Together with warming air temperatures, Arctic ecosystems are expected to experience increases in heavy rainfall events. Recent studies report accelerated degradation of permafrost under heavy rainfall, which could put significant amounts of soil carbon and infrastructure at risk. However, controlled experimental evidence of rainfall effects on permafrost thaw is scarce. We experimentally tested the impact and legacy effect of heavy rainfall events in early and late summer for five sites varying in topography and soil type on the High Arctic archipelago of Svalbard. We found that effects of heavy rainfall on soil thermal regimes are small and limited to one season. Thaw rates increased under heavy rainfall in a loess terrace site, but not in polygonal tundra soils with higher organic matter content and water tables. End-of-season active layer thickness was not affected. Rainfall application did not affect soil temperature trends, which appeared driven by timing of snowmelt and organic layer thickness, particularly during early summer. Late summer rainfall was associated with slower freeze-up and colder soil temperatures the following winter. This implies that rainfall impacts on Svalbard permafrost are limited, locally variable and of short duration. Our findings diverge from earlier reports of sustained increases in permafrost thaw following extreme rainfall, but are consistent with observations that maritime permafrost regions such as Svalbard show lower rainfall sensitivity than continental regions. Based on our experiment, no substantial in-situ effects of heavy rainfall are anticipated for thawing of permafrost on Svalbard under future warming. However, further work is needed to quantify permafrost response to local redistribution of active layer flow under natural rainfall extremes. In addition, replication of experiments across variable Arctic regions as well as long-term monitoring of active layers, soil moisture and local climate will be essential to develop a panarctic perspective on rainfall sensitivity of permafrost. permafrost are limited, locally variable and of short duration. Our findings diverge from earlier reports tained increases in permafrost thaw following extreme rainfall, but are consistent with observations time permafrost regions such as Svalbard show lower rainfall sensitivity than continental regions. Based experiment, no substantial in-situ effects of heavy rainfall are anticipated for thawing of permafrost on under future warming. However, further work is needed to quantify permafrost response to local redistribution active layer flow under natural rainfall extremes. In addition, replication of experiments across variable regions as well as long-term monitoring of active layers, soil moisture and local climate will be essential develop a panarctic perspective on rainfall sensitivity of permafrost.

The knowledge of soil thermal properties is important for determining how a soil will behave under changing climate conditions, especially in the sensitive environment of permafrost affected soils. This paper represents the first complex study of the interplay between the different parameters affecting soil thermal conductivity of soils in Antarctica. Antarctic Peninsula is currently the most rapidly warming region of the whole Antarctica, with predictions of this warming to continue in the upcoming decades. This study focuses on James Ross Island, where the Abernethy Flats automatic weather station is located in a lowland area with semi-arid climate. Air and ground temperature, soil heat flux and soil moisture during the thawing season were monitored on this site from 2015 to 2023. Moreover, two approaches to determining soil thermal conductivity were compared - laboratory measurements and calculation from field data. During this period, mean annual temperatures have increased dramatically for both air (from-6.9 degrees C in 2015/2016 to-3.8 degrees C in 2022/2023) and ground (from-6.5 degrees C to-3.2 degrees C), same as active layer thickness (from 68 cm to 95 cm). Average soil thermal conductivity for the thawing period reached values between 0.49 and 0.74 W/m.K-1 based on field data. Statistically significant relationships were found between the seasonal means of volumetric water content and several other parameters - soil thermal conductivity (r = 0.91), thawing degree days (r = -0.87) and active layer thickness (r = - 0.88). Although wetter soils generally have a higher conductivity, the increase in temperature exhibits a much stronger control over the active layer thickening, also contributing to the overall drying of the upper part of the soil profile.

Active layer and permafrost are important indicators of climate changes in periglacial areas of Antarctica, and the soil thermal regime of Maritime Antarctica is sensitive to the current warming trend. This research aimed to characterize the active layer thermal regime of a patterned ground located at an upper marine terrace in Half Moon Island, during 2015-2018. Temperature and moisture sensors were installed at different soil depths, combined with air temperature, collecting hourly data. Statistical analysis was applied to describe the soil thermal regime and estimate active layer thickness. The thermal regime of the studied soil was typical of periglacial environment, with high variability in temperature and water content in the summer, resulting in frequent freeze-thaw cycles. We detected dominant freezing conditions, whereas soil temperatures increased, and the period of high soil moisture content lasted longer over the years. Active layer thickness varied between the years, reaching a maximum depth in 2018. Permafrost degradation affects soil drainage and triggers erosion in the upper marine terrace, where permafrost occurrence is unlikely. Longer monitoring periods are necessary for a detailed understanding on how current climatic and geomorphic conditions affect the unstable permafrost of low-lying areas of Antarctica (marine terraces).

Analysis of climatic conditions for the period of instrumental measurement in Central Yakutia showed three periods with two different mean annual air temperature (MAAT) shifts. These periods were divided into 1930-1987 (base period A), 1988-2006 (period B) and 2007-2018 (period C) timelines. The MAAT during these three periods amounted -10.3, -8.6 and -7.4 degrees C, respectively. Measurement of active layer depth (ALD) of permafrost pale soil under the forest (natural) and arable land (anthropogenic) were carried out during 1990-2018 period. MAAT change for this period affected an early transition of negative temperatures to positive and a later establishment of negative temperatures. Additionally, a shortening of the winter season and an extension of the duration of days with positive temperatures was found. Since the permafrost has a significant impact on soil moisture and thermal regimes, the deepening of ALD plays a negative role for studied soils. An increase in the ALD can cause thawing of underground ice and lead to degradation of the ice-rich permafrost. This thaw process causes a change of the ecological balance and leads to the destruction of natural landscapes, sometimes with a complete or prolonged loss of their biological productivity. During this observation (1990-2018 period) the active layer of permafrost is characterized by high dynamics, depending on climatic parameters such as air temperature, as well as thickness and duration of snow cover. A significant increase in ALD of forest permafrost soils-by 80 cm and 65 cm-on arable land was measured during the observation period (28 years).

Ground surface temperature (GST) and active layer thickness (ALT) are key indicators of climate change (CC) in permafrost regions, with their relationships with climate and vegetation being crucial for the understanding of future climate change scenarios, as well as of CC feedbacks on the carbon cycle and water balance. Antarctic ice free-areas host simplified ecosystems with vegetation dominated by mosses and lichens, and an almost negligible anthropogenic impact, providing a good template of ecosystem responses to CC. At three different Antarctic Conservation Biogeographical Regions (ACBR) sites in Antarctica located between 74 degrees and 60 degrees S, we compared barren ground and moss vegetated sites to understand and quantify the effects of climate (air temperature and incoming radiation) and of vegetation on GST and ALT. Our data show that incoming radiation is the most important driver of summer GST at the southernmost site, while in the other sites air temperature is the main driver of GST. Our data indicate that there is a decoupling between ALT and summer GST, because the highest GST values correspond with the thinnest ALT. Moreover, our data confirm the importance of the buffering effect of moss vegetation on GST in Antarctica. The intensity of the effect of moss cover on GST and ALT mainly depends on the species-specific moss water retention capacity and on their structure. These results highlight that the correct assessment of the moss type and of its water retention can be of great importance in the accurate modelling of ALT variation and its feedback on CC.

Knowledge on active-layer dynamics and permafrost distribution is of especial importance in Maritime Antarctica, where dramatic climate warming occurred in the last decades. Few long-term studies of active-layer temperatures in this region, and no one focus on recently deglaciated areas under paraglacial conditions. This paper analyses the long-term soil thermal regime of a warm-based glacial front site located at Low Head, King George Island. The monitoring system consists of soil temperature probes connected to a datalogger that recorded data at hourly intervals. We calculated the thawing days (TD), freezing days (FD), number of isothermal days (ID), number of freeze-thaw days (FTD), thawing degree days (TDD), freezing degree days (FDD), and the apparent thermal diffusivity (AID). The results indicate that active layer thermal regime at Low Head is similar to other periglacial environments from Maritime Antarctica, with differences associated with the influence from the nearby warm-based glacier. Surface temperatures show greater variations during the summer resulting in frequent freeze and thaw cycles, mainly (1 cm and 10 cm). The temperature profile during the studied period indicates that the active layer thickness reached a maximum of 106 cm on February 7th 2015. Soil temperature buffering was limited by the low snow cover, low soil moisture, and absence of vegetation. Based on the high interannual variability detected during the five years monitoring run, we stress that longer monitoring periods are necessary for a more detailed knowledge on how permafrost respond to climate changes in this rapidly warming zone. (C) 2016 Elsevier B.V. All rights reserved.

Climate change impacts the biotic and abiotic components of polar ecosystems, affecting the stability of permafrost, active layer thickness, vegetation, and soil. This paper describes the active layer thermal regimes of two adjacent shallow boreholes, under the same soil but with two different vegetations. The study is location in Lions Rump, at King George Island, Maritime Antarctic, one of the most sensitive regions to climate change, located near the climatic limit of Antarctic permafrost. Both sites are a Turbic Cambic Cryosol formed on andesitic basalt, one under moss vegetation (Andreaea gainii, at 85 m a.s.l.) and another under lichen (Usnea sp., at 86 m a.s.l.), located 10 m apart. Ground temperature at same depths (10, 30 and 80 cm), water content at 80 cm depth and air temperature were recorded hourly between March 2009 and February 2011. The two sites showed significant differences in mean annual ground temperature for all depths. The lichen site showed a higher soil temperature amplitude compared to the moss site, with ground surface (10 cm) showing the highest daily temperature in January 2011 (7.3 degrees C) and the lowest daily temperature in August (-16.5 degrees C). The soil temperature at the lichen site closely followed the air temperature trend. The moss site showed a higher water content at the bottommost layer, consistent with the water-saturated, low landscape position. The observed thermal buffering effect under mosses is primarily associated with higher moisture onsite, but a longer duration of the snow-pack (not monitored) may also have influenced the results. Active layer thickness was approximately 150 cm at low-lying moss site, and 120 cm at well-drained lichen site. This allows to classify these soils as Cryosols (VVRB) or Gelisols (Soil Taxonomy), with evident turbic features. (C) 2014 Elsevier B.V. All rights reserved.

This study presents soil temperature and moisture regimes from March 2008 to January 2009 for two active layer monitoring (CALM-S) sites at King George Island, Maritime Antarctica. The monitoring sites were installed during the summer of 2008 and consist of thermistors (accuracy of +/- 0.2 degrees C), arranged vertically with probes at different depths and one soil moisture probe placed at the bottommost layer at each site (accuracy of +/- 2.5%), recording data at hourly intervals in a high capacity datalogger. The active layer thermal regime in the studied period for both soils was typical of periglacial environments, with extreme variation in surface temperature during summer resulting in frequent freeze and thaw cycles. The great majority of the soil temperature readings during the eleven month period was close to 0 degrees C. resulting in low values of freezing and thawing degree days. Both soils have poor thermal apparent diffusivity but values were higher for the soil from Fildes Peninsula. The different moisture regimes for the studied soils were attributed to soil texture, with the coarser soil presenting much lower water content during all seasons. Differences in water and ice contents may explain the contrasting patterns of freezing of the studied soils, being two-sided for the coarser soil and one-sided for the loamy soil. The temperature profile of the studied soils during the eleven month period indicates that the active layer reached a maximum depth of approximately 92 cm at Potter and 89 cm at Fildes. Longer data sets are needed for more conclusive analysis on active layer behaviour in this part of Antarctica. (C) 2011 Elsevier B.V. All rights reserved.