A late-Holocene record of loess deposition in ice-wedge polygons reflecting                 wind activity and ground moisture conditions, Bylot Island, eastern Canadian Arctic

The initial configuration of the syngenetic ice-wedge polygons that developed in the outwash plain of glacier C-79 after 6000 BP was modified by the accumulation of wind-blown and organic sediments that began after 3670 ± 110 BP. The late Holocene sedimentation led to an increase in the thermal contraction coefficient of the soil and the formation of third- and fourth-order contraction cracks, partially explaining the current configuration of the polygonal network. The upturning of the sedimentary strata bordering the ice wedges was associated with the summer thermal expansion and resulting internal creep of the soil. The mean annual soil displacement coefficient was in the order of 2.52.7 × 105 /°C at the thousand-year scale. The late Holocene sedimentary strata under the centre of the polygons were undisturbed, which will make it possible to use this sedimentary record in further studies to attempt paleoenvironmental reconstructions from cores.

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

10.5194/tc-2019-248-supplement ◽

2019 ◽

Author(s):

Frédéric Bouchard ◽

Daniel Fortier ◽

Michel Paquette ◽

Vincent Boucher ◽

Reinhard Pienitz ◽

...

Keyword(s):

Canadian Arctic ◽

Lake Development ◽

Thermokarst Lake ◽

Bylot Island ◽

Ice Wedge ◽

Supplementary Material ◽

Eastern Canadian Arctic

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Modern to millennium-old greenhouse gases emitted from ponds and lakes of the Eastern Canadian Arctic (Bylot Island, Nunavut)

Biogeosciences ◽

10.5194/bg-12-7279-2015 ◽

2015 ◽

Vol 12 (23) ◽

pp. 7279-7298 ◽

Cited By ~ 31

Author(s):

F. Bouchard ◽

I. Laurion ◽

V. Pr&#x0117;skienis ◽

D. Fortier ◽

X. Xu ◽

...

Keyword(s):

Ghg Emissions ◽

Canadian Arctic ◽

Aquatic Systems ◽

Emission Rates ◽

Local Conditions ◽

Bylot Island ◽

Ice Wedge ◽

Global Biogeochemical Cycles ◽

Study Sites ◽

Eastern Canadian Arctic

Abstract. Ponds and lakes are widespread across the rapidly changing permafrost environments. Aquatic systems play an important role in global biogeochemical cycles, especially in greenhouse gas (GHG) exchanges between terrestrial systems and the atmosphere. The source, speciation and emission rate of carbon released from permafrost landscapes are strongly influenced by local conditions, hindering pan-Arctic generalizations. This study reports on GHG ages and emission rates from aquatic systems located on Bylot Island, in the continuous permafrost zone of the Eastern Canadian Arctic. Dissolved and ebullition gas samples were collected during the summer season from different types of water bodies located in a highly dynamic periglacial valley: polygonal ponds, collapsed ice-wedge trough ponds, and larger lakes. The results showed strikingly different ages and fluxes depending on aquatic system types. Polygonal ponds were net sinks of dissolved CO2, but variable sources of dissolved CH4. They presented the highest ebullition fluxes, 1 or 2 orders of magnitude higher than from other ponds and lakes. Trough ponds appeared as substantial GHG sources, especially when their edges were actively eroding. Both types of ponds produced modern to hundreds of years old (< 550 yr BP) GHG, even if trough ponds could contain much older carbon (> 2000 yr BP) derived from freshly eroded peat. Lakes had small dissolved and ebullition fluxes, however they released much older GHG, including millennium-old CH4 (up to 3500 yr BP) from lake central areas. Acetoclastic methanogenesis dominated at all study sites and there was minimal, if any, methane oxidation in gas emitted through ebullition. These findings provide new insights on GHG emissions by permafrost aquatic systems and their potential positive feedback effect on climate.

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

10.5194/tc-2019-248 ◽

2019 ◽

Author(s):

Frédéric Bouchard ◽

Daniel Fortier ◽

Michel Paquette ◽

Vincent Boucher ◽

Reinhard Pienitz ◽

...

Keyword(s):

Sediment Cores ◽

Canadian Arctic ◽

Climatic Conditions ◽

Gradual Transition ◽

Freshwater Environment ◽

Cooling Period ◽

Lake Development ◽

Thermokarst Lake ◽

Ice Wedge ◽

Eastern Canadian Arctic

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.

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Thermokarst lake inception and development in syngenetic ice-wedge polygon terrain during a cooling climatic trend, Bylot Island (Nunavut), eastern Canadian Arctic

The Cryosphere ◽

10.5194/tc-14-2607-2020 ◽

2020 ◽

Vol 14 (8) ◽

pp. 2607-2627

Author(s):

Frédéric Bouchard ◽

Daniel Fortier ◽

Michel Paquette ◽

Vincent Boucher ◽

Reinhard Pienitz ◽

...

Keyword(s):

Sediment Cores ◽

Canadian Arctic ◽

Climatic Conditions ◽

Gradual Transition ◽

Freshwater Environment ◽

Climatic Trend ◽

Cooling Period ◽

Thermokarst Lake ◽

Ice Wedge ◽

Eastern Canadian Arctic

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 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 kyr BP. 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 ∼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 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.

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Modern and past periglacial features in Central Asia and their implication for paleoclimate reconstructions

Progress in Physical Geography Earth and Environment ◽

10.1177/0309133315615778 ◽

2015 ◽

Vol 40 (3) ◽

pp. 369-391 ◽

Cited By ~ 7

Author(s):

Frank Lehmkuhl

Keyword(s):

Central Asia ◽

Late Holocene ◽

Large Degree ◽

Climatic Conditions ◽

Ice Age ◽

Soil Humidity ◽

Air Temperatures ◽

Rock Glaciers ◽

Ice Wedge ◽

Moisture Conditions

In the continental areas of Central and High Asia, periglacial landform assemblages, sediment structures and processes are mainly influenced and determined by of soil humidity during freeze–thaw cycles. These cryogenic processes result in periglacial landforms such as solifluction, earth hummocks or patterned ground. The distribution of rock glaciers as clear indicators of permafrost is additionally determined by rock fall or moraine debris composed of large boulders (e.g. of granite). Periglacial features were used to reconstruct past climatic conditions, e.g. relict involutions and ice-wedge casts provide evidence for the distribution of former permafrost, say, for the Last Glacial Maximum (LGM). Past temperatures, e.g. mean annual air temperatures, can be estimated from these periglacial features and can be compared with other proxy data, such as glacier fluctuations. Examples from late Holocene solifluction activity in the Altai, Khangai and north-eastern Tibetan Plateau show a different intensity of solifluction processes during the late Holocene and Little Ice Age due to a decrease in temperature and higher soil humidity. The distribution of past permafrost in some regions is still a matter of debate because of different interpretations of sediment structures: sometimes features described as ice-wedge casts may be caused by roots or desiccation cracks due to drying of clay rich sediments. Seismically deformed unconsolidated deposits (seismites) can also be misinterpreted as periglacial involutions. The lack of certain landform assemblages and sediment structures does not necessarily mean that the area had no permafrost. Moisture conditions can also determine the periglacial landform generation to a large degree. They can be ordered in Central Asia as follows (from highest moisture availability to lowest): solifluction; rock glacier; permafrost involutions; ice-wedge casts; sand-wedge casts.

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