Paired cosmogenic analysis reveals early Pleistocene burial and exposure history in northwest Greenland

Abstract Long-lived cosmogenic nuclides preserved in erratic boulders in northwest Greenland offer the opportunity to investigate pre–Last Glacial Maximum glacial history and Greenland ice sheet subglacial conditions. In northwest Greenland, there is an expansive ice-free area between the Petermann and Humboldt Glaciers that preserves a record of early Pleistocene glaciation in cosmogenic isotopes that have accumulated in quartz-bearing erratic boulders. There, boulders were sourced from deep within Greenland's interior and deposited on the carbonate bedrock landscape. Here, we report 15 paired 10Be and 26Al measurements that were collected from the surface of 15 erratic boulders in northwest Greenland. The majority of these erratic boulders have complex 10Be and 26Al exposure ages that are tens of thousands of years greater than the established age of deglaciation in this region and therefore contain inherited cosmogenic isotopes from prior glaciations. The measured 26Al/10Be concentration ratios from these boulders are nearly two times lower than if they had undergone a constant exposure history. These low 26Al/10Be ratios are best explained by multiple burial and exposure scenarios during glacial and interglacial periods and suggest that the Greenland ice sheet regularly buried these landscapes over the last ~2 m.y. The preservation of the boulders on the landscape, the presence of significant amounts of inherited isotopes within the samples, and the well-preserved permafrost features on the landscape today all indicate that cold-based ice conditions likely have persisted in this northern sector of Greenland since the early Pleistocene.