Thermokarst lake inception and development in syngenetic ice-wedge polygon terrain during a cooling climatic trend, Bylot Island (Nunavut), eastern Canadian Arctic
<p>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 generall...
Main Authors: | , , , , , |
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Format: | Article |
Language: | English |
Published: |
Copernicus Publications
2020-08-01
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Series: | The Cryosphere |
Online Access: | https://tc.copernicus.org/articles/14/2607/2020/tc-14-2607-2020.pdf |
Summary: | <p>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 of
Siberia, Alaska, and the western Canadian Arctic. Here we present the
gradual transition from syngenetic ice-wedge polygon terrain to a
thermokarst lake in Holocene sediments of the eastern Canadian
Arctic. We combine geomorphological surveys with paleolimnological
reconstructions from sediment cores in an effort to characterize local
landscape evolution from a terrestrial to freshwater
environment. Located on an ice- 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 <span class="inline-formula">kyr BP</span>. Local sedimentation
dynamics were initially controlled by fluctuations in wind activity,
local moisture, and vegetation growth and 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 <span class="inline-formula">∼2000</span> <span class="inline-formula">BP</span>, 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
colder-than-present but 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.</p> |
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ISSN: | 1994-0416 1994-0424 |