The deglacial to postglacial marine environments ofSEBarrowStrait,CanadianArcticArchipelago

Abstract

Core 86027‐144 (74°15.56′N, 91°14.21′W) represents a rare, continuous record of Late Pleistocene to Holocene sediments from High Arctic Canada extending from the end of the Last Glaciation. Based on microfossils (dinocysts, non‐pollen palynomorphs, benthic and planktonic foraminifera), foraminiferal δ18O and δ13C, and sedimentology, seven palaeoenvironmental zones were identified. Zone I (>10.8 cal. ka BP) records deglaciation, ice‐sheet destabilization, float‐off and subsequent break‐up. Zone II (c. 10.8–10.4 cal. ka BP) shows ice‐proximal to ice‐distal glaciomarine conditions, interrupted by pervasive land‐fast sea‐ice marked by a hiatus in coarse sediment deposition. Significant biological activity starts in Zone III (10.4–9.9 cal. ka BP), where planktonic foraminifera (Neogloboquadrina pachyderma) suggest early oceanic throughflow. Surface waters flowed NW–SE; however, the deep‐water origin remains unclear (potentially NW Arctic Ocean or Baffin Bay). Postglacial amelioration (open‐water season greater than present) in Zone IV (9.9–7.8 cal. ka BP) perhaps corresponds to the regional ‘Holocene Thermal Maximum’ previously proposed. A transitional period (Zone V; 7.8–6.7 cal. ka BP) of rapid environmental change fluctuating on a scale not observed today is marked by increasing sea‐ice and reduced oceanic influence. This probably signals the exclusion of deeper Atlantic water owing to the glacio‐isostatic shallowing of inter‐island sills, coupled with generally cooling climate. Conditions analogous to those at present, with increased sea‐ice and modern microfossil assemblages, commence at c. 6.7 cal. ka BP (zones VI–VII). Although climate ultimately forces long‐term environmental trends, core 86027‐144 data imply that regional dynamics, especially changes in sea‐level, exert a significant control on marine conditions throughout the Canadian Arctic Archipelago.

Deglaciation and ice shelf development at the northeast margin of the Laurentide Ice Sheet during the Younger Dryas chronozone

“…The typically low shear strength of this regionally extensive deposit, coupled with its crude stratification and apparent in situ sparse glaciomarine foraminiferal faunas (Pieńkowski et al . , ; this study), suggests that this diamictic facies does not represent subglacial deposition beneath grounded ice. As a diagnostic characteristic, shear strength alone can be problematic.…”

“…Similar units, interrupting coarse diamictic rainout facies, have been described from ice‐proximal deglacial sequences elsewhere within the CAA and suggest time‐transgressive ice‐shelf occupation or pervasive landfast sea‐ice occurrence (Pieńkowski et al . ).…”

“…, ; Pieńkowski et al . , , ). Notably, the uppermost sediments of the record were deposited during the very early Holocene (11.0 and 11.1 cal.…”

“…; Pieńkowski et al . , , ). An east−west connection through Barrow Strait and Lancaster Sound was achieved 11–10.5 cal.…”

The exaggerated radiocarbon age of deposit‐feeding molluscs in calcareous environments

“…What we describe as the ‘ Portlandia effect’ has only recently been taken into consideration by researchers establishing chronologies for marine cores collected from the carbonate‐floored channels of the CAA (Pieńkowski et al . ). This significant chronological effect doubtless applies to deposit feeders in all carbonate terrains, and calls into question data gathered from other sedimentary terrains where carbonate may still be present.…”