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

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 (c. 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 <i>Portlandia arctica</i>, affected by old carbon from carbonate-rich sediments. Sedimentary analysis and judicious sampling for <sup>14</sup>C dating of glaciomarine and marine facies in seabed sediment cores enables development of a late- and postglacial lithostratigraphy that indicates final withdrawal of ice from the drainage basin by 7 ka cal BP.

Deglacial dynamics of the Foxe–Baffin Ice Sheet, Frobisher Bay, Nunavut, Canada revealed by submarine landform mapping

“…12). Further refining ice margin positions, Deering et al (2021) published 86 calibrated radiocarbon dates from marine molluscs extracted from piston and gravity cores that enhance understanding of the glacial history of inner Frobisher Bay. The Frobisher Bay-Hudson Strait palaeogeographic reconstruction of Stravers et al (1992) provides a contextual setting for a discussion of the glacial and glaciomarine landforms presented here.…”

“…In inner Frobisher Bay are a series of sinuous subparallel ridges with an overall southwest–northeast crest orientation (Deering et al , 2021). The ridges, both single‐ and double‐crested, can be traced across the bathymetric variation in the bay from basins 250 m deep to shallows reaching 40 m (Fig.…”

“…These ridges are interpreted as recessional moraines of ice‐contact sediment deposited along the ice‐sheet edge, transverse to the ice flow direction, marking stillstands of the Frobisher Bay ice sheet in its stepwise retreat to the northwest (Deering et al , 2021). Subaerial moraines of the FBMS have been mapped by various workers (summarised by Hodgson, 2005) around inner Frobisher Bay as far southeast as Cape Rammelsberg (Fig.…”