Temporal Changes in Moisture Content of the Active Layer and Near-Surface Permafrost at Barrow, Alaska, U.S.A.: 1962-1994

1996 ◽  
Vol 28 (3) ◽  
pp. 300 ◽  
Author(s):  
K. M. Hinkel ◽  
F. E. Nelson ◽  
Y. Shur ◽  
Jerry Brown ◽  
K. R. Everett
Keyword(s):  
Moisture Content ◽  
Active Layer ◽  
Temporal Changes ◽  
Near Surface

scholarly journals Geophysical imaging of permafrost in the SW Svalbard – the result of two high arctic expeditions to Spitsbergen

2020 ◽  
Author(s):  
Mariusz Majdanski ◽  
Artur Marciniak ◽  
Bartosz Owoc ◽  
Wojciech Dobiński ◽  
Tomasz Wawrzyniak ◽  
...  
Keyword(s):  
Surface Waves ◽  
Active Layer ◽  
High Arctic ◽  
The Arctic ◽  
Seismic Profiles ◽  
Frozen Ground ◽  
Near Surface ◽  
Seismic Processing ◽  
Reflection Seismic ◽  
Sea Coast

<p>The Arctic regions are the place of the fastest observed climate change. One of the indicators of such evolution are changes occurring in the glaciers and the subsurface in the permafrost. The active layer of the permafrost as the shallowest one is well measured by multiple geophysical techniques and in-situ measurements.</p><p>Two high arctic expeditions have been organized to use seismic methods to recognize the shape of the permafrost in two seasons: with the unfrozen ground (October 2017) and frozen ground (April 2018). Two seismic profiles have been designed to visualize the shape of permafrost between the sea coast and the slope of the mountain, and at the front of a retreating glacier. For measurements, a stand-alone seismic stations has been used with accelerated weight drop with in-house modifications and timing system. Seismic profiles were acquired in a time-lapse manner and were supported with GPR and ERT measurements, and continuous temperature monitoring in shallow boreholes.</p><p>Joint interpretation of seismic and auxiliary data using Multichannel analysis of surface waves, First arrival travel-time tomography and Reflection imaging show clear seasonal changes affecting the active layer where P-wave velocities are changing from 3500 to 5200 m/s. This confirms the laboratory measurements showing doubling the seismic velocity of water-filled high-porosity rocks when frozen. The same laboratory study shows significant (>10%) increase of velocity in frozen low porosity rocks, that should be easily visible in seismic.</p><p>In the reflection seismic processing, the most critical part was a detailed front mute to eliminate refracted arrivals spoiling wide-angle near-surface reflections. Those long offset refractions were however used to estimate near-surface velocities further used in reflection processing. In the reflection seismic image, a horizontal reflection was traced at the depth of 120 m at the sea coast deepening to the depth of 300 m near the mountain.</p><p>Additionally, an optimal set of seismic parameters has been established, clearly showing a significantly higher signal to noise ratio in case of frozen ground conditions even with the snow cover. Moreover, logistics in the frozen conditions are much easier and a lack of surface waves recorded in the snow buried geophones makes the seismic processing simpler.</p><p>Acknowledgements               </p><p>This research was funded by the National Science Centre, Poland (NCN) Grant UMO-2015/21/B/ST10/02509.</p>

scholarly journals Monitoring of Beech Glued Laminated Timber and Delamination Resistance of Beech Finger-Joints in Varying Ambient Climates

Forests ◽  
2021 ◽  
Vol 12 (12) ◽  
pp. 1672
Author(s):  
Hannes Stolze ◽  
Mathias Schuh ◽  
Sebastian Kegel ◽  
Connor Fürkötter-Ziegenbein ◽  
Christian Brischke ◽  
...  
Keyword(s):  
Relative Humidity ◽  
Moisture Content ◽  
Wood Moisture Content ◽  
Adhesive Systems ◽  
Wood Moisture ◽  
Near Surface ◽  
Finger Joints ◽  
Glued Laminated Timber ◽  
Delamination Resistance ◽  
Normative Requirements

In this study, varying ambient climates were simulated in a test building by changing temperature and relative humidity. Beech glued laminated timber (glulam, Fagus sylvatica, L.) was freshly installed in the test building and monitoring of the change in wood moisture content of the glulam resulting from the variations in climate was carried out. Subsequently, finger-jointed beech specimens were exposed to the variations in relative humidity measured in the course of the monitoring experiment on a laboratory scale, and thus an alternating climate regime was derived from the conditions in the test building. Its influence on the delamination of the finger-joints was evaluated. In addition, it was examined whether beech finger-joints using commercial adhesive systems fulfil the normative requirements for delamination resistance according to EN 301 (2018) and whether different bonding-wood moisture levels have an effect on the delamination of the finger-joints. In the context of the monitoring experiment, there was a clear moisture gradient in the beech glulam between the inner and near-surface wood. The applied adhesive systems showed almost the same delamination resistance after variation of relative humidity. The normative requirements were met by all PRF-bonded and by most PUR-bonded beech finger-joints with higher bonding wood moisture content.

scholarly journals Unearthing the Boreal Soil Resistome Associated with Permafrost Thaw

2020 ◽  
Author(s):  
Tracie J. Haan ◽  
Devin M. Drown
Keyword(s):  
Antibiotic Resistance ◽  
Active Layer ◽  
Resistance Genes ◽  
Soil Bacteria ◽  
Bacterial Community Composition ◽  
Ecological Niches ◽  
Whole Genome ◽  
Near Surface ◽  
Permafrost Thaw ◽  
Insight Into

ABSTRACTUnderstanding the distribution and mobility of antibiotic resistance genes (ARGs) in soil bacteria from diverse ecological niches is critical in assessing their impacts on the global spread of antibiotic resistance. In permafrost associated soils, climate and human driven forces augment near-surface thaw altering the overlying active layer. Physiochemical changes shift bacterial community composition and metabolic functioning, however, it is unknown if permafrost thaw will affect ARGs comprising the boreal soil resistome. To assess how thaw shifts the resistome, we performed susceptibility testing and whole genome sequencing on soil isolates from a disturbance-induced thaw gradient in Interior Alaska. We found resistance was widespread in the Alaskan isolates, with 87% of the 90 isolates resistant to at least one of the five antibiotics. We also observed positive trends in both the proportion of resistant isolates and the abundance of ARGs with permafrost thaw. However, the number of ARGs per genome and types of genes present were shown to cluster more strongly by bacterial taxa rather than thaw emphasizing the evolutionary origins of resistance and the role vertical gene transfer has in shaping the predominantly chromosomally encoded ARGs. The observed higher proportion of plasmid-borne and distinct ARGs in our isolates compared to RefSoil+ suggests local conditions affect the composition of the resistome along with selection for ARG mobility. Overall taxonomy and geography shape the resistome, suggesting that as microbial communities shift in response to permafrost thaw so will the ARGs in the boreal active layer.IMPORTANCEAs antibiotic resistance continues to emerge and rapidly spread in clinical settings, it is imperative to generate studies that build insight into the ecology of environmental resistance genes that pose a threat to human health. This study provides insight into the occurrence of diverse ARGs found in Alaskan soil bacteria which is suggestive of the potential to compromise health. The observed differences in ARG abundance with increasing permafrost thaw suggest the role of soil disturbance in driving the distribution of resistant determinants and the predominant taxa that shape the resistome. Moreover, the high-quality whole genome assemblies generated in this study are an extensive resource for microbial researchers interested in permafrost thaw and will provide a steppingstone for future research into ARG mobility and transmission risks.

Temperature and moisture controls on non-growing season CO2 emissions in laboratory incubations with soils from northern peatlands

2021 ◽  
Author(s):  
Eunji Byun ◽  
Fereidoun Rezanezhad ◽  
Linden Fairbairn ◽  
Nathan Basiliko ◽  
Jonathan Price ◽  
...  
Keyword(s):  
Moisture Content ◽  
Water Saturation ◽  
Carbon Sink ◽  
Growing Season ◽  
Temperature Sensitive ◽  
Near Surface ◽  
Soil Microbial ◽  
Carbon Budget Model ◽  
Peat Deposits ◽  
Northern High Latitude

<p>Canada has extensive peat deposits in northern high latitude wetlands and permafrost ecosystems. Peat accumulation represents a natural long-term carbon sink attributed to the cumulative excess of growing season net ecosystem production over non-growing season net mineralization. However, near-surface peat deposits are vulnerable to climate change and permafrost landscape transition. One specific concern is a potential rapid increase in the non-growing season carbon loss through enhanced organic matter mineralization under a warming climate. Our experimental study explores the response of peat CO<sub>2</sub> exchanges to (1) temperature, using the conventional <em>Q<sub>10</sub></em> parameter, and (2) moisture content. The observed responses are expected to reflect, at least in part, differential soil microbial adaptations to varying wetland conditions, across two northern ecoclimatic zones. Laboratory incubations were carried out with shallow peat samples from different depths collected at seven Canadian wetland sites and adjusted to five moisture levels. For each subsample (varying by site, depth and moisture content), CO<sub>2</sub> fluxes were measured at 12 sequential temperature settings from -10 to 35˚C. For each subsample, the data were fitted to an exponential equation to derive a <em>Q<sub>10</sub></em> value. In general, boreal peat samples were more temperature sensitive than temperate peat. The optimum moisture level for CO<sub>2</sub> release was determined for all the subsamples and related to variations in wetland vegetation and landform types. As a general trend, increasing water saturation reduced the CO<sub>2</sub> release rate from a given subsample. We further tested a flexible curve-fitting equation, as recently proposed on a theoretical basis, to recompile the data by ecoclimatic peat type and to account for the non-growing season dynamics. These findings will contribute to Canada’s national carbon budget model by guiding the development and calibration of the peatland module.</p>

scholarly journals An integrated approach to investigate climate-driven rockfall occurrence in high alpine slopes: the Bessanese glacial basin, Western Italian Alps

2020 ◽  
Vol 17 (11) ◽  
pp. 2591-2610
Author(s):  
Cristina Viani ◽  
Marta Chiarle ◽  
Roberta Paranunzio ◽  
Andrea Merlone ◽  
Chiara Musacchio ◽  
...  
Keyword(s):  
Climate Change ◽  
Active Layer ◽  
Integrated Approach ◽  
Slope Instability ◽  
High Mountain ◽  
Positive Temperature ◽  
Rock Slopes ◽  
Italian Alps ◽  
Near Surface ◽  
Basin Scale

Abstract Rockfalls are one of the most common instability processes in high mountains. They represent a relevant issue, both for the risks they represent for (infra) structures and frequentation, and for their potential role as terrestrial indicators of climate change. This study aims to contribute to the growing topic of the relationship between climate change and slope instability at the basin scale. The selected study area is the Bessanese glacial basin (Western Italian Alps) which, since 2016, has been specifically equipped, monitored and investigated for this purpose. In order to provide a broader context for the interpretation of the recent rockfall events and associated climate conditions, a cross-temporal and integrated approach has been adopted. For this purpose, geomorphological investigations (last 100 years), local climate (last 30 years) and near-surface rock/air temperatures analyses, have been carried out. First research outcomes show that rockfalls occurred in two different geomorphological positions: on rock slopes in permafrost condition, facing from NW to NE and/or along the glacier margins, on rock slopes uncovered by the ice in the last decades. Seasonal thaw of the active layer and/or glacier debutressing can be deemed responsible for slope failure preparation. With regard to timing, almost all dated rock falls occurred in summer. For the July events, initiation may have been caused by a combination of rapid snow melt and enhanced seasonal thaw of the active layer due to anomalous high temperatures, and rainfall. August events are, instead, associated with a significant positive temperature anomaly on the quarterly scale, and they can be ascribed to the rapid and/or in depth thaw of the permafrost active layer. According to our findings, we can expect that in the Bessanese glacierized basin, as in similar high mountain areas, climate change will cause an increase of slope instability in the future. To fasten knowledge deepening, we highlight the need for a growth of a network of high elevation experimental sites at the basin scale, and the definition of shared methodological and measurement standards, that would allow a more rapid and effective comparison of data.

Interannual variations of the thermal regime of the active layer and near-surface permafrost in northern Alaska

1995 ◽  
Vol 6 (4) ◽  
pp. 313-335 ◽  
Author(s):  
V. E. Romanovsky ◽  
T. E. Osterkamp
Keyword(s):  
Active Layer ◽  
Thermal Regime ◽  
Interannual Variations ◽  
Near Surface ◽  
Northern Alaska

Ignition and fire spread thresholds in gorse (Ulex europaeus)

2010 ◽  
Vol 19 (5) ◽  
pp. 589 ◽  
Author(s):  
Stuart A. J. Anderson ◽  
Wendy R. Anderson
Keyword(s):  
Moisture Content ◽  
Field Experiments ◽  
Fire Management ◽  
Fire Spread ◽  
Operational Experience ◽  
Management Planning ◽  
Near Surface ◽  
Ulex Europaeus ◽  
Fuel Layer ◽  
Major Variable

Field experiments were carried out in stands of gorse (Ulex europaeus L.) in New Zealand to determine the conditions under which fires would both ignite and spread. Research and operational experience in shrub fuels suggest that there is a clear difference between conditions that support ignition only (fuel ignites but does not spread beyond a single bush or clump) and conditions that are conducive to fire spread (fuel ignites and develops into a spreading fire). It is important for fire management agencies to be equipped with knowledge of these thresholds, because the different conditions require different levels of preparedness and response. Results indicate that the major variable influencing both fire ignition and fire spread development in gorse is the moisture content of the elevated dead fine fuel layer. Fires were observed to spread successfully in this elevated fuel layer only, independently of the surface fuels and the near-surface fuels. Elevated dead fuels failed to ignite at a moisture content of greater than 36%, and ignition only resulted in a spreading fire at moisture contents below 19%. The results correlate well with field observations and fire practitioners’ experience in these fuels, and provide reliable guidelines for fire management planning.

Permafrost and active layer research on James Ross Island: An overview

2019 ◽  
Vol 9 (1) ◽  
pp. 20-36 ◽  
Author(s):  
Filip Hrbáček ◽  
Daniel Nývlt ◽  
Kamil Láska ◽  
Michaela Kňažková ◽  
Barbora Kampová ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Layer Thickness ◽  
Active Layer ◽  
Air Temperature ◽  
Thermal Regime ◽  
Ground Temperature ◽  
Active Layer Thickness ◽  
Near Surface ◽  
James Ross Island ◽  
The Mean

This study summarizes the current state of the active layer and permafrost research on James Ross Island. The analysis of climate parameters covers the reference period 2011–2017. The mean annual air temperature at the AWS-JGM site was -6.9°C (ranged from -3.9°C to -8.2°C). The mean annual ground temperature at the depth of 5 cm was -5.5°C (ranged from -3.3°C to -6.7°C) and it also reached -5.6°C (ranged from -4.0 to -6.8°C) at the depth of 50 cm. The mean daily ground temperature at the depth of 5 cm correlated moderately up to strongly with the air temperature depending on the season of the year. Analysis of the snow effect on the ground thermal regime confirmed a low insulating effect of snow cover when snow thickness reached up to 50 cm. A thicker snow accumulation, reaching at least 70 cm, can develop around the hyaloclastite breccia boulders where a well pronounced insulation effect on the near-surface ground thermal regime was observed. The effect of lithology on the ground physical properties and the active layer thickness was also investigated. Laboratory analysis of ground thermal properties showed variation in thermal conductivity (0.3 to 0.9 W m-1 K-1). The thickest active layer (89 cm) was observed on the Berry Hill slopes site, where the lowest thawing degree days index (321 to 382°C·day) and the highest value of thermal conductivity (0.9 W m-1 K-1) was observed. The clearest influence of lithological conditions on active layer thickness was observed on the CALM-S grid. The site comprises a sandy Holocene marine terrace and muddy sand of the Whisky Bay Formation. Surveying using a manual probe, ground penetrating radar, and an electromagnetic conductivity meter clearly showed the effect of the lithological boundary on local variability of the active layer thickness.

Aeolian transport on a wet beach: Field observations from the swash zone

2020 ◽  
Author(s):  
Christy Swann ◽  
sarah trimble
Keyword(s):  
Moisture Content ◽  
Sediment Supply ◽  
Strong Wind ◽  
Field Observations ◽  
Swash Zone ◽  
Aeolian Transport ◽  
Near Surface ◽  
Moisture Contents ◽  
Wind Velocities ◽  
Wind Events

<p>Quantifying aeolian transport within the swash zone is critical to understanding feedbacks between aeolian and nearshore processes in coastal environments. In the swash zone, high moisture contents are thought to significantly limit the amount of sediment available for transport by wind. These assertions are supported by empirical relationships between the threshold for aeolian transport and moisture content that show gravimetric moisture contents greater than ~5% severely restrict the transport of windblown sand. Yet, during strong wind events aeolian transport can occur in the swash zone where moisture content is significantly higher. Here, we present field observations of fully-saturated aeolian transport on a wet beach and highlight the proficiency of winds to sustain aeolian transport in the swash zone.  </p><p>Field observations were collected during the passing of Tropical Storm Nester on a dissipative beach north of Corolla, North Carolina, USA in the early morning hours of October 19. 2019. Beach width ranged between ~50 and 100 meters and observations were made during a falling tide. Alignment of predominate winds and beach orientation provided a nearly unlimited fetch with an abundant sediment supply from the drier upper beach. Mean grain sizes of surface grab samples in the swash zone were 0.17 to 0.19 mm and moisture content in the swash zone ranged from 8 to 13% during the observational period.</p><p>Videos of fully developed, saturated transport in the form of nested streamers, approximately 5-20 cm wide, were recorded. A vertical array of cup and sonic anemometers measured near surface fluid flow. Cup anemometers were sampled at 1 Hz and observed wind velocities at 7, 18, 44, 68 and 93 cm above the surface. Ultrasonic anemometers sampled 3 dimensional velocity components at 32 Hz via at 53 and ~100 cm.  Sustained wind velocities were 9.5 m/s at 93 cm above the surface with gusts reaching 14 m/s. A series of vertically-segregating saltation traps captured particles in transport and showed minimal size-segregation with height. Gravimetric moisture content of captured saltation ranged from 0 to 4%.</p><p>Pulses of abundant aeolian transport during the storm were largely driven by largescale coherent eddies initiating transport from the drier upper beach. These upper beach sediments sustained transport on the lower, wet beach. The spatial and temporal variability of the exceedance of both fluid and impact thresholds strongly controls transport. These field observations demonstrate the proficiency of wind to transport of large volumes sand in the swash zone during strong alongshore wind events.</p>

scholarly journals Multi-channel ground-penetrating radar to explore spatial variations in thaw depth and moisture content in the active layer of a permafrost site

2010 ◽  
Vol 4 (3) ◽  
pp. 269-283 ◽  
Author(s):  
U. Wollschläger ◽  
H. Gerhards ◽  
Q. Yu ◽  
K. Roth
Keyword(s):  
Soil Moisture ◽  
Moisture Content ◽  
Active Layer ◽  
Ground Penetrating Radar ◽  
Soil Moisture Content ◽  
Late Summer ◽  
Bare Soil ◽  
Thaw Depth ◽  
Ground Penetrating ◽  
Gravel Road

Abstract. Multi-channel ground-penetrating radar (GPR) was applied at a permafrost site on the Tibetan Plateau to investigate the influence of surface properties and soil texture on the late-summer thaw depth and average soil moisture content of the active layer. Measurements were conducted on an approximately 85 × 60 m2 sized area with surface and soil textural properties that ranged from medium to coarse textured bare soil to finer textured, sparsely vegetated areas covered with fine, wind blown sand, and it included the bed of a gravel road. The survey allowed a clear differentiation of the various units. It showed (i) a shallow thaw depth and low average soil moisture content below the sand-covered, vegetated area, (ii) an intermediate thaw depth and high average soil moisture content along the gravel road, and (iii) an intermediate to deep thaw depth and low to intermediate average soil moisture content in the bare soil terrain. From our measurements, we found hypotheses for the permafrost processes at this site leading to the observed late-summer thaw depth and soil moisture conditions. The study clearly indicates the complicated interactions between surface and subsurface state variables and processes in this environment. Multi-channel GPR is an operational technology to efficiently study such a system at scales varying from a few meters to a few kilometers.

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