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Perchlorate in the environment originates from both natural and anthropogenic sources. A previous study of a 300‐year Greenland ice core perchlorate record found that anthropogenic impact on environmental perchlorate became significant starting around 1980, while natural formation is the only significant source of environmental perchlorate prior to that. The study also found increased perchlorate deposition in the Arctic following certain volcanic eruptions and suggested that at least some volcanic eruptions could enhance natural perchlorate production. Here we compare the perchlorate record with the volcanic record from sulfate in the same Greenland ice core and find that only stratospheric eruptions—large eruptions injecting volcanic substances directly into the stratosphere—enhance perchlorate production. No contribution to naturally formed perchlorate is detected from non‐stratospheric eruptions. The high‐resolution ice core perchlorate data are used to quantify contributions from volcanic eruptions, non‐volcanic natural processes, as well as from human activities during different periods. For the location in the Arctic in the perchlorate Pre‐Anthropogenic Era (1701–1979), the magnitude (0.26 μg m−2 yr−1 on average) of perchlorate produced during sporadic stratospheric eruptions is comparable to that (0.23 μg m−2 yr−1) produced by non‐volcanic natural processes. In the Anthropogenic Era (1980–2006), the magnitude of both the volcanic and non‐volcanic natural perchlorate production is similar to the enhancement (0.29 μg m−2 yr−1) by human activities. Plain Language Summary: Perchlorate is widespread in the environment. In remote regions such as the Arctic, environmental perchlorate primarily comes from natural formation in the atmosphere from common‐place chemicals containing chlorine. Previously, we studied a 300‐year chronological perchlorate record from a Greenland ice core and found that, prior to 1980, perchlorate production was not affected by human activities. We also found that certain volcanic eruptions may increase the amount of perchlorate produced in the atmosphere and deposited in Greenland snow. In this study, we use the ice‐core perchlorate and sulfate data to determine that only very large eruptions can cause additional perchlorate to be formed in the atmosphere. On average, large volcanic eruptions contribute about 50% of perchlorate from all natural sources at this location in the Arctic. Since 1980, human activities have contributed approximately the same amount of perchlorate to the environment as that from all natural sources. Key Points: Atmospheric perchlorate formation is enhanced by only stratospheric volcanic eruptions, not by non‐stratospheric eruptionsVolcanic perchlorate in the Arctic is on average approximately 50% of all naturally produced perchlorate prior to 1980Contribution from anthropogenic activities since 1980 is approximately equal to that from natural perchlorate sources [ABSTRACT FROM AUTHOR]

Tropospheric reactive bromine (Bry) influences the oxidation capacity of the atmosphere by acting as a sink for ozone and nitrogen oxides. Aerosol acidity plays a crucial role in Bry abundances through acid‐catalyzed debromination from sea‐salt‐aerosol, the largest global source. Bromine concentrations in a Russian Arctic ice‐core, Akademii Nauk, show a 3.5‐fold increase from pre‐industrial (PI) to the 1970s (peak acidity, PA), and decreased by half to 1999 (present day, PD). Ice‐core acidity mirrors this trend, showing robust correlation with bromine, especially after 1940 (r = 0.9). Model simulations considering anthropogenic emission changes alone show that atmospheric acidity is the main driver of Bry changes, consistent with the observed relationship between acidity and bromine. The influence of atmospheric acidity on Bry should be considered in interpretation of ice‐core bromine trends. Plain Language Summary: Reactive bromine in the air impacts major oxidants in our atmosphere, which remove pollutants and greenhouse gases and has changed over time in the Russian Arctic. Ice‐core bromine and acidity show a significant increase from pre‐industrial to the 1970s followed by a decrease. Our study suggests that human activities caused changes in bromine through the emissions of acidic gases from fossil fuel combustion. Considering relationships between atmospheric acidity and bromine is crucial to interpreting bromine variations in ice cores. Key Points: Bromine (Br) concentrations increased 3.5‐fold from pre‐industrial to 1975 and declined 50% by 1999 in a Russian Arctic ice‐coreA robust correlation between ice‐core Br and acidity highlights acidity's key role in influencing the atmospheric Br budgetModel shows acid‐catalyzed sea‐salt debromination is the largest source of reactive Br and drives ice‐core Br trends [ABSTRACT FROM AUTHOR]

Variations in Arctic sea ice are apparent not only in its extent and thickness but also in its internal properties under global warming. The microstructure of summer Arctic sea ice changes due to varying external forces, ice age, and extended melting seasons, which affect its optical properties. Sea ice cores sampled in the Pacific sector of the Arctic obtained by the Chinese National Arctic Research Expedition (CHINARE) during the summers of 2008 to 2016 were used to estimate the variations in the microstructures and inherent optical properties (IOPs) of ice and determine the radiation budget of sea ice based on a radiative transfer model. The variations in the volume fraction of gas bubbles (Va) of the ice top layer were not significant, and the Va of the ice interior layer was significant. Compared with 2008, the mean Va of interior ice in 2016 decreased by 9.1 %. Meanwhile, the volume fraction of brine pockets increased clearly during 2008–2016. The changing microstructure resulted in the scattering coefficient of the interior ice decreasing by 38.4 % from 2008 to 2016, while no clear variations can be seen in the scattering coefficient of the ice top layer. These estimated ice IOPs fell within the range of other observations. Furthermore, we found that variations in interior ice were significantly related to the interannual changes in ice ages. At the Arctic basin scale, the changing IOPs of interior ice greatly changed the amount of solar radiation transmitted to the upper ocean even when a constant ice thickness is assumed, especially for thin ice in marginal zones, implying the presence of different sea ice bottom melt processes. These findings revealed the important role of the changing microstructure and IOPs of ice in affecting the radiation transfer of Arctic sea ice. [ABSTRACT FROM AUTHOR]

Snowpack emissions are recognized as an important source of gas‐phase reactive bromine in the Arctic and are necessary to explain ozone depletion events in spring caused by the catalytic destruction of ozone by halogen radicals. Quantifying bromine emissions from snowpack is essential for interpretation of ice‐core bromine. We present ice‐core bromine records since the pre‐industrial (1750 CE) from six Arctic locations and examine potential post‐depositional loss of snowpack bromine using a global chemical transport model. Trend analysis of the ice‐core records shows that only the high‐latitude coastal Akademii Nauk (AN) ice core from the Russian Arctic preserves significant trends since pre‐industrial times that are consistent with trends in sea ice extent and anthropogenic emissions from source regions. Model simulations suggest that recycling of reactive bromine on the snow skin layer (top 1 mm) results in 9–17% loss of deposited bromine across all six ice‐core locations. Reactive bromine production from below the snow skin layer and within the snow photic zone is potentially more important, but the magnitude of this source is uncertain. Model simulations suggest that the AN core is most likely to preserve an atmospheric signal compared to five Greenland ice cores due to its high latitude location combined with a relatively high snow accumulation rate. Understanding the sources and amount of photochemically reactive snow bromide in the snow photic zone throughout the sunlit period in the high Arctic is essential for interpreting ice‐core bromine, and warrants further lab studies and field observations at inland locations. Plain Language Summary: Bromine is a reactive chemical species emitted from natural and anthropogenic sources and can be reemitted from Arctic snowpack after its deposition on snow. This leads to ozone depletion and alters the record of bromine preserved in ice cores. Here, we studied ice‐core records of bromine from six Arctic locations to quantify the extent of bromine loss from the snowpack since the pre‐industrial era. We found that only one location had significant trends of bromine over time, consistent with trends in bromine sources from both nature and human activities. An atmospheric model including chemical reaction processes suggested that this Russian Arctic location favored preservation of bromine compared to the five Greenland ice cores. Understanding bromine preservation in Arctic snow and ice is important for interpreting ice‐core records. Key Points: Ice‐core and model analysis suggest that the Russian Arctic Akademii Nauk ice core preserves atmospheric bromine signals since preindustrialBromine loss from snow is potentially significant in inland Greenland and should be considered when interpreting ice core bromine records [ABSTRACT FROM AUTHOR]

Arctic warming has accelerated surface melting even in the highland areas of the Greenland ice sheet (GrIS). Understanding the relationship between climate and surface melting is essential for improving the estimates of ice‐sheet mass loss due to warming. Here we analyze a 250 m‐long ice core from the southeastern dome of GrIS (SE‐Dome site; 67°19′17″ N, 36°47′03″ W, 3,161 m a.s.l.), where the annual mean temperature is −20.9°C and the accumulation rate is high and there is a large discrepancy among climate models regarding snow accumulation estimates. A time scale was established for 1799–2020 with a half‐year uncertainty using annual counting of H2O2 concentration and five time horizons determined by electrical conductivity, melt events, and tritium concentration. The annual accumulation rate from the ice core shows no significant trend over 221 years and has an average of 1.04 ± 0.20 m w.e. year−1. In contrast, the frequency and thickness of refrozen melt layer (ML) have increased over 221 years, and are synchronized with temperature changes in the Arctic. The thickness of MLs correlates positively with the time‐integrated summer temperature anomaly using a reanalysis of air temperature. The in‐situ accumulation records in the southeastern GrIS provide an important basis for correcting reanalysis data such as ERA5, which in turn are valuable for improving regional climate models. Plain Language Summary: In recent years, Arctic temperatures have been increasing faster than global temperatures. In the inland Greenland ice sheet (GrIS), the surface snow melts on warm days, then the meltwater percolates in the snowpack and refreezes into melt layers (MLs). Here we describe an ice core, collected from the southeastern GrIS, which contains records of precipitation and MLs from 1799 to 2020. We then compare these results with the climatic data. The annual precipitation rate obtained from the ice core shows neither a decrease nor an increase over 221 years, suggesting no significant trend in the southeastern region. On the other hand, with Arctic warming, the ML thickness per year has increased through the 19th–21st centuries. In addition, there is a positive correlation between ML thickness and summer temperature. We conclude that the annual precipitation rate in southeastern GrIS is constant regardless of Arctic warming and the ice core is favorable for reconstructing environmental records from the pre‐industrial era to the present. Key Points: From an ice core in the southeastern Greenland ice sheet, we establish a time scale spanning 1799–2020 with a half‐year uncertaintyOver 221 years, the annual accumulation rate shows no significant trend, while the melt layer thickness has increased with Arctic warmingThe in‐situ accumulation records provide an important basis for correcting reanalysis data, which in turn are valuable for improving models [ABSTRACT FROM AUTHOR]

Geothermal heat flow is an important boundary condition for ice sheet, affecting for example basal melt rates, but for ice covered regions we only have sparse heat flow observations with partly high uncertainty. In this study, we first investigate the agreement between such point-wise heat flow observations and Solid Earth models, applying a 1D steady state approach to perform a statistical analysis for the entire Arctic region. We find that most of the continental heat flow observations have a high reliability and agreement to 5 Solid Earth models, except a few data points, as for example the NGRIP point in Central Greenland. For further testing, we perform a conditional simulation with focus on Greenland, in which the local characteristics of heat flow structures can be considered. Simple kriging shows that including or excluding the less reliable NGRIP point has a large influence on the surrounding heat flow. The geostatistical analysis with the conditional simulation supports the assumption that NGRIP might not only be problematic for representing a regional feature but likely is an outlier. Basal melt estimates show that such a local spot of high heat flow results in local high basal melt rates, but leads to less variation than existing geophysical models. [ABSTRACT FROM AUTHOR]

Investigating North Pacific climate variability during warm intervals prior to the Common Era can improve our understanding of the behavior of ocean–atmosphere teleconnections between low latitudes and the Arctic under future warming scenarios. However, most of the existing ice core records from the Alaskan and Yukon region only allow access to climate information covering the last few centuries. Here we present a surface-to-bedrock age scale for a 210 m long ice core recovered in 2013 from the summit plateau of Begguya (Mt. Hunter; Denali National Park, Central Alaska). Combining dating by annual layer counting with absolute dates from micro-radiocarbon dating, a continuous chronology for the entire ice core archive was established using an ice flow model. Calibrated 14 C ages from the deepest section (209.1 m, 7.7 to 9.0 ka cal BP) indicate that basal ice on Begguya is at least of early Holocene origin. A series of samples from a shallower depth interval (199.8 to 206.6 m) were dated with near-uniform 14 C ages (3 to 5 ka cal BP). Our results suggest this may be related to an increase in annual net snow accumulation rates over this period following the Northern Hemisphere Holocene Climate Optimum (around 8 to 5 kyr BP). With absolute dates constraining the timescale for the last >8 kyr BP, this paleo-archive will allow future investigations of Holocene climate and the regional evolution of spatial and temporal changes in atmospheric circulation and hydroclimate in the North Pacific. [ABSTRACT FROM AUTHOR]

The search for extant microbial life will be a major focus of future astrobiology missions; however, no direct extant life detection instrumentation is included in current missions to Mars. In this study, we developed the semiautomated MicroLife detection platform that collects and processes environmental samples, detects biosignatures, and characterizes microbial activity. This platform is composed of a drill for sample collection, a redox dye colorimetric system for microbial metabolic activity detection and assessment (μMAMA [microfluidics Microbial Activity MicroAssay]), and a MinION sequencer for biosignature detection and characterization of microbial communities. The MicroLife platform was field-tested on White Glacier on Axel Heiberg Island in the Canadian high Arctic, with two extracted ice cores. The μMAMA successfully detected microbial metabolism from the ice cores within 1 day of incubation. The MinION sequencing of the ice cores and the positive μMAMA card identified a microbial community consistent with cold and oligotrophic environments. Furthermore, isolation and identification of microbial isolates from the μMAMA card corroborated the MinION sequencing. Together, these analyses support the MicroLife platform's efficacy in identifying microbes natively present in cryoenvironments and detecting their metabolic activity. Given our MicroLife platform's size and low energy requirements, it could be incorporated into a future landed platform or rovers for life detection. [ABSTRACT FROM AUTHOR]

The Tibetan Plateau is an important area for studying global climate change, but the answers to many scientific problems remain unknown. Here, we present new information from the lacustrine sedimentary record in the western Tibetan Plateau, related to the third most‐recent glaciations. Continuous sediment data, including sporopollen, particle size, total organic carbon, mass susceptibility, CaCO3, CaSO4, BaSO4 contents and chronological data, were reconstructed and revealed that climate and environmental conditions obviously and distinctly changed between 600 and 700 thousand years ago. In comparison, the data obtained from the Guliya ice core in this area also corresponds to the global glacial climatic characteristics recorded in basin sediments in the eastern and southeastern regions of the plateau and to the information obtained from ice cores in the Antarctic and Arctic regions. In this study, we conclude that the main reason for the glaciations and new tectonic movement must be a geomagnetic polarity reversal 774 thousand years ago (from Matuyama to Brunhes). Indeed, the results of this study suggest that the described reversal event might have influenced the current global climate pattern and will continue to impact climatic changes in the future. [ABSTRACT FROM AUTHOR]

The Arctic is warming at almost four times the global rate. An estimated sixty percent of greenhouse‐gas‐induced Arctic warming has been offset by anthropogenic aerosols, but the contribution of aerosols to radiative forcing (RF) represents the largest uncertainty in estimating total RF, largely due to unknown preindustrial aerosol abundance. Here, sulfur isotope measurements in a Greenland ice core show that passive volcanic degassing contributes up to 66 ± 10% of preindustrial ice core sulfate in years without major eruptions. A state‐of‐the‐art model indicates passive volcanic sulfur emissions influencing the Arctic are underestimated by up to a factor of three, possibly because many volcanic inventories do not include hydrogen sulfide emissions. Higher preindustrial volcanic sulfur emissions reduce modeled anthropogenic Arctic aerosol cooling by up to a factor of two (+0.11 to +0.29 W m−2), suggesting that underestimating passive volcanic sulfur emissions has significant implications for anthropogenic‐induced Arctic climate change. Plain Language Summary: Sulfate aerosols are particles in the atmosphere that have a net cooling effect on the climate. One of the most uncertain aspects of climate modeling is the abundance of sulfate aerosols during the preindustrial era. Without knowing the amount of sulfate aerosols during the preindustrial, it is difficult to estimate how much anthropogenic sulfate aerosols have offset warming from anthropogenic greenhouse gases. In this study, we examine preindustrial sulfate aerosols in a Greenland ice core. We find that sulfate aerosols from passive (i.e., non‐eruptive) volcanic degassing contribute almost two thirds of preindustrial Arctic sulfate aerosols in years without major volcanic eruptions. We compare this result to a state‐of‐the‐art global model and find that most climate models use a volcanic emissions inventory that underestimates preindustrial passive volcanic sulfur emissions. That volcanic inventory only includes one type of sulfur emission (sulfur dioxide), but studies have shown that volcanoes emit hydrogen sulfide, which can also form sulfate aerosols. We show that higher emissions of volcanic sulfur during the preindustrial era decrease the estimated cooling effect of anthropogenic aerosols during the industrial era. Thus, the underestimate of preindustrial volcanic emissions in current climate models has significant implications for anthropogenic climate change in the Arctic. Key Points: Sulfur isotopes in a Greenland ice core show that passive volcanic degassing contributes 66% of preindustrial Arctic sulfateThe volcanic inventory used by most climate models underestimates passive degassing, possibly due to missing hydrogen sulfide emissionsElevated preindustrial passive volcanic degassing reduces the estimated cooling effect of anthropogenic sulfate in the Arctic [ABSTRACT FROM AUTHOR]

Hydrogen (δD) and oxygen (δ18O) isotopic ratios are strongly correlated in precipitation over time and space, defining the meteoric water line, and the slope of this δD‐δ18O relationship reflects covariations of deuterium excess (d‐excess) with δD or δ18O. This δD‐δ18O line provides a tool for inferring hydrologic processes from the evaporation source to condensation site. Here, we present δD‐δ18O relationships on seasonal and annual timescales for daily precipitation, snow pits, and a 15‐m ice core (Owen) at Summit, Greenland. Seasonally, precipitation δD‐δ18O slopes are less than 8 (summer = 7.70; winter = 7.77), while the annual slope is greater than 8 (8.27). We suggest that intra‐season slopes result primarily from Rayleigh distillation, which, under prevailing conditions, produces slopes less than 8. The summer line has a greater intercept (higher d‐excess) than the winter line. This separation causes annual slopes to be greater than seasonal ones. We attribute high summer d‐excess primarily to contributions of vapor sublimated from the Greenland Ice Sheet and other terrestrial sources. High sublimated moisture proportions result in a large separation between seasonal δD‐δ18O lines, and thus high annual slopes. Inter‐seasonal weighting of precipitation amount also influences annual slopes because slopes are weighed by the number of storms each season. Using snow pit measurements, we demonstrate that precipitation isotopic signals translate to the snowpack. We generate indices to determine Sublimation Proportion Index and Precipitation Weighting Index, and find that annual Owen core δD‐δ18O line slopes are significantly related to these indices, demonstrating that these factors are recorded in ice cores. Plain Language Summary: We present water isotope measurements in precipitation, snow pits, and a shallow ice core from Summit, Greenland. We investigate the relationship between hydrogen and oxygen isotope ratios, emphasizing the temporal variation in the slope of the local meteoric water line and its relationship with climate conditions. We demonstrate that, on the annual scale, variations in the hydrogen (δD) versus oxygen (δ18O) isotopic ratio slope is significantly controlled by moisture contribution from sublimation off the Greenland Ice Sheet and by variations in the seasonal weighting of precipitation. We demonstrate that these isotopic signals of precipitation translate directly to the snowpack and thus are potentially transferred to ice cores. We obtained annual δD versus δ18O slopes from a 32‐year ice core and show that the slope variations are related to the relative amount of sublimation and seasonal weighting of the precipitation. These results open a new way of interpreting ice cores for their climatic significance. The work may also help better understand ice sheet mass balance through the quantification of sublimation‐sourced precipitation. Key Points: Deuterium excess annual cycles in precipitation, snow pits, and an ice core at Summit, Greenland have phases opposite to most Arctic sitesSlope of local meteoric water line (LMWL) can be measured in ice cores and can be used to extract past hydroclimatesLMWL slope contains information about sublimation off the Greenland Ice Sheet and seasonal precipitation distribution [ABSTRACT FROM AUTHOR]

Aerosols significantly affect Earth's radiation budget, thus influencing global climate. In the Arctic, sulfate aerosols are thought to have reduced the warming during the twentieth century. However, trends in past sulfate aerosols are poorly known, especially the aerosol sizes and compositions. Here, we analyze a high‐resolution ice core from southeastern Greenland, comparing the seasonal deposition flux of large sulfate salt particles and small sulfur compounds, including non‐neutralized sulfuric acid, between the anthropogenic sulfate maximum (1973–1975) and after sulfur emissions control (2010–2012). Between these periods, we find that the large‐diameter (>0.4 μm) flux remains roughly unchanged, yet the small‐diameter (<0.4 μm) aerosol flux significantly decreases. The results indicate that small sulfates were efficiently activated as cloud condensation nuclei during the 1970s, and thus likely increased cloud albedo, offsetting the warming. Plain Language Summary: Sulfate aerosol compositions and size distributions are important factors in Earth's radiation budget. However, we have little information on past sulfate aerosol sizes and compositions over the Arctic due to a lack of reliable observations, and as such, we have less confidence in modeling historical aerosol composition and transport. We present here the first observational evidence that small sulfate particles increased in the Arctic during the 1970s. With emission controls, anthropogenic SO2 emissions from eastern North America and Western Europe decreased after the 1980s, thus increasing the relative importance of large sulfate particles. Thus, our findings should help to improve the understanding of aerosol‐cloud interactions, and provide new constraints for the parameterization in the model. Key Points: Ice core analyses provide the first evidence of past seasonal deposition flux of large sulfate salt particles and small sulfatesCompared to the 1970s, the small sulfates (<0.4 μm) aerosol flux significantly decreased in the 2010sSmall sulfates were efficiently activated as cloud condensation nuclei during anthropogenic sulfate maximum (1970s) [ABSTRACT FROM AUTHOR]

The two Polar Regions Arctic and Antarctica are geographically different, the Arctic, an ocean covered by ice and Antarctica, a landmass surrounded by waters of the Southern Ocean. The Arctic is governed by the 'Arctic Council', comprising the five Arctic littoral countries who have their respective national jurisdictions over the Arctic region and function under various international treaties and conventions. The Antarctic continent does not belong to any single country as per the 'Antarctic Treaty'; it "freezes" territorial claims of the continent and devotes Antarctica to peace and science. Though the Treaty takes a "bifocal" approach to neither recognise nor deny territorial claims, however there are currently 55 contracting parties associated to research activities on the continent. Though the Polar Regions are increasingly getting securitised due to their natural wealth and resources, this paper concludes that the regions should be a place of peace and cooperation to preserve its vulnerable and unique environment for humanity. [ABSTRACT FROM AUTHOR]

Observations of wave dissipation and dispersion in sea ice are a necessity for the development and validation of wave–ice interaction models. As the composition of the ice layer can be extremely complex, most models treat the ice layer as a continuum with effective, rather than independently measurable, properties. While this provides opportunities to fit the model to observations, it also obscures our understanding of the wave–ice interactive processes; in particular, it hinders our ability to identify under which environmental conditions these processes are of significance. Here, we aimed to reduce the number of free variables available by studying wave dissipation in landfast ice. That is, in continuous sea ice, such as landfast ice, the effective properties of the continuum ice layer should revert to the material properties of the ice. We present observations of wave dispersion and dissipation from a field experiment on landfast ice in the Arctic and Antarctic. Independent laboratory measurements were performed on sea ice cores from a neighboring fjord in the Arctic to estimate the ice viscosity. Results show that the dispersion of waves in landfast ice is well described by theory of a thin elastic plate, and such observations could provide an estimate of the elastic modulus of the ice. Observations of wave dissipation in landfast ice are about an order of magnitude larger than in ice floes and broken ice. Comparison of our observations against models suggests that wave dissipation is attributed to the viscous dissipation within the ice layer for short waves only, whereas turbulence generated through the interactions between the ice and waves is the most likely process for the dissipation of wave energy for long periods. The separation between short and long waves in this context is expected to be determined by the ice thickness through its influence on the lengthening of short waves. Through the comparison of the estimated wave attenuation rates with distance from the landfast ice edge, our results suggest that the attenuation of long waves is weaker in comparison to short waves, but their dependence on wave energy is stronger. Further studies are required to measure the spatial variability of wave attenuation and measure turbulence underneath the ice independently of observations of wave attenuation to confirm our interpretation of the results. [ABSTRACT FROM AUTHOR]

Understanding the history of the Greenland Ice Sheet (GrIS) is critical for determining its sensitivity to warming and contribution to sea level; however, that history is poorly known before the last interglacial. Most knowledge comes from interpretation of marine sediment, an indirect record of past ice-sheet extent and behavior. Subglacial sediment and rock, retrieved at the base of ice cores, provide terrestrial evidence for GrIS behavior during the Pleistocene. Here, we use multiple methods to determine GrIS history from subglacial sediment at the base of the Camp Century ice core collected in 1966. This material contains a stratigraphic record of glaciation and vegetation in northwestern Greenland spanning the Pleistocene. Enriched stable isotopes of pore-ice suggest precipitation at lower elevations implying ice-sheet absence. Plant macrofossils and biomarkers in the sediment indicate that paleo-ecosystems from previous interglacial periods are preserved beneath the GrIS. Cosmogenic 26Al/10Be and luminescence data bracket the burial of the lower-most sediment between <3.2 ± 0.4 Ma and >0.7 to 1.4 Ma. In the upper-most sediment, cosmogenic 26Al/10Be data require exposure within the last 1.0 ± 0.1 My. The unique subglacial sedimentary record from Camp Century documents at least two episodes of ice-free, vegetated conditions, each followed by glaciation. The lower sediment derives from an Early Pleistocene GrIS advance. 26Al/10Be ratios in the upper-most sediment match those in subglacial bedrock from central Greenland, suggesting similar ice-cover histories across the GrIS. We conclude that the GrIS persisted through much of the Pleistocene but melted and reformed at least once since 1.1 Ma. [ABSTRACT FROM AUTHOR]

Arctic regions and their water bodies are affected by a rapidly warming climate. Arctic lakes and small ponds are known to act as an important source of atmospheric methane. However, not much is known about other types of water bodies in permafrost regions, which include major rivers and coastal bays as a transition type between freshwater and marine environments. We monitored dissolved methane concentrations in three different water bodies (Lena River, Tiksi Bay, and Lake Golzovoye, Siberia, Russia) over a period of 2 years. Sampling was carried out under ice cover (April) and in open water (July–August). The methane oxidation (MOX) rate and the fractional turnover rate (k′) in water and melted ice samples from the late winter of 2017 was determined with the radiotracer method. In the Lena River winter methane concentrations were a quarter of the summer concentrations (8 nmol L -1 vs. 31 nmol L -1), and mean winter MOX rate was low (0.023 nmol L -1 d -1). In contrast, Tiksi Bay winter methane concentrations were 10 times higher than in summer (103 nmol L -1 vs. 13 nmol L -1). Winter MOX rates showed a median of 0.305 nmol L -1 d -1. In Lake Golzovoye, median methane concentrations in winter were 40 times higher than in summer (1957 nmol L -1 vs. 49 nmol L -1). However, MOX was much higher in the lake (2.95 nmol L -1 d -1) than in either the river or bay. The temperature had a strong influence on the MOX (Q10=2.72±0.69). In summer water temperatures ranged from 7–14 ∘ C and in winter from -0.7 to 1.3 ∘ C. In the ice cores a median methane concentration of 9 nM was observed, with no gradient between the ice surface and the bottom layer at the ice–water interface. MOX in the (melted) ice cores was mostly below the detection limit. Comparing methane concentrations in the ice with the underlaying water column revealed methane concentration in the water column 100–1000 times higher. The winter situation seemed to favor a methane accumulation under ice, especially in the lake with a stagnant water body. While on the other hand, in the Lena River with its flowing water, no methane accumulation under ice was observed. In a changing, warming Arctic, a shorter ice cover period is predicted. With respect to our study this would imply a shortened time for methane to accumulate below the ice and a shorter time for the less efficient winter MOX. Especially for lakes, an extended time of ice-free conditions could reduce the methane flux from the Arctic water bodies. [ABSTRACT FROM AUTHOR]

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Dated to approximately 13 000 years ago, the Laacher See (East Eifel volcanic zone) eruption was one of the largest midlatitude Northern Hemisphere volcanic events of the Late Pleistocene. This eruptive event not only impacted local environments and human communities but probably also affected Northern Hemispheric climate. To better understand the impact of a Laacher See-type eruption on NH circulation and climate, we have simulated the evolution of its fine ash and sulfur cloud with an interactive stratospheric aerosol model. Our experiments are based around a central estimate for the Laacher See aerosol cloud of 15 Tg of sulfur dioxide (SO2) and 150 Tg of fine ash, across the main eruptive phases in May and a smaller one in June with 5 Tg SO2 and 50 Tg of fine ash. Additional sensitivity experiments reflect the estimated range of uncertainty of the injection rate and altitude and assess how the solar-absorptive heating from the fine ash emitted in the first eruptive phase changed the volcanic clouds' dispersion. The chosen eruption dates were determined by the stratospheric wind fields to reflect the empirically observed ash lobes as derived from geological, paleoecological and archeological evidence linked directly to the prehistoric Laacher See eruption. Whilst our simulations are based on present-day conditions, and we do not seek to replicate the climate conditions that prevailed 13 000 years ago, we consider our experimental design to be a reasonable approximation of the transport pathways in the midlatitude stratosphere at this time of year. Our simulations suggest that the heating of the ash plays an important role for the transport of ash and sulfate. Depending on the altitude of the injection, the simulated volcanic cloud begins to rotate 1 to 3 d after the eruption. This mesocyclone, as well as the additional radiative heating of the fine ash, then changes the dispersion of the cloud itself to be more southward compared to dispersal estimated without fine ash heating. This ash-cloud-generated southerly migration process may at least partially explain why, as yet, no Laacher See tephra has been found in Greenland ice cores. Sulfate transport is similarly impacted by the heating of the ash, resulting in stronger transport to low latitudes, later arrival of the volcanic cloud in the Arctic regions and a longer lifetime compared to cases without injection of fine ash. Our study offers new insights into the dispersion of volcanic clouds in midlatitudes and addresses a likely behavior of the ash cloud of the Laacher See eruption that darkened European skies at the end of the Pleistocene. In turn, this study can also serve as significant input for scenarios that consider the risks associated with re-awakened volcanism in the Eifel. [ABSTRACT FROM AUTHOR]

Iron (Fe) is a key element in the Earth climate system, as it can enhance marine primary productivity in the high-nutrient low-chlorophyll (HNLC) regions where, despite a high concentration of major nutrients, chlorophyll production is low due to iron limitation. Eolian mineral dust represents one of the main Fe sources to the oceans; thus, quantifying its variability over the last glacial cycle is crucial to evaluate its role in strengthening the biological carbon pump. Polar ice cores, which preserve detailed climate records in their stratigraphy, provide a sensitive and continuous archive for reconstructing past eolian Fe fluxes. Here, we show the Northern Hemisphere Fe record retrieved from the NEEM ice core (Greenland), which offers a unique opportunity to reconstruct the past Fe fluxes in a portion of the Arctic over the last 108 kyr. Holocene Fe fluxes (0.042–11.7 ka, 0.5 mg m -2 yr -1) at the NEEM site were 4 times lower than the average recorded over the last glacial period (11.7–108 ka, 2.0 mg m -2 yr -1), whereas they were greater during the Last Glacial Maximum (LGM; 14.5–26.5 ka, 3.6 mg m -2 yr -1) and Marine Isotope Stage 4 (MIS 4; 60–71 ka, 5.8 mg m -2 yr -1). Comparing the NEEM Fe record with paleoceanographic records retrieved from the HNLC North Pacific, we found that the coldest periods, characterized by the highest Fe fluxes, were distinguished by low marine primary productivity in the subarctic Pacific Ocean, likely due to the greater sea ice extent and the absence of major nutrients upwelling. This supports the hypothesis that Fe fertilization during colder and dustier periods (i.e., LGM and MIS 4) was more effective in other regions, such as the midlatitude North Pacific, where a closer relationship between marine productivity and the NEEM Fe fluxes was observed. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Short chain perfluoroalkylcarboxylic acids (scPFCAs, CxF2x+1COOH, x ≤ 3) are persistent compounds formed from atmospheric oxidation of fluorotelomer compounds and chlorofluorocarbon (CFC) replacements introduced as a result of the Montreal Protocol. Understanding sources and impacts of scPFCAs has been limited by observational data. We report multidecadal depositional fluxes for trifluoroacetic acid (TFA), perfluoropropionic acid (PFPrA), and perfluorobutanoic acid (PFBA) from two Arctic ice cores. Fluxes of all three scPFCAs increase starting around 1990. Through comparison with chemical transport models and assessment of temporal trends, we observe the importance of CFC replacements in the increased deposition of TFA. Fluorotelomer degradation may contribute to the deposition of PFBA but is insignificant for TFA and PFPrA. Deposition of TFA is expected to increase as new CFC replacement compounds are phased in. This work demonstrates the increased environmental burden of persistent and potentially toxic scPFCAs as a result of global regulation. Plain Language Summary: Measurements of persistent compounds were made in two Arctic ice cores. The multidecadal records allow us to better understand the sources and deposition of these chemicals to remote areas. We observed that amounts deposited to the Arctic increased with time starting around 1990. Our results suggest that global regulation and replacement of other environmentally harmful chemicals contributed to the increase of these compounds in the Arctic, illustrating that regulations can have important unanticipated consequences. Key Points: First report of multidecadal deposition for short‐chain perfluorocarboxylic acids collected from two Arctic ice capsDeposited short‐chain perfluorocarboxylic acids increased with time starting in 1990Chlorofluorocarbon replacements introduced as a result of the Montreal Protocol likely a major source of trifluoroacetic acid to the Arctic [ABSTRACT FROM AUTHOR]

Arctic regions and their water bodies are being affected by the most rapid climate warming on Earth. Arctic lakes and small ponds are known to act as an important source of atmospheric methane. However, not much is known about other types of water bodies in permafrost regions, which include major rivers and coastal bays as a transition type between freshwater and marine environments. We monitored dissolved methane concentrations in three different water bodies (Lena River, Tiksi Bay and Lake Golzovoye, Siberia, Russia) over a period of two years. Sampling was carried out under ice cover (April) and in open water (July/August). The methane oxidation (MOX) rate in water and melted ice samples from the late winter of 2017 was also investigated. In the Lena River winter methane concentrations were a quarter of the summer concentrations (8 vs 31 nmol L-1) and mean winter MOX rate was low (0.023 nmol L-1 d-1). In contrast, Tiksi Bay winter methane concentrations were 10-times higher than in summer (103 vs 13 nmol L-1). Winter MOX rates showed a median of 0.305 nmol L-1 d-1. In Lake Golzovoye, median methane concentrations in winter were 40-times higher than in summer (1957 vs 49 nmol L-1). However, MOX was much higher in the lake (2.95 nmol L-1 d-1) than in either the river or bay. The temperature had a strong influence on the MOX, (Q10 = 2.72 ± 0.69) compared to temperate environments. In the ice core a median methane concentration of 9 nM was observed, with no gradient between the ice surface and the bottom layer at the ice-water-interface. MOX in the (melted) ice cores was mostly below the detection limit. Comparing methane concentrations in the ice with the underlaying water column revealed 100 - 1000-times higher methane concentration in the water column. The winter situation seemed to favor a methane accumulation under ice, especially in the lake with a stagnant water body. While on the other hand, in the Lena River with its flowing water no methane accumulation under ice was observed. Methane oxidation rate was not able to counteract this winter time accumulation. [ABSTRACT FROM AUTHOR]

An ice core drilled on the Renland ice cap in east-central Greenland contains a continuous climate record dating through the last glacial period. The Renland record is valuable because the coastal environment is more likely to reflect regional sea surface conditions compared to inland Greenland ice cores that capture synoptic variability. Here we present the δ18O water isotope record for the Holocene, in which decadal-scale climate information is retained for the last 8 kyr, while the annual water isotope signal is preserved throughout the last 2.6 kyr. To investigate regional climate information preserved in the water isotope record, we apply spectral analysis techniques to a 300-year moving window to determine the mean strength of varying frequency bands through time. We find that the strength of 15–20-year δ18O variability exhibits a millennial-scale signal in line with the well-known Bond events. Comparison to other North Atlantic proxy records suggests that the 15–20-year variability may reflect fluctuating sea surface conditions throughout the Holocene, driven by changes in the strength of the Atlantic Meridional Overturning Circulation. Additional analysis of the seasonal signal over the last 2.6 kyr reveals that the winter δ18O signal has experienced a decreasing trend, while the summer signal has predominantly remained stable. The winter trend may correspond to an increase in Arctic sea ice cover, which is driven by a decrease in total annual insolation, and is also likely influenced by regional climate variables such as atmospheric and oceanic circulation. In the context of anthropogenic climate change, the winter trend may have important implications for feedback processes as sea ice retreats in the Arctic. [ABSTRACT FROM AUTHOR]

Using high-resolution ice core and tree ring proxies for sea ice extent (SIE), we reconstructed a robust time series of autumn SIE over the Barents-Kara (B-K) sector of the Arctic from AD1289-1993. After intercomparing the results and statistical parameters using the ordinary least squares regression (OLSR), the principle component regression (PCR) and the partial least squares regression (PLSR) methods, SIE time series were synthesized into a more robust series using the weighted average method, which used the explained variances as weights. The results showed that from the end of the 13th century to the end of 18th century, the autumn B-K SIE was large, with large variations and a slightly expanding trend overall. This reflected significant multidecadal oscillations under the Little Ice Age (LIA) background. The B-K SIE began to decrease at the end of the 18th century, and a shrinking trend became significant during the second half of the 19th century, which lasted into the 1930s-1940s. The 1930s-1940s was a period with a relatively low SIE in the B-K Sea, and the SIE had a short period of expansion from the 1940s-1970s. However, the B-K SIE has continuously and significantly shrank since the 1970s. The reduction in the B-K SIE since the end of the 18th century has been unprecedented in both duration and speed over the last 700 years. The B-K SIE has retreated significantly since the 1970s, with a speed 6.18 times greater than the former mean retreating speed. The industrial revolution may be a dominant factor in this result. The Arctic SIE in recent years may be the lowest it has been over the last millennium. [ABSTRACT FROM AUTHOR]

A series of uniaxial compressive tests using ice cores collected in the Arctic Ocean was conducted in the cold laboratory on board R/V Xuelong during the summers of 2012 and 2014. A total of 130 ice samples were tested at temperatures ranging from −9 °C to −3 °C at strain rates ranging from 10 −7  s −1 to 10 −2  s −1 with the loading direction along the core axis. The uniaxial compressive strength of sea ice depends mainly on two parameters: sea ice porosity and strain rate during the test. Arctic sea ice presented characteristics of weak porosity effect and low transition strain rate. The effect of strain rate on the uniaxial compressive strength could be parameterized using a piecewise function for ductile, transition and brittle regimes. A power-law relationship was found between the uniaxial compressive strength of ice samples and their porosity. These relationships made it feasible to estimate the natural uniaxial compressive strength of ice as a function of in-situ porosity and strain rate. The results derived from the ice samples were extended to large-scale strength of ice sheets based on their porosity profiles determined using field measurements of ice physical properties. The strength of Arctic ice sheets in the summers of 2012 and 2014 was far less than previous estimates, probably because of accelerated interior ice melt caused by Arctic warming. [ABSTRACT FROM AUTHOR]

While general trends in the inflow of Atlantic Water (AW) to the European Arctic over the present interglacial (the Holocene) are well known, regional changes in climate and the AW current and subsequent environmental responses are less well established. In particular, there is only limited knowledge on the development of ocean currents after the last deglaciation. Here, to better understand past water mass dynamics and their effects on sea ice cover and the environment throughout the Holocene, we present a multiproxy record from core OCE2019-HR7-GC retrieved from the southwestern Svalbard inner shelf, a highly dynamic frontal area influenced by different ocean currents and local water masses. For sea ice reconstructions, we focus on the specific sea ice biomarker IP 25 in combination with the phytoplankton biomarkers dinosterol and brassicasterol. We further reconstruct surface and bottom water temperatures using alkenones and Mg/Ca and prevailing water masses using foraminifera assemblages. Finally, we compare our sea ice and temperature records with published marine sediment and ice core data from the area. We observe extensive sea ice cover between 11 and 10.2 kyr BP, which was likely linked to the Preboreal Oscillation. Based on our reconstructions, the period between 10 and 7 kyr BP was characterized by the warmest Holocene conditions on the SW Svalbard shelf. This interval is also associated with high surface water productivity and an enhanced AW influx that drove strong erosive activity at the bottom. After 6.5 kyr BP, the SW Svalbard shelf was characterized by a dynamic environment with cold and unstable conditions that lasted until 3.5 kyr BP. After 3.5 kyr BP, we observed an increase in sea ice cover and iceberg rafting over our site once more, which likely indicated seasonally fluctuating ice margins, with low AW influx, which lasted until 2.2 kyr BP. A brief warm period accompanied by strong bottom currents occurred between 2.2 and 1.8 kyr BP. The environment returned to a colder state with the presence of sea ice until 1.5 kyr BP, which was followed by warmer conditions between 1.5 and 1 kyr BP. • A sediment core from the southwest Svalbard is used to study Holocene dynamics of water mass, sea ice, and the environment. • Cold Arctic water from the East Spitsbergen Current and thick sea ice were present between 11 and 10.2 kyr BP. • The warmest period from 10 to 7 kyr BP promoted sediment erosion with low sea ice due to increased Atlantic Water Inflow. • Between 6.5 and 3.5 kyr BP, icebergs and sea ice rafting caused cold surface temperatures in a dynamic environment. • During 2.3 and 1.5 kyr BP, warm Atlantic Water expanded, marked by increased erosive activity, and elevated temperatures. [ABSTRACT FROM AUTHOR]

Wildfires and their emissions have significant impacts on ecosystems, climate, atmospheric chemistry, and carbon cycling. Well-dated proxy records are needed to study the long-term climatic controls on biomass burning and the associated climate feedbacks. There is a particular lack of information about long-term biomass burning variations in Siberia, the largest forested area in the Northern Hemisphere. In this study we report analyses of aromatic acids (vanillic and para-hydroxybenzoic acids) over the past 2600 years in the Eurasian Arctic Akademii Nauk ice core. These compounds are aerosol-borne, semi-volatile organic compounds derived from lignin combustion. The analyses were made using ion chromatography with electrospray mass spectrometric detection. The levels of these aromatic acids ranged from below the detection limit (0.01 to 0.05 ppb; 1 ppb = 1000 ng L-1) to about 1 ppb, with roughly 30% of the samples above the detection limit. In the preindustrial late Holocene, highly elevated aromatic acid levels are observed during three distinct periods (650-300 BCE, 340-660 CE, and 1460-1660 CE). The timing of the two most recent periods coincides with the episodic pulsing of ice-rafted debris in the North Atlantic known as Bond events and a weakened Asian monsoon, suggesting a link between fires and large-scale climate variability on millennial timescales. Aromatic acid levels also are elevated during the onset of the industrial period from 1780 to 1860 CE, but with a different ratio of vanillic and para-hydroxybenzoic acid than is observed during the preindustrial period. This study provides the first millennial-scale record of aromatic acids. This study clearly demonstrates that coherent aromatic acid signals are recorded in polar ice cores that can be used as proxies for past trends in biomass burning. [ABSTRACT FROM AUTHOR]

The physical structures, solar irradiance and reflectance of snow and sea ice in high Arctic were investigated based on snow pit, ice coring, and borehole measurements from August 29 to September 2 in 2012. In all of the six short-term stations, the snow cover was stratified: fresh snow in the top (if any) with dendritic grains (1–4 mm in grain size), fine-grained snow in the middle (4–9 mm), and coarsely spherical grained snow in the bottom (8–16 mm). The incident and reflected irradiance were wavelength-dependent, whereas the albedo and its dependence on wavelength were relatively diverse and scattering. The integrated albedos were 0.47–0.92, largely depending on the snow type, grain size, thickness, and water content. Ice coring and thin sections indicated that all ice covers were first-year, and were dominated by the columnar grained ice. And all the ice cores were characterized by a large number of gas and brine pockets and tubes, the size and content of which were much greater than those of sea ice cover during the winter congelation. The vertical stratifications of ice density, temperature and salinity were quantified using linear regression. Overall, the salinity and density increased with an increasing depth, while the temperature decreased against depth except the top 10–20 cm, where the temperature was dependent on the air and snow temperatures. The estimates of inclusion volume (including gas and brine) gave insight into the sea ice composition (ice-brine/gas matrix). The comparison of the present volumetric fraction of inclusions with previous ones indicated to some degree that the sea ice inclusion volume increased in the ice interior, thus the volumetric fraction of pure ice decreased at the end of summer melt, indicating a rigorous melting within the Pacific Arctic sea ice covers. Our work suggests that the volumetric fraction of sea ice inclusions as a function of temperature, density and salinity can be considered as an alternative indicator for Arctic sea ice reduction, just like the sea ice extent, thickness, age and melting duration. [ABSTRACT FROM AUTHOR]

Glacier ice and firn cores have ecological and biotechnological importance. The present study is aimed at characterizing bacteria in crustal ice cores from Svalbard, the Arctic. Counts of viable isolates ranged from 10 to 7000 CFU/ml (mean 803 CFU/ml) while the total bacterial numbers ranged from 7.20 × 104 to 2.59 × 107 cells ml−1 (mean 3.12 × 106 cells ml−1). Based on 16S rDNA sequence data, the identified species belonged to seven species, namely Bacillus barbaricus, Pseudomonas orientalis, Pseudomonas oryzihabitans, Pseudomonas fluorescens, Pseudomonas syncyanea, Sphingomonas dokdonensis, and Sphingomonas phyllosphaerae, with a sequence similarity ranging between 93.5 and 99.9% with taxa present in the database. The isolates exhibited unique phenotypic properties, and three isolates (MLB-2, MLB-5, and MLB-9) are novel species, yet to be described. To the best of our knowledge, this is the first report on characterization of cultured bacterial communities from Svalbard ice cores. We conclude that high lipase, protease, cellulase, amylase, and urease activities expressed by most of the isolates provide a clue to the potential industrial applications of these organisms. These microbes, producing cold-adapted enzymes may provide an opportunity for biotechnological research. [ABSTRACT FROM AUTHOR]

[Display omitted] • Melting glaciers and human activity shape polar aquatic resistome in the Arctic. • The intI1 gene persists in environments with varied human activity impact. • The variable regions of integrons contain genes determining different functions. The Arctic is one of the regions most affected by global climate change, and is subjected to changes linked with a melting cryosphere and increasing anthropopressure. Although antibiotic resistance is a global problem, the diversity and spread of antibiotic-resistant bacteria (ARB), antibiotic resistance genes (ARGs) and integrons in the Arctic are strongly understudied. Therefore, the main aims of this study are the (1) determination of the type and frequency of integron-integrase genes and characterization of incorporated gene cassettes in the genomes of culturable bacteria and (2) quantitative analysis of class 1 integron-integrase gene and human mitochondrial DNA (Hmt -DNA) in the metagenome as markers of anthropogenic impact on the high Arctic environments of the Svalbard Archipelago. Samples of ice, water and sediments were collected in the most populated area of Svalbard, Longyearbyen and its vicinity. Sampling was conducted along an environmental gradient with varying levels of human activity. The environmental gradient started from glaciers, following the proglacial river, the seashore, and the fjord bottom water, including untreated wastewater outflow to the sea. Class 1 integrons were detected in ARB isolated from glacial environments, freshwater and seawater, including wastewater outflow. Moreover, in the variable regions of integrons, genes determining different functions, including antibiotic resistance, virulence and physiological traits were found. These genes play crucial roles in the adaptation of bacteria to cold and dynamic environments. The relative abundance of intI1 genes were reported in metagenomes with different relationships to human activity (ice cores vs wastewater outflow), with the highest mean values observed in the wastewater outflow, and was positively correlated with abundance of the Hmt gene, revealing both natural and human roles in shaping the polar aquatic resistome. [ABSTRACT FROM AUTHOR]

Increasing reactive nitrogen (Nr) deposition in the Arctic may adversely impact N-limited ecosystems. To investigate atmospheric transport of Nr to Svalbard, Norwegian Arctic, snow and firn samples were collected from glaciers and analysed to define spatial and temporal variations (1–10 years) in major ion concentrations and the stable isotope composition (δ15N and δ18O) of nitrate () across the archipelago. The and averaged −4‰ and 67‰ in seasonal snow (2010–11) and −9‰ and 74‰ in firn accumulated over the decade 2001–2011. East–west zonal gradients were observed across the archipelago for some major ions (non-sea salt sulphate and magnesium) and also for and in snow, which suggests a different origin for air masses arriving in different sectors of Svalbard. We propose that snowfall associated with long-distance air mass transport over the Arctic Ocean inherits relatively low due to in-transport N isotope fractionation. In contrast, faster air mass transport from the north-west Atlantic or northern Europe results in snowfall with higher because in-transport fractionation of N is then time-limited. [ABSTRACT FROM AUTHOR]

Understanding recent Arctic climate change requires detailed information on past changes, in particular on a regional scale. The extension of the depth-age relation of the Akademii Nauk (AN) ice core from Severnaya Zemlya (SZ) to the last 1100 yr provides new perspectives on past climate fluctuations in the Barents and Kara seas region. Here, we present the easternmost high-resolution ice-core climate proxy records (d18O and sodium) from the Arctic. Multiannual AN d18O data as near-surface air-temperature proxies reveal major temperature changes over the last millennium, including the absolute minimum around 1800 and the unprecedented warming to a double-peak maximum in the early 20th century. The long-term cooling trend in d18O is related to a decline in summer insolation but also to the growth of the AN ice cap as indicated by decreasing sodium concentrations. Neither a pronounced Medieval Climate Anomaly nor a Little Ice Age are detectable in the AN d18O record. In contrast, there is evidence of several abrupt warming and cooling events, such as in the 15th and 16th centuries, partly accompanied by corresponding changes in sodium concentrations. These abrupt changes are assumed to be related to sea-ice cover variability in the Barents and Kara seas region, which might be caused by shifts in atmospheric circulation patterns. Our results indicate a significant impact of internal climate variability on Arctic climate change in the last millennium. [ABSTRACT FROM AUTHOR]

Abstract: Ten strains of cryophilic yeast were studied from glacier ice cores of Svalbard, Arctic. The ice melt samples contained about 3×103 – 1×104 colony forming unit (CFUs) per ml. Sequence analysis of the isolates, using D1/D2 domain identified five species of yeasts: Cryptococcus adeliensis (MLB-18 JX192655), Cryptococcus albidosimilis (MLB-19 JX192656), Cryptococcus saitoi (MLB-22 JX192659), Rhodosporidium lusitaniae (MLB-20 JX192657), and Rhodotorula mucilaginosa (MLB-27 JX192664). Effect of temperature on growth of these isolates was studied. The strains are able to grow at temperatures ranging between 1 and 20°C. Screening of the cultures for amylase, cellulase, protease, lipase, urease and catalase activity were carried out indicating varying amounts of enzyme production at different temperatures. Characterization of lipase in strain Cryptococcus sp. MLB-24 was performed. Fatty acid methyl ester (FAME) analysis of the cultures grown at four different temperatures (1, 4, 15, and 20°C) was also done. Decrease in temperature was reported to cause increase in concentration of unsaturated fatty acids. High amount of oleic acid accumulated with increase in temperature. These fatty acids possibly help the strains to survive in glacial ice core cold environment. The extracellular and intracellular filtrate of the cultures showed negative antifreeze protein (AFP) activity. The observations indicate that probably the isolates in the present undertaking adapt to low temperatures, by enzyme and PUFA secretion rather than by antifreeze protein secretion. [Copyright &y& Elsevier]

Using fluorescence spectrometry to map autofluorescence of chlorophyll (Chl) and tryptophan (Trp) versus depth in polar ice cores in the US National Ice Core Laboratory, we found that the Chl and Trp concentrations often showed an annual modulation of up to 25 %, with peaks at depths corresponding to local summers. Using epi- fluorescence microscopy (EFM) and flow cytometry (FCM) triggered on red fluorescence at 670 nm to study microbes from unstained melts of the polar ice, we inferred that picocyanobacteria may have been responsible for the red fluorescence in the cores. Micron-size bacteria in all ice melts from Arctic and Antarctic sites showed FCM patterns of scattering and of red vs. orange fluorescence (interpreted as due to Chl vs. phycoerythrin (PE)) that bore similarities to patterns of cultures of unstained picocyanobacteria Prochlorococcus and Synechococcus. Concentrations in ice from all sites were low, but measurable at ~1 to ~10³ cells cm-3. Calibrations showed that FCM patterns of mineral grains and volcanic ash could be distinguished from microbes with high efficiency by triggering on scattering instead of by red fluorescence. Average Chl and PE autofluorescence intensities showed no decrease per cell with time during up to 150 000 yr of storage in glacial ice. Taking into account the annual modulation of ~25% and seasonal changes of ocean temperatures and winds, we suggest that picocyanobacteria are windtransported year-round from warmer ocean waters onto polar ice. Ice cores offer the opportunity to study evolution of marine microbes over ~300 million generations by analysing their genomes vs. depth in glacial ice over the last 700 000 yr as frozen proxies for changes in their genomes in oceans. [ABSTRACT FROM AUTHOR]

Abstract: Hydrogen peroxide (HOOH) is an important trace constituent in snow and ice, including in Arctic and Antarctic ice cores. To better understand the budget of snowpack HOOH, here we examine its production in illuminated snow and ice. To evaluate what types of compounds might be important photochemical sources of HOOH, we first illuminated laboratory ice samples containing 10 different model organic compounds: guaiacol, phenol, syringol, benzoate, formate, octanal, octanoic acid, octanedioic acid, phenylalanine, and mixtures of oxalate with iron (III). Half of these compounds produced little or no HOOH during illumination, but two classes of compounds were very reactive: phenolic compounds (with rates of HOOH of 6–62nM-HOOH h−1 μM−1-phenolic) and mixtures of Fe(III) with a stoichiometric excess of oxalate (with rates of HOOH production as high as 2,000,000nMh−1 per μM iron). To quantify rates of HOOH production in the environment we also illuminated snow samples collected from the Arctic and Antarctic. The average (±1σ) HOOH production rate in these samples was low, 5.3±5.0nMh−1 and replicate measurements showed high variability. In some natural samples there was an initial burst of HOOH production (with a rate approximately 10 times higher than the average production rate), followed by reduced rates at subsequent time points. Although our laboratory ice samples reveal that illuminated organics and metal-organic complexes can form HOOH, the low rates of HOOH formation in the Arctic and Antarctic snow samples suggest this process has only a modest impact on the HOOH budget in the snowpack. [Copyright &y& Elsevier]

The reliability of Arctic climate predictions is currently hampered by insufficient knowledge of natural climate variability in the past. A sediment core from Lake El'gygytgyn in northeastern (NE) Russia provides a continuous, high-resolution record from the Arctic, spanning the past 2.8 million years. This core reveals numerous "super interglacials" during the Quaternary; for marine benthic isotope stages (MIS) 11c and 31, maximum summer temperatures and annual precipitation values are -4° to 5°C and ~300 millimeters higher than those of MIS 1 and 5e. Climate simulations show that these extreme warm conditions are difficult to explain with greenhouse gas and astronomical forcing alone, implying the importance of amplifying feedbacks and far field influences. The timing of Arctic warming relative to West Antarctic Ice Sheet retreats implies strong interhemispheric climate connectivity. [ABSTRACT FROM AUTHOR]

Abstract: From the 1920s to the 1940s, the Artic experienced significant warming that is comparable to the recent 30-year warming. The former warming was concentrated mostly in high latitudes, in contrast to the recent 30-year warming, which has occurred in all latitudes. Several explanations have been proposed; however, one of these proposed explanations, single external forcing, which could once explain the global average, failed to explain the early 20th century scenario. A second possible explanation was internal atmospheric variability with low frequency. Another candidate for the explanation was still forcing by black carbon deposited on snow and ice surfaces. The answer is most likely to be a combination of intrinsic internal natural climate variability and positive feedbacks that amplified the radiative and atmospheric forcing. We must continue our study by discovering historical data, analyzing ice cores, reanalyzing the Arctic system together with long-term reanalysis dating back to the 1880s, and also determine the contributions of each factor. [Copyright &y& Elsevier]

The Arctic is currently undergoing dramatic environmental transformations, but it remains largely unknown how these changes compare with long-term natural variability. Here we present a lake sediment sequence from the Canadian Arctic that records warm periods of the past 200,000 years, including the 20th century. This record provides a perspective on recent changes in the Arctic and predates by approximately 80,000 years the oldest stratigraphically intact ice core recovered from the Greenland Ice Sheet. The early Holocene and the warmest part of the Last Interglacial (Marine Isotope Stage or MIS 5e) were the only periods of the past 200,000 years with summer temperatures comparable to or exceeding today's at this site. Paleoecological and geochemical data indicate that the past three interglacial periods were characterized by similar trajectories in temperature, lake biology, and lakewater pH, all of which tracked orbitally-driven solar insolation. In recent decades, however, the study site has deviated from this recurring natural pattern and has entered an environmental regime that is unique within the past 200 millennia. [ABSTRACT FROM AUTHOR]

Annual growth of the polar evergreen shrub Cassiope tetragona on Svalbard was evaluated as a proxy for Arctic summer temperatures. Transfer functions were derived from temperature-growth correlations of shoots and from a temperature-growth response, obtained from experimental warming using open top chambers (OTC) in high Arctic tundra vegetation at Isdammen approximately 1.5 km southeast of Longyearbyen, Svalbard (78°N, 15 E) and in Longyeardalen, 3 km west of Isdammen from 2004 to 2006. Air temperatures, monitored throughout the summer months, were 1.3 °C higher inside the OTCs than in the control plots. Annual stem growth was measured by tagging stems and leaves, and in the lab with shoots harvested from OTCs and control plots. Annual growth parameters assessed were leaf production, sum of length and weight of individual leaves, and stem length increment derived from leaf scar distances and the distances between wintermarksepta in the stem. Wintermarksepta are formed at the end of the summer growth period when the pith is narrowing and consist of dense and dark tissue ( Fig. 1b ). The variation of annual growth in a 34-year site chronology (based on Cassiope shoots from the surroundings of the OTCs and control plots) correlated strongly with the mean summer temperature on Svalbard. The number of leaf pairs, leaf length and stem length also increased in the OTC warmed plots in the second and third year of warming. Transfer functions were derived from the temperature-annual growth correlations from a single shoot from Longyeardalen, from the cross-dated Isdammen site chronology and from the growth response to experimental warming. Based on leaf scar distances and distances between wintermarksepta of well-preserved subfossil shoots in arctic tundra soil, annual stem length increase was assessed for the layers of a soil core collected at the Isdammen site. Based on the derived transfer functions summer temperature of the period relating to the 15 cm deep tundra soil core layer, radiocarbon dated at 4230±40 bp, may have been 3.0 °C lower than the present-day 6.2 °C value. These results indicate that the transfer functions can be used to reconstruct past temperatures, beyond the time range of instrumental temperature and ice core records of Svalbard. [ABSTRACT FROM AUTHOR]

The Arctic is a region undergoing continuous and significant changes in land relief due to different glaciological, geomorphological and hydrogeological processes. To study those phenomena, digital elevation models (DEMs) and highly accurate maps with high spatial resolution are of prime importance. In this work, we assess the accuracy of high-resolution photogrammetric DEMs and orthomosaics derived from aerial images captured in 2020 over Hornsund, Svalbard. Further, we demonstrate the accuracy of DEMs generated using point clouds acquired in 2021 with a Riegl VZ®-6000 terrestrial laser scanner (TLS). Aerial and terrestrial data were georeferenced and registered based on very reliable ground control points measured in the field. Both DEMs, however, had some data gaps due to insufficient overlaps in aerial images and limited sensing range of the TLS. Therefore, we compared and integrated the two techniques to create a continuous and gapless DEM for the scientific community in Svalbard. This approach also made it possible to identify geomorphological activity over a one-year period, such as the melting of ice cores at the periglacial zone, changes along the shoreline or snow thickness in gullies. The study highlights the potential for combining other techniques to represent the active processes in this region. [ABSTRACT FROM AUTHOR]

The frequency and the intensity of extreme temperature events have both increased globally because of the effects of climate warming. Such extreme events should be distinct in high-elevation areas owing to the phenomenon of elevation-dependent warming; however, corroborating evidence remains limited because of scarce observations. This study used the percentile method to identify annual extreme temperature events recorded in the δ18O of the Laohugou ice core (1960–2006) retrieved from the high-elevation area of the northeastern Tibetan Plateau (NETP). Comparison of these events with synchronous observations obtained at surrounding meteorological stations indicated that extreme temperature events identified from the ice core corresponded well with most temperature observations from the meteorological stations, suggesting that the δ18O record could be considered a reasonable proxy for regional temperature. However, occasional discord between the ice core and station records might reflect specific climatic shifts. Using circulation synthesis, the influencing circulation mechanism of each event was determined on the basis of differences in atmospheric parameters between each event and the average climatic state during 1970–2000. A double blocking high with warming over the Ural Mountains and east of Kuril–Kamchatka resulted in Eurasian warming, which transported warm air to the NETP and triggered the extreme high-temperature events. Conversely, a polar vortex in the Arctic led to a cold low over Eurasia, which transported cold air to the NETP causing extreme low-temperature events. The finding that variation of the Arctic air mass triggers extreme temperature events at high elevations in the NETP provides crucial insight for improved comprehension and forecasting of regional extreme temperature events. • The annual extreme temperature events recorded in δ18O of Laohugou ice core at the high elevation in northeastern Tibetan plateau (NETP) during 1960–2006 were identified, which matched well with instrumental observation around it. • Double blocking high triggered extreme high-temperature, whereas arctic polar vortex causing extreme low-temperature events. • Variation of the Arctic air mass triggers extreme temperature events at high elevations in the NETP provides crucial insight for improved comprehension and forecasting of extreme temperature events. [ABSTRACT FROM AUTHOR]

We have developed a rapid endospore viability assay (EVA) in which endospore germination serves as an indicator for viability and applied it to (i) monitor UV inactivation of endospores as a function of dose and (ii) determine the proportion of viable endospores in arctic ice cores (Greenland Ice Sheet Project 2 [GISP2] cores; 94 m). EVA is based on the detection of dipicolinic acid (DPA), which is released from endospores during germination. DPA concentrations were determined using the terbium ion (Tb3+)-DPA luminescence assay, and germination was induced by L-alanine addition. The concentrations of germinable endospores were determined by comparison to a standard curve. Parallel EVA and phase-contrast microscopy experiments to determine the percentage of germinable spores yielded comparable results (54.3% ± 3.8% and 48.9% ± 4.5%, respectively), while only 27.8% ± 7.6% of spores produced CFU. EVA was applied to monitor the inactivation of spore suspensions as a function of UV dose, yielding reproducible correlations between EVA and CFU inactivation data. The 90% inactivation doses were 2,773 J/m², 3,947 J/m², and 1,322 J/m² for EVA, phase-contrast microscopy, and CFU reduction, respectively. Finally, EVA was applied to quantify germinable and total endospore concentrations in two GISP2 ice cores. The first ice core contained 295 ± 19 germinable spores/ml and 369 ± 36 total spores/mi (i.e., the percentage of germinable endospores was 79.9% ± 9.3%), and the second core contained 131 ± 4 germinable spores/mi and 162 ± 17 total spores/ml (i.e., the percentage of germinable endospores was 80.9% ± 8.8%), whereas only 2 CFU/ml were detected by culturing. [ABSTRACT FROM AUTHOR]

The North Atlantic was a key locus for circulation-driven abrupt climate change in the past and could play a similar role in the future. Abrupt cold reversals, including the 8.2 ka event, punctuated the otherwise warm early Holocene in the North Atlantic region and serve as useful paleo examples of rapid climate change. In this work, we assess the cryospheric response to early Holocene climate history on Baffin Island, Arctic Canada, using cosmogenic radionuclide dating of moraines. We present 39 new 10Be ages from four sets of multi-crested early Holocene moraines deposited by cirque glaciers and ice cap outlet glaciers, as well as erratic boulders along adjacent fiords to constrain the timing of regional deglaciation. The age of one moraine is additionally constrained by in situ 14C measurements, which confirm 10Be inheritance in some samples. All four moraines were deposited between ∼9.2 and 8.0 ka, and their average ages coincide with abrupt coolings at 9.3 and 8.2 ka that are recorded in Greenland ice cores. Freshwater delivery to the North Atlantic that reduced the flux of warm Atlantic water into Baffin Bay may explain brief intervals of glacier advance, although moraine formation cannot be definitively tied to centennial-scale cold reversals. We thus explore other possible contributing factors, including ice dynamics related to retreat of Laurentide Ice Sheet outlet glaciers. Using a numerical glacier model, we show that the debuttressing effect of trunk valley deglaciation may have contributed to these moraine-building events. These new age constraints and process insights highlight the complex behavior of the cryosphere during regional deglaciation and suggest that multiple abrupt cold reversals—as well as deglacial ice dynamics—likely played a role in early Holocene moraine formation on Baffin Island. • 39 new 10Be dates constrain the age of early Holocene moraines and fiord deglaciation. • In situ 14C confirms inherited 10Be in some samples and clarifies moraine exposure age. • Moraine average ages overlap with known abrupt climate events at 9.3 and 8.2 ka. • A numerical model shows deglacial ice dynamics may also affect moraine formation. [ABSTRACT FROM AUTHOR]

The article presents information on ice cores that records climatic changes in Canadian Arctic that has suffered a meltdown due to freezer failure at a cold storage facility in Edmonton, Canadian Ice Core Archive run by University of Alberta (UA).

The author discusses the article by Ben Orlove and colleagues which highlights the unbalance in the attention given to climate change and its effects. Topics include the four cases including the low-lying islands, the Arctic, and mountains, place acknowledges concept, and the Division of Polar Programs of the U.S. National Science Foundation that funds research in Antarctic and Arctic on ice core study.

In this article, the author discusses aspects of the decrease of glacial environments in the circumpolar Arctic and the increase of the methane greenhouse gas in the last glacial maximum (LGM). He cites the study by A. V. Reyes and C. A. Cooke which shows the development of arctic peatland, tundra, and thermokarst occurred too late to be the cause of increased atmospheric methane in the last deglaciation. He adds that isotopic analysis of Greenland ice cores show methane increase in the period.