Constraining the Timing of Neoglaciation: Moraine Exposure Ages from Baffin Island, Arctic Canada

Abstract:

A long-term Neoglacial cooling trend, beginning ~6 ka, is well documented across the Arctic and correlates with a monotonic decline in Northern Hemisphere summer insolation. However, paleoclimate proxy records point to decadal- to millennial-scale variability superimposed on overall cooling. This climate variability is reflected in the fluctuations of Arctic glaciers over the course of several millennia. The most recent Neoglacial advance, the Little Ice Age (LIA; ~1275–1850 AD), was generally more extensive than pre-LIA advances and thus destroyed most evidence of previous advances. As such, the timing and extent of earlier Neoglacial advances are not well constrained. However, several extant glaciers on Cumberland Peninsula, Baffin Island, are fronted by nested ice-cored moraine sequences in which multiple pre-LIA moraines are preserved. We have generated absolute ages on moraine sequences for Snow Creek and Throne Glaciers using ¹⁰Be in moraine boulders. Nine ¹⁰Be ages from the two most distal moraine crests at Snow Creek Glacier range from ~1.8 ka to ~5.7 ka, and twelve ages from the two most distal moraine crests at Throne Glacier range from ~1.1 ka to ~4.6 ka. The wide spread of exposure ages in these settings is likely due to the degradation of moraine ice cores and the disturbance of older moraines by younger readvances. Because these processes result in the exposure of new clasts on the moraine post-emplacement, the oldest ages in these datasets likely provide the best estimates for the earliest Neoglacial advances. These data also indicate that in some settings, early Neoglacial alpine glacier advances reached similar extents as their LIA maxima, possibly due to large ice-cored moraines impeding LIA advances. Glacier modeling efforts and complementary lacustrine sediment records will help to unravel the complex Neoglacial history in this region.