Origin, burial and preservation of late Pleistocene-age glacier ice in Arctic permafrost (Bylot Island, NU, Canada)

Stephanie Coulombe,Yuri Shur,Mikhail Kanevskiy,Denis Lacelle,Daniel Fortier

doi:10.5194/tc-13-97-2019

Stephanie Coulombe, Yuri Shur + Show 3 more

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https://doi.org/10.5194/tc-13-97-2019

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Abstract

Abstract. Over the past decades, observations of buried glacier ice exposed in coastal bluffs and headwalls of retrogressive thaw slumps of the Arctic have indicated that considerable amounts of late Pleistocene glacier ice survived the deglaciation and are still preserved in permafrost. In exposures, relict glacier ice and intrasedimental ice often coexist and look alike but their genesis is strikingly different. This paper aims to present a detailed description and infer the origin of a massive ice body preserved in the permafrost of Bylot Island (Nunavut). The massive ice exposure and core samples were described according to the cryostratigraphic approach, combining the analysis of permafrost cryofacies and cryostructures, ice crystallography, stable O-H isotopes and cation contents. The ice was clear to whitish in appearance with large crystals (cm) and small gas inclusions (mm) at crystal intersections, similar to observations of englacial ice facies commonly found on contemporary glaciers and ice sheets. However, the δ18O composition (-34.0±0.4 ‰) of the massive ice was markedly lower than contemporary glacier ice and was consistent with the late Pleistocene age ice in the Barnes Ice Cap. This ice predates the aggradation of the surrounding permafrost and can be used as an archive to infer palaeo-environmental conditions at the study site. As most of the glaciated Arctic landscapes are still strongly determined by their glacial legacy, the melting of these large ice bodies could lead to extensive slope failures and settlement of the ground surface, with significant impact on permafrost geosystem landscape dynamics, terrestrial and aquatic ecosystems and infrastructure.

Highlights

In the Arctic, extensive areas of ridged and hummocky moraines are underlain by buried glacier ice (Dyke and Savelle, 2000; Kokelj et al, 2017; Solomatin, 1986)
Evidence that support the englacial origin of the massive ice are (1) sharp and unconformable upper contact between the ice and the overlying glaciofluvial sediments; (2) clear to whitish ice, with large crystals; (3) bubble-rich ice, with small gas inclusions (∼ mm) mainly located at crystal junctions; (4) occasional debris bands of sand and fine gravel cross-cutting older debris-free ice; (5) geochemical similarities with contemporary glacier ice
An origin of massive ice from a Pleistocene glaciation is suggested based on the isotope data: the buried englacial ice is strongly depleted in heavy isotopes, to regional Pleistocene glacier ice

Summary

Introduction

In the Arctic, extensive areas of ridged and hummocky moraines are underlain by buried glacier ice (Dyke and Savelle, 2000; Kokelj et al, 2017; Solomatin, 1986). Areas with buried glacier ice are becoming increasingly vulnerable to climate warming (Kokelj et al, 2017). Buried glacier ice has been commonly observed in the proglacial zone of contemporary glaciers and can be preserved in formerly glaciated areas (the paraglacial to periglacial zones) within large moraine belts, hummocky till and glaciofluvial deposits (Everest and Bradwell, 2003; Tonkin et al, 2016)

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