Postglacial sea-level lowstand on Cumberland Peninsula, Baffin Island, Nunavut1

This study investigates the postglacial sea-level history of eastern Cumberland Peninsula, a region of Baffin Island, Nunavut, where submerged terraces were documented in the 1970s. The elevation gradient of emerged postglacial marine-limit deltas and fiord-head moraines led Arthur Dyke to propose a conceptual model for continuous postglacial submergence of the eastern peninsula. Multibeam mapping over the past decade has revealed eight unequivocal submerged deltas at 19-45 m below present sea level (b.s.l.) and other relict shore-zone landforms (boulder barricade, spits, and sill platform) at 16-51 m b.s.l. Over a distance of 115 km from Qikiqtarjuaq to Cape Dyer, the submerged coastal features increase in depth toward the east, with a slope (0.36 m/km) less than that of the marine-limit shoreline previously documented (0.58-0.62 m/km). The submerged ice-proximal deltas, deglacial ice limits, and radiocarbon ages constrain the postglacial lowstand between 9.9 and 1.4 ka cal BP. The glacial-isostatic model ICE-7G_NA (VM7) computes a lowstand relative sea level at 8.0 ka, the depth of which increases eastward at 0.28 m/km. The difference between observed and model-derived lowstand depths ranges from 1 m in the west to 10 m in the east and the predicted tilt is significantly less than observed (p = 0.0008). The model results, emerging data on Holocene glacial readvances on eastern Baffin Island, and evidence for proglacial delta formation point to a Cockburn (9.5-8.2 ka) age for the lowstand, most likely later in this range. This study confirms the 1970s conceptual model of postglacial submergence in outer Cumberland Peninsula and provides field evidence for further refinement of glacial-isostatic adjustment models.