Landscape chronology and glacial history in Thule, northwest Greenland

• We conducted mapping, stratigraphic analysis, 14C dating, and analysis of 10Be.
• Two distinct diamicts were deposited by different episodes of ice advance.
• Ice cover in the past was likely cold-based and weakly-erosive.
• Deglaciation of the Thule landscape occurred ∼10.8 ± 0.6 ka.
• Harald Moltke Brae outlet glacier re-advanced more recently than ∼10 ka.

Constraining past responses of ice sheets to changes in climate enhances our ability to predict future changes in ice extent and sea level. Here, we employ surficial geologic mapping, stratigraphic analysis, radiocarbon dating of marine mollusks, and analysis of cosmogenic 10Be in glacially-deposited boulders to make inferences about past ice extents in Thule, northwest Greenland. Our work shows the existence of two distinct diamict units in the Thule area; we infer that one diamict was deposited by the main Greenland Ice Sheet while the second was deposited by a subsequent outlet glacier re-advance. Boulders in the two diamicts (n = 13 and n = 15, respectively) have similar bimodal distributions of cosmogenic 10Be ages. Both diamicts have a group of younger 10Be ages as well as a more diffuse group of considerably older 10Be ages (∼20–30 ka). Many of the boulders likely contain nuclides inherited from previous periods of exposure, suggesting that glacial ice in the Thule region has been cold-based and non-erosive in the past. The landscape chronology we develop suggests that deglaciation after the Last Glacial Maximum occurred ∼10.8 ka and was later followed by a re-advance of outlet glaciers, possibly in concert with the 9.3 ka or 8.2 ka cold events.