Greenland Ice Cores Research Articles

The Greenland spatial fingerprint of Dansgaard–Oeschger events in observations and models

Pleistocene Ice Ages display abrupt Dansgaard-Oeschger (DO) climate oscillations that provide prime examples of Earth System tipping points-abrupt transition that may result in irreversible change. Greenland ice cores provide key records of DO climate variability, but gas-calibrated estimates of the temperature change magnitudes have been limited to central and northwest Greenland. Here, we present ice-core δ15N-N2 records from south (Dye 3) and coastal east Greenland (Renland) to calibrate the local water isotope thermometer and provide a Greenland-wide spatial characterization of DO event magnitude. We combine these data with existing records of δ18O, deuterium excess, and accumulation rates to create a multiproxy "fingerprint" of the DO impact on Greenland. Isotope-enabled climate models have skill in simulating the observational multiproxy DO event impact, and we use a series of idealized simulations with such models to identify regions of the North Atlantic that are critical in explaining DO variability. Our experiments imply that wintertime sea ice variation in the subpolar gyre, rather than the commonly invoked Nordic Seas, is both a sufficient and a necessary condition to explain the observed DO impacts in Greenland, whatever the distal cause. Moisture-tagging experiments support the idea that Greenland DO isotope signals may be explained almost entirely via changes in the vapor source distribution and that site temperature is not a main control on δ18O during DO transitions, contrary to the traditional interpretation. Our results provide a comprehensive, multiproxy, data-model synthesis of abrupt DO climate variability in Greenland.

Precipitation changes during the last glacial period in the Ili Basin, northern Central Asia, as inferred from the records of loess dolomite

Understanding the climatic evolution in Central Asia (CA) and its drivers is crucial for informed decision-making and predicting global changes due to its significant contribution as a global dust source. Unfortunately, our current understanding of the pre-Holocene precipitation patterns in CA is lacking due to the limited availability of reliable proxy indicators, and our knowledge of future precipitation projections in the region, based on paleoclimatic dynamics, is also quite limited. In this study, we analyzed variations in carbonate and dolomite contents of a loess section in the Ili Basin, northern CA, to reveal precipitation changes during the last glacial period. The results showed that changes in carbonate minerals were mainly influenced by the source material supply, driven by reduced precipitation and eluviation during glacial period. We thereby established a precipitation index by removing the influence of provenance signals from the dolomite records. The index indicated lower precipitation during mid-marine isotope stage (MIS) 3 compared to MIS2, likely due to meridional shifts and intensity changes of the westerlies caused by changes in precession and obliquity, with precession playing a major role. Through the comparison of the precipitation index with the δ18O records of the Greenland ice core on a millennial timescale, it was observed that the precipitation in northern CA exhibited a positive correlation with the North Atlantic Oscillation (NAO) mode due to migration of the westerlies. By leveraging our understanding of orbital- and millennial-scale precipitation patterns, we utilized the random forest (RF) regression model and the autoregressive integrated moving average model to forecast precipitation changes for the upcoming 5000–10,000 years. The results indicated a variable pattern marked by a general upward trend, suggesting the possibility of favorable development of agricultural-based economies in the Ili River Valley. People should realize that some integrated measures are designed to improve resilience of agricultural sector in the region and enhance its capacity to adapt to challenges posed by climate change. However, more extensive research is necessary to verify these results through thorough examination and comparisons of loess sections in our research location.

Tree-ring anomalies as time markers for ice-core chronologies, with special reference to 5281 BCE as the possible date of the Kikai volcanic event

The synchronization of Greenland and Antarctica ice core data with tree-ring data, other proxies, and direct observations of natural processes and events is important to understand past climatic variation and environmental change. One of the methods that is used to correct the dating of ice layers is to match volcanic eruption footprints in ice cores with tree rings, manifested as sulphate spikes and anomalous rings, respectively. In this study, we inventoried the occurrence of tree-ring anatomical anomalies and extremes in ring width during three 200-year periods. These periods included three of the eight largest Holocene volcanic eruptions, each with a Volcanic Explosivity Index (VEI) of 7. The initial period spanned from 6560 to 6360 BCE and included the eruption of Ilyinsky Volcano in Kamchatka. The second period was from 5780 to 5580 BCE, during which Mount Mazama Volcano in North America erupted. The third period was from 5380 to 5180 BCE when the Kikai Volcano in the Japanese Islands erupted. Throughout the first two periods, no substantial tree-ring anomalies were observed suggesting the absence of any significant climate consequences of a major volcanic eruption. However, in the 5380–5180 BCE period, a clear sharp decline in tree growth and an exceptionally high frequency of tree-ring anomalies were identified in 5281 BCE and the subsequent 5 years. We propose that the exceptionally narrow light rings in these 6 years are indicative of the climatic impact resulting from the Kikai volcanic eruption. We suggest utilising the year 5281 BCE as the reference year for synchronising the Greenland and Antarctica ice core chronologies. In the case that our assumption is correct, this would imply the necessity to adjust the time of the event to an earlier date compared to the dates indicated by the existing ice core chronologies of the GICC05 (Greenland Ice Core Chronology 2005), adjusted according to Kobashi (2017), and WD2014 used for creating HolVol 1.0 (Holocene ice-core volcanic eruption catalogue from 9500 BCE - 1900 CE) by 67 and 54 years, respectively, for the period around 5300 BCE. A verification of our assumption could be conducted by examining the nearby Miyake event, a spike in cosmogenic radiocarbon, of 5258 BCE. Ice core layers displaying potential signs of this event should be approximately 25 years later than the markers of the Kikai volcanic eruption.

Calibration of Arctic ice core bromine enrichment records for past sea ice reconstructions

Bromine in ice cores has been proposed as a qualitative sea ice proxy to produce sea ice reconstructions for the polar regions. Here we report the first statistical validation of this proxy with satellite sea ice observations by combining bromine enrichment (with respect to seawater, Brenr) records from three Greenlandic ice cores (SIGMA-A, NU and RECAP) with satellite sea ice imagery, over three decades. We find that during the 1984–2016 satellite-era, ice core Brenr values are significantly correlated with first-year sea ice formed in the Baffin Bay and Labrador Sea supporting that the gas-phase bromine enrichment processes, preferentially occurring over the sea ice surface, are the main driver for the Brenr signal in ice cores. Moreover, in assessing Brenr's capability to record historical sea ice variability, we compare 20th-century Arctic Sea ice historical and proxy records with our reconstructions, based on an autoregressive–moving-average (ARMA) model, finding overall good agreement. While further enhancements are warranted, including site-specific calibrations and a comprehensive investigation into bromine transport-related concerns, this study presents a new method to quantitatively reconstruct past seasonal sea ice variability through bromine enrichment in ice cores.

Combining traditional and novel techniques to increase our understanding of the lock-in depth of atmospheric gases in polar ice cores – results from the EastGRIP region

Abstract. We investigate the lock-in zone (LIZ) of the East Greenland Ice Core Project (EastGRIP) region, northeastern Greenland, in detail. We present results from the firn air-pumping campaign of the S6 borehole, forward modeling, and a novel technique for finding the lock-in depth (LID, the top of the LIZ) based on the visual stratigraphy of the EastGRIP ice core. The findings in this work help to deepen our knowledge of how atmospheric gases are trapped in ice cores. CO2, δ15N, and CH4 data suggest that the LID lies around 58 to 61 m depth. With the pixel value intensity and bright-spot analysis based on visual stratigraphy, we can pinpoint a change in ice properties to exactly 58.3 m depth, which we define as the optical lock-in depth (OLID). This visual change in ice properties is caused by the formation of rounded and enclosed air bubbles that alter the measured refraction of the light pathways. The results for the LID and OLID agree accurately on the depth. We furthermore use the visual stratigraphy images to obtain information on the sharpness of the open- to closed-porosity transition. Combining traditional methods with the independent optical method presented here, we can now better constrain the bubble closure processes in polar firn.

Characterisation of Dansgaard–Oeschger events in palaeoclimate time series using the matrix profile method

Abstract. Palaeoclimate time series, reflecting the state of Earth's climate in the distant past, occasionally display very large and rapid shifts showing abrupt climate variability. The identification and characterisation of these abrupt transitions in palaeoclimate records is of particular interest as this allows for understanding of millennial climate variability and the identification of potential tipping points in the context of current climate change. Methods that are able to characterise these events in an objective and automatic way, in a single time series, or across two proxy records are therefore of particular interest. In our study the matrix profile approach is used to describe Dansgaard–Oeschger (DO) events, abrupt warmings detected in the Greenland ice core, and Northern Hemisphere marine and continental records. The results indicate that canonical events DO-19 and DO-20, occurring at around 72 and 76 ka, are the most similar events over the past 110 000 years. These transitions are characterised by matching transitions corresponding to events DO-1, DO-8, and DO-12. They are abrupt, resulting in a rapid shift to warmer conditions, followed by a gradual return to cold conditions. The joint analysis of the δ18O and Ca2+ time series indicates that the transition corresponding to the DO-19 event is the most similar event across the two time series.

East Asian summer monsoon evolution during Heinrich Stadial 5

The bi-millennial Heinrich Stadial 5 (HS 5) event, occurring approximately 48 thousand years ago (kyr BP, before 1950 AD), represents a notable cooling episode during the last glacial period in the Northern Hemisphere. However, our comprehension of its impact on Asian summer monsoon variability remains incomplete, largely because of the scarcity of precisely dated and high-resolution records. Here, we present stalagmite δ18O-inferred absolutely dated decadal-resolved evolution of the East Asian summer monsoon (EASM) during HS 5 from Xianyun Cave, southeastern China. Stalagmite chronology constrains the occurrence of HS 5 from 48.67 ± 0.13 to 46.42 ± 0.10 kyr BP. The Xianyun stalagmite record distinctly reveals the three-phase evolution of the EASM during HS 5. It includes a gradual onset lasting for 0.79 kyr (phase 1) from 48.67 to 47.88 kyr BP, a weak EASM oscillation phase (phase 2) with three centennial-scale intensified monsoon events during 47.88–46.94 kyr BP, followed by a gradual 520-yr recovery phase (phase 3). In phases 1 and 2, the synchronous climatic shifts and resemblance to three notable centennial-scale events observed in both the Xianyun and Greenland ice core records suggest a rapid atmospheric teleconnection between the North Atlantic and EASM regions. During phase 3, the 5-century monsoon recovery registered in the Xianyun record contrasts sharply with the rapid 60-yr rebound in the Greenland ice core record. This disagreement suggests a plausible decoupling between low- and high-latitude climates, probably related to tropical sea surface temperatures variabilities and the distinct responses of the regional Intertropical Convergence Zone to El Niño Southern Oscillation variabilities. Our study highlights the essential role of tropical ocean-atmosphere coupling systems in the termination stages of millennial-scale HS events.

Post-depositional modification on seasonal-to-interannual timescales alters the deuterium-excess signals in summer snow layers in Greenland

Abstract. We document the isotopic evolution of near-surface snow at the East Greenland Ice Core Project (EastGRIP) ice core site in northeast Greenland using a time-resolved array of 1 m deep isotope (δ18O, δD) profiles. The snow profiles were taken from May–August during the 2017–2019 summer seasons. An age–depth model was developed and applied to each profile, mitigating the impacts of stratigraphic noise on isotope signals. Significant changes in deuterium excess (d) are observed in surface snow and near-surface snow as the snow ages. Decreases in d of up to 5 ‰ occur during summer seasons after deposition during two of the three summer seasons observed. The d always experiences a 3 ‰–5 ‰ increase after aging 1 year in the snow due to a broadening of the autumn d maximum. Models of idealized scenarios coupled with prior work indicate that the summertime post-depositional changes in d (Δd) can be explained by a combination of surface sublimation, forced ventilation of the near-surface snow down to 20–30 cm, and isotope-gradient-driven diffusion throughout the column. The interannual Δd is also partly explained with isotope-gradient-driven diffusion, but other mechanisms are at work that leave a bias in the d record. Thus, d does not just carry information about source-region conditions and transport history as is commonly assumed, but also integrates local conditions into summer snow layers as the snow ages through metamorphic processes. Finally, we observe a dramatic increase in the seasonal isotope-to-temperature sensitivity, which can be explained solely by isotope-gradient-driven diffusion. Our results are dependent on the site characteristics (e.g., wind, temperature, accumulation rate, snow properties) but indicate that more process-based research is necessary to understand water isotopes as climate proxies. Recommendations for monitoring and physical modeling are given, with special attention to the d parameter.

Nonlinear comparative analysis of Greenland and Antarctica ice cores data.

We analyze the temperature time series of the EPICA Dome C ice cores in Antarctica and of the Greenland project, Summit, with durations of 800 000 and 248 000 years, respectively, with a recent mathematical tool defined through the Fourier phases of the series, known as the J-index. This data driven index can differentiate between purely random dynamics and dynamics with a deterministic component. It is sensitive to nonlinear components and robust to the presence of noise. Our J-index data analysis shows that both Greenland and Antarctica climatic fluctuations possess deterministic traits and suggests the presence of an underlying nonlinear dynamics. Furthermore, in both regions, it reveals the simultaneous occurrence of an important global event known as the "Pelukian transgression." For Antarctica, it also detects the marine isotopic stage 11. Additionally, our calculation of the time series Hurst exponents and our detrended fluctuation analysis show the presence of long-range persistent correlations for Antarctica and anti-persistent correlations for Greenland. For the latter case, our fractal dimension determinations are indicative of a more complex climatic dynamics in Greenland with respect to Antarctica. Our results are encouraging for further development of climate variability deterministic models for these regions.

Full Modeling and Practical Parameterization of Cosmogenic 10Be Transport for Cosmic‐Ray Studies: SOCOL‐AERv2‐BE Model

AbstractA new full model of the atmospheric transport of cosmogenic 10Be is presented based on the specialized SOCOL‐AERv2‐BE chemistry‐climate model coupled with the CRAC:10Be isotope production model. The model includes all the relevant atmospheric processes and allows computing the isotope concentration at any given location and time. The full model is directly compared with 10Be isotope measurements in five Antarctic and Greenland ice cores for the period 1980–2007. The model reasonably well reproduces the average concentration and solar‐cycle dependency or the lack of it for most observational sites but does not perfectly catch the interannual variability at sites with complex orography likely due to the coarse model grid. This implies that the model correctly reproduces the large‐scale atmospheric dynamics but effectively averages out synoptic‐scale variability. It is found that the dominant source of 10Be is located in the middle stratosphere (25–40 km), in the tropical (<30° latitudes) and polar (>60°) regions, as produced by galactic cosmic rays and solar energetic particles, respectively. It is shown that >60% (90%) of 10Be produced in the atmosphere reaches the Earth's surface within one (two) years, respectively. For practical purposes, a simple parameterization of the full‐model results is presented which agrees with the full model within 20% in polar regions. This parameterization allows one to make a quick estimate of near‐ground 10Be concentrations based only on production rates without heavy calculations. This practical approach can be applied to studies of solar and geomagnetic variability using cosmogenic isotopes.

Contribution to Environmental Perchlorate by Stratospheric Volcanic Eruptions

AbstractPerchlorate 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.

Exploiting the Greenland volcanic ash repository to date caldera-forming eruptions and widespread isochrons during the Holocene

Polar ice-cores have long been recognised as unrivalled repositories of past volcanic events. Although tephra products from local eruptions tend to dominate these records, improvements in micro-sampling and analytical techniques are uncovering a growing number of cryptotephras erupted from exceptionally distant volcanoes. We present a series of nine Middle Holocene cryptotephra deposits detected within the NGRIP ice-core that originate from five different volcanic regions across the Northern Hemisphere (Alaska, Cascades, Iceland, Japan, Kamchatka). Unique compositional signatures are employed to identify ash from three large caldera-forming events in Kamchatka (KS2 from Ksudach), the Cascades (Mazama) and North East Japan (Mashu), along with ash from the Hekla 4 eruption in Iceland. High-precision ice-core ages (adopting a 1950 CE datum for the GICC05 timescale assigned to the Greenland ice cores) are derived for each eruption: Hekla 4 (4325 ± 8 a b1.95k), KS2 (7089 ± 26 a b1.95k), Mashu (i-f) (7473 ± 33 a b1.95k) and Mazama (7562 ± 35 a b1.95k), all of which can be employed as chronological fix-points in other proxy records where these deposits are also preserved. Four further cryptotephra deposits and one macro-deposit are also identified and traced to sources in Iceland and Alaska. The cryptotephra originating from Alaska is correlated to a deposit identified in lake records from the Kenai Peninsula, thought to originate from Redoubt Volcano. The remaining four deposits are typical of the products of Katla, Grímsvötn and Veiðivötn in Iceland. This ensemble of Middle Holocene tephra deposits highlights the pivotal position of the Greenland ice-sheet and its ice-cores to capture deposition from the convergence of several far-travelled ash clouds. Precise age estimates derived from the annually resolved ice-core record greatly enhances the value of these tephra isochrons.

Aeolian dynamics at the northern edge of Deliblato (Banat) Sand Sea, Vojvodina, Serbia, at the time of the last deglaciation

Abstract The Deliblato (Banat) Sand Sea, which is one of the largest areas of аeolian sand in Europe, is located near the Iron Gate, which marks the crossing of the Danube River through the biggest gorge of this river. Here, Danubian alluvium has served as the sand source for the Banat Sand Sea, which was formed primarily through southeasterly (Košava) winds. Utilizing a multi-proxy approach, the objective of this study is to gain a better understanding of the environmental dynamics of the Banat Sand Sea. To achieve this goal, we conducted an analysis of an archive representing an approximately 20-m-thick dune formation on the northern edge of this dune field. Using optically stimulated luminescence (OSL) dating, we calculated aeolian sedimentation rates and dune ages. Sand was deposited here approximately between 17 ka and 13 ka. Magnetic susceptibility, grain size, and colorimetric analyses were interpreted in terms of local paleoenvironmental conditions. Calculated sedimentation rates (SR) indicate intensive aeolian deposition during the study period that range from 483 cm/ka to 502 cm/ka. We compared our data with regional and other European archives, as well as with climatic variations recorded in the Greenland ice core North Greenland Ice Core Project (NGRIP).

Transformation of regional vegetation driven by climate change during the last deglacial–early Holocene at Chaohu Lake, eastern China: New pollen insights

Reconstructing the vegetation history of east China during the last glacial–interglacial transition is crucial for understanding the East Asian Summer Monsoon (EASM) evolution. Here, we present a new high-resolution pollen record from Chaohu Lake to determine the detailed process of regional lowland vegetation succession and its response to the EASM changes during the last glacial–Holocene transition (13.9–9.1 cal ka BP) in the lower Yangtze Valley, eastern China. During the Older Dryas (OD, 13.9–13.5 cal ka BP) period, regional forest-steppe indicative of co–dominance of Artemisia, Poaceae, and deciduous Quercus was present under a cool and dry climate. During the Allerød Interstadial (AI, 13.5–12.9 cal ka BP), significant arboreal expansions of deciduous Quercus, Hydrangea type and evergreen Quercus occurred, while herbs retreated significantly, presumably driven by the relatively warm, humid climate. Forest-steppe readvanced during the Younger Dryas (YD) interval, as indicated by increases in Poaceae and Artemisia, suggesting a cool and dry climate. During the early Holocene, extensive oak-pine forest flourished as regional vegetation, responding to pronounced climatic amelioration.Our pollen-based climatic record is closely correlated with stalagmites δ18O records from EASM region and Greenland ice cores δ18O records, indicating the teleconnection between EASM variation and North Atlantic climate during the last deglacial–early Holocene. However, our record indicates an intensified EASM during the early AI and a prolonged onset excursion during the YD, diverging from North Atlantic climate but closely correlated to sea surface temperature (SST) variations in the western tropical Pacific.

Long-term relationships between summer clouds and aerosols over mid-high latitudes of the Northern Hemisphere

While the short-term relationship between clouds and aerosols is well known, no adequate data is available to verify the longer-term, annual to decadal, relationship. It is important to quantify the aerosol–cloud interaction (ACI) for mitigating uncertainty in climate prediction. Here the long-term ACI over the mid-to-high latitudes of the Northern Hemisphere was analyzed by using seasonally-resolved ion fluxes reconstructed from a southeastern Greenland ice core (SE-Dome ice core) as aerosol proxies, and satellite-based summer cloud amount between 1982 and 2014. As a result, SO42− flux in the ice core shows significant positive correlation with total cloud amounts (CCT\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${CC}_{T}$$\\end{document}) and cloud droplet concentration (Nd\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${N}_{d}$$\\end{document}) in the summer over the southeastern Greenland Sea, implying that the sulfate aerosols may contribute to the variability of CCT\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${CC}_{T}$$\\end{document} via microphysical cloud processes. Significant positive correlations are persistent even under the constrained conditions when cloud formation factors such as relative humidity, air temperature at cloud height, and summer North Atlantic Oscillation are limited within ± 1σ variability. Hence sulfate aerosols should control the interannual variability of summer CCT\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${CC}_{T}$$\\end{document} In terms of decadal changes, CCT\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${CC}_{T}$$\\end{document} was approximately 3–5% higher in the 1960s–1970s than in the 1990s–2000s, which can be explained by changes in the, SO42-\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${{{\ ext{SO}}}_{4}}^{2-}$$\\end{document} flux preserved in the SE-Dome ice core.

Spatial and temporal stable water isotope data from the upper snowpack at the EastGRIP camp site, NE Greenland, sampled in summer 2018

Abstract. Stable water isotopes stored in snow, firn and ice are used to reconstruct climatic parameters. The imprint of these parameters at the snow surface and their preservation in the upper snowpack are determined by a number of processes influencing the recording of the environmental signal. Here, we present a dataset of approximately 3800 snow samples analysed for their stable water isotope composition, which were obtained during the summer season next to the deep drilling site of the East Greenland Ice Core Project in northeast Greenland (75.635411° N, 36.000250° W). Sampling was carried out every third day between 14 May and 3 August 2018 along a 39 m long transect. Three depth intervals in the top 10 cm were sampled at 30 positions with a higher resolution closer to the surface (0–1 and 1–4 cm depth vs. 4–10 cm). The sample analysis was carried out at two renowned stable water isotope laboratories that produced isotope data with the overall highest uncertainty of 0.09 ‰ for δ18O and 0.8 ‰ for δD. This unique dataset shows the strongest δ18O variability closest to the surface, damped and delayed variations in the lowest layer, and a trend towards increasing homogeneity towards the end of the season, especially in the deepest layer. Additional information on the snow height and its temporal changes suggests a non-uniform spatial imprint of the seasonal climatic information in this area, potentially following the stratigraphic noise of the surface. The data can be used to study the relation between snow height (changes) and the imprint and preservation of the isotopic composition at a site with 10–14 cm w.e. yr−1 accumulation. The high-temporal-resolution sampling allows additional analyses on (post-)depositional processes, such as vapour–snow exchange. The data can be accessed at https://doi.org/10.1594/PANGAEA.956626 (Zuhr et al., 2023a).

Insights Into Changing Interglacial Conditions in Subarctic Canada From MIS 11 Through MIS 5e From Seasonally Resolved Speleothem Records

AbstractHigh‐resolution records from past interglacial climates help constrain future responses to global warming, yet are rare. Here, we produce seasonally resolved climate records from subarctic‐Canada using micron‐scale measurements of oxygen isotopes (δ18O) in speleothems with apparent annual growth bands from three interglacial periods—Marine Isotope Stages (MIS) 11, 9, and 5e. We find 3‰ lower δ18O values during MIS 11 than MIS 5e, despite MIS 11 likely being warmer. We explore controls on high‐latitude speleothem δ18O and suggest low MIS 11 δ18O values reflect greater contribution of cold‐season precipitation to dripwater from longer annual ground thaw durations. Other potential influences include changes in precipitation source and/or increased fraction of cold‐season precipitation from diminished sea ice in MIS 11. Our study highlights the potential for high‐latitude speleothems to yield detailed isotopic records of Northern Hemisphere interglacial climates beyond the reach of Greenland ice cores and offers a framework for interpreting them.

Decadal-to-centennial increases of volcanic aerosols from Iceland challenge the concept of a Medieval Quiet Period

AbstractExisting global volcanic radiative aerosol forcing estimates portray the period 700 to 1000 as volcanically quiescent, void of major volcanic eruptions. However, this disagrees with proximal Icelandic geological records and regional Greenland ice-core records of sulfate. Here, we use cryptotephra analyses, high-resolution sulfur isotope analyses, and glaciochemical volcanic tracers on an array of Greenland ice cores to characterise volcanic activity and climatically important sulfuric aerosols across the period 700 to 1000. We identify a prolonged episode of volcanic sulfur dioxide emissions (751–940) dominated by Icelandic volcanism, that we term the Icelandic Active Period. This period commences with the Hrafnkatla episode (751–763), which coincided with strong winter cooling anomalies across Europe. This study reveals an important contribution of prolonged volcanic sulfate emissions to the pre-industrial atmospheric aerosol burden, currently not considered in existing forcing estimates, and highlights the need for further research to disentangle their associated climate feedbacks.

Statistical appraisal of geothermal heat flow observations in the Arctic

Abstract. Geothermal heat flow is an important boundary condition for ice sheets, affecting, for example, basal melt rates, but for ice-covered regions, we only have sparse heat flow observations with partly high uncertainty of up to 30 m W m−2. In this study, we first investigate the agreement between such pointwise 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 solid Earth models, except a few data points, such as, for example, the NGRIP (North Greenland Ice Core Project) 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.

Statistical precursor signals for Dansgaard–Oeschger cooling transitions

Abstract. Given growing concerns about climate tipping points and their risks, it is important to investigate the capability of identifying robust precursor signals for the associated transitions. In general, the variance and short-lag autocorrelations of the fluctuations increase in a stochastically forced system approaching a critical or bifurcation-induced transition, making them theoretically suitable indicators to warn of such transitions. Paleoclimate records provide useful test beds if such a warning of a forthcoming transition could work in practice. The Dansgaard–Oeschger (DO) events are characterized by millennial-scale abrupt climate changes during the glacial period, manifesting most clearly as abrupt temperature shifts in the North Atlantic region. Some previous studies have found such statistical precursor signals for the DO warming transitions. On the other hand, statistical precursor signals for the abrupt DO cooling transitions have not been identified. Analyzing Greenland ice core records, we find robust and statistically significant precursor signals of DO cooling transitions in most of the interstadials longer than roughly 1500 years but not in the shorter interstadials. The origin of the statistical precursor signals is mainly related to so-called rebound events, humps in the temperature observed at the end of interstadial, some decades to centuries prior to the actual transition. We discuss several dynamical mechanisms that give rise to such rebound events and statistical precursor signals.