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The Cryosphere An interactive open-access journal of the European Geosciences Union
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Discussion papers
https://doi.org/10.5194/tc-2019-248
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/tc-2019-248
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 30 Oct 2019

Submitted as: research article | 30 Oct 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal The Cryosphere (TC).

Thermokarst lake development in syngenetic ice-wedge polygon terrain in the Eastern Canadian Arctic (Bylot Island, Nunavut)

Frédéric Bouchard1,2, Daniel Fortier2,3, Michel Paquette4, Vincent Boucher5, Reinhard Pienitz2,5, and Isabelle Laurion2,6 Frédéric Bouchard et al.
  • 1Géosciences Paris Sud (GEOPS), Université Paris Saclay, Orsay, France
  • 2Centre d’études nordiques (CEN), Université Laval, Québec, Canada
  • 3Département de géographie, Université de Montréal, Montréal, Canada
  • 4Department of Geography and Planning, Queen’s University, Kingston, Canada
  • 5Département de géographie, Université Laval, Québec, Canada
  • 6Centre Eau Terre Environnement, Institut national de la recherche scientifique (INRS-ETE), Québec, Canada

Abstract. Thermokarst lakes are widespread and diverse across permafrost regions and they are considered significant contributors to global greenhouse gas emissions. Paleoenvironmental reconstructions documenting the inception and development of these ecologically important water bodies are generally limited to Pleistocene-age permafrost deposits (Yedoma) of Siberia, Alaska, and the western Canadian Arctic. Here we present the gradual transition from syngenetic ice-wedge polygon terrains to a thermokarst lake in the Eastern Canadian Arctic. We combine geomorphological surveys with paleolimnological reconstructions from sediment cores in an effort to characterize local landscape evolution from terrestrial to freshwater environment. Located on an ice-rich and organic-rich polygonal terrace, the studied lake is now evolving through active thermokarst, as revealed by subsiding and eroding shores, and was likely created by water pooling within a pre-existing topographic depression. Organic sedimentation in the valley started during the mid-Holocene, as documented by the oldest organic debris found at the base of one sediment core and dated at 4.8 kyr BP. Local sedimentation dynamics were initially controlled by fluctuations in wind activity, local moisture and vegetation growth/accumulation, as shown by alternating loess (silt) and peat layers. Fossil diatom assemblages were likewise influenced by local hydro-climatic conditions and reflect a broad range of substrates available in the past (both terrestrial and aquatic). Such conditions likely prevailed until ~ 2000 BP, when peat accumulation stopped as water ponded the surface of degrading ice-wedge polygons, and the basin progressively developed into a thermokarst lake. Interestingly, this happened in the middle of the Neoglacial cooling period, likely under wetter-than-average conditions. Thereafter, the lake continued to develop as evidenced by the dominance of aquatic (both benthic and planktonic) diatom taxa in organic-rich lacustrine muds. Based on these interpretations, we present a four-stage conceptual model of thermokarst lake development during the late Holocene, including some potential future trajectories. Such a model could be applied to other formerly glaciated syngenetic permafrost landscapes.

Frédéric Bouchard et al.
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Frédéric Bouchard et al.
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Underwater camera video of submerged degraded ice-wedge polygons at the bottom of the peripheral shallow platform of Gull Lake, Bylot Island, Nunavut, Canada F. Bouchard https://doi.org/10.5446/43923

Frédéric Bouchard et al.
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Short summary
We combine lake mapping, landscape observations and sediment core analyses to document the evolution of a thermokarst (thaw) lake in the Canadian Arctic over the last millennia. We conclude that climate is not the only driver of thermokarst development, as the lake likely started to form during a cooler period around 2000 years ago. The lake is now located in frozen layers with an organic carbon content that is an order of magnitude higher than the usually reported values across the Arctic.
We combine lake mapping, landscape observations and sediment core analyses to document the...
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