Pathways of ice-wedge degradation in polygonal tundra under different hydrological conditions

Nitzbon, Jan; Langer, Moritz; Westermann, Sebastian; Martin, Léo; Schanke, Kjetil; Boike, Julia

doi:10.5194/tc-13-1089-2019

Cited by 69 publications

(192 citation statements)

References 49 publications

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“…In this study, we modify CG3 to improve the water balance and evapotranspiration scheme as described below. The version of CG3 used in Nitzbon et al () includes the same modifications.…”

Section: Methodsmentioning

confidence: 99%

Stability Conditions of Peat Plateaus and Palsas in Northern Norway

et al. 2019

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Peat plateaus and palsas are characteristic morphologies of sporadic permafrost, and the transition from permafrost to permafrost‐free ground typically occurs on spatial scales of meters. They are particularly vulnerable to climate change and are currently degrading in Fennoscandia. Here we present a spatially distributed data set of ground surface temperatures for two peat plateau sites in northern Norway for the year 2015–2016. Based on these data and thermal modeling, we investigate how the snow depth and water balance modulate the climate signal in the ground. We find that mean annual ground surface temperatures are centered around 2 to 2.5 °C for stable permafrost locations and 3.5 to 4.5 °C for permafrost‐free locations. The surface freezing degree days are characterized by a noticeable threshold around 200 °C.day, with most permafrost‐free locations ranging below this value and most stable permafrost ones above it. Freezing degree day values are well correlated to the March snow cover, although some variability is observed and attributed to the ground moisture level. Indeed, a zero curtain effect is observed on temperature time series for saturated soils during winter, while drained peat plateaus show early freezing surface temperatures. Complementarily, modeling experiments allow identifying a drainage effect that can modify 1‐m ground temperatures by up to 2 °C between drained and water accumulating simulations for the same snow cover. This effect can set favorable or unfavorable conditions for permafrost stability under the same climate forcing.

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“…In this study, we modify CG3 to improve the water balance and evapotranspiration scheme as described below. The version of CG3 used in Nitzbon et al () includes the same modifications.…”

Section: Methodsmentioning

confidence: 99%

Stability Conditions of Peat Plateaus and Palsas in Northern Norway

et al. 2019

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“…From the former, a detailed conceptual model has been developed in which thermokarst may follow any of several trajectories, which vary according to how severely an ice wedge melts before it is stabilized by organic matter accumulation or trough drainage. Inspired by this conceptual model, several investigations in the past several years have begun exploring process‐rich, physically based computer simulations as a means of capturing ice wedge dynamics at large spatial and temporal scales (Aas et al, ; Jan et al, ; Nitzbon et al, ). To date, these simulations have captured some essential components of thermokarst—such as an initial acceleration of melting as thermokarst pools develop, followed by a gradual deceleration—but in each case, the models have employed a highly simplified representation of polygonal microtopography.…”

Section: Introductionmentioning

confidence: 99%

Feedbacks Between Surface Deformation and Permafrost Degradation in Ice Wedge Polygons, Arctic Coastal Plain, Alaska

et al. 2020

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In the past three decades, an abrupt, pan‐Arctic acceleration of ice wedge melting has transformed tundra landscapes, spurring the formation of hummock‐like features known as high‐centered polygons (HCPs). This rapid geomorphic transition profoundly alters regional hydrology and influences surface emissions of CO2 and CH4. In Arctic Alaska, most recent instances of ice wedge degradation have arrested within 15–20 years of inception, stabilizing HCP microtopography. However, feedbacks between ground surface deformation and permafrost stability are incompletely understood, limiting our capacity to predict trajectories of landscape evolution in a still warmer future. Here, we use field data from a site near Prudhoe Bay, Alaska, to develop a modeling‐based framework for assessing the strength of positive (i.e., exacerbating) feedbacks on ice wedge degradation, focusing on the importance of heterogeneity in surface drainage and microtopographic conditions. Our simulations suggest that, when troughs are narrow, positive feedbacks on ice wedge melting (associated with thermokarst pool formation) are relatively weak. Positive feedbacks are markedly stronger beneath wide troughs, such as those that form above older, larger ice wedges. Seasonal thaw abruptly accelerates once a talik begins to form beneath wide and deep thermokarst pools. Once a talik initiates, winter severity and snowpack thickness increase in importance as predictors of thaw intensity in summer. Our results indicate that meter‐scale heterogeneity in polygonal microtopography potentially exerts strong, nonlinear controls on thermokarst trajectories. These findings are useful for predicting future thermokarst dynamics and for interpreting the results from coarser‐resolution land surface models operating at greater spatial and temporal scales.

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“…1b;Boike et al, 2013Boike et al, , 2018). All degradation stages described by Liljedahl et al (2016) can be found here, from non-degraded low-centered polygons to high-centered polygons with connected troughs (see Nitzbon et al, 2018). Between 1997 and 2017 the mean annual air temperature at the island was approximately -12.3 °C, with an annual liquid precipitation of 169 mm and mean end-of-winter snow depth of 0.3 m (Boike et al, 2018).…”

Section: Samoylov Island Northern Siberiamentioning

confidence: 81%

“…These are in reality of different sizes and shapes ( Fig. 1), but can to a first approximation be considered a selfrepeating pattern, as also described by Nitzbon et al (2018). Due to symmetry, a larger region can then be represented as a single feature with a representative geometry, where the interaction between the different polygons can be ignored.…”

Section: Polygonal Tundra On Samoylov Island Northern Siberiamentioning

confidence: 99%

“…Due to symmetry, a larger region can then be represented as a single feature with a representative geometry, where the interaction between the different polygons can be ignored. For simplicity, we here simulate a representative polygon as a circular feature with center and rim of equal area, and a total diameter of 10 m. Assuming instead hexagons, like Nitzbon et al (2018), would only require minor modifications to the parameters shown in Fig. 3, particularly the distance parameter and the interaction length.…”

Section: Polygonal Tundra On Samoylov Island Northern Siberiamentioning

confidence: 99%

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Thaw processes in ice-rich permafrost landscapes represented with laterally coupled tiles in a Land Surface Model

Schanke¹,

Martin²,

Nitzbon³

et al. 2018

Preprint

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Abstract. Earth System Models (ESMs) are our primary tool for projecting future climate change, but are currently limited in their ability to represent small-scale land-surface processes. This is especially the case for permafrost landscapes, where melting of excess ground ice and subsequent subsidence affect lateral processes which can substantially alter soil conditions and fluxes of heat, water and carbon to the atmosphere. Here we demonstrate how dynamically changing microtopography and related lateral fluxes of snow, water and heat can be represented with a tiling approach suitable for implementation in large-scale models, and investigate which of these lateral processes are important to reproduce observed landscape evolution. Combining existing methods for representing excess ground ice, snow redistribution and lateral water and energy fluxes in two coupled tiles, we show how the same model approach can simulate known degradation processes in two very different kinds of permafrost landscapes. Applied to polygonal tundra in the cold, continuous permafrost zone, we are able to simulate the transition from low-centered to high-centered polygons, and show how this results in i) more realistic representation of soil conditions through drying of elevated features and wetting of lowered features with related changes in energy fluxes, ii) reduced average permafrost temperatures at 13 m depth with up to 2 °C in current (2000–2009) climate, iii) delayed permafrost degradation in the future RCP4.5 scenario by several decades, and iv) more rapid degradation through snow and soil water feedback mechanisms once subsidence starts. Applied to warm, sporadic permafrost features, this two-tile system can represent an elevated peat plateau underlain by permafrost in a surrounding permafrost-free fen, and how it degrades in the future following a moderate warming scenario. These results show the importance of representing lateral fluxes to realistically simulate both the current permafrost state and its degradation trajectories as the climate continues to warm; both of which are likely to have important implications for simulations of the magnitude and timing of the permafrost carbon feedback.

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Pathways of ice-wedge degradation in polygonal tundra under different hydrological conditions

Cited by 69 publications

References 49 publications

Stability Conditions of Peat Plateaus and Palsas in Northern Norway

Stability Conditions of Peat Plateaus and Palsas in Northern Norway

Feedbacks Between Surface Deformation and Permafrost Degradation in Ice Wedge Polygons, Arctic Coastal Plain, Alaska

Thaw processes in ice-rich permafrost landscapes represented with laterally coupled tiles in a Land Surface Model

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