Initial Insights into the Quaternary Evolution of the Laurentide Ice Sheet on Southeastern Baffin Island

Abstract:

Increasing Arctic summer temperatures in recent decades and shrinking cold-based ice caps on Cumberland Peninsula, Baffin Island, are exposing ancient landscapes complete with uneroded bedrock surfaces. Previous work has indicated that these upland surfaces covered with cold-based ice experience negligible erosion compared with the valleys and fjords systems that contain fast-flowing ice. Given the appearance of highly weathered bedrock, it is argued that these landscapes have remained largely unchanged since at least the last interglaciation (~120 ka), and have likely experienced multiple cycles of ice expansion and retraction with little erosion throughout the Quaternary. To explore this hypothesis, we use multiple cosmogenic radionuclides (²⁶Al and ¹⁰Be) to investigate and provide insight into longer-term cryosphere activity and landscape evolution. ²⁶Al/¹⁰Be in surfaces recently exposed exhibit a wide range of exposure-burial histories. Total exposure-burial times range from ~0.3 – 1.5 My and estimated erosion rates from 0.5 – 6.2 m Ma^-1. The upland surfaces of the Penny Ice cap generally experienced higher erosion rates (~0.45 cm ka^-1) than those covered by smaller ice caps (~0.2 cm ka^-1). The cumulative burial/exposure histories in high, fjord-edge locations indicate that significant erosion north of the Penny Ice Cap ceased between ~600 and 800 ka, suggesting that Laurentide Ice Sheet (LIS) organization and fjord inception was underway by at least this time. Additionally, ²⁶Al/¹⁰Be ratios near production values despite high inventories from a coastal summit 50 km east of the Penny Ice Cape suggest that that area has not experienced appreciable burial by ice, suggesting that it was never inundated by the LIS. Moreover, these initial data suggest a variable and dynamic cryosphere in the region and provide insight into how large ice sheets evolved and organized themselves during the Quaternary.