Permafrost hydrology in changing climatic conditions: seasonal variability of stable isotope composition in rivers in discontinuous permafrost

Role of changing climatic conditions on permafrost degradation and hydrology was investigated in the transition zone between the tundra and forest ecotones at the boundary of continuous and discontinuous permafrost of the lower Yenisei River. Three watersheds of various sizes were chosen to represent the characteristics of the regional landscape conditions. Samples of river flow, precipitation, snow cover, and permafrost ground ice were collected over the watersheds to determine isotopic composition of potential sources of water in a river flow over a two year period. Increases in air temperature over the last forty years have resulted in permafrost degradation and a decrease in the seasonal frost which is evident from soil temperature measurements, permafrost and active-layer monitoring, and analysis of satellite imagery. The lowering of the permafrost table has led to an increased storage capacity of permafrost affected soils and a higher contribution of ground water to river discharge during winter months. A progressive decrease in the thickness of the layer of seasonal freezing allows more water storage and pathways for water during the winter low period making winter discharge dependent on the timing and amount of late summer precipitation. There is a substantial seasonal variability of stable isotopic composition of river flow. Spring flooding corresponds to the isotopic composition of snow cover prior to the snowmelt. Isotopic composition of river flow during the summer period follows the variability of precipitation in smaller creeks, while the water flow of larger watersheds is influenced by the secondary evaporation of water temporarily stored in thermokarst lakes and bogs. Late summer precipitation determines the isotopic composition of texture ice within the active layer in tundra landscapes and the seasonal freezing layer in forested landscapes as well as the composition of the water flow during winter months

NEW PERMAFROST FEATURE – DEP CRATER IN CENTRAL YAMAL (WEST SIBERIA, RUSIA) AS A RESPONSE TO LOCAL CLIMATE FLUCTUATIONS

This paper is based on field data obtained during short visits to a newly formed permafrost feature in a form of relatively narrow, deep crater. Excluding impossible and improbable versions of the crater’s development, the authors conclude that it originated from warmerground temperatures and an increase in unfrozen water content, leading to an increase in pressure from gas emissions from permafrost and ground ice. This conclusion is also supported by known processes in the palaeo-geography of Yamal lakes and recent studies of gas-hydrate behavior and subsea processes in gas-bearing provinces

Methane Content in Ground Ice and Sediments of the Kara Sea Coast

Permafrost degradation of coastal and marine sediments of the Arctic Seas can result in large amounts of methane emitted to the atmosphere. The quantitative assessment of such emissions requires data on variability of methane content in various types of permafrost strata. To evaluate the methane concentrations in sediments and ground ice of the Kara Sea coast, samples were collected at a series of coastal exposures. Methane concentrations were determined for more than 400 samples taken from frozen sediments, ground ice and active layer. In frozen sediments, methane concentrations were lowest in sands and highest in marine clays. In ground ice, the highest concentrations above 500 ppmV and higher were found in massive tabular ground ice, with much lower methane concentrations in ground ice wedges. The mean isotopic composition of methane is −68.6‰ in permafrost and −63.6‰ in the active layer indicative of microbial genesis. The isotopic compositions of the active layer is enriched relative to permafrost due to microbial oxidation and become more depleted with depth. Ice-rich sediments of Kara Sea coasts, especially those with massive tabular ground ice, hold large amounts of methane making them potential sources of methane emissions under projected warming temperatures and increasing rates of coastal erosion

Rates of coastal destruction in areas of tabular ground ice occurrence in the western Russian Arctic

Tabular ground ice bodies are widely spread on Eurasian and North American Arctic plains. Exposed tabular ground ice in coastal bluffs favors the activation of thermal abrasion and thermal denudation, which in turn causes increasing coastal destruction rates. Thermo-denudation under conditions of ground ice exposures includes thawing of ice and frozen sediments along retreating headwalls of retrogressive thaw slumps and their constant enlargement. Thermo-cirques and thermo-terraces are two basic landform types that either feature channelized or broad open outlets, depending on the initial ice body outcrop by the denudation processes inland or in the retreating coastal bluffs. We study key-sites on Kolguev Island (Barents Sea) and on Yugorsky Peninsula (Kara Sea), continuing and extending earlier research efforts on coastal dynamics in the region. New data on thermo-denudation and thermo-abrasion rates for these key-sites have been obtained using a set of multi-temporal satellite images of high and very-high spatial resolution covering the period from 2002 to 2016. For orthorectification purposes of imagery collected prior to TanDEM-X acquisitions, we used an edited version of the 12 m TanDEM-X DEM. Along erosive coastline segments the former relief situation was reconstructed through extrapolation of coastal bluff edge elevation values and restoration of the coastal plain relief towards the sea. On the western coast of Kolguev Island, average coastal bluff retreat rates between 2002 and 2012 varied from 1.7 to 2.4 m/year, while averaged rates of thermo-cirques headwalls retreat were 2.6 m/year. Maximum rates at some sections increased up to 14.5-15.1 m/year in the recent past. High rates of thermo-denudation increase were not only observed on western Kolguev Island, but also on the Yugorsky Peninsula, were rates raised up to 13 m/year in recent years. Activation of thermo-denudation is also noted in other parts of Kara Sea coasts and were generally correlated with changing environmental factors, particularly expressed in an increase on the thaw index during recent years

Gas‐emission craters of the Yamal and Gydan peninsulas: Aproposed mechanism for lake genesis and development ofpermafrost landscapes

This paper describes two gas‐emission craters (GECs) in permafrost regions of the Yamal and Gydan peninsulas. We show that in three consecutive years after GEC formation (2014–2017), both morphometry and hydrochemistry of the inner crater lakes can become indistinguishable from other lakes. Craters GEC‐1 and AntGEC, with initial depths of 50–70 and 15–19 m respectively, have transformed into lakes 3–5 m deep. Crater‐like depressions were mapped in the bottom of 13 out of 22 Yamal lakes. However, we found no evidence that these depressions could have been formed as a result of gas emission. Dissolved methane (dCH4) concentration measured in the water collected from these depressions was at a background level (45 ppm on average). Yet, the concentration of dCH4 from the near‐bottom layer of lake GEC‐1 was significantly higher (824–968 ppm) during initial stages. We established that hydrochemical parameters (dissolved organic carbon, major ions, isotopes) measured in GEC lakes approached values measured in other lakes over time. Therefore, these parameters could not be used to search for Western Siberian lakes that potentially resulted from gas emission. Temperature profiles measured in GEC lakes show that the water column temperatures in GEC‐1 are lower than in Yamal lakes and in AntGEC – close to values of Gydan lakes. Given the initial GEC depth > 50 m, we suggest that at least in GEC‐1 possible re‐freezing of sediments from below might take place. However, with the present data we cannot establish the modern thickness of the closed talik under newly formed GEC lakes

The Zhenya Mammoth ( Mammuthus primigenius (Blum.)): Taphonomy, geology, age, morphology and ancient DNA of a 48,000 year old frozen mummy from western Taimyr, Russia

This paper reports the results of an in-depth analysis of the frozen remains of a woolly mammoth (Mammuthus primigenius) named Zhenya, which has been dated to 48,000 cal BP. The carcass, found near the mouth of the Yenisey River in eastern Siberia, was a juvenile male whose ontogenetic age at death was 8-10 AEY. Its reconstructed live height at the shoulders (pSH 227.4 cm) was the equal of some adult female woolly mammoths and extant elephants. The large stature and a flaked off tusk tip that matches breaks on tusks of male African elephants are indirect indications that this mammoth most likely had reached sexual maturity, had been expelled from its maternal herd, and had been in at least one fight with another male. The mammoth's bones were relatively healthy, although some had minor lesions. Rudimentary upper second molars (M2/m2) were present, but no lower second molars were found in the alveoli, and the left tusk had never developed. Despite the abnormal development of the upper and lower second molars, the cheek teeth which were in wear (Dp4/dp4 and M1/m1) showed normal function without any indications of developmental delay. The completed growth of the light-colored dentin bands on the tusk strongly suggests the Fall of the year was the season of death. This season is also supported by accumulated fat in the upper parts of the torso, indicative of physiological preparation for the winter ahead. The few minor traces of carnivore scavenging, the little disturbed condition of the carcass, and the absence of bone modifications made by human actions, along with the social status of this young male animal, are interpreted here as highly probable evidence that the Zhenya Mammoth died from unrecoverable injuries inflicted during a bull-to-bull fight. The mineralogical analysis of site sediments revealed that the mammoth's burial in situ took place in the Yenisey River valley seasonally inundated by the river, which together with Fall's freezing temperatures protected the carcass from scavengers. An analysis of ancient DNA provides strong support for Zhenya's mitochondrial lineage within the deeply diverging clade III haplogroup B