Drivers of Holocene palsa distribution in North America

Fewster, Richard E.; Morris, Paul J.; Swindles, Graeme T.; Gregoire, Lauren; Ivanovic, Ruza; Valdes, Paul J.; Mullan, Donal

doi:10.1016/j.quascirev.2020.106337

Cited by 13 publications

(25 citation statements)

References 104 publications

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“…Further north, where permafrost is continuous, ice-wedge polygons form where extreme winter temperatures cause thermal cracking of peatland surfaces 13,14 . Modern permafrost peatland distributions are well-constrained in Fennoscandia 15,16 and Western Siberia 17,18 , but observations from North America are more sporadic 19,20 and are absent across much of central and eastern Siberia. We may expect these distinct ice forms, and their carbon stocks, to exhibit different responses to climate, yet large-scale, forward-looking simulations have never compared them.…”

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confidence: 99%

“…Bioclimatic models fitted specifically to palsa/peat plateau distributions in Fennoscandia 15,16,21,22 and North America 20 suggest that these landforms occupy narrow climate envelopes of cold, dry conditions. Such models have suggested that a 1°C temperature increase could halve the present palsa extent in Fennoscandia, and that medium to high anthropogenic emissions could render the entire region climatically unsuitable for palsas by 2070-2099 15 .…”

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confidence: 99%

“…The increased warming projected by CMIP6 models suggests that previous studies may have underestimated the extent of near-future permafrost peatland degradation. Climate envelope models are powerful tools for understanding permafrost peatland responses to changing climate 9,15,20,22 , but such models have not yet been fitted to palsas, peat plateaus and polygon mires in Western Siberia. Here, we determine the changing climate envelopes of permafrost peatlands in Europe and Western Siberia during the 21 st century, and estimate the associated risk for peat carbon stocks.…”

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Imminent loss of climate space for permafrost peatlands in Europe and Western Siberia

et al. 2022

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Human-induced climate warming by 2100 is expected to thaw large expanses of northern permafrost peatlands. However, the spatio-temporal dynamics of permafrost peatland thaw remain uncertain due to complex permafrost-climate interactions, the insulating properties of peat soils, and variation in model projections of future climate. Here we show that permafrost peatlands in Europe and Western Siberia will soon surpass a climatic tipping point under scenarios of moderate-to-high warming (SSP2-4.5, SSP3-7.0, and SSP5-8.5). The total peatland area affected under these scenarios contains 37.0-39.5 Gt carbon (equivalent to twice the amount of carbon stored in European forests). Our bioclimatic models indicate that all of Fennoscandia will become climatically unsuitable for peatland permafrost by 2040. Strong action to reduce emissions (SSP1-2.6) by the 2090s could retain suitable climates for permafrost peatlands storing 13.9 Gt carbon in northernmost Western Siberia, indicating that socioeconomic policies will determine the rate and extent of permafrost peatland thaw. Main

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Imminent loss of climate space for permafrost peatlands in Europe and Western Siberia

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“…When these mounds are joined to cover a larger area, they are known as peat plateaus. Palsas / peat plateaus are found in the discontinuous and sporadic permafrost zones, and are also widespread, though not to the extent of polygons (Martin et al, 2019;Kremenetski et al, 2003;Fewster et al, 2020). While it is hard to get an estimate for the total extent of palsas and peat plateaus, permafrost peatlands 95 are estimated to cover 1.7 million km 2 (Hugelius et al, 2020).…”

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“…Recently, remote sensing and machine learning tools have enabled the mapping of the location and areas of different permafrost 940 landforms for large regions, and the mapping of how these are changing (Nitze et al, 2018). At the same time, climate envelope models have allowed for pan-arctic assessment of climatic suitability for palsas (Fewster et al, 2020) and ice wedge polygons, and which areas may be subject to change in the future. These data will enable microtopographic models to be initialised and provide a basis for model evaluation.…”

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Explicitly modelling microtopography in permafrost landscapes in a land-surface model (JULES vn5.4_microtopography)

Smith

Burke

Schanke

et al. 2021

Preprint

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Abstract. Microtopography can be a key driver of heterogeneity in the ground thermal and hydrological regime of permafrost landscapes. In turn, this heterogeneity can influence plant communities, methane fluxes and the initiation of abrupt thaw processes. Here we have implemented a two-tile representation of microtopography in JULES (the Joint UK Land Environment Simulator), where tiles are representative of repeating patterns of elevation difference. We evaluate the model against available spatially resolved observations at four sites, gauge the importance of explicitly representing microtopography for modelling methane emissions and quantify the relative importance of model processes and the model’s sensitivity its parameters. Tiles are coupled by lateral flows of water, heat and redistribution of snow. A surface water store is added to represent ponding. The model is parametrised using characteristic dimensions of landscape features at sites. Simulations are performed of two Siberian polygon sites, Samoylov and Kytalyk, and two Scandinavian palsa sites, Stordalen and Iškoras. The model represents the observed differences between greater snow depth in hollows vs raised areas well. The model also improves soil moisture for hollows vs the non-tiled configuration (‘standard JULES’) though the raised tile remains drier than observed. For the two palsa sites, it is found that drainage needs to be impeded from the lower tile, representing the non-permafrost mire, to achieve the observed soil saturation. This demonstrates the need for the landscape-scale drainage to be correctly modelled. Causes of moisture heterogeneity between tiles are decreased runoff from the low tile, differences in snowmelt, and high to low-tile water flow. Unsaturated flows between tiles are negligible, suggesting the adequacy of simpler water-table based models of lateral flow in wetland environments. The modelled differences in snow depths and soil moistures between tiles result in the lower tile soil temperatures being warmer for palsa sites. When comparing the soil temperatures for July at 20 cm depth, the difference in temperature between tiles, or ‘temperature splitting’, is smaller than observed (3.2 vs 5.5 °C). The mean temperature of the two tiles remains approximately unchanged (+0.4 °C) vs standard JULES, and lower than observations. Polygons display small (0.2 °C) to zero temperature splitting, in agreement with observations. Consequently, methane fluxes are near identical (+0 to 9 %) to those for standard JULES for polygons, though can be greater than standard JULES for palsa sites (+10 to 49 %). Through a sensitivity analysis we identify the parameters resulting in the greatest uncertainty in modelled temperature. We find that at the sites tested, varying the parameters can result in the modelled July temperature splitting being at most 0.9 or 3 °C larger than observed for palsa or polygon sites respectively. Varying the palsa elevation between 0.5 and 3 m has little effect on modelled soil temperatures, showing that having only two tiles can still be a valid representation of sites with a large variability of palsa elevations. Lateral conductive fluxes, while small, reduce the temperature splitting by ~1 °C, and correspond to the order of observed lateral degradation rates in peat plateau regions, indicating possible application in an area-based thaw model.

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The mid‐latitude hydrolaccolith of the Spanish Central System (Southern Europe): A top‐to‐bottom integration of geomatic, geophysical and sedimentary datasets for characterising a singular periglacial landform

Fernández‐Lozano,

Turu,

Carrasco

et al. 2023

Land Degrad Dev

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Permafrost study in the Spanish Central System (~41°N) has remained elusive in past decades. Although numerous periglacial features have been described, none has yielded conclusive information about the existence/distribution of permafrost across these mountains. This work focuses on integrating light detection and ranging and unmanned aerial vehicle data with geophysical methods and sedimentary records, along with preliminary thermal information, for the comprehensive study of a frost mound. The singularity of this feature resides in its location, currently dominated by a seasonal frost regime, and its size reaching 59 m long, 22.5 m wide and 4 m high, representing the largest landform of this type in Iberia. From top‐to‐bottom, the internal structure comprises three resistivity units (G1, G2 and G3). The most superficial unit (G1) consists of a sequence of burial soils alternating with sand and silts, with pebbles and gravel at the bottom, followed by a high porous layer that belongs to a landslide deposit (G2), likely composed of gravel and pebbles laying over unit G3 (bedrock). Calibrated 14C ages suggest this landform formed at least ~4300 years ago during the mid‐Holocene. Finally, the preliminary surface thermal map indicates the presence of sectors affected by strong thermal gradients likely driven by water table variations. Our results conclude that the dynamics are primarily controlled by the seasonal frost regime influencing local subsurface drainage, which allows us to classify this landform as a hydrodynamic pingo‐like structure. We also demonstrate that our approach is suitable for assessing the evolution of this type of periglacial landform. Implementing long‐lasting annual monitoring programmes would help to understand local periglacial dynamics better.

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Drivers of Holocene palsa distribution in North America

Cited by 13 publications

References 104 publications

Imminent loss of climate space for permafrost peatlands in Europe and Western Siberia

Imminent loss of climate space for permafrost peatlands in Europe and Western Siberia

Explicitly modelling microtopography in permafrost landscapes in a land-surface model (JULES vn5.4_microtopography)

The mid‐latitude hydrolaccolith of the Spanish Central System (Southern Europe): A top‐to‐bottom integration of geomatic, geophysical and sedimentary datasets for characterising a singular periglacial landform

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