Thermokarst landslide (TL) activity in the Qinghai-Tibet Plateau (QTP) is intensifying due to climate warminginduced permafrost degradation. However, the mechanisms driving landslide formation and evolution remain poorly understood. This study investigates the spatial distribution, annual frequency, and monthly dynamics of TLs along the Qinghai-Tibet engineering corridor (QTEC), in conjunction with in-situ temperature and rainfall observations, to elucidate the interplay between warming, permafrost degradation, and landslide activity. Through the analysis of high-resolution satellite imagery and field surveys, we identified 1298 landslides along the QTEC between 2016 and 2022, with an additional 386 landslides recorded in a typical landslide-prone subarea. In 2016, 621 new active-layer detachments (ALDs) were identified, 1.3 times the total historical record. This surge aligned with unprecedented mean annual and August temperatures. The ALDs emerged primarily between late August and early September, coinciding with maximum thaw depth. From 2016 to 2022, 97.8 % of these ALDs evolved into retrogressive thaw slumps (RTSs), identified as active landslides. Landslides typically occur in alpine meadows at moderate altitudes and on gentle northward slopes. The thick ice layer near the permafrost table serves as the material basis for ALD occurrence. Abnormally high temperature significantly increased the active layer thickness (ALT), resulting in melting of the ice layer and formation of a thawed interlayer, which was the direct causing factor for ALD. By altering the local material, micro-topography, and thermal conditions, ALD activity significantly increases RTS susceptibility. Understanding the mechanisms of ALD formation and evolution into RTS provides a theoretical foundation for infrastructure development and disaster mitigation in extreme environments.

An active layer detachment slide (ALDS) in the interior portion of the Qinghai-Tibet Plateau (QTP) was investigated within 2 days of its formation on September 21, 2018. The ALDS developed on a relatively gentle slope (4.8 degrees to 9 degrees) at an elevation of 4,850 m above sea level (asl) and was about 145 m long and 45 m wide, with a headscarp 2.2-2.5 m high. Analyses of meteorological data and soil temperatures indicated that it was probably triggered by a record thaw depth which intersected a layer with high ice content at the base of the active layer and in the top of the permafrost. Based on the time window, the minimum downslope velocity of the main slide mass was about 20 m/h which is higher than previously reported values. The ALDS ran into the embankment of the Qinghai-Tibet Railway (QTR) but did not damage the railbed. However, extensive rehabilitation of the slope was needed subsequent to the failure to clear the slide mass and as minor headscarp recession and thaw settlement continued on the slope. In this work, we describe this feature and the most likely mechanisms of development.

This paper reviews the impacts of permafrost change on hydrological and related hydrochemical, particulate and organic fluxes in small Arctic catchments. While the emphasis is directed at High Arctic systems, literature and recent developments from other Arctic regions are also included. Hydrological change, particularly a shift from nival (snowmelt) dominance to increasing pluvial (rainfall) runoff contributions has important consequences for the timing and magnitude of hydrological fluxes. A key distinction is made between thermal perturbation, where changing melt season thaw conditions result in deep thaw with minimal geomorphic or surface hydrological effects, in contrast to physical perturbation, where permafrost change results in some form of thermokarst or physical disturbance such as mass movement or enhanced erosion. The latter disturbances are commonly expressed as localized thermo erosional gullies, active layer detachments and retrogressive thaw slumps. Results from recent research emphasise the importance of hydrological connectivity in terms of the downstream effect of a particular permafrost perturbation. Well-connected systems, either at the surface as channelized flows, or in the subsurface, through new or altered active layer flow pathways, result in substantial changes in downstream fluvial fluxes. Surface hydrological connectivity of localized permafrost disturbances increases transport of suspended sediment and particulate organic matter, the latter of which is often old and comparatively labile. Exposed ice in retrogressive thaw slumps sustains discharge during the melt season, further increasing fluxes. Thermal perturbation holds a substantially greater potential downstream impact due to widespread mobilization of solutes and dissolved organic carbon and nitrogen, and several studies point to rapid microbial alteration of carbon and inorganic nitrogen transformation in the shallow subsurface. Collectively, these results point to altered runoff, sediment transport and hydrochemical fluxes with spatial and hydrological controls.

Arctic warming may induce slope failure in upland permafrost soils. These landslide-like events, referred to as active layer detachments (ALDs), redistribute soil material into hydrological networks during spring melt and heavy rainfall. In 2011, 2013 and 2014, fluvial sediments from the West River at the Cape Bounty Arctic Watershed Observatory were sampled where ALDs occurred in 2007-2008. Two ALD-impacted subcatchments were examined exhibiting either continuing disturbance or short-term stabilization. Solid-state C-13 nuclear magnetic resonance (NMR) spectroscopy and targeted biomarker analysis via gas chromatography-mass spectrometry were used to investigate shifts in organic matter (OM) composition. Additionally, radiocarbon ages were determined using accelerator mass spectrometry. Biomarker concentrations and O-alkyl carbon assessed via NMR were both lower in sediments nearest the active disturbance and increased in sediments downstream where other aquatic inputs became more dominant. This suggests immobilization of recalcitrant OM near the ALD and the sustained transport of labile ALD-derived OM further downstream. Shifts toward older radiocarbon dates along the river between 2011 and 2014 suggest the continued transport of permafrost-derived OM downstream. The stabilizing subcatchment revealed high O-alkyl carbon via NMR and increased concentrations of unaltered terrestrial-derived biomarkers indicative of enhanced OM accumulation following ALD activity. The relatively young radiocarbon ages from these sediments suggest accumulation from contemporary sources and potential burial of the previously dispersed ALD inputs. Within the broader context of Arctic climate change, these results portray a complex environmental trajectory for thaw-released permafrost-derived OM and highlight uncertainty in the relationship between lability and persistence upon release by permafrost disturbance. (C) 2018 Elsevier Ltd. All rights reserved.

Arctic landscapes are experiencing intense warming and modification of precipitation regimes with climate change. Permafrost disturbances and climate change impacts on hydrology of Arctic watersheds are likely to modify the quantity and composition of exported dissolved organic matter (DOM). In July 2007, intense rainfall and active layer thickening caused widespread active layer detachments at Cape Bounty, Melville Island (Canada). This study investigates the impacts of seasonal hydrology and permafrost disturbance on DOM composition exported from High Arctic headwater catchments. In 2012, streams were sampled from three disturbed catchments and one undisturbed catchment. The composition of DOM was characterized using absorbance and fluorescence spectroscopy. DOM was mostly exported during the spring freshet. Throughout this period, the undisturbed catchment exported humifiedDOMwith high humic-like fluorescence that likely originated from runoff through shallow organic rich soil. In contrast, DOM exported from disturbed catchments was fresher, less humified with a high proportion of low molecular weight humic acid. We demonstrate that disturbed catchments delivered likely more labile DOM derived from either thawed permafrost or enhanced microbial activity. If this labile DOM comes from an ancient pool, as indicated by other studies at this site, disturbances may strengthen the permafrost carbon feedback on climate change.

This study investigates the impacts of active layer detachments (ALDs) on nitrogen in seasonal runoff from High Arctic hillslope catchments. We examined dissolved nitrogen in runoff from an undisturbed catchment (Goose (GS)) and one that was disturbed (Ptarmigan (PT)) by ALDs, prior to disturbance (2007) and 5 years after disturbance (2012). The seasonal dynamics of nitrogen species concentrations and fluxes were similar in both catchments in 2007, but the mean seasonal nitrate concentration and mass flux from the disturbed catchment were on the order of 30 times higher relative to the undisturbed catchment in 2012. Stormflow yielded 45% and 60% of the 2012 total dissolved nitrogen flux in GS and PT, respectively, although rainfall runoff provided less than 25% of seasonal discharge. Results support that through the combined effects of increased disturbance and rainfall, climate change stands to significantly enhance the export of nitrate from High Arctic watersheds. This study highlights that the increase in the delivery of nitrate from disturbance is especially pronounced late in the season when downstream productivity and the biological demand for this often limiting nutrient are high. Our results also demonstrate that the impact of ALDs on nitrate export can persist more than 5 years following disturbance.

With increased warming in the Arctic, permafrost thaw may induce localized physical disturbance of slopes. These disturbances, referred to as active layer detachments (ALDs), redistribute soil across the landscape, potentially releasing previously unavailable carbon (C). In 2007-2008, widespread ALD activity was reported at the Cape Bounty Arctic Watershed Observatory in Nunavut, Canada. Our study investigated organic matter (OM) composition in soil profiles from ALD-impacted and undisturbed areas. Solid-state C-13 nuclear magnetic resonance (NMR) and solvent-extractable biomarkers were used to characterize soil OM. Throughout the disturbed upslope profile, where surface soils and vegetation had been removed, NMR revealed low O-alkyl C content and biomarker analysis revealed low concentrations of solvent-extractable compounds suggesting enhanced erosion of labile-rich OM by the ALD. In the disturbed downslope region, vegetation remained intact but displaced material from upslope produced lateral compression ridges at the surface. High O-alkyl content in the surface horizon was consistent with enrichment of carbohydrates and peptides, but low concentrations of labile biomarkers (i.e., sugars) suggested the presence of relatively unaltered labile-rich OM. Decreased O-alkyl content and biomarker concentrations below the surface contrasted with the undisturbed profile and may indicate the loss of well-established pre-ALD surface drainage with compression ridge formation. However, pre-ALD profile composition remains unknown and the observed decreases may result from nominal pre-ALD OM inputs. These results are the first to establish OM composition in ALD-impacted soil profiles, suggesting reallocation of permafrost-derived soil C to areas where degradation or erosion may contribute to increased C losses from disturbed Arctic soils.

Localized permafrost disturbances such as active layer detachments (ALDs) are increasing in frequency and severity across the Canadian Arctic impacting terrestrial ecosystem functioning. However, the contribution of permafrost disturbance-carbon feedbacks to the carbon (C) balance of Arctic ecosystems is poorly understood. Here, we explore the short-term impact of active layer detachments (ALDs) on carbon dioxide (CO2) exchange in a High Arctic semi-desert ecosystem by comparing midday C exchange between undisturbed areas, moderately disturbed areas (intact islands of vegetation within an ALD), and highly disturbed areas (non-vegetated areas due to ALD). Midday C exchange was measured using a static chamber method between June 23 and August 8 during the 2009 and 2010 growing seasons. Results show that areas of high disturbance had significantly reduced gross ecosystem exchange and ecosystem respiration (R (E)) compared to control and moderately disturbed areas. Moderately disturbed areas showed significantly enhanced net ecosystem exchange compared to areas of high disturbance, but were not significantly different from control areas. Disturbance did not significantly impact soil thermal, physical or chemical properties. According to average midday fluxes, ALDs as a whole (moderately disturbed areas: -1.942 mu mol m(-2) s(-1)+ highly disturbed areas: 2.969 mu mol m(-2) s(-1)) were a small CO2 source of 1.027 mu mol m(-2) s(-1) which did not differ significantly from average midday fluxes in control areas 1.219 mu mol m(-2) s(-1). The findings of this study provide evidence that the short-term impacts of ALDs on midday, net C exchange and soil properties in a High Arctic semi-desert are minimal.

High Arctic river responses to changing hydroclimatic and landscape processes are poorly understood. In non-glacierized basins, snowmelt and rainfall generate river discharge, which provides first order control over fluxes. Further factors include the seasonality of precipitation, seasonal active layer development, and permafrost disturbance. These controls were evaluated in terms of sedimentary and biogeochemical fluxes from paired catchments at Cape Bounty, Melville Island, Nunavut during 20062009. Results indicate that the source of runoff can be more important than the amount of runoff for sediment, solutes, and organic yields. Although the snowmelt period is typically the most important time for these yields, heavy late summer precipitation events can create disproportionately large yields. Rainfall increases yields because it hydrologically connects areas otherwise isolated. Inorganic solute yields from late summer rainfall are higher because the thick active layer maximizes hydrologic interactions with mineral soils and generates high solute concentrations. Results also indicate that while the catchments are broadly similar, subtle topographic differences result in important inter-catchment differences in runoff and suspended and dissolved loads. The East watershed, which had less extensive permafrost disturbance, consistently had higher concentrations of dissolved solids. These higher dissolved fluxes cannot therefore be explained by thermokarst features, but rather by deeper active layer development, due to a greater proportion of south-facing slopes. Although warm temperatures in 2007 led to extensive active layer disturbance in the West watershed, because the disturbances were largely hydrologically disconnected, the total disturbed area was small, and inter-annual variability in discharge was high, there was no detectable response in dissolved loads to disturbances. Sediment availability increased after 2007, but yields have largely returned to pre-disturbance levels. Results indicate that seasonality and frequency-magnitude characteristics of projected increases in precipitation must be considered along with active layer changes to predict the fluvial sedimentary and biogeochemical response to regional climate change. Copyright (c) 2011 John Wiley & Sons, Ltd.