Last ice sheet recession and submarine slope failures in a complex arctic inlet, Inner Frobisher Bay, Baffin Island, Nunavut

Abstract

The Cockburn Substage readvance marks the last major late-glacial advance of the northeast sector of the Laurentide Ice Sheet, but has been examined at only a handful of sites on Baffin Island. The causes of this abrupt, late reversal of retreat are still unclear, but greater chronological control may provide some insight. To date, the literature has focused on the large terminal moraines common in the region, providing a singular date of readvance (prior to c. 9.5-8.5 ka cal BP). In Frobisher Bay, the Cockburn Substage readvance and recession are marked by a series of end moraines spanning ~20 km on either side of the inner bay. New acoustic marine mapping reported here from inner Frobisher Bay (IFB) reveals five distinct seafloor ridges that roughly correspond to the onshore moraines, as well as two fields of DeGeer moraines. These differing types of ridges indicate that the style of ice retreat changed over time from an episodic recession to a more regular tidewater ice front retreat. Radiocarbon dated shells from cored glaciomarine and postglacial sediments adjacent to and between the moraines indicate that ice readvanced prior to 9.4 ka cal BP and did not retreat from IFB before 7.6 ka cal BP. Sedimentary characteristics indicate changes in provenance and deposition rate as ice retreated. This paper describes the final retreat of Laurentide ice out of IFB, showing how style of deglaciation and depositional environments changed from the end of the Cockburn Readvance until recently. Inner Frobisher Bay is home to an abnormally high density of submarine slope failures (SSF; at least 246; ~1/20 km2). Understanding the causes of such an abundance of failure products and their chronology contributes to hazard reduction in the capital region of Nunavut. SSFs have the potential to destroy seafloor and coastal infrastructure directly and, when sufficiently large, can be tsunamigenic. Morphometric analysis of SSFs provides an insight into their spatial distribution, relative chronology, triggers, and preconditioning factors. SSFs in IFB are asynchronous and have been occurring in IFB since at least 5.7 ka cal BP, with some features dated to within the last 500 years, indicating the possibility of SSFs being an active process in the basin. Factors preconditioning these events in the basin appear to be connected to the geotechnical properties of deglacial sediments and the complex bathymetry of IFB. Triggering mechanisms appear to act asynchronously, suggesting probable triggers include small seismic events or cyclic tidal loading.