First direct dating of Late Pleistocene ice-wedges by AMS

We present the first direct dating by C-14-accelerator mass spectrometry of three Late Pleistocene syngenetic ice-wedges from the Seyaha cross-section. They are representative of permafrost with multistage ice-wedges from the North of Western Siberia. The most important result is the clear vertical age stratification of the ice, i.e. the old ice is located beneath the young. This shows that a timescale can be assigned to these ice-wedges penetrating down into the permafrost. The age of the ice shows a depth of not more than 3-5 m for frost cracking; water penetrated into the ice-wedges at that depth. The lower part of the ice-wedges from the Seyaha cross-section has been dated between 21 000 and 14 000 BP. (C) 2000 Elsevier Science B.V. All rights reserved

Special Issue: Recent advances (2008 – 2015) in the study of ground ice and cryostratigraphy

Cryostratigraphy involves the description, interpretation and correlation of ground-ice 17 structures (cryostructures) and their relationship to the host deposits. Recent advances in the 18 study of ground ice and cryostratigraphy concern permafrost aggradation and degradation, 19 massive-ice formation and evaluation of ground-ice content. Field studies have increased our 20 knowledge of cryostructures and massive ground ice in epigenetic and syngenetic permafrost. 21 Epigenetic permafrost deposits are relatively ice-poor and composed primarily of pore-filled 22 cryostructures, apart from an ice-enriched upper section and intermediate layer. Syngenetic 23 permafrost deposits are commonly identified from cryostructures indicative of an aggrading 24 permafrost table and are characterized by a high ice content, ice-rich cryofacies, and nested 25 wedge ice. Degradation of ice-rich permafrost can be marked by thaw unconformities, 26 truncated buried ice wedges, ice-wedge pseudomorphs, and organic-rich ‘forest beds’. 27 Studies of massive ground ice have focused on wedge ice, thermokarst-cave ice, intrusive ice, 28 and buried ice. Significant advances have been made in methods for differentiating between 29 tabular massive ice bodies of glacier and intrasedimental origin. Recent studies have utilized 30 palynology, isotope geochemistry and hydrochemistry, in addition to sedimentary and 31 cryostratigraphic analyses. The application of remote sensing techniques and laboratory 32 methods such as CT scanning has improved estimations of the ice content of frozen 33 sediments

Ice wedges as archives of winter palaeoclimate: a review

Ice wedges are a characteristic feature of northern permafrost landscapes and grow mainly by snowmelt that refreezes in thermal contraction cracks that open in winter. In high latitudes the stable‐isotope composition of precipitation (δ18O and δD) is sensitive to air temperature. Hence, the integrated climate information of winter precipitation is transferred to individual ice veins and can be preserved over millennia, allowing ice wedges to be used to reconstruct past winter climate. Recent studies indicate a promising potential of ice‐wedge‐based paleoclimate reconstructions for more comprehensive reconstructions of Arctic past climate evolution. We briefly highlight the potential and review the current state of ice‐wedge paleoclimatology. Existing knowledge gaps and challenges are outlined and priorities for future ice‐wedge research are suggested. The major research topics are (1) frost cracking and infilling dynamics, (2) formation and preservation of the stable‐isotope information, (3) ice‐wedge dating, (4) age‐model development and (5) interpretation of stable‐isotope time series. Progress in each of these topics will help to exploit the paleoclimatic potential of ice wedges, particularly in view of their unique cold‐season information, which is not adequately covered by other terrestrial climate archives

Syngenetic sand veins and anti-syngenetic sand wedges, Tuktoyaktuk Coastlands, western Arctic Canada

Sand-sheet deposits of full-glacial age in the Tuktoyaktuk Coastlands, western Arctic Canada, contain syngenetic sand veins 1-21 cm wide and sometimes exceeding 9 m in height. Their tall and narrow, chimney-like morphology differs from that of known syngenetic ice wedges and indicates an unusually close balance between the rate of sand-sheet aggradation and the frequency of thermal-contraction cracking. The sand sheets also contain rejuvenated (syngenetic) sand wedges that have grown upward from an erosion surface. By contrast, sand sheets of postglacial age contain few or sometimes no intraformational sand veins and wedges, suggesting that the climatic conditions were unfavourable for thermal-contraction cracking. Beneath a postglacial sand sheet near Johnson Bay, sand wedges with unusually wide tops (3.9 m) extend down from a prominent erosion surface. The wedges grew vertically downward during deflation of the ground surface, and represent anti-syngenetic wedges. The distribution of sand veins and wedges within the sand sheets indicates that the existence of continuous permafrost during sand-sheet aggradation can be inferred confidently only during full-glacial conditions

Реконструкция зимней температуры воздуха в голоцене по стабильным изотопам из ледяных жил в районе города Анадырь

The object of research is syncryogenic Holocene strata on the coast of the Onemen Bay, 2 km from the town of Anadyr. In July 2017, the outcrop of the first marine terrace uncovered by strong storms was examined. The stratigraphy of the outcrop was represented mainly by sandy loam (5–7 m thick) covered by peat (1–1.5 m) and underlain by sand. Numerous ice wedges were opened in the upper part of this outcrop. Along with that another outcropping of transect of a lakemarsh basin represented by a peat bog of 2–2.5 m thick underlain by sandy loam was also investigated. Ice wedges occur below the polygonal trenches. The present-day narrow ice wedges were found in the upper part of the peat bog. Two representative fragments of both the above outcrops were thoroughly examined. Radiocarbon dating had shown that accumulation of peat on surface of the first marine terrace started in early Holocene (about 8 ka BP). Accumulation of peatland within the lake-marsh basin was also dated to the beginning of the Holocene (about 9 ka BP). In the middle of the Holocene, it was most likely interrupted as a result of thermokarst processes and bogging of the surface. Formation of peatlands in Chukotka during the Holocene is known to be accompanied by active growth of the ice wedges inside them, so the age of the wedges studied by us was estimated as the beginning of the Holocene. The analysis of stable oxygen and hydrogen isotopes in the Holocene and the modern ice wedges had allowed establishing mainly the atmospheric type of moisture feeding of the wedges (due to melted snow) and lack of noticeable isotope fractionation during the ice formation. It has been found that δ18О and δ2Н values in the Holocene ice wedges were lower than in the modern wedges and snow by an average 2–3 and 7–12 ‰, respectively. Paleotemperature reconstructions performed on the basis of isotopeoxygen data showed that the air temperature of the coldest winter month in the first half of the Holocene in the Onemen Bay area was lower than the present-day ones by an average 2–3 °C, which is in a good agreement with the trend of rising winter temperatures throughout the Chukotka Peninsula, as well as in other areas of Eastern Siberia and Alaska. Объект исследований – синкриогенные голоценовые толщи на побережье залива Онемен, в 2 км от г. Анадырь. Изучены повторно-жильные льды, вскрытые в двух фрагментах обнажения первой морской террасы. При радиоуглеродном датировании вмещающего торфа установлено, что жилы начали активно формироваться в раннем голоцене (около 9–8 тыс. лет назад). Согласно палеотемпературным реконструкциям на основе изотопно-кислородных данных, температура воздуха самого холодного зимнего месяца в первой половине голоцена в районе залива Онемен была ниже современной на 2–3 оС

Реконструкция средних температур января в раннем голоцене на северо-востоке Большеземельской тундры

The aim of the study was to establish the period of accumulation of peatland with ice wedges near Vorkuta town based on series of calibrated radiocarbon dates, to anchor in time the isotope-oxygen curve of syngenetic ice wedge from peatland and to reconstruct the mean January air temperature for the appropriate Holocene period. Analysis of a series of 14C dates showed that peatland near Vorkuta was actively formed between 10.5 and 6 cal. ka BP. Winter conditions in the Vorkuta area were quite severe, that favored to frost cracking of the peatland and syngenetic growth of ice wedges within the drier sites and peat-soil wedges within the watered sites. Ice wedge growth was the most active within the Greenlandian Stage of Holocene, between 10,5 and 9,7 cal. ka BP, the reconstructed mean January air temperature for this period varied between −23 and −25 oC; currently, such temperatures are recorded only during the coldest winters.Вблизи г. Воркута процессы заболачивания и образования торфа начались в первой половине гренландского периода голоцена – около 11–10 тыс. калиб. лет назад. Завершилось формирование торфяника 3–2 тыс. калиб. лет назад. Время активного формирования в торфянике сингенетических повторно-жильных льдов приходится на период между 10,5 и 9,7 тыс. калиб. лет назад, когда среднеянварская температура воздуха варьировала между −23 и −25 oC

ВАРИАЦИИ ИЗОТОПОВ КИСЛОРОДА И ВОДОРОДА В СОВРЕМЕННОЙ ПЛАСТОВОЙ ЛЕДЯНОЙ ЗАЛЕЖИ В УСТЬЕ Р. АККАНИ, ВОСТОЧНАЯ ЧУКОТКА

The object of this study is a recently (or in the Holocene) formed thick (up 2.7 m in height) buried massive ice body, exposed in 2 km South-East from the mouth of the river Akkani in the North-East of Chukotka in the vicinity of the settlement Lavrentiya. The structural-textural characteristics of ice and enclosing deposits are considered. It is shown that the overlying layers of sediments are loams with a slab structure and vertical-layer medium and thin-chill cryogenic structure and ice sockets. The ice of the body is very pure and transparent, visible to a depth of 0.5 m. There are some inclusions found in massive ice: sand and loams presented in forms of thin interlayers of particles or granules. The ice is full of bubbles. The main method of the research was the analysis of isotopes of oxygen and hydrogen within the stratified ice body, and also relationships between them as well as ratios between the deuterium excess and δ2Н. The thick and relatively contemporary massive ice layer buried under a layer of proluvial sediments had been found for the first time, and together with this, the isotope variations of the buried ice (δ2Н and δ18O) were determined. The mean values of δ18О and δ2H in the ice are rather stable and equal to −17.1 and −128.3‰, respectively. These isotope characteristics may be used for cryogenic reconstructions of massive ice formations widely distributed in the late Quaternary deposits in Eastern Chukotka.Изучен изотопный состав кислорода и водорода мощного современного (голоценового) ледяного пласта, погребённого под слоем пролювиальных отложений на побережье Чукотки вблизи посёлка Лаврентия. Значения δ18О и δ2H во льду довольно однородны и составляют −17,1 и −128,3 ‰ соответственно. Изученный пластовый лёд в устье р. Аккани представляет собой захороненный перелетовывающий снежник, сформировавшийся с участием поверхностных вод и атмосферной влаги весенне-летнего периода

Реконструкция зимней температуры воздуха раннего и среднего голоцена по изотопному составу ледяных жил восточного побережья полуострова Дауркина, Чукотка

The object of research is the Holocene massive ice veins on the Eastern coast of the Daurkin Peninsula, the easternmost part of the Chukotka. Peat bogs with ice veins occur on the surface of marine terraces (near Uelen and Lorino settlements) and on flood plain of the Koolen’ Lake; the thickness of peat varies from 0.7 to 2.5 m. Radiocarbon dating of the peat enclosing the investigated ice veins near Uelen and Lorino indicated that the beginning of peat accumulation began at the end of Late Pleistocene – early Holocene, about 11 cal ka BP. On the flood plain of the Koolen’ Lake peat bogs began to accumulate in the middle Holocene, i.e. around 6 cal ka BP. At the initial stage of peat bogs formation the rate of peat accumulation was high and could reach 1 cm/10 years. Ice veins occur at a depth of 0.5–1 m, and their lower parts are located in the underlying peat sandy loams and loams. In the upper levels of the peat bogs, narrow present-day ice veins are found, which are sometimes embedded in the upper parts of Holocene veins. A clear sign of syngenetic growth of veins is the upward bending of the layers of the host peat at the lateral contacts with the veins. The main source of water for the formation of ice veins is snow, as evidenced by the ratio of stable isotopes of oxygen and hydrogen and the values of deuterium excesses in the ice. A slight admixture of saline water (probably from a seasonally thawed layer) was noted in the veins near the Lorino settlement. Reconstructions of winter air paleotemperatures, performed on the basis of data of isotope-oxygen composition of ice from the veins, did show that at the period between 11 and 6 cal Ka BP, the mean winter air temperature on the Daurkin Peninsula was by 2–5 oC lower than today, but the air temperature of the coldest month (January or February) was still lower (by 4-8 oC) than today. The noticeable trend of increase of stable isotope values in the ice veins from early Holocene to the present time is indicative of a steady positive trend of mean winter air temperatures in the Holocene.Реконструкции зимних палеотемператур воздуха на основе данных изотопно-кислородного состава льда жил показали, что между 11 и 6  тыс.  кал.  лет назад среднезимняя температура воздуха была на 2–5оС ниже современной, а температура воздуха самого холодного месяца (января или февраля) – на 4–8оС ниже современной. Установлен устойчивый положительный тренд зимних температур воздуха от раннего голоцена до настоящего времени

High biolability of ancient permafrost carbon upon thaw

Ongoing climate warming in the Arctic will thaw permafrost and remobilize substantial terrestrial organic carbon (OC) pools. Around a quarter of northern permafrost OC resides in Siberian Yedoma deposits, the oldest form of permafrost carbon. However, our understanding of the degradation and fate of this ancient OC in coastal and fluvial environments still remains rudimentary. Here, we show that ancient dissolved OC (DOC, &gt;21,000 (14)Cyears), the oldest DOC ever reported, is mobilized in stream waters draining Yedoma outcrops. Furthermore, this DOC is highly biolabile: 34 +/- 0.8% was lost during a 14 day incubation under dark, oxygenated conditions at ambient river temperatures. Mixtures of Yedoma stream DOC with mainstem river and ocean waters, mimicking in situ mixing processes, also showed high DOC losses (14 days; 17 +/- 0.8% to 33 +/- 1.0%). This suggests that this exceptionally old DOC is among the most biolabile DOC in any previously reported contemporary river or stream in the Arctic.</p

Два подхода к расчёту расчленения гидрографа стока реки с ледниковым питанием с помощью изотопных методов

Application of the stable isotope method in the balance equations used to calculate separation of the runoff hydrograph from the Djankuat Glacier basin is demonstrated. Simultaneous solution of equations of water, isotope and ion balances is applied to estimate contributions of different components and processes to formation of the Djankuat River runoff regime. For June 2014, we made calculations for the purpose to separate contributions of the spring (isotopically weighted) snow and winter (isotopically depleted) snow. Field works in the glacial basin Djankuat were performed during two ablation seasons, i.e. from June to September of 2013 and 2014. Two approaches were used when calculating separation of the runoff hydrograph by means of solution of systems of equations for isotopic and ion balances: 1) taking account of the isotope fractionation during snow melting, and 2) with no account for the fractionation. Separation of the hydrograph for June 2014 have shown that about 15–20% of the Djankuat River runoff is formed by spring snow melting, sometimes increasing up to 36%. Contribution of spring meltwater to the total runoff increases when the isotope fractionation during the snow melting is taken into account for the calculations. In this case, the contribution of spring snow changes from 30 to 50%.Рассмотрено применение метода стабильных изотопов в балансовых расчётах расчленения гидрографа стока с ледника Джанкуат. Изученные изотопные вариации стока на замыкающем створе р. Джанкуат для двух сезонов абляции 2013 и 2014 г. совместно с измерениями δ18О и минерализации различных источников питания р. Джанкуат (атмосферные осадки, снег разных сезонов, фирн, лёд и грунтовые воды) позволили расчленить гидрограф стока 2014 г. Применялись два методических подхода к расчётам: разделение гидрографа стока решением систем уравнений ионного и изотопного баланса с учётом изотопного фракционирования при таянии снега и без учёта фракционирования. Установлена величина погрешности расчётов с использованием значений δ18О и абсолютных концентраций 18О