Marine record of late-glacial readvance and last recession of Laurentide ice, inner Frobisher Bay, Baffin Island, Arctic Canada

Robert Deering,Trevor Bell,Donald L Forbes

doi:10.1139/cjes-2021-0004

Abstract

The Cockburn Substage readvance marks the last major late-glacial advance of the northeast sector of the Laurentide Ice Sheet 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 in the region, providing a date of readvance (circa 9.5–8.5 ka cal BP). In Frobisher Bay, the Cockburn Substage readvance and recession onshore are marked by a series of moraines spread over ∼20 km along the inner bay. Acoustic marine mapping reveals five distinct transverse ridges, morphologically suggestive of grounding-zone wedges, and two later fields of DeGeer moraines on the floor of the inner bay. These indicate that the style of ice retreat (beginning no later than 8.5 ka cal BP) changed over time from punctuated recession of a floating ice front (20 km over >680 years, with four pauses) to more regular tidewater ice-front retreat, reaching the head of the bay 900 years or more after withdrawal from the outer Cockburn limit. The established chronology for final recession in the region is based largely on radiocarbon dating of bulk shell samples and single shells of deposit-feeding molluscs, notably Portlandia arctica, affected by old carbon from carbonate-rich sediments. Sedimentary analysis and judicious sampling for 14C dating of glaciomarine and marine facies in seabed sediment cores enables development of a late- and post-glacial lithostratigraphy that indicates final withdrawal of ice from the drainage basin by 7 ka cal BP.

Highlights

Short-term decelerations or pauses of otherwise retreating glacial margins are commonly recognized in past and presentday ice sheets (Batchelor et al 2018; Kingslake et al 2018)
This section begins by describing the moraines and other deglacial features mapped on the seafloor in inner Frobisher Bay using acoustic surveying
Seabed deglacial features Over the course of several field seasons (2012–2016), approximately 75% of inner Frobisher Bay was mapped using multibeam echosounders (MBES), revealing seafloor features relating to past glaciation

Summary

Introduction

Short-term decelerations or pauses of otherwise retreating glacial margins are commonly recognized in past and presentday ice sheets (Batchelor et al 2018; Kingslake et al 2018). During the last glacial maximum, continental ice originating from the Foxe and Amadjuak domes of the LIS to the northwest covered much of southeast Baffin Island, extending locally onto the continental shelf (Hodgson 2005; Miller et al 2005; Tremblay et al 2015; Dalton et al 2020). In Frobisher Bay, continental ice reached the mouth of the bay, with a grounded ice stream extending to at least the mid-bay islands (Fig. 1B; Margold et al 2015a, 2015b). Cumberland Sound was occupied by an ice stream originating from the confluence of Foxe–Amadjuak ice and a local ice cap on Hall Peninsula (Fig. 1B; Jennings 1993; Margold et al 2015a, 2015b). Small ice caps (Grinnell and Terra Nivea) occupied the highlands of outer Meta Incognita Peninsula (Fig. 1B)

Methods

Results

Discussion

Conclusion