Permafrost Meltwater Research Articles

Small-scale hydrological patterns in a Siberian permafrost ecosystem affected by drainage

Abstract. Climate warming and associated accelerated permafrost thaw in the Arctic lead to a shift in landscape patterns, hydrologic conditions, and release of carbon. In this context, the lateral transport of carbon and shifts therein following thaw remain poorly understood. Crucial hydrologic factors affecting the lateral distribution of carbon include the depth of the saturated zone above the permafrost table with respect to changes in water table and thaw depth and the connectivity of water-saturated zones. Landscape conditions are expected to change in the future due to rising temperatures and polygonal or flat floodplain Arctic tundra areas in various states of degradation; hydrologic conditions will also change. This study is focused on an experimental site near Chersky, northeast Siberia, where a drainage ditch was constructed in 2004 to simulate landscape degradation features that result in drier soil conditions and channeled water flow. We compared water levels and thaw depths in the drained area (dry soil conditions) with those in an adjacent control area (wet soil conditions). We also identified the sources of water at the site via stable water isotope analysis. We found substantial spatiotemporal changes in the water conditions at the drained site: (i) lower water tables resulting in drier soil conditions, (ii) quicker water flow through drier areas, (iii) larger saturation zones in wetter areas, and (iv) a higher proportion of permafrost meltwater in the liquid phase towards the end of the growing season. These findings suggest decreased lateral connectivity throughout the drained area. Shifts in hydraulic connectivity in combination with a shift in vegetation abundance and water sources may impact carbon sources and sinks as well as transport pathways. Identifying lateral transport patterns in areas with degrading permafrost is therefore crucial.

Groundwater composition and stable isotopes as proxies to investigate paleoclimate change in permafrost thawing regions

The paleoclimate since the late Pleistocene has gained substantial attention due to its profound effects on hydrology, ecosystems, and landforms, particularly in regions experiencing permafrost thawing. Northeast China is acknowledged for exhibiting distinctive yet contentious paleoclimate, which has been elucidated through various proxies. In this case, we emphasize the significance of stable isotopes within the northern Songnen Plain as complementary proxies for paleoclimate interpretation, bolstered by radiocarbon dating. The Cretaceous sandstone confined aquifer (CSA) is designated as the reference aquifer, based on the hydrogeochemical and isotopic characteristics. The 14C results indicate that the CSA preserves groundwater from the late Pleistocene to the modern. These findings, in conjunction with isotope variations, delineate specific climate events, which are aligning with results derived from conventional proxies. The late Pleistocene-early Holocene showed a climate shift from cold to warm. The middle Holocene was warm and humid. Then the late Holocene entered the Neoglacial, which characterized by a cold climate environment. Our analysis also reveals fluctuations in the age and TDS concentration along the groundwater runoff. The paleo groundwater exhibits simultaneous lower TDS concentration, maximum δ18O depletion and minimum recharge temperature. Neither latitude nor altitude effects could account for the sufficient isotopic depletion, instead, we found that the humid climate and permafrost meltwater also contributed to the isotope depletion. Simultaneously, the paleoclimatic environment such as freeze-thaw cycles of permafrost exerts a significant influence on the groundwater. The formation of permafrost hinders groundwater recharge, while its thawing dilutes the solute content of groundwater. Additionally, the recharge gaps also potentially result from arid climate, inadequate samples, and the effects of mixing water. The study substantiates the reliability of confined aquifers in permafrost thawing regions as robust paleoclimatic archives and emphasizes the utility of stable isotopes in combination with radiocarbon dating as ideal climate proxies.

Hydrogeochemical characteristics and processes of thermokarst lake and groundwater during the melting of the active layer in a permafrost region of the Qinghai–Tibet Plateau, China

Permafrost degradation and the development of thermokarst lakes are important factors driving the variability of regional hydrologic processes. Hydrogeochemical and isotopic analyses are important methods for investigating the hydrologic processes of thermokarst lakes. This study focused on comparing the chemical and hydrogeochemical characteristics between lake water and groundwater during the melting of the active layer in a typical thermokarst lake region on the Qinghai–Tibet Plateau (QTP). Ninety-five samples were collected during different periods of active layer melting and analyzed using statistical, isotope, hydrogeochemical, and modeling methods. Statistical results showed that the average concentrations of almost all ions were lower in lake water than in groundwater, with wider spatial variability in groundwater. The lake water is of the ClNa and HCO3-Ca type with low TDS (total dissolved solids), whereas groundwater is of the HCO3-Ca and mixed type (or transition type) with high TDS. The chemical types of the lake water and groundwater are mainly driven by rock weathering. In terms of the saturation index (SI), halite and gypsum are unsaturated dissolved, whereas dolomite and calcite are generally saturated. Evaporation significantly affects the chemical composition of groundwater, while the hydrochemical compositions of lake water are relatively stable under the joint control of evaporation, precipitation, surface runoff, and groundwater. The isotopic analysis results showed that the contribution of permafrost meltwater and precipitation to groundwater and lake water varied during different stages of active layer melting. According to hydrogeochemical modeling, the main chemical reactions in groundwater are the precipitation of calcite and the dissolution of halite, dolomite, and gypsum. The intensity of groundwater flow determines the degree of chemical reactions along the flow path at different stages of active layer melting. The findings can provide deeper insight into hydrogeochemical processes in thermokarst lake regions under the background of permafrost degradation.

Partitioning the contributions of cryospheric change to the increase of streamflow on the Nu River

Over the past few decades, the Nu River Watershed (NRW), which originates in the Qinghai–Tibet Plateau and covers an area of 113,414 km2, has experienced increased streamflow, temperatures, and precipitation along with cryospheric degradation. To determine the mechanism of increase of the observed streamflow composition, a distributed hydrological model (WEP-C) was developed to investigate the streamflow composition and its changes in the NRW from 1979 to 2019. During this period, glaciers, snowmelt, permafrost, groundwater, and precipitation accounted for 3.2%, 13.4%, 0.8%, 10.4%, and 72.2% of the NRW streamflow, respectively. The streamflow of the watershed increased at a rate of 1.36 mm/year. Among the contribution rates to the increase of streamflow, glaciers increased at a rate of 0.28 mm/year and snowmelt decreased at a rate of −0.53 mm/year. Additionally, permafrost meltwater, groundwater, and precipitation increased at a rate of 0.03 mm/year, 0.60 mm/year, and 0.98 mm/year, respectively. Thus, this study provides an understanding of the composition and change of streamflow in the Qinghai–Tibet Plateau and similar watersheds, wherein the cryosphere plays an important part in the hydrological cycle.

Spatial-temporal trends of hydrological transitions in thermokarst lakes on Northeast Qinghai-Tibet Plateau based on stable isotopes

Regarded as the water towers of numerous large rivers in Asia, the Source Area of Yellow River (SAYR) on Northeast Qinghai-Tibet Plateau (QTP) contains substantial thermokarst lakes, which have exerted significant roles on the regional hydrology and water resources under permafrost degradation. To address the potential impact of climate- and permafrost-induced changes in surface hydrological processes in the SAYR, the hydrological transitions and water balance of thermokarst lakes were characterized on large scales during three years using stable isotope method. Spatial and seasonal deviations in hydrological processes of thermokarst lakes were remarkable. Calculations of evaporation-to-inflow (E/I) ratios based on an isotope-mass balance model revealed substantial evaporation for all thermokarst lakes during June due to the control of climate conditions and limited input water. Substantial feeds from summer/fall rain and permafrost meltwater resulted in lower evaporation and positive water balance of lakes during July, August, September, and October. Based on the relationship between lake-specific input water isotope compositions (δI) and annual average isotope value of precipitation (δP), the recharge patterns of thermokarst lakes in the SAYR were classified: supra-permafrost water/rainfall-dominated lakes were mainly concentrated during June and October regardless of spatial divergences, and summer precipitation/ permafrost thaw-dominated lakes are popular during July and August. Qualitatively, seasonal diversities in the water balance of thermokarst lakes are combinatively controlled by air temperature, precipitation regimes, permafrost degradation in the SAYR. Lastly, the future hydrological trajectories of thermokarst lakes are expected under climatic warming and permafrost degradation. This study serves as an important contribution for understanding future hydrological changes and allocation of water resources on the QTP, as well as an indication of permafrost degradation under climate warming.

Using tritium and 222Rn to estimate groundwater discharge and thawing permafrost contributing to surface water in permafrost regions on Qinghai-Tibet Plateau

On the Qinghai-Tibet Plateau, permafrost degradation and associated release of permafrost meltwater has undoubtedly modified the annual and seasonal streamflow patterns and influenced groundwater conditions. However, it is still unclear how extensively permafrost degradation has influenced surface and subsurface water systems due to very sparse observations. Isotope mass models combining tritium and 222Rn measurements are developed here to quantify the contributions of groundwater discharge and thawing permafrost to rivers and lakes in the Source Area of the Yellow River. Results demonstrate the spatial variability of permafrost thaw impacts and confirm significant influence on surface and subsurface runoff processes including effects on water yield capacity and water drainage connectivity. While results to date are conclusive, further work to refine the method and extend observations is warranted.

Ladakh: diverse, high-altitude extreme environments for off-earth analogue and astrobiology research

AbstractThis paper highlights unique sites in Ladakh, India, investigated during our 2016 multidisciplinary pathfinding expedition to the region. We summarize our scientific findings and the site's potential to support science exploration, testing of new technologies and science protocols within the framework of astrobiology research. Ladakh has several accessible, diverse, pristine and extreme environments at very high altitudes (3000–5700 m above sea level). These sites include glacial passes, sand dunes, hot springs and saline lake shorelines with periglacial features. We report geological observations and environmental characteristics (of astrobiological significance) along with the development of regolith-landform maps for cold high passes. The effects of the diurnal water cycle on salt deliquescence were studied using the ExoMars Mission instrument mockup: HabitAbility: Brines, Irradiance and Temperature (HABIT). It recorded the existence of an interaction between the diurnal water cycle in the atmosphere and salts in the soil (which can serve as habitable liquid water reservoirs). Life detection assays were also tested to establish the best protocols for biomass measurements in brines, periglacial ice-mud and permafrost melt water environments in the Tso-Kar region. This campaign helped confirm the relevance of clays and brines as interest targets of research on Mars for biomarker preservation and life detection.

Evaluation of thermokarst lake water balance in the Qinghai–Tibet Plateau via isotope tracers

Thermokarst lakes are a ubiquitous landscape feature, which widely distributed in the pan-arctic and some low latitude regions, and are associated with regional hydrological processes. The studies were taken to obtain a better understanding of the water balance of thermokarst lakes in the Qinghai–Tibet Plateau (QTP) in order to gain insight of the regional hydrological cycle. The characteristics of the stable isotopes δ 18O and δ D were investigated in precipitation, permafrost meltwater, and thermokarst lake water in the continuous permafrost region of the QTP and analyzed the lake water balance using the isotope mass model. The results showed that the δ D–δ 18O relationship in the thermokarst lakes (δ D = 5.45 δ 18O − 18.95) differed from that of the local precipitation (δ D = 8.30 δ 18O + 18.49) and permafrost meltwater (δ D = 5.78 δ 18O − 23.41), and the mean isotope compositions in the thermokarst lakes were −7.2‰ in δ 18O and −58.0‰ in δ D. The more positive isotope signals in thermokarst lakes than in the precipitation and permafrost meltwater revealed that the lakes had experienced stronger isotope enrichment. Additionally, the evaporation-to-inflow ratio (E/I) values were < 1 in most of the thermokarst lakes (84%), which might be explained by the recent expansion of the lake surfaces. However, 16% of the thermokarst lakes had shrunk, owing to thermokarst erosion, lateral expansion as the temperature increases, and lower recharge volume. Moreover, precipitation on the lake surface was only 14–18% of the inflow volume in the thermokarst lakes, and the surface-subsurface inflow and permafrost meltwater are very important for recharging the lakes and maintaining the water balance. The results of this study provide a comprehensive understanding of the influence of climate warming on hydrological processes in the permafrost regions in the QTP.

Glaciers, Permafrost and Lake Levels at the Tsengel Khairkhan Massif, Mongolian Altai, During the Late Pleistocene and Holocene

Understanding paleo—and recent environmental changes and the dynamics of individual drivers of water availability is essential for water resources management in the Mongolian Altai. Here, we follow a holistic approach to uncover changes in glaciers, permafrost, lake levels and climate at the Tsengel Khairkhan massif. Our general approach to describe glacier and lake level changes is to combine traditional geomorphological field mapping with bathymetric measurements, satellite imagery interpretation, and GIS analyses. We also analysed climate data from two nearby stations, and measured permafrost temperature conditions at five boreholes located at different elevations. We identified four glacial moraine systems (M4-M1) and attribute them to the period from the penultimate glaciation (MIS 4/5) until the Little Ice Age (MIS 1). During the Local Last Glacial Maximum (LLGM; MIS 2), a glacier reached down into the western Kharganat Valley and blocked it, resulting in the formation of the endorheic Khar Lake basin. Subsequently, the lake was fed mainly by precipitation and permafrost meltwater. In recent years, glaciers have been in strong recession, yet Khar Lake levels have remained relatively stable, which is in contrast to mainly decreasing lake levels in other regions throughout Mongolia. While temperatures in the Altai are increasing (leading to increasing evaporation), precipitation in higher elevations has increased, which—in addition to increased glacier and permafrost melting—would counteract the increasing aridity effects. A systematic and holistic monitoring of glaciers, permafrost, lake levels and climate in the Mongolian Altai is necessary, and results from (sub-)disciplines need to be correlated.

Temperature variability and its influence on macroinvertebrate assemblages of alpine springs

AbstractConstant water temperature is thought to be a key factor for macroinvertebrates inhabiting springs. Springs in low mountain ranges are usually fed by deep groundwater. At high altitudes, they are, to a certain degree, fed by near‐surface aquifers and are influenced by snow and permafrost meltwater. This may alter temperature constancy. In this study, we examined 13 springs in the Bernese Alps in Switzerland during 1 year. The aim was to investigate the variability of water temperature and its influence on macroinvertebrate assemblages of alpine springs at different altitudes. Water temperature and solar radiation were continuously monitored; electrical conductivity, pH, and oxygen were measured; and a quantitative sampling of the macroinvertebrates was conducted 3 times from June 2010 to July 2011. Using linear correlation analysis, we detected a significant decrease of the variability of water temperature along the altitudinal gradient. Electrical conductivity was significantly lower in springs at high altitude. This might indicate an influence of snow and permafrost meltwater. The percentage of alpine species significantly increased with altitude. Taxon richness and the percentage of crenobiontic species were not significantly correlated with any physicochemical parameter. Monthly temperature amplitude and snow cover had a significant influence on the composition of macroinvertebrate assemblages, distinguishing high alpine springs from those at lower altitude. Harsh environmental conditions with low but constant water temperatures fostered alpine rhithrobiontic species, also directly at the outflow, that is, in springs. A loss of such highly adapted species is predicted due to climate change.

Landscape-gradient assessment of thermokarst lake hydrology using water isotope tracers

Thermokarst lakes are widespread in arctic and subarctic regions. In subarctic Québec (Nunavik), they have grown in number and size since the mid-20th century. Recent studies have identified that these lakes are important sources of greenhouse gases. This is mainly due to the supply of catchment-derived dissolved organic carbon that generates anoxic conditions leading to methane production. To assess the potential role of climate-driven changes in hydrological processes to influence greenhouse-gas emissions, we utilized water isotope tracers to characterize the water balance of thermokarst lakes in Nunavik during three consecutive mid- to late summer sampling campaigns (2012–2014). Lake distribution stretches from shrub-tundra overlying discontinuous permafrost in the north to spruce-lichen woodland with sporadic permafrost in the south. Calculation of lake-specific input water isotope compositions (δI) and lake-specific evaporation-to-inflow (E/I) ratios based on an isotope-mass balance model reveal a narrow hydrological gradient regardless of diversity in regional landscape characteristics. Nearly all lakes sampled were predominantly fed by rainfall and/or permafrost meltwater, which suppressed the effects of evaporative loss. Only a few lakes in one of the southern sampling locations, which overly highly degraded sporadic permafrost terrain, appear to be susceptible to evaporative lake-level drawdown. We attribute this lake hydrological resiliency to the strong maritime climate in coastal regions of Nunavik. Predicted climate-driven increases in precipitation and permafrost degradation will likely contribute to persistence and expansion of thermokarst lakes throughout the region. If coupled with an increase in terrestrial carbon inputs to thermokarst lakes from surface runoff, conditions favorable for mineralization and emission of methane, these water bodies may become even more important sources of greenhouse gases.

Evaluation of the hydrological contributions of permafrost to the thermokarst lakes on the Qinghai–Tibet Plateau using stable isotopes

Considering the widespread distribution of thermokarst lakes and their significant influence on the hydrological cycle in permafrost regions on the Qinghai–Tibet Plateau (QTP), it is necessary to study their hydrological regimes, which are responding to ongoing climate-induced permafrost thaw. In this paper, water isotopic tracers were used to assess the temporal and interannual hydrological variations and the hydrological processes of two thermokarst lakes (TL-A and TL-B) associated with thawing permafrost in Beiluhe Basin on the QTP. The isotopic results revealed significant differences between the two thermokarst lakes: the TL-A showed more positive isotopic values and small fluctuations than TL-B did. This can be attributed to the hydrological discrepancies between them. Based on the water isotopic mass balance (IMB) model and estimated evaporation, the contributions of permafrost melt water and precipitation to the thermokarst lakes were determined. In both 2011 and 2012, the contributions of thawing permafrost water to thermokarst lakes were of significance, as high as 61.3%. The modeled isotopic composition of input water (δI), and the relationships between climatic factors and lake water isotopes were evaluated. Results suggested that the two lakes originated from multiple sources and confirmed the modeling process well. It also indicated that thawing of permafrost significantly affected the development and hydrological regime of thermokarst lakes on the QTP. It is necessary to emphasize the significant impact of thawing permafrost on the thermokarst lakes on the QTP. Findings demonstrate that ongoing permafrost thaw may have major implications for thermokarst landscapes as climate change continues.

Origin-specific molecular signatures of dissolved organic matter in the Lena Delta

Large Arctic rivers discharge significant amounts of dissolved organic matter (DOM) into the Arctic Ocean. We sampled natural waters of the Lena River, the Buor-Khaya Bay (Laptev Sea), permafrost melt water creeks, ice complex melt water creeks and a lake. The goal of this study was to characterize the molecular DOM composition with respect to different water bodies within the Lena Delta. We aimed at an identification of source-specific DOM molecular markers and their relative contribution to DOM of different origin. The molecular characterization was performed for solid-phase extracted DOM by Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). Average dissolved organic carbon concentrations in the original samples were 490 ± 75 µmol C L−1 for riverine and bay samples and 399 ± 115 µmol C L−1 for permafrost melt water creeks. Average TDN concentrations were elevated in the permafrost melt waters (19.7 ± 7.1 µmol N L−1) in comparison to the river and the bay (both 13.2 ± 2.6 µmol N L−1). FT-ICR MS and statistical tools demonstrated that the origin of DOM in the Lena Delta was systematically reflected in its molecular composition. Magnitude weighted parameters calculated from MS data (O/Cwa, H/Cwa, C/Nwa) highlighted preliminary sample discrimination. The highest H/Cwa of 1.315 was found for DOM in melt water creeks in comparison to 1.281 for river and 1.230 for the bay samples. In the bay samples we observed a higher fraction of oxygen-rich components which was reflected in an O/Cwa ratio of 0.445 in comparison to 0.425 and 0.427 in the river and creeks, respectively. From the southernmost location to the bay a relative depletion of nitrogenous molecular markers and an enrichment of oxidized DOM components occurred. The highest contribution of nitrogenous components was indicative for creeks reflected in a C/Nwa of 104 in comparison to 143 and 176 in the river and bay, respectively. These observations were studied on a molecular formula level using principal component and indicator value analyses. The results showed systematic differences with respect to water origin and constitute an important basis for a better mechanistic understanding of DOM transformations in the changing Arctic rivers.

Using the deuterium isotope composition of permafrost meltwater to constrain thermokarst lake contributions to atmospheric CH4 during the last deglaciation

Thermokarst lakes are thought to have been an important source of methane (CH4) during the last deglaciation when atmospheric CH4 concentrations increased rapidly. Here we demonstrate that meltwater from permafrost ice serves as an H source to CH4production in thermokarst lakes, allowing for region‐specific reconstructions ofδDCH4 emissions from Siberian and North American lakes. δDCH4 reflects regionally varying δD values of precipitation incorporated into ground ice at the time of its formation. Late Pleistocene‐aged permafrost ground ice was the dominant H source to CH4production in primary thermokarst lakes, whereas Holocene‐aged permafrost ground ice contributed H to CH4 production in later generation lakes. We found that Alaskan thermokarst lake δDCH4 was higher (−334 ± 17‰) than Siberian lake δDCH4 (−381 ± 18‰). Weighted mean δDCH4values for Beringian lakes ranged from −385‰ to −382‰ over the deglacial period. Bottom‐up estimates suggest that Beringian thermokarst lakes contributed 15 ± 4 Tg CH4 yr−1 to the atmosphere during the Younger Dryas and 25 ± 5 Tg CH4 yr−1during the Preboreal period. These estimates are supported by independent, top‐down isotope mass balance calculations based on ice coreδDCH4 and δ13CCH4 records. Both approaches suggest that thermokarst lakes and boreal wetlands together were important sources of deglacial CH4.

Alkenone sea surface temperature in the Okhotsk Sea for the last 15 kyr.

A sediment core collected from the Sea of Okhotsk, a marginal sea of the western North Pacific, has been analyzed for alkenones to reconstruct changes in the sea surface temperatures (SST) over the last 15 kyrs. A comparison of the core-top U 37′ value with the modern surface temperatures indicates that alkenones are produced at present in summer-fall season, a production seasonality probably identical to the one prevailing in the past, as suggested by evidences of enhanced sea ice cover and subsequent limitation of the phytoplankton growth period to summer‐fall at the glacial/deglacial transition. The alkenone downcore profile indicated that summer SST at the early deglaciation period (15 kyrs BP) were around 5 °C lower than today (ca. 11°C). A rapid SST increase (more than 3°C) was found to occur from 13.7 to 11.6 kyrs BP, following the melting water pulse event (MWP-1A). This warming was assumed to be the consequence of a radical change in the atmospheric/oceanic circulations which induced an enhanced heat transport from the sub-tropical to the northern North Pacific. A significant surface water cooling was evidenced from 11 to 8 kyrs BP, possibly caused by the supply of cold Siberian permafrost melt-water to the Okhotsk Sea through the Amur River.