Active Layer Thickness Values Research Articles

Resource limitation and population fluctuation drive spatiotemporal order in microbial communities.

Microbial communities display complex spatiotemporal behaviors leading to spatially-structured and ordered organization driven by species interactions and environmental factors. Resource availability plays a pivotal role in shaping the dynamics of bacterial colonies. In this study, we delve into the intricate interplay between resource limitation and the emergent properties of a growing colony of two visually distinct bacterial strains having similar growth and mechanical properties. Employing an agent-based modeling and computer simulations, we analyze the resource-driven effect on segregation and sectoring, cell length regulation and nematic ordering within a growing colony. We introduce a dimensionless parameter referred to as the active layer thickness, derived from nutrient diffusion equations, indicating effective population participation due to local resource availability. Our results reveal that lower values of active layer thickness arising from decreased resource abundance lead to rougher colony fronts, fostering heightened population fluctuations within the colony and faster spatial genetic diversity loss. Our temporal analyses unveil the dynamics of mean cell length and fluctuations, showcasing how initial disturbances evolve as colonies are exposed to nutrients and subsequently settle. Furthermore, examining microscopic details, we find that lower resource levels yield diverse cell lengths and enhanced nematic ordering, driven by the increased prevalence of longer rod-shaped cells. Our investigation sheds light on the multifaceted relationship between resource constraints and bacterial colony dynamics, revealing insights into their spatiotemporal organization.

Main results of permafrost monitoring in the French Alps through the PermaFrance network over the period 2010–2022

AbstractThis study presents data from the first years of permafrost monitoring in boreholes in the French Alps that started at the end of 2009 in the framework of the PermaFrance network. Nine boreholes are instrumented, among which six monitored permafrost temperature and active layer thickness (ALT) over >10 years. Ice‐poor and cold permafrost in high‐elevation north‐facing rock walls has warmed by up to >1°C at 10 m depth over the reference decade (2011–2020), whereas ice‐rich permafrost (rock glacier) temperatures remained stable. ALT has increased at four of the five boreholes for which decadal data are available. Summer 2015 marks a turning point in ALT regime and greatest ALT values were observed in 2022 (available for six boreholes), but thawing intensity did not show an obvious change. At one site with a layer of coarse blocks about 2 m thick, ALT was stable over 2018–2022 and response to the hottest years was dampened. Linear trends suggest an ALT increase of 2 m per decade for some ice‐poor rock walls, independently of their thermal state. The data reveal a variety of permafrost patterns and evolution with significant intraregional and local differences. Snow modulates the response to air temperature signal in various ways, with an important effect on near‐surface temperature trends and ALT: early snow melting in spring favors an ALT increase in rock walls. Maintaining these monitoring systems and understanding the physical processes controlling heterogeneous responses to climate signals is crucial to better assess permafrost dynamics and to adapt to its consequences.

Active Layer and Permafrost Investigations Using Geophysical and Geocryological Methods—A Case Study of the Khanovey Area, Near Vorkuta, in the NE European Russian Arctic

Permafrost in the NE European Russian Arctic is suffering from some of the highest degradation rates in the world. The rising mean annual air temperature causes warming permafrost, the increase in the active layer thickness (ALT), and the reduction of the permafrost extent. These phenomena represent a serious risk for infrastructures and human activities. ALT characterization is important to estimate the degree of permafrost degradation. We used a multidisciplinary approach to investigate the ALT distribution in the Khanovey railway station area (close to Vorkuta, Arctic Russia), where thaw subsidence leads to railroad vertical deformations up to 2.5 cm/year. Geocryological surveys, including vegetation analysis and underground temperature measurements, together with the faster and less invasive electrical resistivity tomography (ERT) geophysical method, were used to investigate the frozen/unfrozen ground settings between the railroad and the Vorkuta River. Borehole stratigraphy and landscape microzonation indicated a massive prevalence of clay and silty clay sediments at shallow depths in this area. The complex refractive index method (CRIM) was used to integrate and quantitatively validate the results. The data analysis showed landscape heterogeneity and maximum ALT and permafrost thickness values of about 7 and 50 m, respectively. The active layer was characterized by resistivity values ranging from about 30 to 100 Ωm, whereas the underlying permafrost resistivity exceeded 200 Ωm, up to a maximum of about 10 kΩm. In the active layer, there was a coexistence of frozen and unfrozen unconsolidated sediments, where the ice content estimated using the CRIM ranged from about 0.3 – 0.4 to 0.9. Moreover, the transition zone between the active layer base and the permafrost table, whose resistivity values ranged from 100 to 200 Ωm for this kind of sediments, showed ice contents ranging from 0.9 to 1.0. Taliks were present in some depressions of the study area, characterized by minimum resistivity values lower than 10 Ωm. This thermokarst activity was more active close to the railroad because of the absence of insulating vegetation. This study contributes to better understanding of the spatial variability of cryological conditions, and the result is helpful in addressing engineering solutions for the stability of the railway.

Modeling permafrost distribution over the river basins of Mongolia using remote sensing and analytical approaches

The spatial distribution of permafrost and associated mean annual ground temperature (MAGT) and active layer thickness (ALT) are crucial data for hydrological studies. In this paper, we present the current state of knowledge on the spatial distribution of the permafrost properties of 29 river basins in Mongolia. The MAGT and ALT values are estimated by applying TTOP and Kudryavtsev methods. The main input of both methods is the spatially distributed surface temperature. We used the 8-day land surface temperature (LST) data from the day- and night-time Aqua and Terra images of the moderate resolution imaging spectroradiometer (MODIS). The gaps of the MODIS LST data were filled by spatial interpolation. Next, an LST model was developed based on 34 observational borehole data using a panel regression analysis (Baltagi, Econometric analysis of panel data, 3 edn, Wiley, New York, 2005). The model was applied for the whole country and covered the period from August 2012 to August 2013. The results show that the permafrost covers 26.3% of the country. The average MAGT and ALT for the permafrost region is − 1.6 °C and 3.1 m, respectively. The MAGT above -2 °C (warm permafrost) covers approximately 67% of the total permafrost area. The permafrost area and distribution in cold and warm permafrost varies highly over the country, in particular in regions where the river network is highly developed. High surface temperatures associated with climate change would result in changes of permafrost conditions, and, thus, would impact the surface water availability in these regions. The data on permafrost conditions presented in this paper can be used for further research on changes in the hydrological conditions of Mongolia.

Картографирование закономерностей распространения и современных условий мерзлотных ландшафтов Якутии

Digital thematic maps of the modern condition of permafrost landscapes of Yakutia on a scale of 1:1 500 000 have been compiled. A quantitative analysis of the patterns of their spatial distribution was carried out, the differentiation of permafrost landscapes by geocryological characteristics was made, and the areas that are most vulnerable to modern climate change and anthropogenic impacts were identified. The analysis of a series of digital thematic maps of the modern condition of permafrost landscapes in Yakutia showed that 34% of the total territory is occupied by landscapes with soil temperatures from −2 to −4 °C, the least common high-temperature permafrost landscapes (from 0 to −2 °C) – about 4% of the territory. Landscapes with active layer thickness values of about 1 m are spread over 36% of the territory, which is the highest indicator. Insignificant territories (up to 3%) are occupied by landscapes with active layer thickness of up to 3 and 3,5 m. The most widespread landscapes are those with low-ice deposits (less than 0,2) – 38,7%, and landscapes with heavy-ice deposits (more than 0,4) occupy 31%. The most dangerous process is thermokarst, which occurs in the interalassic and slightly drained types of terrain. Key words: permafrost landscape, temperature of soils, ice content of deposits, cryogenic processes, digital maps, GIS model.

Retrieval of Permafrost Active Layer Properties Using Time-Series P-Band Radar Observations

We propose a method to estimate the active layer properties, including soil dielectric profiles and active layer thickness (ALT), in permafrost regions using time-series P-band polarimetric synthetic aperture radar (SAR) observations. The active layer and underlying permafrost are modeled as a three-layer dielectric structure with the layer dielectric constants representing the soil moisture and freeze-thaw state of the layer. To resolve the ambiguity of the retrieved layer thicknesses, an approach of finding the largest possible depths (LPDs) is combined with time-series observations, where the ALT is assumed time-invariant between the maximum thaw and before the upward freezing front rises significantly from the permafrost table. The LPD-assisted time-series retrieval algorithm is applied to the radar data acquired by the Airborne Microwave Observatory of Subcanopy and Subsurface (AirMOSS) P-band SAR in August and October 2014 and 2015 over the Alaska North Slope. The results show that the retrieved ALT values are generally underestimated for the sites where the in situ ALT is larger than the P-band sensing depth, with a retrieval bias ranging from −0.05 to −0.24 m as validated against the in situ ALT collected at Circumpolar Active Layer Monitoring (CALM) sites. For the sites where the in situ ALT is smaller than 0.55 m, the retrieval errors are generally less than 0.1 m. The retrieval results also show that the active layer properties are strongly influenced by the land cover types at the regional scale, and not as much by the North–South temperature gradient across a 180-km-long transect along the Deadhorse flight line.

Mid‐Holocene frozen ground in China from PMIP3 simulations

Extensive degradation of frozen ground in the mid‐Holocene is widely assumed on the basis of sparse proxy data. Here, the simulated soil temperature from the Paleoclimate Modelling Intercomparison Project Phase 3 is used to address this issue over China. By comparing with the results of a preindustrial (0 ka, baseline) simulation, we show that frozen ground in the mid‐Holocene (6 ka) simulation is degraded mainly in northeast China and on the northern Tibetan Plateau. The change follows closely orbitally induced variations in insolation. Quantitatively, permafrost area reduces by 0.02×106 km2 in northeast China in response to an orbitally induced increase in boreal summer insolation but increases by 0.08×106 km2 on the southern Tibetan Plateau due to local summer cooling. Changing values of active layer thickness vary greatly amongst different locations. On average, they are 3 and 4 cm thicker than the preindustrial values in northeast China and on the Tibetan Plateau, respectively. No degradation in seasonally frozen ground is detected over China as a whole. Regionally, its coverage increases by 0.21×106 km2 near the middle and lower reaches of the Yangtze River valley. In addition, the maximum depth of seasonal frost penetration is on average 8.5 cm deeper than preindustrial values due to widespread winter cooling. The changes in frozen ground are consistent amongst models. However, the models disagree with proxy data in terms of not only the changes in frozen ground but also climate. Further modelling improvements and adequate proxy data are both needed to fill in the gaps between models and the data in our knowledge of the mid‐Holocene frozen ground.

Discussion on ‘Active Layer Thickness Prediction on the Western Antarctic Peninsula’ by Wilhelmet al. ()

Wilhelm et al. (2015) employed the widely used Stefan and Kudryavtsev equations to predict the maximum active-layer thickness (ALT) on Amsler Island, Western Antarctic Peninsula. Their predictions far exceed the observations of ALT reported from other parts of the region. Here, I demonstrate that the values of ALT are significantly overestimated by the predictive equations because the authors incorrectly assumed that little or no latent heat of phase change is absorbed during thawing. Although the area is the warmest in the Antarctic Peninsula region, with a rapid increase in air temperature and permafrost temperatures close to 0 °C, the active layer is likely to be substantially thinner than values predicted by Wilhelm et al. (2015). Copyright © 2016 John Wiley & Sons, Ltd.

Last glacial maximum permafrost in China from CMIP5 simulations

The distributions of frozen ground and active layer thickness (ALT) during the last glacial maximum (LGM) and pre-industrial periods in China were investigated using Coupled Model Intercomparison Project Phase 5 (CMIP5) model experiments. Compared to the pre-industrial period, the LGM climate was ~5°C colder and featured significantly higher freezing indices on the Tibetan Plateau and in Northeast China. Frozen ground expanded widely in the LGM. The extents of permafrost and seasonally frozen ground in China were 4.11×106km2 and 4.97×106km2, respectively, which are 2.42×106km2 larger and 1.45×106km2 smaller, respectively, than the pre-industrial levels. Moreover, the colder climate and longer duration also resulted in LGM ALT values that were 1.3m less than the pre-industrial values in the permafrost areas common to both periods. Altitudinal permafrost was present mainly on the Tibetan Plateau and adjacent mountains in West China between 28°N and 41°30′N and covered an area of ~2.63×106km2. Latitudinal permafrost was present mainly in Northeast China and occupied an area of 1.48×106km2. The southern limit of latitudinal permafrost was located ~10° of latitude farther south during the LGM than during the pre-industrial period. The LGM simulation results agree reasonably well with previous reconstructions, with the exception of an underestimation in the permafrost extent. Although relatively high-level disagreement exists between the models in terms of the exact locations of the southern limits, the ensemble average is still able to represent the large-scale spatial pattern of frozen ground remarkably well.

Estimating 1992–2000 average active layer thickness on the Alaskan North Slope from remotely sensed surface subsidence

The measurement of temporal changes in active layer thickness (ALT) is crucial to monitoring permafrost degradation in the Arctic. We develop a retrieval algorithm to estimate long‐term average ALT using thaw‐season surface subsidence derived from spaceborne interferometric synthetic aperture radar (InSAR) measurements. Our algorithm uses a model of vertical distribution of water content within the active layer accounting for soil texture, organic matter, and moisture. We determine the 1992–2000 average ALT for an 80 × 100 km study area of continuous permafrost on the North Slope of Alaska near Prudhoe Bay. We obtain an ALT of 30–50 cm over moist tundra areas, and a larger ALT of 50–80 cm over wet tundra areas. Our estimated ALT values match in situ measurements at Circumpolar Active Layer Monitoring (CALM) sites within uncertainties. Our results demonstrate that InSAR can provide ALT estimates over large areas at high spatial resolution.

Estimating Active-Layer Thickness over a Large Region: Kuparuk River Basin, Alaska, U.S.A.

Active-layer thickness was mapped over a 26,278-km2 area of northern Alaska containing complex and highly variable patterns of topography, vegetation, and soil properties. Procedures included frequent probing to ascertain thaw depth in representative land-cover units, extensive thermal monitoring with data loggers, and application of spatial analytic techniques. Geographic information systems technology was used analytically to merge thaw-depth and temperature data with a digital land-cover map, a digital elevation model, and a topoclimatic index, yielding a spatial time series of active-layer thickness for the map area at weekly intervals over the summer of 1995. Although the maps show a strong regional trend in the thickness of the active layer, extreme local variation occurs in complex terrain and in areas with sharp discontinuities in soil moisture content. Because active-layer thickness is influenced strongly by vegetation and soil properties, the relative volume of thawed soil beneath several landscape units is not proportional to the relative surface area occupied by those units. Predicted values of active-layer thickness are within approx. 6 cm of measured mean values in representative 1-km units distributed over the latitudinal extent of the study area. If computed and averaged for a series of years (e.g, one decade), the integrated products yielded by the mapping procedures could be used as baseline documents for comparison with calculations based on climate-change simulations.

Influence of AlxGa1−xAs layer thickness on threshold current density and differential quantum efficiency for GaAs−AlxGa1−xAs DH lasers

Measurements of the threshold current density Jth and differential quantum efficiency ηd havd been made on GaAs−Al0.3Ga0.7As double−heterostructure (DH) lasers to determine the effect of AlxGa1−xAs layer thickness on Jth and ηd. For DH lasers with active layer thicknesses near 0.12 μ, Jth increases and ηd decreases drastically for p−type Al0.3Ga0.7As layers less than ∼0.8 μ in thickness. This effect is also considered for other values of active layer thickness d, and AlAs mole fraction x.