The Process of Thermokarst Lake Formation in Ice-rich Yedoma Permafrost. Stage I: Permafrost stage, Yedoma with major ice wedges. Stage II: Thaw processes lead to thermokarst lake formation. Stages III, IV: Thaw progression results in horizontal and vertical lake expansion. Figure based on data from [141,142].

The Process of Thermokarst Lake Formation in Ice-rich Yedoma Permafrost. Stage I: Permafrost stage, Yedoma with major ice wedges. Stage II: Thaw processes lead to thermokarst lake formation. Stages III, IV: Thaw progression results in horizontal and vertical lake expansion. Figure based on data from [141,142].

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Permafrost covers a quarter of the northern hemisphere land surface and contains twice the amount of carbon that is currently present in the atmosphere. Future climate change is expected to reduce its near-surface cover by over 90% by the end of the 21st century, leading to thermokarst lake formation. Thermokarst lakes are point sources of carbon d...

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Context 1
... thaw progression is generally rapid in the first years and slows down over time [44]. Overall, taliks facilitate rapid thaw beneath lakes and cause deeper carbon stocks to become bioavailable (Figure 1) [21,[47][48][49] [141,142]. ...
Context 2
... thermokarst lakes also undergo horizontal expansion (Figure 1). The collapse of surrounding Yedoma increases lake surface area, whereas slumping of adjacent sediment introduces organic material into the lake [45]. ...

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... There has been a growing interest in how climate warming will affect northern wetlands here, because temperature increases can enhance evaporation rates, thaw permafrost, drain ponds, or initiate the development of new ponds. Warmer substrates can increase the thaw depth of water bodies, and temperature has an impact on vegetation growth and greenhouse gases, including water vapor, methane, and carbon dioxide (Negandhi et al., 2013;Andresen and Lougheed, 2015;Wrona et al., 2016;Zandt et al., 2020;Kreplin et al., 2021;Dyke and Sladen, 2022;Miner et al., 2022;Rehder et al., 2023). This study of pond thermal regimes at Polar Bear Pass (PBP) adds to this body of literature by evaluating the seasonal and inter-seasonal temperature regime of small tundra ponds ubiquitous to an extensive, low-gradient wetland in the Canadian High Arctic spanning warm and cool spring and summer. ...
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... These numerous and widespread ponds result from abrupt permafrost thaw (Walter Anthony et al., 2018) and generally exhibit sizes below 0.01 km 2 and depths under 5 m, and are much more active biogeochemically than larger lakes (Abnizova et al., 2012;Bégin and Vincent, 2017;Arsenault et al., 2022). Throughout their life span, they show diverse optical and morphological dynamics and are biogeochemical hotspots for the release of carbon dioxide (CO 2 ), nitrous oxide (N 2 O) and especially methane (CH 4 ), from permafrost to the atmosphere, through microbial and photochemical transformations (Breton et al., 2009;Edwards et al., 2009;Vonk et al., 2015;Zandt et al., 2020). Accounting for the role of these ponds is increasingly important due to permafrost warming, which generates more thaw ponds, potentially increasing greenhouse gas emissions (Holgerson and Raymond, 2016;Kuhn et al., 2018;Heslop et al., 2020). ...
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... On the other hand, CH4 production potentials over 96 days were several orders of magnitude higher than in undisturbed PF samples. This may be due 420 to proliferation of a highly productive methanogenetic community over time, but also due to additional nutrient input from surrounding non-PF fens or bogs (In ' T Zandt et al., 2020). ...
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Permafrost soils are undergoing rapid thawing due to climate change and global warming. Permafrost peatlands are especially vulnerable since they are located near the southern margin of the permafrost domain in the discontinuous and sporadic permafrost zones. They store large quantities of carbon (C) which, upon thawing, are decomposed and released as carbon dioxide (CO2), methane (CH4) or dissolved organic carbon (DOC). This study compares carbon degradation in three permafrost peatland ecosystems in Finnmark, Norway, which represent a well-documented chronosequence of permafrost formation. Peat cores from active layer, transition zone and permafrost zone were thawed under controlled conditions and incubated for up until 350 days under initially-oxic or anoxic conditions while measuring CO2, CH4 and DOC production. Carbon degradation varied among the three peat plateaus but showed a similar trend over depth with largest CO2 production rates in the top of the active layer and in the permafrost. Despite marked differences in peat chemistry, post-thaw CO2 losses from permafrost peat throughout the first 350 days in the presence of oxygen reached 67–125 % of those observed from the top of the active layer. CH4 production was only measured after a prolonged anoxic lag phase in samples from transition zone and permafrost, but not in active layer samples. CH4 production was largest in thermokarst peat sampled next to decaying peat plateaus. DOC production by active layer samples throughout 350 days incubation exceeded gaseous C loss (up to 23-fold anoxically), whereas little DOC production or uptake was observed for permafrost peat after thawing. Taken together, permafrost peat in decaying Norwegian peat plateaus degrades at rates similar to active layer peat, while highest CH4 production can be expected after inundation of thawed permafrost material in thermokarst ponds.
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