With the gradual increase of global temperature, thermokarst lakes are widely developed and become major environmental disasters in the Tundra Plateau which have impacted the stability of the project such as the Qinghai-Tibetan highway. In this study, some typical thermokarst lakes in the Qinghai-Tibet Plateau (QTP) were selected as the research object. And four samples were taken from different freezing-thawing processes of the lakes in 2019 to analyze the hydrogeochemical process of the thermokarst lake in the context of climate change. Results show that the main hydrogeochemical types of the lake water in the northern part of the study area were HCO3 center dot Cl - Na center dot Ca center dot Mg or Cl center dot HCO3 - Na center dot Mg, whereas in the central and southern parts were mainly Cl - Na center dot Mg. The variations of hydrogeochemical concentration in thermokarst lake water are mainly affected by evaporation concentration, rock differentiation, freezing desalination in the active layer, and plant photosynthesis, which are mainly due to temperature changes. Furthermore, the results of the saturation index (SI) show that dolomite and calcite leaching control the hydrogeochemical composition in thermokarst lakes. In addition, the evaporation-to-inflow (E/I) ratios of the lake reach the maximum in the middle and later periods of the active layer thawing. On the contrary, the E/I values of the lakes decrease during the initial thawing or freezing periods of the active layer.

Permafrost regions at high latitudes and altitudes store about half of the Earth's soil organic carbon (SOC). These areas are also some of the most intensely affected by anthropogenic climate change. The Tibetan Plateau or Third Pole (TP) contains most of the world's alpine permafrost, yet there remains substantial uncertainty about the role of this region in regulating the overall permafrost climate feedback. Here, we review the thermal and biogeochemical status of permafrost on the TP, with a particular focus on SOC stocks and vulnerability in the face of climate warming. SOC storage in permafrost-affected regions of the TP is estimated to be 19.0 +/- 6.6 Pg to a depth of 2 m. The distribution of this SOC on the TP is strongly associated with active layer thickness, soil moisture, soil texture, topographic position, and thickness of weathered parent material. The mean temperature sensitivity coefficient (Q(10)) of SOC decomposition is 9.2 +/- 7.1 across different soil depths and under different land-cover types, suggesting that carbon on the TP is very vulnerable to climate change. While the TP ecosystem currently is a net carbon sink, climate change will likely increase ecosystem respiration and may weaken or reverse the sink function of this region in the future. Although the TP has less ground ice than high latitude permafrost regions, the rugged topography makes it vulnerable to widespread permafrost collapse and thermoerosion (thermokarst), which accelerates carbon losses. To reduce uncertainty about SOC quantities and sensitivity to warming, future studies are needed that explain variation in Q(10) (e.g. based on SOC source or depositional position) and quantify the role of nutrient availability in regulating SOC dynamics and ecosystem recovery following disturbance. Additionally, as for the high latitude permafrost region, soil moisture and thermokarst formation remain major challenges to predicting the permafrost climate feedback on the TP. We present a conceptual model for of greenhouse gas release from the TP and outline the empirical observations and modeling approaches needed to test it.

Thermokarst lakes form following the thaw of ice-rich permafrost and drain after a few decades to millennia. Drained thermokarst lake basins (DTLBs) become epicenters for peat accumulation and re-aggradation of ice-rich permafrost. This re-aggradation of permafrost may be interrupted by subsequent thermokarst lake formation with sufficient disturbance. Thermokarst lakes and DTLBs are abundant near Old Crow, Yukon, Canada, but little is known about their evolution through the Holocene. In this study, we investigate the hydrology and drainage histories of seven DTLBs from the Old Crow Flats on the basis of cryostratigraphy, radiocarbon dating, and pore-ice delta O-18 and delta H-2 records. Cryostratigraphic evidence implies only one of the seven studied DTLBs underwent multiple thermokarst cycles. Radiocarbon age-depth models demonstrate a slowdown in the rate of post-drainage peat accumulation with time. Pore-ice isotope analyses reveal a spectrum of possible post-drainage isotopic histories resulting from spatial variability in permafrost, vegetation, and hydrology. Unlike lacustrine silt, post-drainage peat contains relatively constant pore-ice isotope trends. In light of our findings, we propose that syngenetic peat permafrost in DTLBs preserve a warm-season sampling of local meteoric waters. These pore-ice delta O-18 and delta H-2 records may aid millennial-scale paleoclimate investigations, as we demonstrate through our reconstruction of Holocene climate change in northern Yukon.

The Central Yakutian permafrost landscape is rapidly being modified by land use and global warming, but small-scale thermokarst process variability and hydrological conditions are poorly understood. We analyze lake-area changes and thaw subsidence of young thermokarst lakes on ice-complex deposits (yedoma lakes) in comparison to residual lakes in alas basins during the last 70 years for a local study site and we record regional lake size and distribution on different ice-rich permafrost terraces using satellite and historical airborne imagery. Statistical analysis of climatic and ground-temperature data identified driving factors of yedoma- and alas-lake changes. Overall, lake area is larger today than in 1944 but alas-lake levels have oscillated greatly over 70 years, with a mean alas-lake-radius change rate of 1.63.0 m/yr. Anthropogenic disturbance and forest degradation initiated, and climate forced rapid, continuous yedoma-lake growth. The mean yedoma lake-radius change rate equals 1.21.0 m/yr over the whole observation period. Mean thaw subsidence below yedoma lakes is 6.21.4 cm/yr. Multiple regression analysis suggests that winter precipitation, winter temperature, and active-layer properties are primary controllers of area changes in both lake types; summer weather and permafrost conditions additionally influence yedoma-lake growth rates. The main controlling factors of alas-lake changes are unclear due to larger catchment areas and subsurface hydrological conditions. Increasing thermokarst activity is currently linked to older terraces with higher ground-ice contents, but thermokarst activity will likely stay high and wet conditions will persist within the near future in Central Yakutian alas basins.

To better understand the linkage between lake area change, permafrost conditions and intra-annual and inter-annual variability in climate, we explored the temporal and spatial patterns of lake area changes for a 422382-ha study area within Yukon Flats, Alaska using Landsat images of 17 dates between 1984 and 2009. Only closed basin lakes were used in this study. Among the 3529 lakes greater than 1 ha, closed basin lakes accounted for 65% by number and 50% by area. A multiple linear regression model was built to quantify the temporal change in total lake area with consideration of its intra-annual and inter-annual variability. The results showed that 80.7% of lake area variability was attributed to intra-annual and inter-annual variability in local water balance and mean temperature since snowmelt (interpreted as a proxy for seasonal thaw depth). Another 14.3% was associated with long-term change. Among 2280 lakes, 350 lakes shrank, and 103 lakes expanded. The lakes with similar change trends formed distinct clusters, so did the lakes with similar short term intra-annual and inter-annual variability. By analysing potential factors driving lake area changes including evaporation, precipitation, indicators for regional permafrost change, and flooding, we found that ice-jam flooding events were the most likely explanation for the observed temporal pattern. In addition to changes in the frequency of ice jam flooding events, the observed changes of individual lakes may be influenced by local variability in permafrost distributions and/or degradation. Copyright (c) 2012 John Wiley & Sons, Ltd.

Arctic warming alters regional hydrological systems, as permafrost thaw increases active layer thickness and in turn alters the pathways of water flow through the landscape. Further, permafrost thaw may change the connectivity between deeper and shallower groundwater and surface water altering the terrestrial water balance and distribution. Thermokarst lakes and wetlands in the Arctic offer a window into such changes as these landscape elements depend on permafrost and are some of the most dynamic and widespread features in Arctic lowland regions. In this study we used Landsat remotely sensed imagery to investigate potential shifts in thermokarst lake size-distributions, which may be brought about by permafrost thaw, over three distinct time periods (1973, 1987-1988, and 2007-2009) in three hydrological basins in northwestern Siberia. Results revealed fluctuations in total area and number of lakes over time, with both appearing and disappearing lakes alongside stable lakes. On the whole basin scales, there is no indication of any sustained long-term change in thermokarst lake area or lake size abundance over time. This statistical temporal consistency indicates that spatially variable change effects on local permafrost conditions have driven the individual lake changes that have indeed occurred over time. The results highlight the importance of using multi-temporal remote sensing data that can reveal complex spatiotemporal variations distinguishing fluctuations from sustained change trends, for accurate interpretation of thermokarst lake changes and their possible drivers in periods of climate and permafrost change.