2, dO2/N2, and dO2/Ar), and total air content of the trapped air to determine that this ice, previously dated to an age of 450-800 ka, is indeed glacial ice and not superimposed ice or accreted melt water. Dating of the trapped air was then achieved by measuring the paleoatmospheric d40Ar/38Ar and 17D of O2, which dates the air to 440 ka (±230 ka), with a minimum age of 130 ka. This confirms that the Dye-3 site was ice covered through the last interglacial, providing a significant constraint for climate and glaciological models of the GIS.