ABSTRACT: Northwest Passage marine sediments: A record of Quaternary history and climate change.

CGRG Bibliography of Canadian Geomorphology
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Abstract

The spatially extensive occurrence of glacially deposited sediments along the Northwest Passage and on the floors of adjoining inter-island channels strongly suggest that these sediments were deposited by one or more ice sheets that were regional in extent. There is a widespread distribution of ice-contact sediments (glacial drift) deposited by grounded glacial ice and possibly eroded by high-velocity subglacial meltwater discharge. The ice-contact sediments are locally overlain by glaciomarine sediments deposited proximal or distal to glacial ice margins. Postglacial mud locally overlies glaciomarine sediments or directly on ice-contact sediments. Finite ages on the ice-contact deposits are not available from marine data. However, a radiocarbon date of 9460 rcybp obtained from sediments in McDougall Sound, and an extrapolated age of 9,000-10,000 ybp for the transition from glaciomarine to postglacial conditions in eastern Barrow Strait - western Lancaster Sound both indicate that deposition of the underlying ice-contact sediments occurred prior to those dates in those areas. Correlation with the onshore record of glacial to recent sediment stratigraphy is required to clearly define Laurentide and Innuitian ice sheet dynamics as well as the postglacial sequence of events in the Arctic Archipelago. High resolution shallow seismic and subbottom profiles were used to identify localized pondings of thick Holocene sediment accumulation for box and piston coring sites. These high sedimentation rate, high-resolution sample sites are being used to resolve the paleoceanographic history, evolution of sea ice regime, and ultimately the climate record of the last 10,000 years. Benthic foraminifera data from a 5 m sediment core in McDougall Sound indicate the >500 m thick glacial ice sheet at LGM had retreated from the area by 9460 rcybp. The ice front was probably not far from the entrance to McDougall Sound. An ice shelf extending from a lingering icecap may have been present at this time. From >9,460 rcybp to about 6,000 years ago benthic foraminifera data indicate continuous pack ice cover. From 6,000-2,000 rcybp, sea ice cover was less than that observed today. The past ~2,000 years is dominated by persistent pack ice with periodic summer melting as observed during historic times. Dinoflagellate cyst assemblages in a core from Jones Sound were used with palaeotransfer functions to provide quantitative estimates of changes in sea surface temperature and sea ice cover. From ~6500-2600 BP, there were large oscillations in summer temperatures from 2-4oC cooler than present to 6oC warmer, and ice cover ranged from 2 months more sea ice to 4 months more open water. These climate oscillations are associated with apparent archaeological cultural adjustments. The warmer intervals correspond to the period of pre-Dorset cultures that hunted muskox and caribou. Subsequent Dorset and Neoeskimo cultures correspond to progressively cooler intervals with expanded sea ice and a shift to a predominantly marine-based livelihood focused on walrus and seal hunting.

Bibliography of Canadian Geomorphology