Understanding long-term interactions between climate, permafrost, and vegetation provides an essential context for interpreting current Arctic greening. Using 65 fossil pollen records from northern Siberia and a Random Forest model trained on a dataset of 835 modern pollen-climate assemblages, we quantitatively reconstructed mean temperature of the warmest month (Mtwa: mean July temperature) anomalies over the past 40 thousand years (ka) and assessed associated vegetation changes. During the Last Glacial Period, herbaceous taxa overwhelmingly dominated, and warming of similar to 1 degrees C during similar to 40-35 cal ka BP was insufficient to deepen the active layer beyond the threshold required for tree establishment, leaving woody cover minimal. In the early Holocene, sustained warming of nearly 2 degrees C triggered permafrost degradation and active-layer thickening, enabling forest expansion, although tree taxa lagged shrubs by several millennia. These results reveal a clear threshold effect in vegetation-permafrost interactions and show that only sustained warming can overcome permafrost constraints. By providing quantitative temperature estimates, our reconstruction offers critical benchmarks for predicting how ongoing Arctic warming may transform vegetation patterns and permafrost stability.

BackgroundAccelerated glacial retreat driven by climate change is rapidly reshaping alpine and polar environments, exposing deglaciated terrains that serve as critical sites for microbial colonization and early ecosystem development. These newly exposed substrates provide a unique setting for studying primary microbial succession, the onset of soil formation, and the initiation of biogeochemical cycles, particularly carbon cycling. Microbial communities, including bacteria, archaea, fungi, algae, and viruses, play pivotal roles in regulating elemental fluxes and establishing foundational ecosystem processes in these nascent landscapes.ResultsRecent studies highlight substantial shifts in microbial community structure and function across different glacial forefields and cryospheric habitats. Microbial assemblages display pronounced spatial heterogeneity shaped by physicochemical gradients and successional age. Functional analyses reveal diverse metabolic pathways involved in carbon fixation, organic matter transformation, and long-term carbon storage. Additionally, viral populations emerge as influential regulators of microbial metabolism and potential archives of past environmental conditions. The assembly of these communities is influenced by a combination of abiotic factors, dispersal mechanisms, and local adaptation, with cascading effects on carbon fluxes and nutrient dynamics.ConclusionsMicrobial processes in deglaciated environments are central to early biogeochemical transformations and represent key drivers of carbon sequestration in retreating glacial landscapes. Understanding the ecological roles, functional diversity, and climate sensitivity of these microbial communities is essential for projecting biogeochemical and climate system feedbacks in the context of ongoing glacial loss. Integrating microbial ecology into Earth system models will enhance predictions of carbon dynamics and inform conservation and climate mitigation strategies in polar and alpine regions.

Lakes are commonly accepted as a sensitive indicator of regional climate change, including the Tibetan Plateau (TP). This study took the Ranwu Lake, located in the southeastern TP, as the research object to investigate the relationship between the lake and regional hydroclimatological regimes. The well-known Budyko framework was utilized to explore the relationship and its causes. The results showed air temperature, evapotranspiration and potential evapotranspiration in the Ranwu Lake Basin generally increased, while precipitation, soil moisture, and glacier area decreased. The Budyko space indicated that the basin experienced an obviously drying phase first, and then a slightly wetting phase. An overall increase in lake area appears inconsistent with the drying phase of the basin climate. The inconsistency is attributable to the significant expansion of proglacial lakes due to glacial melting, possibly driven by the Atlantic Multidecadal Oscillation. Our findings should be helpful for understanding the complicated relationships between lakes and climate, and beneficial to water resources management under changing climates, especially in glacier basins.

Differential frost heave between fine (earthy) and coarse (gravelly) domains was monitored over 10 years (2013-2023) on a mountain-top flat ground subjected to both frequent diurnal and deep seasonal freezing. Monitoring objects include, ground heave, soil temperature down to 55 cm, soil moisture, air temperature, rainfall, and snow depth. The two domains, differing only in the presence of uppermost platy gravel about 1 cm in thickness, undergo frequent diurnal frost heave with about 1-cm-thick needle ice formation. Annual frequency and cumulative amount of frost heave are not significantly different between the two, but the fine domain is slightly more active particularly in spring when the near-surface soil at just above 0 degrees C permits rapid frost penetration. Differential heave mainly occurs as a time lag in the start and peak of heaving, on average, by about 1 h preceded at the fine domain, which tends to concentrate stones to the coarse domain. Frost heave activity shows a large interannual variation, primarily depending on the duration of snow-covered days. Frost heave activity also roughly correlates with annual mean air temperature, possibly reflecting a decrease in snowfall days.

We review the progress of research on permafrost and periglacial dynamics over the last two decades and explore future periglacial landscapes in Svalbard, High Arctic. This area has been subjected to rapid air and ground warming at a rate of 0.10.2 degrees C yr-1, as well as simultaneous thawing of the top layer of permafrost at a rate of about 1 cm yr-1 over the last two decades. Periglacial features studied include ice-wedge polygons, mudboils, sorted patterned ground, pingos, solifluction lobes, active-layer detachment slides, and rock glaciers. These landforms are concentrated within narrow alluvial plains and valley-side slopes but separated by geomorphological specifics and ground materials. Decadal-scale monitoring highlights climatic control of the morphology and dynamics of three landforms & horbar;ice-wedge polygons, mudboils, and rock glaciers & horbar;and the impact of long-term warming on their dynamics. Despite the location close to the southern limit of continuous permafrost, multiple cold spells in mid-winter activate thermal contraction cracking, which permits the growth of ice wedges. If such cold spells continue under a warmer climate, ice wedge could still grow below the deepening active layer. In a mudboil-small polygon landscape, seasonal frost heaving (or thaw settlement) of the central mound is coupled with closing (or opening) of the marginal crack. This movement would be maintained under a warmer climate and at a deeper active layer if the active layer is kept very humid. Although the contemporary cold climate is generally unfavorable for the growth of well-developed rock glaciers in Svalbard, slow permafrost creep at a rate of a few centimeters per year produces basal bulging of the valley-side talus slopes. The warming trend in the last decade has led to a steady acceleration of the movement. Further warming in the near future is expected to develop longer valley-side rock glaciers.

On Spitsbergen, Svalbard, the Nordenski & ouml;ld Land Permafrost Observatory provides ground temperature time series from 2008 to the present in 16 boreholes located in a variety of periglacial landforms. This study presents trends in permafrost temperatures and active layer thickness, compares these trends to observed climatic changes, and differentiates the climate sensitivity of the studied periglacial landforms. Ground temperature variability in these landforms is driven by Svalbard's air temperature gradients due to elevation and from the warmer west coast to the colder interior, in addition to snow cover and landform dynamics. During the study period, increases in permafrost temperatures and active layer thickness, closely tied to rapid climate warming on Svalbard, were observed at nearly all sites. The observed rates of active layer thickness increase, ranging from 0.5 to 10.7 cm/year, are on the high end of observed values across the circum-Arctic. Decadal increase in temperature at 20 m depth reaches 0.9 degrees C; the Canadian High Arctic and the Beaufort-Chukchi region are the only Arctic areas with permafrost warming of comparable magnitude. The landforms that are entirely or predominately composed of bedrock or a blocky substrate are the most thermally sensitive to climate change.

Mountain permafrost extends over a vast area throughout the Chilean and Argentinean Andes, making it a key component of these mountain ecosystems. To develop an overview of the current state of knowledge on southern Andean permafrost, it is essential to outline appropriate research strategies in a warmer climate context. Based on a comprehensive review of existing literature, this work identifies eight main research themes on mountain permafrost in the Chilean and Argentinean Andes: paleoenvironmental reconstructions, permafrost-derived landforms inventories, permafrost distribution models, internal structure analysis, hydrogeochemistry, permafrost dynamics, geological hazards, and transitional landscape studies. This extensive review work also highlights key debates concerning the potential of permafrost as a water resource and the factors influencing its distribution. Furthermore, we identified several challenges the scientific community must address to gain a deeper understanding of mountain permafrost dynamics. Among these challenges, we suggest tackling the need to broaden spatial focus, along with the use of emerging technologies and methodologies. Additionally, we emphasize the importance of developing interdisciplinary approaches to effectively identify the impacts of climate change on mountain permafrost. Such efforts are essential for adequately preparing scientists, institutional entities, and society to address future scenarios.

Soil creep is a slow gravitational process. It differs from other catastrophic slope processes such as landslides, snow avalanches, and rockfalls in its dynamics and character. However, it can significantly affect tree growth. Creep movements can be analyzed based on the tree rings. This study analyzed the dynamics and spatiotemporal activity of creep in the Balea glacial valley (Southern Carpathians) under the Transfagarasan highway on an anthropogenic slope, using tree rings to define the spatiotemporal activity of creep and assess its potential driving and triggering factors. The dendrogeomorphological analysis included 54 Norway spruces (Picea abies (L.) Karst). A total of 118 tree-ring series were obtained, and a 35-year chronology was constructed based on the eccentric growth of tree rings and reaction wood, with a mean recurrence interval of 17.4 years. The spatial pattern of the disturbed trees in the event years was tested using Moran's I index. The presence of creep in this area is indicated by the stems of young trees taking on a 'd' shape or a 'pistol-butted' form, as well as the predominant inclination of the stems downslope direction. This inclination is not chaotic, as is typical of forests affected by landslides. The manifestation of creep is influenced by pre-existing factors, such as the substrate consisting of crystalline shale and the blanket of rubble arranged in the direction of the slope, as well as causal factors, such as the slope and precipitation. Precipitation falling within 24 h during June or July and intervals with frosty cycles from November to December and January to March were also contributing factors.

Ny-& Aring;lesund, located in Arctic Svalbard, is one of the most sensitive areas on Earth to global warming. In recent years, accelerated glacier ablation has become remarkable in Ny-& Aring;lesund. Glacial meltwaters discharge a substantial quantity of materials to the ocean, affecting downstream ecosystems and adjacent oceans. In August 2015, various water samples were taken near Ny-& Aring;lesund, including ice marginal meltwater, proglacial meltwater, supraglacial meltwater, englacial meltwater, and groundwater. Trace metals (Al, Cr, Mn, Fe, Co, Cu, Zn, Cd, and Pb), major ions, alkalinity, pH, dissolved oxygen, water temperature and electric conductivity were also measured. Major ions were mainly controlled by chemical weathering intensity and reaction types, while trace metals were influenced by both chemical weathering and physicochemical control upon their mobility. Indeed, we found that Br & oslash;ggerbreen was dominated by carbonate weathering via carbonation of carbonate, while Austre Lov & eacute;nbreen and Pedersenbreen were dominated by sulfide oxidation coupled with carbonate dissolution with a doubled silicate weathering. The higher enrichment of trace metals in supraglacial meltwater compared to ice marginal and proglacial meltwater suggested anthropogenic pollution from atmospheric deposition. In ice marginal and proglacial meltwater, principal component analysis indicated that trace metals like Cr, Al, Co, Mn and Cd were correlated to chemical weathering. This implies that under accelerated glacier retreat, glacier-derived chemical components are subjected to future changes in weathering types and intensity.

Schmidt-hammer exposure-age dating (SHD) was applied to similar to 180 medium- to large-scale solifluction features on the northern edge of Juyflye, Jotunheimen (southern Norway) using an electronic Schmidt-hammer (RockSchmidt) and an improved local SHD age-calibration equation. Age estimates from four different types of solifluction landforms were analysed and compared with those from recalibrated estimates from patterned ground previously investigated on Juvflye. Average SHD-age estimates are c. 9.8 and 9.3 ka for the two dominant morphological types of solifluction features ('type A' boulder tongues and 'type B' stone-banked solifluction lobes) and c. 8.6 ka for sorted stripes and circles. Our results indicate that active formation of all investigated types of solifluction features, sorted stripes, and sorted circles ceased in the Early Holocene, prior to the onset of the regional Holocene Thermal Maximum (HTM) at c. 7.7 ka. Formation of all of these periglacial landforms appears to have commenced shortly after local deglaciation (c. 11.4 ka) in water-saturated till. Alternative origins are rejected, including the possibility of development before the last glaciation, survival beneath cold-based glaciers, and exhumation in the Early Holocene. Cessation of activity is attributed to changing ground conditions affecting active layer processes, particularly reduced soil moisture and pore water pressure. Temporal variations of the altitudinal permafrost limits had little or no impact on the timing of either the Early Holocene climax in activity or subsequent stabilisation. Caution is therefore urged in the utilisation of large-scale solifluction and patterned ground landforms as palaeoclimatic indicators.