Using Ground Penetrating Radar for Permafrost Monitoring from 2015–2017 at CALM Sites in the Pechora River Delta

This paper describes the results of ground penetrating radar (GPR) research combined with geocryological data collected from the Circumpolar Active Layer Monitoring (CALM) testing sites in Kashin and Kumzha in August 2015, 2016, and 2017. The study area was located on the Pechora River delta. Both sites were composed of sandy ground and the permafrost depth at the different sites ranged from 20 cm to 8–9 m. The combination of optimum offset and multifold GPR methods showed promising results in these investigations of sandy permafrost geological profiles. According to direct and indirect observations after the abnormally warm conditions in 2016, the thickness and water content of the active layer in 2017 almost returned to the values in 2015 in the Kashin area. In contrast, the lowering of the permafrost table continued at Kumzha, and lenses of thin frozen rocks that were observed in the thawed layer in August of 2015 and 2017 were absent in 2016. According to recent geocryological and geophysical observations, increasing permafrost degradation might be occurring in the Pechora River delta due to the instability of the thermal state of the permafrost.

Thermal Regime and Variations in the Island Permafrost Near the Northern Permafrost Boundary in Xidatan, Qinghai–Tibet Plateau

Although the thermal regime and degradation of permafrost on the Qinghai-Tibet Plateau (QTP) have been widely documented, little information exists regarding the island permafrost in the area. Ground temperatures were therefore measured for 8 years (2013–2020) at a permafrost island and at two contrasting sites in the Xidatan region to elucidate the permafrost in this area. Results indicate that the ground temperatures in the island permafrost were markedly higher than those at the same depth in the nearby marginal permafrost and the interior continuous permafrost. In addition, a distinct increasing trend was observed in the ground temperature of the island permafrost over the past 8 years, and warming was signficanty faster in the deep soil than in the topsoil, indicating a bottom–up degradation pattern in the island permafrost. Moreover, due to the persistent increase in the thickness of the active-layer and the decrease in the depth of permafrost table, the permafrost island abruptly disappeared in 2018, which may be attributed to the anomalously high air temperatures that occurred in 2016 and 2017. The results of this study may provide references for understanding of the thermal regime and degradation process of island permafrost on the QTP.

Study on the Effect of Unilateral Sand Deposition on the Spatial Distribution and Temporal Evolution Pattern of Temperature beneath the Embankment

In the context of climate warming and the frequent wind-sand hazards in the Qinghai-Tibet Engineering Corridor (QTEC), the construction of the embankment will affect the thermal regime of permafrost underground. The influence of embankment construction on the variation of the permafrost table beneath it is different, especially for the regime with different mean annual ground temperatures (MAGTs). In this study, the effects of the unilateral sand particles deposition on the spatial distribution and temporal evolution pattern of temperature beneath the embankment are investigated through the numerical simulations, in which the heat transfer is considered. The model is validated by the field observed data of soil temperatures around an experimental zone built at the sand hazard area in Honglianghe, the interior of Qinghai-Tibet Plateau (QTP). The simulated results indicate that the temperature field beneath the embankment is asymmetrically distributed under the condition of unilateral sand particles deposition. This asymmetry gradually weakened with the increase of operation time and the gradual adjustment of the permafrost temperature field. By comparing the permafrost table beneath the natural surface, the sand deposition center, and the middle of the embankment center, it could be found that the unilateral sand particles deposition has less effect on the degradation of the permafrost table in the center of the embankment. However, for the center of the sand deposition, the change of the permafrost table is larger with the increase of time and the corresponding rate of permafrost table degradation is higher than that without sand particles deposition, especially for the high-temperature permafrost. In addition, with different sand thickness and width conditions, the effect of “narrow-thick” form sand particles deposition on the temperature field beneath embankment is greater than that of “wide-thin” form sand deposition. Hence, in order to reduce its impact on the long-term thermal condition beneath the embankment, it is necessary to clean the thicker deposition sand particles at the toe of the embankment.

Potential greenhouse gas production by organic matter decomposition in thawing subsea permafrost

<p>Subsea permafrost extends over vast areas across the East Siberian Arctic Ocean shelves and might harbor a large and vulnerable organic matter pool. Field campaigns have observed strongly elevated concentrations of CH<sub>4</sub> in seawater above subsea permafrost that might stem from microbial degradation of thawing subsea permafrost organic matter, from release of CH<sub>4</sub> stored within subsea permafrost, from shallow CH<sub>4</sub> hydrates or from deeper thermogenic/petrogenic CH<sub>4</sub> pools. We here assess the potential production of CH<sub>4</sub>, as well as CO<sub>2</sub> and N<sub>2</sub>O by organic matter degradation in subsea permafrost after thaw. To that end, we employ a set of subsea permafrost drill cores from the Buor-Khaya Bay in the south-eastern Laptev Sea where previous studies have observed a rapid deepening of the ice-bonded permafrost table. Preliminary data from an ongoing laboratory incubation experiment suggest the production of both CH<sub>4</sub> and CO<sub>2</sub> by decomposition of thawed subsea permafrost organic matter, while N<sub>2</sub>O production was negligible. These data will be combined with detailed biomarker analysis to constrain the vulnerability of subsea permafrost organic matter to degradation to greenhouse gases upon thaw.</p>

Absence of ice-bonded permafrost beneath an Arctic lagoon revealed by electrical geophysics

Relict permafrost is ubiquitous throughout the Arctic coastal shelf, but little is known about it near shore. The presence and thawing of subsea permafrost are vital information because permafrost stores an atmosphere’s worth of carbon and protects against coastal erosion. Through electrical resistivity imaging across a lagoon on the Alaska Beaufort Sea coast in summer, we found that the subsurface is not ice-bonded down to ~20 m continually from within the lagoon, across the beach, and underneath an ice-wedge polygon on the tundra. This contrasts with the broadly held idea of a gently sloping ice-bonded permafrost table extending from land to offshore. The extensive unfrozen zone is a marine talik connected to on-land cryopeg. This zone is a potential source and conduit for water and dissolved organic matter, is vulnerable to physical degradation, and is liable to changes in biogeochemical processes that affect carbon cycling and climate feedbacks.

Permafrost table depth in soils of Eastern Antarctica oases, King George and Ardley Islands (South Shetland Islands)

This study was aimed to investigate the electrical resistivity in soils and permafrost of various ice-free areas of Antarctica and Sub-Antarctica (from coastal Eastern Antarctica oases to Maritime Antarctica). Measurements of electrical resistivity of soil and permafrost strata were performed with a portable device LandMapper. It was found that the permafrost table depth ranged 82 to106 cm in Bunger Hills, 95 to 122 cm in Larsemann Hills, 27 to 106 in Thala Hills, and 89 to 100 cm on King George Island and Ardley Island. Presence (and thickness) of organic layer and influence of snow patches melting were found the main reasons for differentiation of permafrost table depth in the studied ice-free areas. Anthropogenic disturbance at waste disposal sites resulted in more pronounced soil profile heterogeneity and formation of scattered electrical resistivity profiles. Permafrost layer was found less homogenous in the upper part of permafrost strata compared to the lower part. An application of vertical electrical resistivity sounding (VERS) may be very useful for evaluation of active layer thickness in Antarctic environments, especially when they are facing severe anthropogenic influence due to maintaining of numerous Antarctic research stations and logistical operations

Multi-methodological investigation of a retrogressive thaw slump in the Richardson Mountains, Northwest Territories, Canada

<p>The Mackenzie-Delta Region is known for strong morphological activity in context of global warming and permafrost degradation, which reveals in a large number of retrogressive thaw slumps. These are frequently found along the shorelines of inland lakes and the coast; however, this geomorphological phenomenon also occurs at inland ​​streams and creeks of the Peel Plateau and the Richardson Mountains, located in the southwest of the delta. Here several active retrogressive thaw slumps are found of which some have reached an extent of several hectares, e.g. the mega slump at the Dempster Creek.</p><p>In this study we investigated a recent retrogressive thaw slump at the edge of the Richardson Mountains close to the Dempster Highway to determine the subsurface properties using non-invasive geophysical methods. We performed three-dimensional Ground Penetrating Radar (GPR) surveys, as well as quasi-three-dimensional Electrical Resistivity Tomography (ERT) surveys in order to investigate the subsurface characteristics adjacent to the retreating headwall of the slump. These measurements provide information on the topography of the permafrost table, ice content and/or water pathways on top, within or under the permafrost layer. Additionally, we performed manual measurements of the active layer thickness for validation of the geophysical models. The approach was complemented by the analysis of high-resolution photogrammetric digital elevation models (DEM) that were generated using in situ drone acquisitions.</p><p>The measured active layer depths show a strong influence of the relief and especially of small creeks on the permafrost table topography. Likely, this influence also is the primary trigger for the initial slump activity. In addition, the ERT measurements show strong variations of the electrical resistivity values in the upper few meters, which are indicative for heterogeneities, also within the ice-rich permafrost body. Especially noticeable is a layer of low resistivity values in an area adjacent to the slump headwall. This layer is found at depths between 4m to 7m, which approximately corresponds to the base of the headwall. Here, the low resistivity values could be indicative for an unfrozen or water-rich layer below the ice-rich permafrost. Consequently, this layer may have contributed to the initial formation of the slump and is important for the spatial extension of the slump.</p><p>These results present new insights into the subsurface of an area adjacent to an active retrogressive thaw slump and may contribute to a better understanding of slump development.</p>

Uptake of urea by “drunken” trees on permafrost

<p>Boreal forest productivity on permafrost is limited by availability of soil nitrogen (N) in the active layer. Low soil temperature and summer flooding limit microbial N mineralization on shallow permafrost table. Uptake of amino acids by plant root-mycorrhizal association is known to mitigate N limitation in boreal forest soils. However, amino acid hypothesis can not fully explain advantage of black spruce trees in drunken forests due to competition of amino acids between plants, bryophytes, and microbes. Based on the observation of urea accumulation in deeper soil, we test another hypothesis that black spruce trees take up intact urea in deeper soil. Mixture solutions (glutamic acid, urea, ammonium, nitrate), with only one N form labeled by <sup>13</sup>C and/or <sup>15</sup>N, was injected into the organic/mineral soil layers. We compared two black spruce forest sites with/without shallow permafrost table in northern Canada. We found that black spruce trees take up intact urea as well as amino acids in the shallow permafrost sites. Urea accumulation is explained by low microbial activities to mineralize <sup>14</sup>C-labeled urea. The other plants or bryophyte compete with black spruce for amino acids, but not for urea. Since the other black spruce trees in the deeper soil sites rely on amino acids and inorganic N, urea uptake strategy is specific to black spruce trees on shallow permafrost table. The root expansion on hummocky microrelief provides opportunity for leaning trees to access urea. The uptake of intact urea could be one of strategy of black spruce trees to mitigate N limitation in permafrost-affected hummocky soils.</p>

Numerical analysis of temperature fields around the buried arctic gas pipeline in permafrost regions

Based on one planned arctic natural gas pipeline engineering which will cross continuous, discontinuous, sporadic and non-permafrost areas from north to south, with different pipeline temperatures set, a thermal model of the interaction between pipeline and permafrost is established to investigate the influence of pipelines on the freezing and thawing of frozen soil around pipeline and thermal stability of permafrost. The results show that different pipeline temperatures influence the permafrost table greatly. Especially in discontinuous permafrost areas the permafrost table is influenced in both positive temperature and negative temperature. The warm gas pipeline of 5?C could decrease the value of permafrost table about 1 to 3 times pipe diameter and aggravate the degradation of permafrost around pipeline; -1?C and -5?C chilled gas pipeline can effectively improve the permafrost table and maintain the temperature stability of frozen soil , but the temperature of soils below pipeline of -5?C decreases obviously, which may lead to frost heave hazards. In terms of thermal stability around pipeline, it is advised that transporting temperature of -1?C is adopted in continuous permafrost area; in discontinuous permafrost area pipeline could operate above freezing in the summer months with the station discharge temperature trending the ambient air temperature, but the discharge temperature must be maintained as -1?C throughout the winter months; in seasonal freezing soil area chilled pipeline may cause frost heave, therefore pipeline should run in positive temperature without extra temperature cooling control.