Permafrost In Alaska Research Articles

Frozen no more, a case study of Arctic permafrost impacts of oil and gas withdrawal

Approximately 8100 km2 of Alaska are leased to the oil and gas industry for exploration and extraction. According to industry estimates, subsurface expansion from these leases could cover up to 130.2 km2 per pad. As industrial oil extraction activities increase across the thawing Alaskan permafrost, impacts on the permafrost environment will include rapid thaw, increased hydrological flux, and the release of climate warming greenhouse gases. Here, we use remote sensing and field observations to provide a first-order comparison of the direct impacts to the permafrost tundra from oil well pads, and the long-term consequences of a legacy oil pads on the warming North Slope of Alaska. We find that oil well pads on the permafrost accelerate permafrost degradation and persist despite remediation.

Deciphering the Intricate Control of Minerals on Deep Soil Carbon Stability and Persistence in Alaskan Permafrost.

Understanding the fate of organic carbon in thawed permafrost is crucial for predicting climate feedback. While minerals and microbial necromass are known to play crucial roles in the long-term stability of organic carbon in subsoils, their exact influence on carbon persistence in Arctic permafrost remains uncertain. Our study, combining radiocarbon dating and biomarker analyses, showed that soil organic carbon in Alaskan permafrost had millennial-scale radiocarbon ages and contained only 10%-15% microbial necromass carbon, significantly lower than the global average of ~30%-60%. This ancient carbon exhibited a weak correlation with reactive minerals but a stronger correlation with mineral weathering (reactive iron to total iron ratio). Peroxidase activity displayed a high correlation coefficient (p < 10-6) with Δ14C and δ13C, indicating its strong predictive power for carbon persistence. Further, a positive correlation between peroxidase activity and polysaccharides indicates that increased peroxidase activity may promote the protection of plant residues, potentially by fostering the formation of mineral-organic associations. This protective role of mineral surfaces on biopolymers was further supported by examining 1451 synchrotron radiation infrared spectra from soil aggregates, which revealed a strong correlation between mineral OH groups and organic functional groups at the submicron scale. An incubation experiment revealed that increased moisture contents, particularly within the 0%-40% range, significantly elevated peroxidase activity, suggesting that ancient carbon in permafrost soils is vulnerable to moisture-induced destabilization. Collectively, this study offers mechanistic insights into the persistence of carbon in thawed permafrost soils, essential for refining permafrost carbon-climate feedbacks.

Predictive Analytics of Air Temperature in Alaskan Permafrost Terrain Leveraging Two-Level Signal Decomposition and Deep Learning

Local weather forecasts in the Arctic outside of settlements are challenging due to the dearth of ground-level observation stations and high computational costs. During winter, these forecasts are critical to help prepare for potentially hazardous weather conditions, while in spring, these forecasts may be used to determine flood risk during annual snow melt. To this end, a hybrid VMD-WT-InceptionTime model is proposed for multi-horizon multivariate forecasting of remote-region temperatures in Alaska over short-term horizons (the next seven days). First, the Spearman correlation coefficient is employed to analyze the relationship between each input variable and the forecast target temperature. The most output-correlated input sequences are decomposed using variational mode decomposition (VMD) and, ultimately, wavelet transform (WT) to extract time-frequency patterns intrinsic in the raw inputs. The resulting sequences are fed into a deep InceptionTime model for short-term forecasting. This hybrid technique has been developed and evaluated using 35+ years of data from three locations in Alaska. Different experiments and performance benchmarks are conducted using deep learning models (e.g., Time Series Transformers, LSTM, MiniRocket), and statistical and conventional machine learning baselines (e.g., GBDT, SVR, ARIMA). All forecasting performances are assessed using four metrics: the root mean squared error, the mean absolute percentage error, the coefficient of determination, and the mean directional accuracy. Superior forecasting performance is achieved consistently using the proposed hybrid technique.

Scale‐Dependent Influence of Permafrost on Riverbank Erosion Rates

AbstractWhether permafrost systematically alters the rate of riverbank erosion is a fundamental geomorphic question with significant importance to infrastructure, water quality, and biogeochemistry of high‐latitude watersheds. For over four decades, this question has remained unanswered due to a lack of data. Using remotely sensed imagery, we addressed this knowledge gap by quantifying riverbank erosion rates across the Arctic and subarctic. To compare these rates to non‐permafrost rivers, we assembled a global data set of published riverbank erosion rates. We found that erosion rates in rivers influenced by permafrost are on average nine times lower than non‐permafrost systems; erosion rate differences increase up to 40 times for the largest rivers. To test alternative hypotheses for the observed erosion rate difference, we examined differences in total water yield and erosional efficiency between these rivers and non‐permafrost rivers. Neither of these factors nor differences in river sediment loads provided compelling alternative explanations, leading us to conclude that permafrost limits riverbank erosion rates. This conclusion was supported by field investigations of rates and patterns of erosion along three rivers flowing through discontinuous permafrost in Alaska. Our results show that permafrost limits maximum bank erosion rates on rivers with stream powers greater than 900 Wm−1. On smaller rivers, however, hydrology rather than thaw rate may be the dominant control on bank erosion. Our findings suggest that Arctic warming and hydrological changes should increase bank erosion rates on large rivers but may reduce rates on rivers with drainage areas less than a few thousand km2.

Impacts of Lightweight Aggregate Interlayers for Air Convection Embankment on Pavement Thermal Profile and Pavement Performance in Alaskan Permafrost Regions

Crushed-rock air convection embankment (ACE) has been used to mitigate pavement distresses caused by climatic extremes in permafrost regions for more than three decades. This study proposes using lightweight aggregates as cost-effective alternative materials to overcome the shortage of desired crushed rocks needed for ACE in interior Alaska. This paper presents an investigation of the performance of six selected pavement structures: an asphalt pavement typical of the northern region of Alaska and five pavements reinforced with different paving interlayers (i.e., silty sand/gravel, crushed rocks, cellular concrete aggregate, foam glass aggregate, and lightweight expanded clay aggregate). Pavement thermal analyses using Temperature Estimate Model for Pavement Structures (TEMPS) program and ANSYS Fluent software were performed to predict heat transfer patterns and thermal performance for each case. Pavement performance analyses using viscoelastic-based FlexPAVE™ and the elastic-based Alaska Flexible Pavement Design (AKFPD) program were conducted to evaluate the long-term performance and structural stability of subgrade soil with different types of interlayers. The results showed that the lightweight aggregate ACEs improved cooling performance more effectively than the crushed-rock ACE. The lightweight aggregate interlayers could maintain desired thermal insulation in summer and enhance the cooling effect in winter. The modeling results identified the high potential of using lightweight aggregates as alternative ACE materials to improve pavement service life and subgrade stability.

High nitrate variability on an Alaskan permafrost hillslope dominated by alder shrubs

Abstract. In Arctic ecosystems, increasing temperatures are driving the expansion of nitrogen (N) fixing shrubs across tundra landscapes. The implications of this expansion to the biogeochemistry of Arctic ecosystems are of critical importance and more work is needed to better understand the form, availability, and transportation potential of N from these shrubs across a variety of Arctic landscapes. To gain insights into the processes controlling N within a permafrost hillslope system, the spatiotemporal variability of nitrate (NO3-) and its environmental controls were investigated at an alder (Alnus viridis spp. fruticosa) dominated permafrost tundra landscape in the Seward Peninsula, Alaska, USA. Soil pore water was collected from locations within alder shrubland growing along a well-drained hillslope and was compared to soil pore water collected from locations outside (upslope, downslope, and between) the alder shrubland. Soil pore water collected within alder shrubland had an average NO3-N (nitrogen from nitrate) concentration of 4.27±8.02 mg L−1 and differed significantly from locations outside alder shrubland (0.23±0.83 mg L−1; p&lt;0.05). Temporal variation in NO3-N within and downslope of alder shrubland co-occurred with precipitation events where NO3- that accumulated in the soil was likely flushed downslope during rainfall. These findings have important implications for nutrient availability and mobility in N-limited permafrost systems that are experiencing shrub expansion in response to a warming Arctic.

The Impact of Freeze‐Thaw History on Soil Carbon Response to Experimental Freeze‐Thaw Cycles

AbstractFreeze‐thaw is a disturbance process in cold regions where permafrost soils are becoming vulnerable to temperature fluctuations above 0°C. Freeze‐thaw alters soil physical and biogeochemical properties with implications for carbon persistence and emissions in Arctic landscapes. We examined whether different freeze‐thaw histories in two soil systems led to contrasting biogeochemical responses under a laboratory‐controlled freeze‐thaw incubation. We investigated controls on carbon composition through Fourier‐transform ion cyclotron resonance mass spectrometry (FT‐ICR‐MS) to identify nominal carbon oxidation states and relative abundances of aliphatic‐type carbon molecules in both surface and subsurface soils. Soil cores (∼60 cm‐depth) were sampled from two sites in Alaskan permafrost landscapes with different in situ freeze‐thaw characteristics: Healy (&gt;40 freeze‐thaw cycles annually) and Toolik (&lt;15 freeze‐thaw cycles annually). FT‐ICR‐MS was coupled with in situ temperature data and soil properties (i.e., soil texture, mineralogy) to assess (a) differences in soil organic matter composition associated with previous freeze‐thaw history and (b) sensitivity to experimental freeze‐thaw in the extracted cores. Control (freeze‐only) samples showed greater carbon oxidation in Healy soils compared with Toolik, even in lower mineral horizons where freeze‐thaw history was comparable across both sites. Healy showed the most loss of carbon compounds following experimental freeze‐thaw in the lower mineral depths, including a decrease in aliphatics. Toolik soils responded more slowly to freeze‐thaw as shown by intermediary carbon oxidation distributed across multiple carbon compound classes. Variations in the response of permafrost carbon chemistry to freeze‐thaw is an important factor for predicting changes in soil function as permafrost thaws in high northern latitudes.

Detection of thermokarst lake drainage events in the northern Alaska permafrost region

The rapidly warming Arctic climate is reducing the stability of near-surface permafrost, and the thawing of ice-rich permafrost causes landscape changes known as thermokarst processes. Growing evidence suggests an increasing trend in the frequency and magnitude of thermokarst lake drainage events, which would significantly alter topography and hydrology, affecting ecosystem stability and carbon cycling. Dynamic monitoring of thermokarst lakes through satellite imagery remains a challenging task, as current temporal trend analysis methods have difficulty in accurately detecting when thermokarst lake drainage events occur. In this study, to improve the detection of time series breakpoints, an advanced temporal segmentation and change detection algorithm developed for forest change detection was, for the first time, transposed to monitor thermokarst lake dynamics. Moreover, to filter out spurious signals caused by fluctuations in lake area, we developed a hybrid algorithm to validate the detected thermokarst lake drainage events at the pixel-level and lake object-level, respectively. The method developed in this study demonstrates its effectiveness in detecting thermokarst lake drainage events in Arctic permafrost ecosystems and the potential to monitor the evolution of thermokarst landscapes using Landsat archive. A time-series analysis of changes in the thermokarst lake region of northern Alaska since 2000 using all available Landsat continuous data was performed on the Google Earth Engine platform. In total, 90 drainage lakes larger than 5 ha in size were detected in our study area, nearly a third of which were almost completely drained. As thermokarst lakes drainage represent hotspots of permafrost degradation, we publicly share information on these drained lakes to help select more targeted sites for costly fieldwork and validation activities. This study provides a basis for understanding and quantifying thermokarst lake dynamics in the Arctic permafrost region, which will contribute to the goal of integrating thermokarst processes into earth system models.

Ongoing Landslide Deformation in Thawing Permafrost

AbstractThawing permafrost influences landslide initiation, but observation of landslide development in thawing permafrost is limited. To evaluate the impact of landslide age, morphology, and permafrost conditions, we quantified topographic deformation of three shallow‐angle, thaw‐initiated landslides in discontinuous permafrost in Alaska. Two of the landslides initiated &lt;3 years ago and the third initiated 20–50 years ago. The two recent landslides are still mobile, with maximum elevation loss of 0.8 ± 0.04 and 1.0 ± 0.08 m over the study period. At one site, shallow permafrost (&lt;2.3 m) is present at 0.4–1.9 m depth adjacent to the landslide but not within the landslide. The lack of shallow permafrost within the slide indicates that permafrost has thawed faster within the landslide because ground surface disturbance increased heat flux to the subsurface. We propose that a positive feedback between permafrost thaw and landslide development exists. Climate warming will accelerate loss of permafrost in recent landslides.

Recent degradation of interior Alaska permafrost mapped with ground surveys, geophysics, deep drilling, and repeat airborne lidar

Abstract. Permafrost underlies one-quarter of the Northern Hemisphere but is at increasing risk of thaw from climate warming. Recent studies across the Arctic have identified areas of rapid permafrost degradation from both top-down and lateral thaw. Of particular concern is thawing syngenetic “yedoma” permafrost which is ice-rich and has a high carbon content. This type of permafrost is common in the region around Fairbanks, Alaska, and across central Alaska expanding westward to the Seward Peninsula. A major knowledge gap is relating belowground measurements of seasonal thaw, permafrost characteristics, and residual thaw layer development with aboveground ecotype properties and thermokarst expansion that can readily quantify vegetation cover and track surface elevation changes over time. This study was conducted from 2013 to 2020 along four 400 to 500 m long transects near Fairbanks, Alaska. Repeat active layer depths, near-surface permafrost temperature measurements, electrical resistivity tomography (ERT), deep (&gt; 5 m) boreholes, and repeat airborne light detection and ranging (lidar) were used to measure top-down permafrost thaw and map thermokarst development at the sites. Our study confirms previous work using ERT to map surface thawed zones; however, our deep boreholes confirm the boundaries between frozen and thawed zones that are needed to model top-down, lateral, and bottom-up thaw. At disturbed sites seasonal thaw increased up to 25 % between mid-August and early October and suggests measurements to evaluate active layer depth must be made as late in the fall season as possible because the projected increase in the summer season of just a few weeks could lead to significant additional thaw. At our sites, tussock tundra and spruce forest are associated with the lowest mean annual near-surface permafrost temperatures while mixed-forest ecotypes are the warmest and exhibit the highest degree of recent temperature warming and thaw degradation. Thermokarst features, residual thaw layers, and taliks have been identified at all sites. Our measurements, when combined with longer-term records from yedoma across the 500 000 km2 area of central Alaska, show widespread near-surface permafrost thaw since 2010. Projecting our thaw depth increases, by ecotype, across the yedoma domain, we calculate a first-order estimate that 0.44 Pg of organic carbon in permafrost soil has thawed over the past 7 years, which, for perspective, is an amount of carbon nearly equal to the yearly CO2 emissions of Australia. Since the yedoma permafrost and the variety of ecotypes at our sites represent much of the Arctic and subarctic land cover, this study shows remote sensing measurements, top-down and bottom-up thermal modeling, and ground-based surveys can be used predictively to identify areas of the highest risk for permafrost thaw from projected future climate warming.

Landsat-based lake distribution and changes in western Alaska permafrost regions between the 1970s and 2010s

Lakes are an important ecosystem component and geomorphological agent in northern high latitudes and it is important to understand how lake initiation, expansion and drainage may change as high latitudes continue to warm. In this study, we utilized Landsat Multispectral Scanner System images from the 1970s (1972, 1974, and 1975) and Operational Land Imager images from the 2010s (2013, 2014, and 2015) to assess broad-scale distribution and changes of lakes larger than 1 ha across the four permafrost zones (continuous, discontinuous, sporadic, and isolated extent) in western Alaska. Across our 68 000 km2 study area, we saw a decline in overall lake coverage across all permafrost zones with the exception of the sporadic permafrost zone. In the continuous permafrost zone lake area declined by −6.7% (−65.3 km2), in the discontinuous permafrost zone by −1.6% (−55.0 km2), in the isolated permafrost zone by −6.9% (−31.5 km2) while lake cover increased by 2.7% (117.2 km2) in the sporadic permafrost zone. Overall, we observed a net drainage of lakes larger than 10 ha in the study region. Partial drainage of these medium to large lakes created an increase in the area covered by small water bodies <10 ha, in the form of remnant lakes and ponds by 7.1% (12.6 km2) in continuous permafrost, 2.5% (15.5 km2) in discontinuous permafrost, 14.4% (74.6 km2) in sporadic permafrost, and 10.4% (17.2 km2) in isolated permafrost. In general, our observations indicate that lake expansion and drainage in western Alaska are occurring in parallel. As the climate continues to warm and permafrost continues to thaw, we expect an increase in the number of drainage events in this region leading to the formation of higher numbers of small remnant lakes.

Permafrost thaw‐related slope failures in Alaska’s Arctic National Parks, c. 1980–2019

AbstractActive‐layer detachments (ALD) and retrogressive thaw slumps (RTS) are landslides that occur as a result of thaw in permafrost regions. I mapped the extent of bare soil exposed in these thaw‐related slope failures in four study areas with continuous permafrost in Alaska’s Arctic National Parks, on mosaics of aerial photographs from 1977–1985 (sampling episode 1), satellite images from 2006–2009 (sampling episode 2), and satellite images from 2018–2019 (sampling episode 3). In all four study areas the count of ALD and RTS, and the area of bare soil they exposed, was greater during the first or second sampling episode than the third sampling episode, in spite of record high mean annual temperatures in 2014–2019. One study area had frozen debris lobes (FDL) in addition to ALD and RTS. In that study area the bare ground exposed by destabilization and rapid movement of FDL was greatest in the third sampling episode, probably as a result of deep thaw and talik formation. The destabilization of FDL in episode 3 was probably a long‐term consequence of warming and permafrost loss, while the observed pulses of ALD and RTS in episodes 1 and 2 were closely tied to short‐term deep thaw events in areas where the underlying permafrost remained stable.

Thawing permafrost: an overlooked source of seeds for Arctic cloud formation

As the Arctic warms at twice the global rate, radiative feedbacks from clouds will lead to compounding impacts on the surface energy budget that affect both regional and global weather, and climate. In a future warmer world, the Arctic is projected to become cloudier. However, the formation and evolution of Arctic clouds remain highly uncertain in part due to a limited understanding of current and future sources of ice nucleating particles (INPs). In particular, the sources and abundance of biologically-derived INPs are poorly characterized, yet they may be pivotal for cloud ice formation, especially at temperatures in which Arctic mixed-phase clouds (AMPCs) persist (i.e. >−15 °C). Here, we show for the first time that permafrost is a remarkably rich source of biologically-derived INPs, both heat labile (probably proteinaceous) and other organic INPs of biomolecular origin (41%–100% and 99%–100% of the total INPs, respectively). INP concentrations in 1000 to 30 000 year old permafrost were comparable to the most active of other Arctic and midlatitude soil sources (up to 1010 INPs per gram of soil). Thawing of permafrost—which promotes metabolic activity in microbes—and subsequent mobilization of those soils directly into the atmosphere or into lakes, rivers, and the ocean, suggests the intriguing possibility that increasing emissions of INPs from this hitherto overlooked reservoir could be widespread, and, in time, greatly impact Arctic cloud cloud glaciation and radiative properties. This discovery is timely given the rapidly-thawing permafrost in Alaska and across Earth’s high latitudes. Since permafrost covers 15% of Northern Hemisphere land, this novel and prevalent INP source may become central to predictions of aerosol-cloud-precipitation interactions in AMPCs.

Feasibility evaluation of hydraulic fracturing in hydrate-bearing sediments based on analytic hierarchy process-entropy method (AHP-EM)

Natural gas hydrate is an attractive potential as alternative energy source. The initial studies of natural gas hydrate production test have shown that the hydrate productivity via conventional depressurization is still far to reach the commercial level, hence, hydraulic fracturing has been proposed to stimulate the hydrated formation to enhance production. However, the buried depth of hydrate-bearing sediments is generally shallow, and the cementation of sediments is weak. Whether the hydrate-bearing sediments has adequate and commercially viable fracability is a question yet to be answered. In this study, a novel feasibility evaluation model of hydraulic fracturing in hydrate-bearing sediments is developed based on analytic hierarchy process-entropy method. The fracability index is proposed to evaluate the fracability of hydrate-bearing sediments. Representative samples were built based on the physical and mechanical characteristics of Alaska permafrost, and hydraulic fracturing experiments were carried out to evaluate the feasibility of hydraulic fracturing as a stimulation technique. The results showed that the hydrate-bearing sediments with fracability index >0.72 can form fractures under different fracturing fluid viscosity ratio. For hydrate-bearing sediments with fracability index <0.39, when the fracturing fluid viscosity ratio is 1, no fracture network is formed during hydraulic fracturing. However, when the fracturing fluid viscosity ratio is increased to more than 120, fractures may develop. For the hydrate-bearing sediments with fracability index between 0.39 and 0.72, the results are not promising when fracturing fluid viscosity ratio is 1, however, when fracturing fluid viscosity ratio is more than 120, fractures observed to grow. In general, the results indicate that the samples with high fracability index are sweet spots in hydrate sediments in terms of fracability. At low fracability index values, the viscosity of fracturing fluid has a key role in fracability, where increasing the viscosity will result in higher fracability index.

A revised pan-Arctic permafrost soil Hg pool based on Western Siberian peat Hg and carbon observations

Abstract. Natural and anthropogenic mercury (Hg) emissions are sequestered in terrestrial soils over short, annual to long, millennial timescales before Hg mobilization and run-off impact wetland and coastal ocean ecosystems. Recent studies have used Hg-to-carbon (C) ratios (RHgC's) measured in Alaskan permafrost mineral and peat soils together with a northern circumpolar permafrost soil carbon inventory to estimate that these soils contain large amounts of Hg (between 184 and 755 Gg) in the upper 1 m. However, measurements of RHgC on Siberian permafrost peatlands are largely missing, leaving the size of the estimated northern soil Hg budget and its fate under Arctic warming scenarios uncertain. Here we present Hg and carbon data for six peat cores down to mineral horizons at 1.5–4 m depth, across a 1700 km latitudinal (56 to 67∘ N) permafrost gradient in the Western Siberian Lowland (WSL). Mercury concentrations increase from south to north in all soil horizons, reflecting a higher stability of sequestered Hg with respect to re-emission. The RHgC in the WSL peat horizons decreases with depth, from 0.38 Gg Pg−1 in the active layer to 0.23 Gg Pg−1 in continuously frozen peat of the WSL. We estimate the Hg pool (0–1 m) in the permafrost-affected part of the WSL peatlands to be 9.3±2.7 Gg. We review and estimate pan-Arctic organic and mineral soil RHgC to be 0.19 and 0.63 Gg Pg−1, respectively, and use a soil carbon budget to revise the pan-Arctic permafrost soil Hg pool to be 72 Gg (39–91 Gg; interquartile range, IQR) in the upper 30 cm, 240 Gg (110–336 Gg) in the upper 1 m, and 597 Gg (384–750 Gg) in the upper 3 m. Using the same RHgC approach, we revise the upper 30 cm of the global soil Hg pool to contain 1086 Gg of Hg (852–1265 Gg, IQR), of which 7 % (72 Gg) resides in northern permafrost soils. Additional soil and river studies in eastern and northern Siberia are needed to lower the uncertainty on these estimates and assess the timing of Hg release to the atmosphere and rivers.

A pseudo-kinetic model to simulate phase changes in gas hydrate bearing sediments

Modeling of the phase transitions anticipated in gas hydrate bearing sediments (GHBS) is critical for a proper understanding of time-dependent changes in states and volumes (e.g. the production of methane from this type of soils). We propose a new pseudo-kinetic approach to simulate the typical phase changes anticipated in GHBS, using published experimental results involving gas hydrate dissociation that are the basis of a widely used kinetic model. The proposed pseudo-kinetic model is formulated in the pressure-temperature (P-T) plane and assumes a rate of gas hydrate dissociation (or formation) proportional to the distance between the current state and the phase boundary. The model consists of only one parameter and is simple to implement in numerical simulators. A similar concept is used to model ice formation/thawing phenomena, but based on the ice/liquid-water phase boundary. We implemented the pseudo-kinetic model in a fully coupled thermo-hydro-chemo-mechanical (THCM) finite element code and validated it against experimental results performed on the dissociation of synthetic gas hydrate. We also evaluated the pseudo-kinetic model using synthetic cases covering several scenarios associated with gas hydrate formation/dissociation and ice formation/thawing. The model successfully reproduced the gas production test from a natural GHBS core from Korea (scaled gas venting experiment over 14 h), and also the formation of gas hydrate and ice in permafrost in Alaska (over 2 × 106 years). -The analyses show the versatility of the proposed pseudo-kinetic approach by applying it to model the different types of phase transitions typically encounter in GHBS. The simple formulation, easy implementation in numerical simulator, and reduced number of parameters (only one per phase change) make this model an attractive option for simulating phase transformations in problems involving GHBS.

Carbon Thaw Rate Doubles When Accounting for Subsidence in a Permafrost Warming Experiment

AbstractPermafrost thaw is typically measured with active layer thickness, or the maximum seasonal thaw measured from the ground surface. However, previous work has shown that this measurement alone fails to account for ground subsidence and therefore underestimates permafrost thaw. To determine the impact of subsidence on observed permafrost thaw and thawed soil carbon stocks, we quantified subsidence using high‐accuracy GPS and identified its environmental drivers in a permafrost warming experiment near the southern limit of permafrost in Alaska. With permafrost temperatures near 0°C, 10.8 cm of subsidence was observed in control plots over 9 years. Experimental air and soil warming increased subsidence by five times and created inundated microsites. Across treatments, ice and soil loss drove 85–91% and 9–15% of subsidence, respectively. Accounting for subsidence, permafrost thawed between 19% (control) and 49% (warming) deeper than active layer thickness indicated, and the amount of newly thawed carbon within the active layer was between 37% (control) and 113% (warming) greater. As additional carbon thaws as the active layer deepens, carbon fluxes to the atmosphere and lateral transport of carbon in groundwater could increase. The magnitude of this impact is uncertain at the landscape scale, though, due to limited subsidence measurements. Therefore, to determine the full extent of permafrost thaw across the circumpolar region and its feedback on the carbon cycle, it is necessary to quantify subsidence more broadly across the circumpolar region.

The role of changing temperature in microbial metabolic processes during permafrost thaw.

Approximately one fourth of the Earth’s Northern Hemisphere is underlain by permafrost, earth materials (soil, organic matter, or bedrock), that has been continuously frozen for at least two consecutive years. Numerous studies point to evidence of accelerated climate warming in the Arctic and sub-Arctic where permafrost is located. Changes to permafrost biochemical processes may critically impact ecosystem processes at the landscape scale. Here, we sought to understand how the permafrost metabolome responds to thaw and how this response differs based on location (i.e. chronosequence of permafrost formation constituting diverse permafrost types). We analyzed metabolites from microbial cells originating from Alaskan permafrost. Overall, permafrost thaw induced a shift in microbial metabolic processes. Of note were the dissimilarities in biochemical structure between frozen and thawed samples. The thawed permafrost metabolomes from different locations were highly similar. In the intact permafrost, several metabolites with antagonist properties were identified, illustrating the competitive survival strategy required to survive a frozen state. Interestingly, the intensity of these antagonistic metabolites decreased with warmer temperature, indicating a shift in ecological strategies in thawed permafrost. These findings illustrate the impact of change in temperature and spatial variability as permafrost undergoes thaw, knowledge that will become crucial for predicting permafrost biogeochemical dynamics as the Arctic and Antarctic landscapes continue to warm.

Below Freezing: Elegy for the Melting Planet by Donald Anderson

Reviewed by: Below Freezing: Elegy for the Melting Planet by Donald Anderson Daryl W. Palmer Donald Anderson, Below Freezing: Elegy for the Melting Planet. Albuquerque: U of New Mexico P, 2018. 161 pp. Paper, $24.95. In memorable lines from “The Snow Man,” Wallace Stevens tells us, “One must have a mind of winter / To regard the frost. . . .” For many readers, the pronouncement is simply chilling, but some of us consider it a manifesto. We “regard” frost and embrace being, in the poet’s words, “cold a long time.” We treasure wintrum frod, the Old English phrase for the wisdom that comes from living through many winters. Because I am this sort of person, I have written about Muscovites and Englishmen in the Renaissance. I have tried to explain the cold in Hamlet. I read Laura Ingalls Wilder’s The Long Winter every year when the first snow comes. My brumal bona fi-des matter because I want to recommend Donald Anderson’s Below Freezing: Elegy for the Melting Planet to you as essential reading for winter minds trapped on a warming planet. A gifted and accomplished writer of fiction and poetry, Anderson curates a life of reading about and living in the cold. In her eloquent foreword, Aritha van Herk rightly describes the book as a “collage-ledger,” creating a kind of “chiaroscuro.” In Below Freezing, Anderson’s stories of memory drift alongside boreal history (the Children’s Blizzard of 1888, the Air Florida plane crash in 1982), frigid facts (the summit temperature of Mt. Everest and the age of permafrost in Alaska), and a wide range of voices. We hear from Jimbo from Wreckmasters, reporters in the Denver Post, and Travis, who once ran out into the Alaskan cold on Christmas Eve. In striking ways, these voices jostle with those of Emily Dickinson, Robert Hayden, James Joyce, John Krakauer, Barry Lopez, and Jeanette Winterson, to name a few. Along the way, Anderson caches bits of cold classics such as Jack London’s “To Build a Fire” and Robert Frost’s “Stopping by Woods on a Snowy Evening.” [End Page 295] Through it all, Anderson never loses sight of his focus: here is a timely, perhaps belated, reckoning with climate change and memory. The book’s first page announces the focus with a precise juxta-position of a Denver Post article quantifying the reduction of Arctic sea ice and Anderson’s memories of mittens. Readers with a special interest in the American West will find the book particularly appealing. With the opening paragraph, Anderson orients his project on the map of North America: “That mittens outwork gloves was a lesson learned, growing up in Montana— sure knowledge more aptly confirmed when an Air Force assignment landed me at a radar site in Alaska, three degrees north of the Arctic Circle” (3). Skipping back and forth between Butte, Montana, and the Arctic Circle, between recollections of family life and Air Force duties, Anderson assays Western memories of winter, holding them up in mittened hands. One need not have a mind of winter to appreciate the craftsmanship of the book and relish the accumulated wisdom. In fact, it is Anderson’s memory work that creates arcs, large and minute, in the book as he recalls attaching his tongue to a galvanized elementary school post, falling behind his father while snowshoeing through a storm, his father making ice cream out of icicles, his daughter determined to drive the old Datsun on a bitter day, and Bill Secours having survived a Grizzly Bear attack. In memory after memory, Anderson’s wry voice brings the book to life, sometimes for what he writes, other times for how he has listened: “I asked [Secours] for advice to survive in the North. Don’t eat yellow snow, he advised, serious as a bear attack” (148). The result is often bracing and beautiful, marked by wonder and wit, but never precious. Late in the book, readers may anticipate some sort of fanciful consolation as Anderson collects snowflake encomia: Winterson remarking on the wonder of snowflakes; a Zen proverb observing “No snowflake ever falls in the wrong place”; Thoreau remembering a particular snowflake and how it “reminded me...

Linking vegetation cover and seasonal thaw depths in interior Alaska permafrost terrains using remote sensing

Permafrost in Interior Alaska is protected against summer thaw by an insulating layer of moss and mixed vegetative cover that regulates seasonal thaw and the end-of-summer season permafrost active layer depth. Thaw depths are laborious point scale measurements that can be difficult to translate regionally. Since disturbances are present on the landscape across many temporal and spatial scales they can greatly affect the soil and vegetation regime. Furthermore, many areas are denied full assessment due to terrain complexity or limited accessibility. As such, a remotely sensed means for estimating surface thaw based on insular vegetation composition would be advantageous. A synoptic evaluation of this insulating layer could eventually benefit regional mapping of areas where vegetation cover helps regulate thaw depths during the local growing season. Herein, we present multi-year data collected from three terrain types in Interior Alaska that relates seasonal thaw depth to vegetative cover type. Field samples for spectral reflectance, vegetation, soil, elevation and seasonal thaw depths were obtained from surveyed 1 m2 quadrats during the local growing season (late July, each summer from 2014 to 2017) across three lowland boreal landscapes. Statistical relationships between vegetation and samples were explored using CCA and showed vegetative cover distributions were highly correlated in two dimensions with the principal variables represented almost evenly by the soil variable pH and thaw depth. Class maps representing vegetation and associated thaw depth were derived from hyperspectral imagery using field and imagery training data. Map accuracy assessment, conducted using random points to establish truth data, yielded overall accuracies of >85%. Regression analysis and root mean square error testing of the predictive capacity of the vegetation classes and thaw depth was variable but encouraging, ranging from 5 to 11 cm or between an 8 and 37% chance of error. We feel the results are strong enough to stimulate more study in the evaluation of vegetation and thaw depth mapping during the local growing season.