Observations on permafrost ground thermal regimes from Antarctica and the Italian Alps, and their relevance to global climate change

Active-layer monitoring and the permafrost thermal regime are key indicators of climate change. The results of 3 years (1997-1999) of active-layer monitoring at one high-mountain site (La Foppa, 46degrees28' 42" N; 10degrees11' 18" E, 2670 m a.s.l.) and at one Antarctic site (Boulder Clay, 74degrees44' 45" S; 164degrees01' 17" E, 205 m a.s.l) are presented. The initial analysis of a thermal profile in a borehole (100.3 m deep) within mountain permafrost at Stelvio (3000 m a.s.l., 46degrees30' 59"N; 10degrees28' 35" E) is also presented. At the alpine site, the active-layer thickness variations (between 193 and 229 cm) relate to both the snow cover and to the air temperature changes. By contrast, at the Antarctic site, there is a strong direct linkage only between air temperature fluctuations and active-layer variations. At the alpine (La Foppa) site, the relationship between climate and active-layer thickness is complicated by thermal offset that is almost negligible at both the Stelvio and Antarctic sites. The permafrost temperature profile at Stelvio site contains a climate signal suitable for paleoclimate reconstruction. The permafrost at this site has a mean annual ground surface temperature (MAGST) of - 1.9degreesC (during 1998/1999), an active layer of about 2.5 in thick and a total thickness of - 200 m. Analysis of the MAGST history, obtained by applying a simple heat conduction one-dimensional model, revealed the occurrence of a cold period from 1820 to 1940 followed by a warming period until 1978. Since the beginning of the 1980s, temperature dropped (less than 2degreesC) until the middle 1990s, when a new period of warming started. All these climatic changes fit well with the glacial fluctuations in the area and with other paleoclimatic information derived from different proxy dat

A permafrost warming in a cooling Antarctica?

The magnitude and even direction of recent Antarctic climate change is still debated because the paucity of long and complete instrumental data records. While along Antarctic Peninsula a strong warming coupled with large retreat of glaciers occurred, in continental Antarctica a cooling was recently detected. Here, the first existing permafrost data set longer than 10 years recorded in continental Antarctica is presented. Since 1997 summer ground surface temperature showed a strong warming trend (0.31\ub0C per year) although the air temperature was almost stable. The summer ground surface temperature increase seemed to be influenced mainly by the increase of the total summer radiation as confirmed also by the increase of the summer thawing degree days. In the same period the active layer exhibited a thickening trend (1 cm per year) comparable with the thickening rates observed in several Arctic locations where air warming occurred. At all the investigated depths permafrost exhibited an increase of mean annual temperature of approximately 0.1\ub0C per year. The dichotomy between active layer thickness and air temperature trends can produce large unexepected and unmodelled impacts on ecosystems and CO2 balance

How can the floor area types of a university campus mitigate the increase of urban air temperature?

The urban heat island (UHI) under the current climate change scenario could have a major impact on the lives of urban residents. The presence of green areas undoubtedly mitigates the UHI, and modifes some selected anthropized surfaces with particular characteristics (e.g., albedo). Here, we use a university campus as a good template of the urban context to analyze the mitigation efect of diferent surface types on the air temperature warming. This study provides some of the best practices for the future management of land surface types in urban areas. Through the development of a simple air temperature mitigation index (ATMI) that uses the temperature, water content (WC), and albedo of the investigated surface types, we fnd the green and anthropized surfaces according to their areal distribution and mitigation efects. The fndings address the importance of poorly managed green areas (few annual mowings) and anthropized materials that permit a good balance between water retention capacity and high albedo. In the case of impervious surfaces, priority should be given to light-colored materials with reduced pavement units (blocks or slabs) to reduce the UHI

Relationships between vegetation patterns and periglacial landforms in northwestern Svalbard

We studied the small-scale vegetation pattern in the high Arctic at Ny Angstromlesund to assess if the plant distribution was related to periglacial landforms. The whole area has been deglaciated for millennia but only a modest part of the area was covered by mature vegetation. The plant cover varied considerably in relation to ground patterning originated by periglacial processes, especially frost heave, frost creep, gelifluction and ice segregation, giving rise to a mosaic of microhabitats sharply differing from each other as regards physical properties and microclimate. The distributional patterns of vascular plants, lichens and bryophytes were primarily affected by complex responses to substrate texture, soil moisture content and substrate disturbance. Since global warming will probably affect both periglacial processes and plant responses to altered habitat conditions, we concluded that long-term monitoring of relationships between landforms and vegetation represents a suitable tool for assessing the impact of global change on arctic regions

Thermal photogrammetry on a permafrost rock wall for the active layer monitoring

Permafrost and active layer models often cannot explain the high spatial variability, especially in heterogeneous environments like the mountainous regions due to their scarce resolution, paucity of climatic data and topographic details. In this study, we want to introduce a new application of the unmanned aerial vehicle (UAV) in thermal photogrammetry to model the active layer thickness (ALT) of an alpine rock wall through the computation of the thermal inertia and compare the results with a widespread ALT model. On the Gran Zebrù South rock wall, 8 thermal UAV surveys has been conducted in 4 different summer days during 2021-2022 in order to have two 3D thermal models per day at different solar radiation inputs. By analyzing topographic data, visible imagery and the thermal models, the apparent thermal inertias (ATIs) have been converted into heat transfer coefficients (HTCs) and then into ALT of 2021 and 2022. These maps have been validated through the placement of thermistors at different elevations and with variable depths (2, 15 and 40 cm from the rock surface). The resulting ALT has been compared with the Stefan's solution and the alpine permafrost index map (APIM), which showed large underestimations and a noncorrespondence with permafrost occurrence. The average ALT increase of 29.3 cm from 2021 to 2022 has been discussed regarding permafrost formation/degradation future trend under the climatic change and potential risks of alpine areas

A new simple topo-climatic model to predict surface displacement in paraglacial and periglacial mountains of the European Alps: The importance of ground heating index and floristic components as ecological indicators

Landscape evolution is occurring at rapid rates in alpine areas in response to recent climate warming, also due to the susceptibility and the heterogeneity of these environments. Here we present a prediction model of surface displacements that takes into account both topographic and climatic variables. Observed points of surficial displacements have been associated to non-climatic (altitude, slope, solar radiation, till deposit type, deposit age, vegetation coverage) and climatic (days of snow permanence, ground surface temperature index, ground heating index, ground cooling index) variables through a general regression model in the European central Alps. The model output shows the importance of slope and ground heating index (GHI) \u2013 an estimation of the amount of energy transferred to the ground, to predict surface displacements independently from the type of considered processes. In particular, the general regression model shows that steep zones with high GHI are more susceptible to undergo periglacial and paraglacial processes producing surface displacements. As expected, slope is fundamental to trigger processes such as gravitation, nivation, solifluction and their interactions. The results of our model emphasize the key role of GHI, highlighting the importance of climate in controlling the surface displacement. Indeed, in areas in which GHI is higher, the ground can remain snow free for a longer time and snow melting can be faster, the former favoring more runoff and slopewash, and the latter promoting the saturation of the deposits consequent to a higher intensity of solifluction and/or mass movements processes. Within the study area, the sites with the largest displacements (>35 cm) were detected where permafrost degradation occurred since 1990. This permafrost degradation process could remain one of the main triggering factors of future surface displacements. Our results confirm that when movement involves material with coarse texture (pebbles and boulders) exceeding the rooting depth, only tolerant plant species can withstand the high movement rates. The areas where this can happen (like rock glaciers or screes) act as a physical barrier to grasslands species not adapted to surface displacements and trying to shift towards higher altitude in response to climate warming. However, plant species not considered as indicators of movement (such as graminoids), can develop also with large surface displacements in specific geomorphic conditions. Therefore, the combination of surface displacement type (deep vs surficial), material texture (fine vs coarse) and vegetation cover (high vs low) and floristic composition can be used as a valuable ecological indicator of movement. Our results suggest that both landscape degradation and vegetation displacement can be rapid especially where the air warming was strong as in the selected study area

Unexpected impacts of climate change on Alpine vegetation

The vegetation in a high alpine site of the European Alps experienced changes in area between 1953 and 2003 as a result of climate change. Shrubs showed rapid expansion rates of 5.6% per decade at altitudes between 2400 m and 2500 m. Above 2500 m, vegetation coverage exhibited unexpected patterns of regression associated with increased precipitation and permafrost degradation. As these changes follow a sharp increase in both summer and annual temperatures after 1980, we suggest that vegetation of the alpine (2400-2800 m) and nival (above 2800 m) belts respond in a fast and flexible way, contradicting previous hypotheses that alpine and nival species appear to have a natural inertia and are able to tolerate an increase of 1-2 degrees C in mean air temperature

Salix shrub encroachment along a 1000 m elevation gradient triggers a major ecosystem change in the European Alps

Shrub encroachment, a globally recognized response to climate warming, usually involves late successional species in mountain environments, without alteration to climax communities. We show that a major ecosystem change is occurring in the European Alps across a 1000 m elevation gradient, with pioneer hygrophilous Salix shrubs, previously typical of riparian forests, wetlands and avalanche ravines, encroaching into the climax communities of subalpine and alpine belts shrublands and grasslands, as well as snowbeds, pioneer vegetation and barren grounds in the nival belt. We analyzed Salix recruitment through dendrochronological methods, and assessed its relationships with climate and atmospheric CO2 concentration. The dendrochronological data indicated that Salix encroachment commenced in the 1950s (based on the age of the oldest Salix individuals, recruited in 1957), and that it was correlated with increasing atmospheric CO2 concentration, spring warming and snow cover decrease. Hygrophilous Salix shrubs are expanding their distribution both through range filling and upwards migration, likely achieving competitive replacement of species of subalpine and alpine climax communities. They benefit from climate warming and CO2 fertilization and are not sensitive to spring frost damage and soil limitations, being observed across a gradient of soil conditions from loose glacial sediments in recently deglaciated areas (where soils had not had sufficient time to develop) to mature soils such as podzols (when colonizing late successional subalpine shrublands). Salix encroachment may trigger ecosystem and landscape transformations, promoting the development of forests that replace pre-existing subalpine shrublands, and of open woodlands invading alpine grasslands and snowbeds, making the alpine environment similar to sub-Arctic and Arctic areas. This results in a new threat to the conservation of the plant species, communities and landscapes typical of the alpine biota, as mountain ranges such as the Alps provide limited opportunities for upward migration and range-shift

The spatio-temporal variability of frost blisters in a perennial frozen lake along the antarctic coast as indicator of the groundwater supply

Remote sensing, and unmanned aerial vehicles (UAVs) in particular, can be a valid tool for assessing the dynamics of cryotic features as frost blisters and to monitor the surface changes and the sublimation rates on perennially frozen lakes that host important ecosystems. In this paper, through the use of these remote sensing techniques, we aim to understand the type of groundwater supply of an Antarctic perennial frozen lake that encompasses two frost blisters (M1 and M2) through the temporal analysis of the features\u2019 elevation changes (frost blisters and lake ice level). The frozen lake is located at Boulder Clay (northern Victoria Land, Antarctica). We relied on several photogrammetric models, past satellite images and ground pictures to conduct differencing of digital elevation models, areal variations and pixel counting. In addition, in situ measurements of the ice sublimation or snow accumulation were carried out. The two frost blisters showed different elevation trends with M1 higher in the past (1996\u20132004) than recently (2014\u20132019), while M2 showed an opposite trend, similarly to the ice level. Indeed, the linear regression between M2 elevation changes and the ice level variation was statistically significant, as well as with the annual thawing degree days, while M1 did not show significant results. From these results we can infer that the groundwater supply of M1 can be related to a sublake open talik (hydraulic system) as confirmed also by pressurized brines found below M1, during a drilling in summer 2019. For M2 the groundwater flow is still not completely clear although the hydrostatic system seems the easiest explanation as well as for the uplift of the lake ice