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The Batagay megaslump (67.58 °N, 134.77 °E) is the largest known retrogressive thaw slump on Earth, and located in the Yana River Uplands near the town of Batagay in east Siberia. The slump headwall is about 55 m high and exposes ancient permafrost deposits that provide a discontinuous record of the Middle and Late Pleistocene that dates back to at least 650 ka.In this contribution, we compile cryostratigraphic observations and dating results for the permafrost exposed in the Batagay megaslump. Both provide evidence for several periods of permafrost formation and degradation. Permafrost formation and stability during Marine Isotope Stage (MIS) 16 or earlier (lower ice complex), MIS 7–6 or earlier (lower sand unit), MIS 4–2 (upper ice complex), and MIS 3–2 (upper sand unit) are reflected by the presence of deposits hosting syngenetic ice wedges and composite (i.e., ice–sand) wedges. In contrast, permafrost thaw and erosion are indicated by sharp, erosional discordances above reddish and organic-rich layers and by the accumulation of woody (forest) remains in erosional downcuts below and above the lower sand unit, and above the upper ice complex. Permafrost thaw and erosion likely took place during one or several periods between MIS 16 and MIS 7–6 as well as during MIS 5 and the late Pleistocene–Holocene transition.To gain seasonal-scale climate signals, we analyzed the stable isotope composition of ground ice (ice and composite wedges and pore ice) from all four main stratigraphic units reflecting permafrost aggradation exposed in the Batagay megaslump. Ice and composite wedges contain winter climate signals. Their distinctly depleted δ18O values reflect the extreme continentality of the region with large seasonal temperature differences. Pore ice is mostly characterized by less depleted δ18O values and rather reflects summer to annual climate signals subject to post-depositional isotopic fractionation.To draw large-scale conclusions on climate–permafrost interactions we compare our data to independent climate and permafrost reconstructions from terrestrial (cave deposits, lake sediment cores, and permafrost deposits) and marine sediment cores across the Arctic.

The reconstruction of past sea-ice distribution in the Southern Ocean is crucial for an improved understanding of ice–ocean–atmosphere feedbacks and the evaluation of Earth system and Antarctic ice sheet models. The Antarctic Peninsula (AP) has been experiencing a warming since the start of regular monitoring of the atmospheric temperature in the 1950s. The associated decrease in sea-ice cover contrasts the trend of growing sea-ice extent in East Antarctica. To reveal the long-term sea-ice history at the northern Antarctic Peninsula (NAP) under changing climate conditions, we examined a marine sediment core from the eastern basin of the Bransfield Strait covering the last Deglacial and the Holocene. For sea-ice reconstructions, we focused on the specific sea-ice biomarker lipid IPSO25, a highly branched isoprenoid (HBI), and sea-ice diatoms, whereas a phytoplankton-derived HBI triene (C25:3) and warmer open-ocean diatom assemblages reflect predominantly ice-free conditions. We further reconstruct ocean temperatures using glycerol dialkyl glycerol tetraethers (GDGTs) and diatom assemblages and compare our sea-ice and temperature records with published marine sediment and ice core data. A maximum ice cover is observed during the Antarctic Cold Reversal 13 800–13 000 years before present (13.8–13 ka), while seasonally ice-free conditions permitting (summer) phytoplankton productivity are reconstructed for the late Deglacial and the Early Holocene from 13 to 8.3 ka. An overall decreasing sea-ice trend throughout the Middle Holocene coincides with summer ocean warming and increasing phytoplankton productivity. The Late Holocene is characterized by highly variable winter sea-ice concentrations and a sustained decline in the duration and/or concentration of spring sea ice. Overall diverging trends in GDGT-based TEX86L and RI-OH' subsurface ocean temperatures (SOTs) are found to be linked to opposing spring and summer insolation trends, respectively.

Reconstructions of global hydroclimate during the Common Era (CE; the past ∼2000 years) are important for providing context for current and future global environmental change. Stable isotope ratios in water are quantitative indicators of hydroclimate on regional to global scales, and these signals are encoded in a wide range of natural geologic archives. Here we present the Iso2k database, a global compilation of previously published datasets from a variety of natural archives that record the stable oxygen (δ18O) or hydrogen (δ2H) isotopic compositions of environmental waters, which reflect hydroclimate changes over the CE. The Iso2k database contains 759 isotope records from the terrestrial and marine realms, including glacier and ground ice (210); speleothems (68); corals, sclerosponges, and mollusks (143); wood (81); lake sediments and other terrestrial sediments (e.g., loess) (158); and marine sediments (99). Individual datasets have temporal resolutions ranging from sub-annual to centennial and include chronological data where available. A fundamental feature of the database is its comprehensive metadata, which will assist both experts and nonexperts in the interpretation of each record and in data synthesis. Key metadata fields have standardized vocabularies to facilitate comparisons across diverse archives and with climate-model-simulated fields. This is the first global-scale collection of water isotope proxy records from multiple types of geological and biological archives. It is suitable for evaluating hydroclimate processes through time and space using large-scale synthesis, model–data intercomparison and (paleo)data assimilation. The Iso2k database is available for download at https://doi.org/10.25921/57j8-vs18 (Konecky and McKay, 2020) and is also accessible via the NOAA/WDS Paleo Data landing page: https://www.ncdc.noaa.gov/paleo/study/29593 (last access: 30 July 2020).

The Batagay megaslump (67.58 °N, 134.77 °E) is the largest known retrogressive thaw slump on Earth, and located in the Yana River Uplands near the town of Batagay in east Siberia. The slump headwall is about 55 m high and exposes ancient permafrost deposits that provide a discontinuous record of the Middle and Late Pleistocene that dates back to at least 650 ka. Such deposits are usually deeply (>45 m) buried in frozen ground.The cryostratigraphy of the Batagay megaslump provides evidence for several periods of both permafrost formation and degradation. Permafrost formation and stability are reflected by the presence of deposits with syngenetic ice wedges and composite (i.e., ice–sand) wedges, whereas permafrost thaw and erosion are shown by sharp erosional discordances above reddish and organic-rich layers and by the accumulation of woody (forest) remains in erosional downcuts.The main cryostratigraphic units with syngenetic ice and composite wedges indicate the formation of permafrost during MIS 16 or earlier (lower ice complex), MIS 7–6 or earlier (lower sand unit), MIS 4–2 (upper ice complex), and MIS 3–2 (upper sand unit). Intense permafrost thaw and erosion likely took place during one or several periods between MIS 16 and MIS 7–6, including MIS 5 and the late Pleistocene–Holocene transition.In this contribution we compile cryostratigraphic observations and dating results for the permafrost exposed in the Batagay megaslump. To draw large-scale conclusions on climate–permafrost interactions we compare our data to independent climate and permafrost reconstructions from terrestrial (cave deposits, lake sediment cores, and permafrost deposits) and marine sediment cores across the Arctic with a focus on East Siberia.To gain regional climate signals for this extremely continental region, we also present ground-ice stable-isotope data from all four main stratigraphic units of the Batagay megaslump. We consider ice and composite wedges (winter signals) and pore ice (summer to annual signals) to derive seasonal-scale information and to assess continentality for selected time periods.

Permafrost has a huge potential as a source for greenhouse gas release under global warming. In this context, it is very important to understand biogeochemical mechanisms of permafrost-related greenhouse gas formation and capacity. As ice wedges are an essential component of ice-rich permafrost and often occupy a large volume fraction of permafrost deposits, it is necessary to study the their gas chemistry. The Batagay megaslump (Yana Uplands, Northeast Siberia) exposes ice-rich permafrost deposits (Ice Complex) that have formed in the Middle and Late Pleistocene. Previous studies suggest the ages of these deposits as MIS 4-2 and at least MIS 16 for the Upper and Lower Ice Complexes, respectively. In this study, we analyzed mixing ratios of gas in air bubbles occluded in ice wedges of both ice complexes. We extracted gas by both, wet and dry extraction methods that connected with a gas chromatography system to analyze CO2, N2O, and CH4 concentrations. We observe CO2 concentrations of 1.9–10.3%, N2O of 0.1–8 ppm, and CH4 of 30–170 ppm for the Lower Ice Complex, and CO2 of 0.03–8.89%, N2O of 0.3–70 ppm, and CH4 of 5–980 ppm for the Upper Ice Complex. Greenhouse gas mixing ratios higher than atmospheric level indicate active microbial activity. This is supported by the δ(O2/Ar) values, which range from –89.01 to –67.43% and from –98.07 to –47.06% for the Lower and Upper Ice Complexes, respectively. The highly depleted δ(O2/Ar) values may indicate strong oxidation reactions by microbial activity and/or non-biological oxidation reactions. Even though there is no significant correlation between CO2 and CH4, abiotic CH4 formation might be negligible because it is unlikely to occur under permanently frozen conditions. Interestingly, CH4 and N2O show a weak negative correlation in both ice complexes, which can be explained by the nitrogen compounds’ inhibitory effect for methanogenesis. The δ(N2/Ar) values range from –8.06% to 33.86% for the Lower Ice Complex and from –5.49% to 30.64% for the Upper Ice Complex. Since nitrogen is more soluble in water than argon, this might indicate that ice wedges may have formed without a major contribution of snowmelt but mainly by dry snow compaction, which is also supported by the spherical shape of gas bubbles within the wedge ice. Furthermore, in ice the argon permeation coefficient is higher than that of nitrogen. Thus, high δ(N2/Ar) values (>10%) are due to argon’s diffusion through ice. Our future research will focus on deciphering the biogeochemical process of greenhouse gas formation for both ice complexes by comparison with ice wedges from other Siberian locations which have experienced different biogeochemical conditions in the past.

The Batagay megaslump, a permafrost thaw feature in northeastern Siberia, provides access to ancient permafrost up to ~650 ka old. We aimed to assess the permafrost-locked organic matter (OM) quality and to deduce paleoenvironmental information on glacial-interglacial timescales. We sampled five stratigraphic units exposed on the 55-m-high slump headwall and analyzed lipid biomarkers. Our findings revealed similar biogeochemical signatures for the glacial periods: the Lower Ice Complex (Marine Isotope Stage (MIS) 16 or earlier), the Lower Sand Unit (some time between MIS 16-6) and the Upper Ice Complex (MIS 4-2). The OM in these units has a terrestrial character, and microbial activity was likely limited. Contrarily, the n-alkane and fatty acid distributions differed for the units from interglacial periods: the Woody Layer (MIS 5), separating the Lower Sand and the Upper Ice Complex, and the Holocene Cover (MIS 1), on top of the Upper Ice Complex. The Woody Layer, marking an permafrost degradation disconformity, contained markers of terrestrial origin (sterols) and high microbial decomposition (iso- and anteiso-fatty acids). In the Holocene Cover, biomarkers pointed to wet depositional conditions and we identified branched and cyclic alkanes, which are likely of microbial or bacterial origin. Higher OM decomposition characterized the interglacial periods. As climate warming will continue permafrost degradation in the Batagay megaslump and in other areas, large amounts of deeply buried, ancient OM with a variable composition and degradability are mobilized, likely significantly enhancing greenhouse gas emissions from permafrost regions.

The role of seasonality is indisputable in climate and ecosystem dynamics. Seasonal temperature and precipitation variability are of vital importance for the availability of food, water, shelter, migration routes, and raw materials. Thus, understanding past climatic and environmental changes at seasonal scale is equally important for unearthing the history and for predicting the future of human societies under global warming scenarios. Alas, in palaeoenvironmental research, the term ‘seasonality change’ is often used liberally without scrutiny or explanation as to which seasonal parameter has changed and how.\ud \ud Here we provide fundamentals of climate seasonality and break it down into external (insolation changes) and internal (atmospheric CO2 concentration) forcing, and regional and local and modulating factors (continentality, altitude, large-scale atmospheric circulation patterns). Further, we present a brief overview of the archives with potentially annual/seasonal resolution (historical and instrumental records, marine invertebrate growth increments, stalagmites, tree rings, lake sediments, permafrost, cave ice, and ice cores) and discuss archive-specific challenges and opportunities, and how these limit or foster the use of specific archives in archaeological research.\ud \ud Next, we address the need for adequate data-quality checks, involving both archive-specific nature (e.g., limited sampling resolution or seasonal sampling bias) and analytical uncertainties. To this end, we present a broad spectrum of carefully selected statistical methods which can be applied to analyze annually- and seasonally-resolved time series. We close the manuscript by proposing a framework for transparent communication of seasonality-related research across different communities.

The Batagay megaslump, a permafrost thaw feature in north-eastern Siberia, provides access to ancient permafrost up to ∼650 kyr old. We aimed to assess the permafrost-locked organic matter (OM) quality and to deduce palaeo-environmental information on glacial–interglacial timescales. We sampled five stratigraphic units exposed on the 55 m high slump headwall and analysed lipid biomarkers (alkanes, fatty acids and alcohols). Our findings revealed similar biogeochemical signatures for the glacial periods: the lower ice complex (Marine Isotope Stage (MIS) 16 or earlier), the lower sand unit (sometime between MIS 16–6) and the upper ice complex (MIS 4–2). The OM in these units has a terrestrial character, and microbial activity was likely limited. Contrarily, the n-alkane and fatty acid distributions differed for the units from interglacial periods: the woody layer (MIS 5), separating the lower sand unit and the upper ice complex, and the Holocene cover (MIS 1), on top of the upper ice complex. The woody layer, marking a permafrost degradation disconformity, contained markers of terrestrial origin (sterols) and high microbial decomposition (iso- and anteiso-fatty acids). In the Holocene cover, biomarkers pointed to wet depositional conditions and we identified branched and cyclic alkanes, which are likely of microbial origin. Higher OM decomposition characterised the interglacial periods. As climate warming will continue permafrost degradation in the Batagay megaslump and in other areas, large amounts of deeply buried ancient OM with variable composition and degradability are mobilised, likely significantly enhancing greenhouse gas emissions from permafrost regions.

High-accumulation sites are crucial for understanding the patterns and mechanisms of climate and environmental change in Antarctica since they allow gaining high-resolution proxy records from firn and ice. Here, we present new glacio- and isotope-geochemical data at sub-annual resolution from a firn core retrieved from an ice cap on Plateau Laclavere (LCL), northern Antarctic Peninsula, covering the period 2012–2015. The signals of two volcanic eruptions and two forest fire events in South America could be identified in the non-sea-salt sulphur and black carbon records, respectively. Mean annual snow accumulation on LCL amounts to 2500 kg m−2 a−1 and exhibits low inter-annual variability. Time series of δ18O, δD and d excess show no seasonal cyclicity, which may result from (1) a reduced annual temperature amplitude due to the maritime climate and (2) post-depositional processes. The firn core stratigraphy indicates strong surface melt on LCL during austral summers 2013 and 2015, likely related to large-scale warm-air advection from lower latitudes and temporal variations in sea ice extent in the Bellingshausen-Amundsen Sea. The LCL ice cap is a highly valuable natural archive since it captures regional meteorological and environmental signals as well as their connection to the South American continent.

Dating of ancient relict permafrost is essential for understanding permafrost stability and interpreting past climate and environmental conditions over Pleistocene timescales but presents substantial challenges to geochronology. Here, we date ancient permafrost from the world’s largest thaw slump at Batagay, East Siberia, which potentially provides one of the longest records of Pleistocene environments in western Beringia (East Siberia). We apply four dating methods to the permafrost deposits: (1) optically-stimulated luminescence (OSL) dating of quartz and (2) post-infrared infrared-stimulated luminescence (pIRIR) dating of K-feldspar from sand, (3) ³⁶Cl/Cl dating of ice wedges, and (4) radiocarbon dating of organic material from within wedge ice and its host sediments. Individually, each of the four independent chronometers produces ages consistent with their relative stratigraphic position. Comparability of ages between dating methods is also observed. However, at Batagay quartz OSL appears to date MIS 2/MIS 3 deposits more reliably than K-feldspar pIRIR250, whereas the latter is more consistent with independent chronological controls for older deposits. Collectively, the ages indicate that the lower ice complex developed approximately 650 ka ago during Marine Isotope Stage (MIS) 16, and the upper ice complex approximately 60 to 30 ka ago during late MIS 4 to MIS 3. Sand units below and above the upper ice complex are dated to MIS 6 and 3–2, respectively. Overall, the lower ice complex represents the oldest dated relict permafrost in western Beringia and indicates that thick and cold permafrost at a depth of ~50 m below the ground surface has survived multiple warm interglacials, including the MIS 11c super-interglacial.

Stable isotopes (δ18O, δD) of wedge ice hold potential to reconstruct past winter climate conditions. Here, we present records of the marine isotope stages (MIS) 3 and 2 including the last Glacial maximum (LGM) from Bol’shoy Lyakhovsky Island (NE Siberia). MIS 3 wedge ice dated from 52 to 40 Kyr b2k varies between −32 and −29‰ in δ18O. Colder LGM conditions are implied by δ18O of −37‰ around 25 Kyr b2k. Similar Deuterium excess values indicate comparable moisture sources during MIS 3 and MIS 2. Regional LGM climate reconstructions depend on the seasonal resolution of the proxies and model simulations. Our wedge‐ice record reflects coldest winters during global minima in atmospheric CO2 and sea level. The extreme LGM winter cooling is not represented in model projections of global LGM climate where West Beringia shows noticeably little cooling or even warming in mean annual temperatures compared to the late Holocene., Plain Language Summary: The geochemical signature of stable isotopes of permafrost ground ice preserves information about past climate conditions. A common type of ground ice is ice wedges that form by the freezing of snowmelt in frost cracks developed on the ground and grow over time in width and length. Winter temperatures, and the type (snow or rain) and origin (regional moisture source) of winter precipitation largely control the stable isotope characteristics of oxygen and hydrogen in ice wedges. Here, we study the stable isotope composition of ice wedges from the last glacial period in northeastern Siberia. Plant and animal fossils that were found within the ice and in the surrounding frozen ground provide age control spanning from more than 50 to 24 thousand years ago when the ice wedges grew. The coldest winter conditions are inferred from a New Siberian Island ice‐wedge site as indicated by the lowest stable isotope values of all our sampled ice wedges at times, corresponding to the last Glacial maximum around 25 thousand years ago., Key Points: Pronounced west Beringian MIS 3 to MIS 2 winter cooling delineated in wedge‐ice stable isotope signatures. Coldest winters reflected by exceptionally depleted values of −37.4 ± 0.4‰ in δ18O and −292 ± 3‰ in δD in LGM wedge ice. LGM wedge ice directly radiocarbon‐dated to 25,890 and 23,980 yr b2k., Deutsche Forschungsgemeinschaft (DFG) http://dx.doi.org/10.13039/501100001659, German Federal Ministry of Education and Research

Global warming is drawing keen attention to people all over the people. Especially, the history of climate in permafrost area is of great interest to better understand greenhouse gas emission due to the thaw of permafrost in the future. In this context, formation of ice wedges and greenhouse gas was studied based on gas chemistry in permafrost ice wedges. The study areas are Batagay and Zyryanka in northeastern Siberia, and North Slope in Alaska. The gas was extracted using a dry extraction method that physically breaks down ice, and cryogenically collects gas in a stainless steel tube. The gas mixing ratios were analyzed by gas chromatography. N2 and Ar occluded in the air bubbles in the ice are relatively unaffected by microbial activity, but if liquid water contacted atmospheric air and froze, the N2/Ar ratio in the ice will differ from the atmospheric value due to difference in the gas solubility in water. On the other hand, if O2 was consumed by microorganisms in the ice, the concentration of O2 will decrease and consequently the O2/Ar ratio will also decrease. Our results show that the δ(O2/Ar) and δ(N2/Ar) of the ice wedges in Zyryanka and North Slope areas range from -86.5% to -12.2% and from -16.0% to 5.5%, respectively with regard to modern air. The 14C ages of Zyryanka and North Slope samples are 810±30 BP and 1920±30 BP, respectively, corresponding to the late Holocene. Because the late Holocene was a relatively warm period, it may be interpreted that the ice wedges formed predominantly from snow melt water, resulting in the negative values of δ(N2/Ar). This is in contrast with our earlier study on ice wedges in Central Yakutia region (Syrdakh, Cyuie, and Churapcha) (Kim et al., 2019). The Central Yakutian ice wedges formed during the Last Glacial Maximum (LGM) and the δ(N2/Ar) values of ~0% indicates that the ice did not form from snow melting. The δ(O2/Ar) of the Zyryanka and North Slope is much less depleted than that of Central Yakutian (close to -100%). Oxygen consumption by microorganisms in the Central Yakutian ice is more completed probably by the longer time period for the biogeochemical reaction compared to the Zyranka and North Slope ice (>20,000 years vs. < 2,000 years). The ages of Batagay ice wedges range to earlier part of the Late Pleistocene, and may allow us to study longer biogeochemical reactions in ice. The concentrations of CO2, N2O and CH4 in the Batagay ice range 260-71,000 ppm, 0.11-68 ppm and 4.7-130 ppm, respectively. Further geochemical analyses are in progress. Future study will include scrutinizing correlations among the three greenhouse gas concentrations. Our study shows that the gas mixing ratios in ice wedges may hlep us better understand the biogeochemical reactions in the ice and climate conditions when the permafrost formed.

The degradation of ice-rich permafrost deposits has the potential to release large amounts of previously freeze-locked carbon (C) and nitrogen (N) with local implications, such as affecting riverine and near-shore ecosystems, but also global impacts such as the release of greenhouse gases into the atmosphere. Here, we study the rapid erosion of the up to 27.7 m high and 1,660 m long Sobo-Sise yedoma cliff in the Lena River Delta using a remote sensing-based time-series analysis covering 53 years and calculate the mean annual sediment as well as C and N release into the Lena River. We find that the Sobo-Sise yedoma cliff, which exposes ice-rich late Pleistocene to Holocene deposits, had a mean long-term (1965–2018) erosion rate of 9.1 m yr–1with locally and temporally varying rates of up to 22.3 m yr–1. These rates are among the highest measured erosion rates for permafrost coastal and river shoreline stretches. The fluvio-thermal erosion led to the release of substantial amounts of C (soil organic carbon and dissolved organic carbon) and N to the river system. On average, currently at least 5.2 × 106kg organic C and 0.4 × 106kg N were eroded annually (2015–2018) into the Lena River. The observed sediment and organic matter erosion was persistent over the observation period also due to the specific configuration of river flow direction and cliff shore orientation. Our observations highlight the importance to further study rapid fluvio-thermal erosion processes in the permafrost region, also because our study shows increasing erosion rates at Sobo-Sise Cliff in the most recent investigated time periods. The organic C and N transport from land to river and eventually to the Arctic Ocean from this and similar settings may have severe implications on the biogeochemistry and ecology of the near-shore zone of the Laptev Sea as well as for turnover and rapid release of old C and N to the atmosphere.

The present study examines the formation history and cryolithological properties of late Pleistocene Yedoma Ice Complex (IC) and its Holocene cover in the eastern Lena Delta on Sobo-Sise Island. The sedimentary sequence was continuously sampled in 0.5 m resolution at a vertical Yedoma cliff starting from 24.2 m above rivel level (arl). The sequence differentiates into three cryostratigraphic units; unit A: dated from ca. 52 to 28 cal ka BP; unit B: dated from ca. 28 to 15 cal ka BP; unit C: dated from ca. 7 to 0 cal ka BP. Three chronologic gaps in the record are striking. The hiatus during the interstadial MIS 3 (36–29 cal ka BP) as well as during stadial MIS 2 (20–17 cal ka BP) might be related to fluvial erosion and/or changed discharge patterns of the Lena River caused by repeated outburst floods from the glacial Lake Vitim in Southern Siberia along the Lena River valley towards the Arctic Ocean. The hiatus during the MIS 2-1 transition (15–7 cal ka BP) is a commonly observed feature in permafrost chronologies due to intense thermokarst activity of the deglacial period. The chronologic gaps of the Sobo-Sise Yedoma record are similarly found at two neighbouring Yedoma IC sites on Bykovsky Peninsula and Kurungnakh-Sise Island, and most likely of regional importance. The three cryostratigraphic units of the Sobo-Sise Yedoma exhibit distinct signatures in properties of their clastic, organic and ice components. Higher permafrost aggradation rates of 1 m ka-1 with higher organic matter (OM) stocks (29±15 kg C m-3, 2.2±1.0 kg N m-3) and mainly coarse silt are found for the interstadial MIS 3 unit A if compared to the stadial MIS 2 unit B with 0.7 m ka-1 permafrost aggradation, lower OM stocks (14±8 kg C m-3, 1.4±0.4 kg N m-3 in unit B) and pronounced peaks in the coarse silt and medium sand fractions. Geochemical signatures of intrasedimental ice reflect the differences in summer evaporation and moisture regime by higher ion contents and less depleted stable δ18O and δD isotope ratios but lower deuterium excess (d) values during interstadial MIS 3 if compared to stadial MIS 2. The δ18O and δD composition of MIS 3 and MIS 2 ice wedges shows characteristic well-depleted values and low d values, while MIS 1 ice wedges have elevated mean d values between 11‰ and 15‰ and surprisingly low δ18O and δD values. Hence, the isotopic difference between late Pleistocene and Holocene ice wedges is more pronounced in d than in δ values. The present study of the permafrost exposed at the Sobo-Sise Yedoma cliff provides a comprehensive cryostratigraphic inventory, insights into permafrost aggradation and degradation over the last about 52 thousand years, and their climatic and morphodynamic controls on the regional scale of the Central Laptev Sea coastal region in NE Siberia.

The most massive and fast-eroding thaw slump of the Northern Hemisphere located in the Yana uplands of northern Yakutia was investigated to assess in detail the cryogenic inventory and carbon pools of two distinctive Ice Complex stratigraphic units and the uppermost cover deposits. Differentiating into modern and Holocene near-surface layers (active layer and shielding layer), highest total carbon contents were found in the active layer (18.7 kg m-2), while the shielding layer yielded much lower carbon content of 1.8 kg m-2. The late Pleistocene upper Ice Complex contained 10.4 kg m-2 total carbon, and the mid-Pleistocene lower Ice Complex 17.7 kg m-2. The proportion of organic carbon from total carbon content is well above 70% in all studied units with 94 % in the active layer, 73% in the shielding layer, 83% in the upper Ice Complex and 79% in the lower Ice Complex. Inorganic carbon is low in the overall structure of the deposits.

Funding: National Science Foundation grants 1925417, 1023672, and 0909541 to J.R.M., and 1824770 to J.G.M. and F.M.L. funded this research, as well as support to A.I.W. and J.R.M. from the John Fell Oxford University Press (OUP) Research Fund and All Souls College, Oxford. Clare Hall, Cambridge provided additional support to J.R.M. through the Sir Nicholas Shackleton fellowship. F.M.L. also acknowledges support from an Irish Research Council Laureate Award (CLICAB project, IRCLA/2017/303). Swiss National Science Foundation grant 18001 funded C.C.R. and W.M.K. European Research Council grant 820047 under the European Union’s Horizon 2020 research and innovation programme supported M.S. A.B. was supported by Marie Curie Career Integration Grant CIG14-631752. The assassination of Julius Caesar in 44 BCE triggered a power struggle that ultimately ended the Roman Republic and, eventually, the Ptolemaic Kingdom, leading to the rise of the Roman Empire. Climate proxies and written documents indicate that this struggle occurred during a period of unusually inclement weather, famine, and disease in the Mediterranean region; historians have previously speculated that a large volcanic eruption of unknown origin was the most likely cause. Here we show using well-dated volcanic fallout records in six Arctic ice cores that one of the largest volcanic eruptions of the past 2,500 y occurred in early 43 BCE, with distinct geochemistry of tephra deposited during the event identifying the Okmok volcano in Alaska as the source. Climate proxy records show that 43 and 42 BCE were among the coldest years of recent millennia in the Northern Hemisphere at the start of one of the coldest decades. Earth system modeling suggests that radiative forcing from this massive, high-latitude eruption led to pronounced changes in hydroclimate, including seasonal temperatures in specific Mediterranean regions as much as 7 °C below normal during the 2 y period following the eruption and unusually wet conditions. While it is difficult to establish direct causal linkages to thinly documented historical events, the wet and very cold conditions from this massive eruption on the opposite side of Earth probably resulted in crop failures, famine, and disease, exacerbating social unrest and contributing to political realignments throughout the Mediterranean region at this critical juncture of Western civilization. Postprint

In the last decades, changing climate conditions have had a severe impact on sea ice at the Western Antarctic Peninsula (WAP), an area rapidly transforming under global warming. To study the development of spring sea ice and environmental conditions in the pre-satellite era we investigated three short marine sediment cores for their biomarker inventory with particular focus on the sea ice proxy IPSO25 and micropaleontological proxies. The core sites in the Bransfield Strait are located in shelf to deep basin areas characterized by a complex oceanographic frontal system, coastal influence and sensitivity to large-scale atmospheric circulation patterns. We analyzed geochemical bulk parameters, biomarkers (highly branched isoprenoids, glycerol dialkyl glycerol tetraethers, sterols), and diatom abundances and diversity over the past 200 years (210Pb dating), and compared them to observational data, sedimentary and ice core climate archives as well as results from numerical models. Based on biomarkers we could identify four different stratigraphic units with (1) stable conditions and moderate sea ice cover before 1860, (2) low to moderate sea ice cover between 1860 and 1930, (3) high seasonal variability and changes in sea ice regimes from 1930 to 1990 and (4) a shift to increasing sea ice cover despite anthropogenic warming since 1990. Although IPSO25 concentrations correspond quite well with satellite sea ice observations for the past 40 years, we note discrepancies between the biomarker-based sea ice estimates and the long-term model output for the past 200 years, ice core records and reconstructed atmospheric circulation patterns such as El Niño Southern Oscillation (ENSO) and Southern Annular Mode (SAM). We propose that the sea ice biomarker proxies IPSO25 and PIPSO25 are not linearly related to sea ice cover and, additionally, each core site reflects specific, local environmental conditions. High IPSO25 and PIPSO25 values may not be directly interpreted as referring to high spring sea ice cover because variable sea ice conditions and enhanced nutrient supply may affect the production of both the sea-ice associated and phytoplankton-derived (open marine, pelagic) biomarker lipids. For a more meaningful interpretation we recommend to carefully consider individually biomarker records to distinguish between cold, sea ice favoring and warm, sea ice diminishing environmental conditions.

Dating of ancient permafrost is essential for understanding permafrost stability and interpreting past climate and environmental conditions over Pleistocene timescales but faces substantial challenges to geochronology.Here, we date permafrost from the world’s largest retrogressive thaw slump at Batagay in the Yana Upland, East Siberia (67.58 °N, 134.77 °E). The slump headwall exposes four generations of ice and sand-ice (composite) wedges that formed synchronously with permafrost aggradation. The stratigraphy differentiates into a Lower Ice Complex (IC) overlain by a Lower Sand Unit, an Upper IC and an Upper Sand Unit. Two woody beds below and above the Lower Sand Unit represent the remains of two episodes of taiga forest development prior to the Holocene forest. Thus, the ancient permafrost at Batagay potentially provides one of the longest terrestrial records of Pleistocene environments in western Beringia.We apply four dating methods to the permafrost deposits to disentangle the chronology of the Batagay permafrost archive – optically-stimulated luminescence (OSL) dating of quartz and post-infrared-stimulated luminescence (pIR-IRSL) dating of feldspar as well as accelerator mass spectrometry-based Cl-36/Cl dating of wedge ice and radiocarbon dating of organic material.The age information obtained so far indicates that the Batagay permafrost sequence is discontinuous and that the Lower IC developed well before MIS 7, the overlying Lower Sand Unit formed during MIS 6, and the Upper IC and the Upper Sand Unit formed both during MIS 3-2.Additional sampling for all dating approaches presented here took place in spring 2019, and is part of ongoing research to enhance the geochronology of the exceptional palaeoenvironmental archive of the Batagay megaslump.

In recent years, permafrost ground ice (i.e. ice wedges and pore ice) has been frequently utilized as a paleoclimate archive for the Late Pleistocene and Holocene, mainly using stable isotopes from water as proxies for local air temperatures. Due to their formation processes (frost cracking in winter and crack infilling mainly with snowmelt in spring), ice wedges have a unique winter seasonality, whereas pore ice integrates summer or annual precipitation.The world’s largest retrogressive thaw slump at Batagay in the Yana Upland, East Siberia (67.58 °N, 134.77 °E), provides unique access to Late and Middle Pleistocene permafrost formations usually deeply buried in the frozen ground. The Batagay megaslump exposes syngenetic ice wedges and composite wedges (ice–sand wedges) along with pore ice in four cryostratigraphic units: (1) the Lower Ice Complex, (2) the Lower Sand, (3) the Upper Ice Complex, and (4) the Upper Sand.Here, we present ground-ice stable-isotope data from all four units. This dataset is accompanied by precipitation stable-isotope values from winter snowpack and summer rain as a first stable-isotope framework for this region.The high continentality of the study region with – extremely low winter temperatures – is clearly reflected by the stable-isotope composition for ice wedges from the Upper Ice Complex (MIS 3) and nearby Holocene ice wedges. Both are much more depleted than for any other ice-wedge study site in East Siberia. The ice wedges from the Lower Ice Complex are likely the oldest ice wedges (>0.5 Ma) ever analyzed isotopically and also point to very cold winter climate during formation. Stable-isotope signatures of composite wedges and pore ice are less distinctive and require detailed studies of formation processes and seasonality.

Antarctica is well known to be highly susceptible to atmospheric and oceanic warming. However, due to the lack of long-term and in situ meteorological observations, little is known about the magnitude of the warming and the meteorological conditions in the intersection region between the Antarctic Peninsula (AP), the West Antarctic Ice Sheet (WAIS) and the East Antarctic Ice Sheet (EAIS). Here we present new stable water isotope data (δ18O, δD, d excess) and accumulation rates from firn cores in the Union Glacier (UG) region, located in the Ellsworth Mountains at the northern edge of the WAIS. The firn core stable oxygen isotopes and the d excess exhibit no statistically significant trend for the period 1980–2014, suggesting that regional changes in near-surface air temperature and moisture source variability have been small during the last 35 years. Backward trajectory modelling revealed the Weddell Sea sector, Coats Land and Dronning Maud Land (DML) to be the main moisture source regions for the study site throughout the year. We found that mean annual δ18O (δD) values in the UG region are negatively correlated with sea ice concentrations (SICs) in the northern Weddell Sea but not influenced by large-scale modes of climate variability such as the Southern Annular Mode (SAM) and the El Niño–Southern Oscillation (ENSO). Only mean annual d-excess values show a weak positive correlation with the SAM. On average annual snow accumulation in the UG region amounts to 0.245 m w.e. a−1 in 1980–2014 and has slightly decreased during this period. It is only weakly related to sea ice conditions in the Weddell Sea sector and not correlated with SAM and ENSO. We conclude that neither the rapid warming nor the large increases in snow accumulation observed on the AP and in West Antarctica during the last decades have extended inland to the Ellsworth Mountains. Hence, the UG region, although located at the northern edge of the WAIS and relatively close to the AP, exhibits rather stable climate characteristics similar to those observed in East Antarctica.

Late Pleistocene and Holocene ground ice are common throughout the Arctic. Some forms of relict ground ice preserve local meteoric water, and their stable oxygen‐ and hydrogen‐isotope ratios can be used to reconstruct past air temperatures. In this paper, we review the formation and sampling of two forms of relict ground ice—wedge ice and pore ice—and recent (2010–2019) advances in paleoclimatological studies of ground‐ice stable isotope records in the Arctic. Recent advances are attributed to better chronological constraints and refined understandings of the systematics and seasonality of relict wedge ice and pore ice. A rich network of ice‐wedge records has emerged, primarily from the Siberian Arctic, whereas pore‐ice records are less common. The ice‐wedge network depicts a robust pattern of late Pleistocene cooling, and remarkably similar temperature depressions during Marine Isotope Stages 3 and 2. Very high‐resolution wedge‐ and pore‐ice stable isotope chronologies have been established recently and used to reconstruct winter and summer climate histories and to assess seasonal dependencies in insolation‐forced climate. Reports of ancient (>125 ka BP) ground ice demonstrate its long‐term persistence, and its potential to expand our knowledge of Quaternary climate dynamics in the terrestrial Arctic.

Ground ice and sedimentary records of a pingo exposure reveal insights into Holocene permafrost, landscape and climate dynamics. Early to mid-Holocene thermokarst lake deposits contain rich floral and faunal paleoassemblages, which indicate lake shrinkage and decreasing summer temperatures (chironomid-based T-July) from 10.5 to 3.5 cal kyr BP with the warmest period between 10.5 and 8 cal kyr BP. Talik refreezing and pingo growth started about 3.5 cal kyr BP after disappearance of the lake. The isotopic composition of the pingo ice (delta O-18 - 17.1 +/- 0.6 parts per thousand, delta D -144.5 +/- 3.4 parts per thousand, slope 5.85, deuterium excess -7.7 +/- 1.5 parts per thousand) point to the initial stage of closed-system freezing captured in the record. A differing isotopic composition within the massive ice body was found (delta O-18 - 21.3 +/- 1.4 parts per thousand, delta D -165 +/- 11.5 parts per thousand, slope 8.13, deuterium excess 4.9 +/- 3.2 parts per thousand), probably related to the infill of dilation cracks by surface water with quasi-meteoric signature. Currently inactive syngenetic ice wedges formed in the thermokarst basin after lake drainage. The pingo preserves traces of permafrost response to climate variations in terms of ground-ice degradation (thermokarst) during the early and mid-Holocene, and aggradation (wedge-ice and pingo-ice growth) during the late Holocene.

Arctic climate has experienced major changes over the past millennia that are not fully understood in terms of their controls and seasonality. Stable isotope data from ice wedges in permafrost provide unique information on past winter climate. Recently, an ice-wedge record from the Lena River Delta suggested for the first time that Siberian winter temperatures increased throughout the Holocene, contradicting most other Arctic palaeoclimate reconstructions which are likely biased towards the summer. However, the representativeness of this single record and the spatial extent of its reconstructed winter warming signal is unclear. Here, we present a new winter temperature record based on paired stable oxygen (δ18O) and radiocarbon age data spanning the last two millennia from the Oyogos Yar coast in northeast Siberia. The record confirms the long-term winter warming signal as well as the unprecedented temperature rise in recent decades. This confirmation demonstrates that winter warming over the last millennia is a coherent feature in the northeastern Siberian Arctic, supporting the hypothesis of an insolation-driven seasonal Holocene temperature evolution followed by a strong warming likely related to anthropogenic forcing.

Holocene permafrost from ice wedge polygons in the vicinity of large seabird breeding colonies in the Thule District, NW Greenland, was drilled to explore the relation between permafrost aggradation and seabird presence. The latter is reliant on the presence of the North Water Polynya (NOW) in the northern Baffin Bay. The onset of peat accumulation associated with the arrival of little auks (Alle alle) in a breeding colony at Annikitisoq, north of Cape York, is radiocarbon-dated to 4400 cal BP. A thick-billed murre (Uria lomvia) colony on Appat (Saunders Island) in the mouth of the Wolstenholme Fjord started 5650 cal BP. Both species provide marine-derived nutrients (MDNs) that fertilize vegetation and promote peat growth. The geochemical signature of organic matter left by the birds is traceable in the frozen Holocene peat. The peat accumulation rates at both sites are highest after the onset, decrease over time, and were about 2-times faster at the little auk site than at the thick-billed murre site. High accumulation rates induce shorter periods of organic matter (OM) decomposition before it enters the perennially frozen state. This is seen in comparably high C∕N ratios and less depleted δ13C, pointing to a lower degree of OM decomposition at the little auk site, while the opposite pattern can be discerned at the thick-billed murre site. Peat accumulation rates correspond to δ15N trends, where decreasing accumulation led to increasing depletion in δ15N as seen in the little-auk-related data. In contrast, the more decomposed OM of the thick-billed murre site shows almost stable δ15N. Late Holocene wedge ice fed by cold season precipitation was studied at the little auk site and provides the first stable-water isotopic record from Greenland with mean δ18O of -18.0±0.8 ‰, mean δD of -136.2±5.7 ‰, mean d excess of 7.7±0.7 ‰, and a δ18O-δD slope of 7.27, which is close to those of the modern Thule meteoric water line. The syngenetic ice wedge polygon development is mirrored in testacean records of the little auk site and delineates polygon low-center, dry-out, and polygon-high-center stages. The syngenetic permafrost formation directly depending on peat growth (controlled by bird activity) falls within the period of neoglacial cooling and the establishment of the NOW, thus indirectly following the Holocene climate trends.

Lead pollution in Arctic ice reflects large-scale historical changes in midlatitude industrial activities such as ancient lead/silver production and recent fossil fuel burning. Here we used measurements in a broad array of 13 accurately dated ice cores from Greenland and Severnaya Zemlya to document spatial and temporal changes in Arctic lead pollution from 200 BCE to 2010 CE, with interpretation focused on 500 to 2010 CE. Atmospheric transport modeling indicates that Arctic lead pollution was primarily from European emissions before the 19th-century Industrial Revolution. Temporal variability was surprisingly similar across the large swath of the Arctic represented by the array, with 250- to 300-fold increases in lead pollution observed from the Early Middle Ages to the 1970s industrial peak. Superimposed on these exponential changes were pronounced, multiannual to multidecadal variations, marked by increases coincident with exploitation of new mining regions, improved technologies, and periods of economic prosperity; and decreases coincident with climate disruptions, famines, major wars, and plagues. Results suggest substantial overall growth in lead/silver mining and smelting emissions—and so silver production—from the Early through High Middle Ages, particularly in northern Europe, with lower growth during the Late Middle Ages into the Early Modern Period. Near the end of the second plague pandemic (1348 to ∼1700 CE), lead pollution increased sharply through the Industrial Revolution. North American and European pollution abatement policies have reduced Arctic lead pollution by >80% since the 1970s, but recent levels remain ∼60-fold higher than at the start of the Middle Ages.

A major research focus of the DREsden Accelerator Mass Spectrometry (DREAMS) facility is sample preparation: in-house and at cooperating laboratories. Besides routine applications, developments are mainly driven by the users' demands such as "new" radionuclides (e.g. short-lived 7Be), radionuclides from new matrices or in larger sample amounts and at lower concentrations. Within the chemical preparation of BeO for 7,10Be, Al2O3 for 26Al, AgCl for 36Cl, and Fe2O3 for 60Fe and actinide AMS targets, we investigated and improved mostly particular steps: For oxide preparation alteration for several hours and two-times rinsing of hydroxides is recommended, especially for Be(OH)2 and Al(OH)3, to prevent losses in the final preparation steps. Rinsing of freshly precipitated hydroxides can yield to losses as high as 31%. For Al(OH)3 rinsing with H2O (pH5) instead of pH8-9 is recommended for further reducing redissolving. For 60Fe and coprecipitated actinides (the latter tested by U6+ and Er3+), rinsing of overnight-altered Fe(OH)3, yield to 2.6-3.5% losses. The depletion of the isobar 7Li for (7)BeO is easily gained by hydroxide precipitation and rinsing. The quality of BeO and Al2O3 AMS targets can be monitored and improved (e.g. by using larger ion exchanger columns) by using the so-called "quality factor", which is the current of the stable nuclide (9Be or 27Al), normalised to the current of the standard of the same batch. Finally, there is a high potential for ion exchange as a pre-enrichment tool for Cl for large ice samples containing low natCl concentrations and low absolute amounts of natCl.

Late Quaternary landscapes of unglaciated Beringia were largely shaped by ice-wedge polygon tundra. Ice Complex (IC) strata preserve such ancient polygon formations. Here we report on the Yukagir IC from Bol'shoy Lyakhovsky Island in northeastern Siberia and suggest that new radioisotope disequilibria (230Th/U) dates of the Yukagir IC peat confirm its formation during the Marine Oxygen Isotope Stage (MIS) 7a–c interglacial period. The preservation of the ice-rich Yukagir IC proves its resilience to last interglacial and late glacial–Holocene warming. This study compares the Yukagir IC to IC strata of MIS 5, MIS 3, and MIS 2 ages exposed on Bol'shoy Lyakhovsky Island. Besides high intrasedimental ice content and syngenetic ice wedges intersecting silts, sandy silts, the Yukagir IC is characterized by high organic matter (OM) accumulation and low OM decomposition of a distinctive Drepanocladus moss-peat. The Yukagir IC pollen data reveal grass-shrub-moss tundra indicating rather wet summer conditions similar to modern ones. The stable isotope composition of Yukagir IC wedge ice is similar to those of the MIS 5 and MIS 3 ICs pointing to similar atmospheric moisture generation and transport patterns in winter. IC data from glacial and interglacial periods provide insights into permafrost and climate dynamics since about 200 ka.

The role of sea ice in the Earth climate system is still under debate, although it is known to influence albedo, ocean circulation, and atmosphere-ocean heat and gas exchange. Here we present a reconstruction of 1950 to 1998 AD sea ice in the Laptev Sea based on the Akademii Nauk ice core (Severnaya Zemlya, Russian Arctic). The chemistry of halogens bromine (Br) and iodine (I) is strongly active and influenced by sea ice dynamics, in terms of physical, chemical and biological process. Bromine reacts on the sea ice surface in autocatalyzing >bromine explosion> events, causing an enrichment of the Br/Na ratio and hence a bromine excess (Br) in snow compared to that in seawater. Iodine is suggested to be emitted from algal communities growing under sea ice. The results suggest a connection between Brexc and spring sea ice area, as well as a connection between iodine concentration and summer sea ice area. The correlation coefficients obtained between Br and spring sea ice (r = 0.44) as well as between iodine and summer sea ice (r = 0.50) for the Laptev Sea suggest that these two halogens could become good candidates for extended reconstructions of past sea ice changes in the Arctic., This study contributes to the Eurasian Arctic Ice 4k project and was supported by the Deutsche Forschungs- gemeinschaft (grant OP 217/2-1 awarded to Thomas Opel). The drilling project on the Akademii Nauk ice cap was funded by the German Ministry of Education and Research (BMBF research project 03PL 027A). Analysis and interpretation of the Akademii Nauk ice core at the Desert Research Institute was funded by US National Science Foundation grant 1023672. The research leading to these results received funding from the European Research Council under the European Community’s Seventh Framework Programme (FP7/2007–2013)/ERC grant agreement no. 610055. We thank the University of Bremen, supported by the State of Bremen; the German Aerospace Center, DLR; and the European Space Agency for the satellite BrO imagines. Opel)

Ice wedges in the Yana Highlands of interior Yakutia – the most continental region of the Northern Hemisphere – were investigated to elucidate the winter climate and continentality during the Middle to Late Pleistocene. The Batagay megaslump exposes ice wedges and composite wedges that were sampled from three cryostratigraphic units: the lower sand unit of Marine Isotope Stage (MIS) 6 age, the upper Ice Complex (Yedoma) and the upper sand unit (both MIS3 to MIS2). A terrace of the nearby Adycha River provides a Late Holocene (MIS1) ice wedge that serves as a modern endmember for analysis. Stable-isotope values of ice wedges in the MIS3 upper Yedoma Ice Complex at Batagay are more depleted (mean δ18O about −35 ‰) than those from 17 other ice-wedge sites across coastal and central Yakutia. This observation points to lower winter temperatures and, therefore, higher continentality in the Yana Highlands during MIS3. Likewise, more depleted isotope values compared to other sites in Yakutia are found in Holocene wedge ice (mean δ18O about −29 ‰). Ice-wedge isotopic signatures of the MIS6 lower sand unit (mean δ18O about −33 ‰) and of the MIS3-2 upper sand unit (mean δ18O from about −33 to −30 ‰) are less distinctive regionally and preserve traces of fast formation in rapidly accumulating sand sheets and of post-depositional fractionation.

West Antarctica is well-known as a region that is highly susceptible to atmospheric and oceanic warming. However, due to the lack of long–term and in–situ meteorological observations little is known about the magnitude of the warming and the meteorological conditions in the region at the intersection between the Antarctic Peninsula (AP), the West Antarctic Ice Sheet (WAIS) and the East Antarctic Ice Sheet (EAIS). Here we present new stable water isotope data (δ18O, δD, d excess) and accumulation rates from firn cores in the Union Glacier (UG) region, located in the Ellsworth Mountains at the northern edge of the WAIS. The firn core stable oxygen isotope composition reveals no statistically significant trend for the period 1980–2014 suggesting that regional changes in near-surface air temperature have been small during the last 35 years. As for stable oxygen isotopes no statistically significant trend has been found for the d excess suggesting overall little change in the main moisture sources and the origin of precipitating air masses for the UG region at least since 1980. Backward trajectory modelling revealed the Weddell Sea sector to be the likely main moisture source region for the study site throughout the year. We found that mean annual δ–values in the UG region are correlated with sea ice concentrations in the northern Weddell Sea, but are not strongly influenced by large-scale modes of climate variability such as the Southern Annular Mode (SAM) and the El Niño–Southern Oscillation (ENSO). Only mean annual d excess values are weakly positively correlated with the SAM. On average snow accumulation in the UG region amounts to about 0.25 m w.eq. a−1 between 1980 and 2014. Mean annual snow accumulation has slightly decreased since 1980 (−0.001 m w.eq. a−1, p–value = 0.006). However, snow accumulation at UG is neither correlated with sea ice nor with SAM and ENSO confirming that the large increases in snow accumulation observed on the AP and in other coastal regions of Antarctica have not extended inland to the Ellsworth Mountains. We conclude that the UG region – located in the transition zone between the AP, the WAIS and the EAIS – is exhibiting rather East than West Antarctic climate characteristics.