Passage and removal of the Amundsen Gulf Ice Stream, NW Laurentide Ice Sheet, recorded by the glacial and sea level history of southern Banks Island, Arctic Canada

Earlier reconstructions of the glacial history of the western Canadian Arctic Archipelago, commonly portrayed Banks Island as an ice-free biological refugium during the Last Glacial Maximum, ostensibly constituting the northeast extremity of Beringia. This has now been contradicted by widespread fieldwork across the northern and western coasts documenting their inundation by the northwest Laurentide Ice Sheet that extended onto the polar continental shelf. Here we report the surficial geology and deglacial sea levels across southern Banks Island completing the island-wide evidence for a pervasive ice cover during the Late Wisconsinan.

Moraines and erratics confirm the passage of an ice stream at least 1.1 km thick through Amundsen Gulf that onlapped the south coast of the island. The inland margin of the ice stream is marked by a prominent 80 km long shear moraine (Sachs moraine) that contacted thin, cold-based Laurentide ice crossing the island's interior. Subsequent thinning and retreat of the Amundsen Gulf Ice Stream from the Sachs moraine occurred in concert with its separation from topographically-confined ice lobes in the interior recorded by prominent ice-marginal meltwater channels. As the ice stream retreated offshore, a prominent kettled outwash plain was deposited along the coast marking marine limit at 20 m asl. From an unknown position offshore, the ice stream readvanced deforming the south shore of the kettled lowland marked by the 40 km long ‘Sand Hills moraine’. Based on updated field mapping, the 'Sand Hills moraine' is now recognized as the westward extension of the more widespread Jesse moraine belt.

Deglacial marine limit rises eastward across the island from 11 to 40 m asl, bordering Prince of Wales Strait. Marine limit and all lower shorelines across the island's south coast (for ∼ 200 km) are barren of marine shells. This is because sea level had regressed from marine limit to a lowstand offshore before Pacific molluscs recolonized the western Canadian Arctic at 13.7 cal ka BP, their entry occasioned by the resubmergence of Bering Strait. This requires that the breakup of the western Amundsen Gulf Ice Stream (including the M'Clure Strait Ice Stream along northern Banks Island) occurred before 14 cal ka BP, documenting that the NW Laurentide Ice Sheet must have contributed to Meltwater-Pulse-1A. Although the retreat from the outermost parts of the Jesse moraine belt also pre-date the arrival of shells, we show that the youngest (central) segment along eastern Amundsen Gulf dates to ∼12.9 cal ka BP, documenting that the Jesse moraine belt is highly time transgressive (spanning >13.7 to 12.9 cal ka BP). Radiocarbon dates on woody plants and bryophytes demonstrate that the island was biologically viable as early as 12.6 cal ka BP and that all coastlines were submergent soon afterwards and remain so today.